CONTENTS. PART L—ELECTRO-PLATING. CHAPTER L PRELIMINARY CONSIDERATIONS.—PRIMARY AND SECONDARY BATTERIES. PA The Electric Current.—Electricity Moving Force.—The Electric Circuit.—Sources* ot Elcctiieity Moving Force.—Chemical Kiectric Batteries—Magnitudes of E.M.F. ot Batteries.—l'olan^ation.— Polurit\ ot Batteries—Primary Batteries—The Lalaude (ell.—The Daniell Cell —Amalgamation of Zincs.—Management of Primary Batteries.—Relative Activity of Primary Cells.—Constancy of Piiinarx CelU—General ltemaikson Primary Batteries.—Secondary Batteues.—Care and Rep in ot becondaiy Batteries.—Annual Cost of Upkeep ot ^ei'ondan Batteries—Electrolytes.—Short Ciicuits.— Connection ot Batteries in Seues and Paiallel.—Ammeters and Voltmeters . . . . . . . . . < . CHAPTER II THERMOPILES.—DYNAMOS.—THE COST OF ELECTRICAL INSTALLATIONS OF SMALL OUTPUT FOR ELECTRO-PLATING, ETC. The Thermopile.—The Gulcher Thermopile.—The Cox Thermopile.— The Clamond Thermopile.—The Dsnamo —Points to be consideied in Buying a D\namo.—Caie ot Dynamo.—Driving Belts.—Staiting and Stopping a D\namo.—Cost of Small Dynamo**.—Cost of Motor- Dynamos.—Specih'cations tor and Choice ot Motor-Dvnamos. Safety Precautions with Motors of Motor-Dynamos.—Choice of
The Electric Current.—Electricity Moving Force.—The ElectricCircuit.—Sources* ot Elcctiieity Moving Force.—Chemical KiectricBatteries—Magnitudes of E.M.F. ot Batteries.—l'olan^ation.—Polurit\ ot Batteries—Primary Batteries—The Lalaude (ell.—TheDaniell Cell —Amalgamation of Zincs.—Management of PrimaryBatteries.—Relative Activity of Primary Cells.—Constancy ofPiiinarx CelU—General ltemaikson Primary Batteries.—SecondaryBatteues.—Care and Rep in ot becondaiy Batteries.—Annual Costof Upkeep ot ^ei'ondan Batteries—Electrolytes.—Short Ciicuits.—Connection ot Batteries in Seues and Paiallel.—Ammeters andVoltmeters . . . . . . . . . < .
CHAPTER II
THERMOPILES.—DYNAMOS.—THE COST OF ELECTRICALINSTALLATIONS OF SMALL OUTPUT FOR
ELECTRO-PLATING, ETC.
The Thermopile.—The Gulcher Thermopile.—The Cox Thermopile.—The Clamond Thermopile.—The Dsnamo —Points to be consideiedin Buying a D\namo.—Caie ot Dynamo.—Driving Belts.—Staitingand Stopping a D\namo.—Cost of Small Dynamo**.—Cost of Motor-Dynamos.—Specih'cations tor and Choice ot Motor-Dvnamos.Safety Precautions with Motors of Motor-Dynamos.—Choice of
Xll PKEFACE TO FIRST EDITION.
important details ; and having himself worked most of theoperations of the art upon a very extensive scale, he isenabled in many instances to give the results of his ownpractical experience.
ELECTHO-METALLURGY, which is now recognised as adistinct branch of electro-chemistry, has been treated sepa-rately, and those processes which have been practicallyadopted, such as the electrolytic refining of crude copper; areexhaustively given, while other processes, now only upontheir trial, are described. In this section also will be founda description of the new process of electric smelting, as ap-plied, more especially, to the production of aluminium andsilicon bronzes.
In conclusion, the author tenders his best thanks tothose who kindly furnished him with information, for thereadiness and pi omptitude with which they complied withhis requests.
ALEXANDER WATT.LOISDON, December', 1885.
CONTENTS. XV11
CHAPTER XIV.
ELECTRO-DEPOSITION OF SILVER.PAGE
Preparation of Nitrate of Silver.—Observations on Commercial Cyan-ide.—Preparation of Silver Solutions.—Bright Plating.—Deposi-tion by Simple Immersion.—Whitening Articles by SimpleImmersion.—Whitening Brass Clock Dials, &c. , 227
CHAPTER XV.
ELECTRO-DEPOSITION OF SILVER (continued).
Preparation of New Work for the Bath.—Quicking Solutions, or MercuryDips.—Potash Bath.—Acid Dips.—Dipping.—Spoon and ForkWork.—Wiring the Work.—Arrangement of the Plating Bath.—Plating Battery.—Motion given to Articles while in the Bath.—Cruet Stands, &c.—Tea and Coffee Services.—Scratch-Brushing . 241
CHAPTER XVL
ELECTRO-DEPOSITION OF SILVER (continued).
Plating Britannia Metal, <fcc—Plating Zinc, Iron, &c—Replating OldWork—Preparation of Old Plated Ware.—Stripping Silver fromOld Plated Articles.—Stripping Gold from Old Plated Articles.—Hand Polishing.—Re-silvering Electro-plate.—Characteristics ofElectro-plate.—Depositing Silver by Weight.—Roseleur's Argyro-metric Scale.—Solid Silver Deposits.—On the Thickness ofElectro-deposited Silver.—Pyro-plating.—Whitening Electro-platedArticles.—Whitening Silver Work . 258
CHAPTER XVII.
IMITATION ANTIQUE SILVER.
Oxidised Silver.—Oxidising Silver.—Oxidising with Solution ofPlatinum.—Oxidising with Sulphide of Potassium.—Oxidisingwith the Paste.—Part-gilding and Oxidising.—Dr. EUner'sProcess.—Satin Finish.—Sulphuring Silver.—Niello, or NielledSilver.—Pink Tint upon Silver.—Silvering Notes . . . . 2 7 7
b
XVI CONTENTS.
CHAPTER X.
ELECTRO- DEPOSITION OF GOLD.p
Gilding by Direct Current, or Electro-Gilding.— Preparation of GildingSolutions.—Gilding Solutions (Becquerel's.—Fizeau's.—Wood's.—M. de Brianfs).—French Gilding Solutions.—Gilding Solutionsmade by the Battery Process (De Ruolz's).—Cold Electro-GildingSolutions—Observations on Gilding in Cold Baths.—FerrocyanideGilding Solution.—Watt's Gilding Solution.—Recoid'i, GildingBath
CHAPTER XL
ELECTRO-DEPOSITION OF GOLD {continued).
General Manipulations of Electro-gilding.—Preparation of the Woik.—Dfad Gilding.—Causes which affect the Colour of the Deposit.—-Gilding Gold Articles.—Gilding Insides of Vessels.—Gilding SilverFiligree Work.—Gilding Army Accoutrement Work.—GildingGerman Silver.—Gildizjg Steel.—Gilding Watch Movements , 185
CHAPTER XII.
VAHIOUS GILDING OPERATIONS.
Electro-gilding Zinc Articles.—Gilding Metals with Gold Leaf.—CcKlGilding.—Gilding bilk, Cotton, &c.—P\ro-gilding.—Colour ofElectro-deposited Gold.—Gilding in Various Co'ours.—ColoutiugProcesses.—Re-colouring Gold Articles.—Wet colour Process.—French Wet-colouring.—London Process of Wet-colouring , . 200
CHAPTER XIII.
MERCURY GILDING.
Preparation of the Amalgam.—The Murcurial Solution.—Applying theAmalgam.—Evaporation of the Mercury.—Colouring.—Bright andDead Gilding in Parts.—Gilding Bronzes with Amalgam.—OrmouluColour.—Red-Gold Colour.—Ormoulu.—Red Ormoulu.—YellowOrmoulu.—Dead Ormoulu.—Gilder's Wax.—Notes on Gilding . 210
CONTENTS. X1S.
PAOB
Tin.—Koseleur ' s Solution.-—Fearn's Process.—-Steele's Process .—
Elec t ro - t i nn ing Sheet I ron .—Spence ' s Process —Recove ry of Tin
from T i n S c r a p b y Electrolysis . . . . . . . 339
CHAPTER XXII.
ELECTRO-DEPOSITION OF IRON AND ZINC.
Electro-deposition of Iron.—Facing Engraved Copper-plates.—Klein'sProcess for Depositing Iron upon Copper.—Jacobi and Klein'sProcess.—Ammonio-sulphate of Iron Solution.—Boettger's Ferro-cyanide Solution.—Ammonio chloride of Iron Solution.—Sulphateof Iron and Chloride of Ammonium Solution.—Electro-deposi-tion of Zinc.—Watt's Solution.—Zincing Solutions.—Person andSire's Solution.—Deposition of Zinc by Simple Immersion.—Her-mann's Zinc Process . . . . . . . . . 348
CHAPTER XXIII.
ELECTRO-DEPOSITION OF VARIOUS METALS.
Electro-deposition of Platinum.—Electro-deposition of Cobalt.—Electro-depo>ition of Palladium.—Deposition of Bismuth.—Deposition ofAntimony.—Deposition of Lead.—Metallo-Chromes.—Deposition ofAluminium.—Deposition of Cadmium.—Deposition of Chromium.—Deposition of Manganium.—Deposition of Magnesium.—Depositionof Silicon # 356
CHAPTER XXIV.ELECTRO-DEPOSITION OF ALLOYS.
Electro-deposition of Brass and Bronze.—Brassing Solutions.—Brunei,Bisson, and Co 's Processes.—DeSalzede's Processes.—Newton's Pro-cesses.—Kussell and Woolrich's Process.—Wood's Process.—Morrisand Johnson's Process.—Dr. Ueeren's Process.—Roseleur's Pro-cesses.—Walenn's Processes.—Bacco's Solution.—Winckler's Solu-tion.—American Formulae lor Brassing Solutions.—Thick BrabsDeposits.—Brass Solution prepaied by Battery Process 374
CHAPTER XXV.ELECTRO-DEPOSITION OF ALLOYS (continued).
Electro-bi assing Cast-iron Work —Scouring.—Electro-bra^singWrought-iron Work.—Electro-bracsing Zinc Work —Electio-brassing Lee.c\
XV111 CONTENTS.
CHAPTER XVIII.
ELECTRO-DEPOSITION OF NICKEL.PAGI
Application of Nickel-plating.—The Depositing Tank.—ConductingRods.—Preparation of the Nickel Solution.—Nickel dnodes.—Nickel-plating by Battery.—The Twin-Carbon Battery.—Observa-tions on Preparing Work for Nickel-plating.—The Potish Bath.—Dips, or Steeps.—Dipping Acid.—Pickling Bath . . . . 2S8
CHAPTER XIX.
ELECTRO-DEPOSITION OF NICKEL {continued).
Preparation of Nickeling Solutions.—Adams* Process. —Unwin's Pro-cess. — Weston's Process. — Powell's Process. — Potts' Process.—Double Cyanide of Nickel and Potassium Solution.—Solution forNickeling Tin, Britannia Metal, &c.—Simple Method of PreparingNickel baits.—Desmur's Solution for Nickeling Small Articles . 299
CHAPTER XX.
ELECTRO-DEPOSITION OF NICKEL (continued).
Prepaiation of the Work for Nickel-plating.—The Scouring Tray.—-Brass and Copper Work.—Nickeling small Steel Articles.—Nickel-ing small Brass and Copper Articles.—Nickeling by Dynamo-electricity.—Nickeling Mullers, Sausage Warmers, &c.—NickelingBar Fittings, Sanitary Work, <fec.—Nickeling Long Pieces of Work.—Dead Work.—Nickeling Stove Fronts, &c.—Nickeling Bicycles,<fcc.—Nickeling Second-hand Bicycles, &c.—Nickeling Sword-scabbards, <fcc.—Nickeling Harness Furniture, Bits, Spurs, &c.—Nickeling Cast-iron Work.—Nickeling Chain Work.—Re-NickelingOld Work.—Nickeling Notes . 309
CHAPTER XXL
DEPOSITION AND ELECTRO-DEPOSITION OF TIN.
Deposition by Simple Immersion.—Tinning Iron Articles by SimpleImmersion.—Tinning Zinc by Simple Immersion.—Tinning byContact with Zinc.—Koseleur's Tinning Solutions.— Deposition ofTin by Single Cell Process.—Dr. HilliePs Method of Tinning Metals.—Ileeren's Method of Tinning Iron Wire—Electro-deposition of
CONTENTS. XXI
Caustic Potash.—Chloride of Gold.—Chloride of Platinum.—Chloride of Zinc.—Cyanide of Potassium.—Dipping Acid.—Ferro-cyanide of Potassium.—Hydrochloric Acid.—Liquid Ammonia.—Mercury, or Quicksilver.—Muriatic Acid.—Nickel Anodes.—NickelSalts.-—Nitric Acid.— Phosphorus.—Pickles. — Plumbago. — Pyro-phosphate of Soda.—Sal-ammoniac.—Sheffield Lime.—Solution ofPhosphorus.—Sulphate of Copper.—Sulphate of Iron.—SulphuricAcid.—Trent Sand . . . . . . . . 429
APPENDIX (PART I.) ON ELECTRO-PLATING.
Electro-deposition of Platinum —Platinising Silver Plates for Smee Cells.—Electro-deposition of Iron.—Steel Facing Copper Plates.—Coloura-tion and Staining of Metals.—Oxidising Copper Surfaces.—Electro-deposition of Alloys.—Test for Free Cyanide.—Antidotes and Reme-dies in Cases of Poisoning . . , . , . . . 441
APPENDIX (PART II.) ON ELECTRO-PLATING.
Effect of Nitrate^ upon Nickel Deposits.—Dary's Barrel Method of Nickel-plating.—Employment of the Barrel Method of Plating for Metalsother than Nickel.—The Electrolytic Manufacture of Metal-coatedPaper.—Electro-deposition of Cobalt.—Professor S. P. Thompson'sProcess of Cobalt Deposition.—The Electrolytic Formation of Para-bolic Mirrors for Search-lights.—"Areas" Silver-plating.—AnHotel Silver-plating Plant.—Aluminium Plating by Electrolysisand Otherwise.—Pitting Aluminium with other Metals . 460
CONTENTS.
PAGE
Pewter, and Tin Work.—Observations on Electro-brassing.—Bronz-ing Electro-brassed Work.—French Method of Bronzing Electro-brassed Zinc Work.—Green or Antique Bronze.—Bronze Powders.—Dipping Electro-brassed Work.—Lacquering Electro-brassedWork.—Electro-deposition of Bronze.—Electro-deposition of German Silver.—Morris and Johnson's Process.—Deposition of an Alloy of Tin andSilver.—Deposition of Alloys of Gold, Silver, <tc.—Deposition ofChromium Alloys.—Slater's Process.—Deposition of Magnesium andits Alloys.—Alloy of Platinum and Silver.—New White Allots.—Notes on Electro-brassing 387
CHAPTER XXVI.
RECOVERY OF GOLD AND SILVER FROM WASTESOLUTIONS, &o.
Recovery of Gold from Old Cyanide Solutions.—Recovery of Silver fromOld Cyanide Solutions.—Extraction of Silver by the Wet Method.—Recovery of Gold and Silver from Scratch-brush Waste.—Recoveryof Gold and Silver from Old Stripping Solutions.—StrippingMetals from each other.—Stripping Solution for Silver.—ColdStripping Solution for Silver.—Stripping Silver from Iron, Steel,Z;nc, &c.—Stripping Silver by Battery.—Stripping Gold fromSilver Work.—Stripping Nickel-plated Articles.—Stopping-off.—Applying Stopping-off Varnishes.—Electrolytic Soldering.—Solder-ing.—Removing Soft Solder from Gold and Silver Work . , 403
Metal Polishing.—Brass Polishing.—The Polishing Lathe.—BrassFinishing.—Lime Finishing.—Nickel Polishing and Finishing.—Steel Polishing.—Polishing Silver or Plated Work.—Burnishing.—Burnishing Silver or Plated Work.—Electro-gilt Work . . . 419
CHAPTER XXVIII.
MATERIALS USED IN ELECTRO-DEPOSITION.
Acetate of Copper.—Acetate of Lead.—Acetic Acid.—Aqua Fortis.-Aqua Regia.—Bisulphide of Carbon.—Carbonate of Potash.-
PON TENTS. xxm
refined Cnpper.—Composition of Anode Qludge.—Weight of AnodeSludge.—Purification ot Electrohte—Efteet oi* Organic Matter onCopper Deposits.—Formation ot Nodule* and Tree-hke Growths.—Production of Finished Refined Copper without Re-melting.—rlheElmoie Procev.—Copper Refining at High Current Densities.—Dumoulin's Process—Cowper Coles' Centrifugal Process—Wilde'sCentrifugal Process.—Sander's Process.—David's Process.—Tho-fehen's Process.—Alan Williams' Theory of High Current DensityProcess .— The Pi ice uf Copper ami its Fluctuations . . . 524
CHAPTER IV.
ELECTROLYTIC GOLD AND SILVER BULLIONREFINING.
Electrolytic Refinery of Gold Bullion.—Wohlwill's Prnce^.—PforzheimProcess of Recovering Gold and Silver from Complex JewelleryAllots.—Eleetroh tic Silver Refining.—Mobius' Process . , . 5 6 3
CHAPTER V.
THE ELECTROLYTIC TREATMENT OF TIN.
The Electiohtic Refining of Tin.—The Recovery of Tin from WasterJin-plate by Acid Processes—The Recovery of Tin from WasteTin-plate by Alkaline Processes.—Properties of Iron Contaminatedwith Tin.—Cost of Scrap and Waste Tin-plate.—Cost of Collectionand Cairiage . . . . . . . . 578
CHAPrER VI.
THE ELECTROLYTIC REFINING OF LEAD.
Keith's Electrolytic Lead Refining Process for Base Bullion.—Tommasi'sElectrolytic Lead Refining Process.—Formation of Spongy Lead.—Richly Argentifeious Lead Treated by Tommasi's Process.—RefiningArgentiferous Lead in Lead Nitrate Solution.—Remarks on theElectro-deposition of Lead , 595
CHAPTER VII.
THE ELECTROLYTIC PRODUCTION OF ALUMINIUMAND THE ELECTROLYTIC REFINING OF
NICKEL.
Properties of Aluminium.—Effect of Mercury on Aluminium.—Electro-h t i c Smelting ot Aluminium from Alumina.—Heroult's Process.—
XX11 CO JN TENTS.
PART II.—ELECTKO-METALLUBGY.
CHAPTER I.
THE ELECTRO-METALLURGY OF COPPER.-CHIEFLYHISTORICAL.
PAGE
Electro-metallurgy.—The Electric Refining of Copper by SeparateCurrent.—Dr. Kiliani's Observations on Electrolytic Refining ofCopper.—Progress in Electrolytic Copper Refining up to 1889.—Elkington's Copper Refinery.—Wohlwill's North German Refineryat Hamburg.—The Biache Refinery.— Hilarion Roux's MarseillesRefinery.-—The Oker Refinery.—The Elliott Metal Refining Com-pany's Refinery at Birmingham.—Electrolytic Refining in America.—Early Attempts at Estimates of Cost of Refining Copper . . 4fic
CHAPTER II.
THE COST OF ELECTROLYTIC COPPER REFINING.—CURRENT DENSITY AS A FACTOR IN PROFITS.
Advances in Electrolytic Copper Refining.—Preparing Estimates ofCost of Erection of Refinery.—Cost of Offices, Refinery Buildings,Power Plant, Dynamos, Electrolytic Vats, Electrolyte, CopperAnodes, Stock Copper, Copper Leads, Circulating and PurifyingPlant.—Total Capital Invested, Annual Running Costs, Interest onCapital Invested, Depreciation and Repairs, Labour, Melting Re-fined Copper, Casting Anodes, Fuel, Salaries of Managementand Clerical Staff. Rent of Ground.—Importance of CurrentDensity.—Annual Total Profits.—Examples of Estimates workedout,—Actual Costs of Electrolytic Copper Refineries.—Further Con-siderations on Current Density.—Current Density in Copper Con-ductors in Electrolytic Refineries 499
CHAPTER III
SOME IMPORTANT DETAILS IN ELECTROLYTICCOPPER REFINERIES.
Arrangement of Vats in a Copper Refinery.—Arrangement of Anodesand Cathodes in Electrolytic Vats.—The Hayden System.—BestSize and Number of Electrolytic Vats.—Avoidance of ShortCircuits.—Circulation of the Electrolyte.—Heating the ElectrolyteVoltage and Output of Dynamos for Copper Refining.—Compositionof Anode Copper employed in Refineries.—Composition of Electro-
The Electric Current.—Electricity Moviug Force.—The Electric Circuit.—Source of Electricity Moviug Force.—Chemical Electric Bat-teries.—Magnitudes of e. m. f. of Batteries.—Polarisation.—Polarityof Batteries.—Primary Batteries.—The Lalaude Cell.—TheDaniellCell.—Amalgamation of Zincs.—Management of Primary Bat-teries.—llelative Activity of Primary Cells.—Constancy of PrimaryCells.—General Remarks on Primary Batteries.—Secondary Bat-teries.—Care and Repair of Secondary Batteries.—Annual Cost ofUpkeep of Secondary Batteries.—Electrolytes.—Short Circuits.—Connection of Batteries in Series and Parallel.—Ammeters andVoltmeters.—Regulating Resistances.
IT is not the object of this treatise to enter into discussions on, andexplanations of, the theories of chemistry, electricity and magnetism,or the methods of construction and design of dynamos. Suchquestions must be studied in some one or more of the numerousexcellent text books now existing which deal especially with thesebranches of pure and applied chemifetry, electricity and magnetism.The present work is intended above all to deal with the question of thechemical action of the electric current from a practical standpoint andail theory is as far as possible omitted, except in its simplest and mostgeneralised form. It must not be imagined, however, that the presentwriter wishes in any way to induce the student of this particularbranch of applied electricity to consider that the theory of the subjectis unimportant. The theory is of the greatest value to guide anddirect experimental work, and it cannot be too strongly urged that
B
XXIV CONTENTS.
flail's Process.—Preparation of Pure Alumina.—Increase of Purityof Commercial Aluminium in Kecent Years.—Minet's Process ofSmelting.—Bucherer's Aluminium Sulphide Process.—The Cowles'Process of Producing Aluminium Alloys.—The Electrolytic Refiningof Nickel.—Secret Processes.—Ludvvig Mond's Nickel RefiningProcess , 613
CHAPTER VIII.
ELECTE0-GALVAN1SING.
Nature of Solutions.—Protective Effect of Electro-deposited Zinc—firmsElectro-galvanising prior to 1891.—Richter's Process.—Cowper-Coles' Process.—Employment of Zinc Dust.—Estimates of Cost ofElectro-Galvanising Plant.—Advantages of Electro-galvanisingIron.—Pickling and Cleansing Iron and other Metal Surfaces byChemical and Electrolytic Methods.—Removal of Scale fromPickling Vats.—Effect of Pressure on Electro-zincing.—ZincSponge.—Sources of Zinc Dust.—Price of Zinc and Zinc Dust . 63/
USEFUL TABLES.TABLE
I.—Elements, their Symbols and Atomic Weights . . . o 651II.—Relative Conductivity of Metals 652
III.—Specific Resistance of Solutions of Sulphate of Copper . . 653IV.—Specific Resistance of Solutions of Sulphate of Copper at 500
Fahr 653V.—Table o f High Temperatures . . . . . . . 653
VI.—Comparative French and English Thermometer Scales . . 654VII.—Birmingham Wire Gauge for Sheet Copper and Lead . . 655
VIII.—New Legal Standard Wire Gauge 655IX.—Chemical and Electio-Chemical Equivalents . . . . 656X.—Specific Gravities of Metals 657
XI.—Tables of Weights and Measures 653XII.—Specific Gravities corresponding to Degrees of Baume's Hydro-
meter for Liquids heavier than Water . . . . . 659XIII.—Specific Gravities on .Baume's Scale for Liquids lighter than
Water C59XIV.—Degrees on Twaddell's Hydrometer and the corresponding Specific
Gravities . 660E l e c t r i c a l U n i t s . . . . . . . . . 6 6 0
S U B J E C T I N D E X 661
N A M E I N D E X 6 7 8
SOURCES OF ELECTRICITY MOTIVE FORCE. 3
Sources of Electricity Motive Force.—Practically there arethree different types of sources of electricity motive force :—
1. The electro-chemical battery, generally known as the electricbattery.
2. The thermopile.3. The dynamo.
We shall immediately consider the relative merits and importanceof these sources.
For technical purposes the prime consideration in conducting anyprocess is economy of both time and money, and as the cost of theelectric current obtained from any given source depends upon theprime cost of the generator, its rate of depreciation, and the cost ofmaintenance, it is of vital importance to consider thebe matters withevery care.
In the writer's opinion the most advantageous source of electricalenergy for small work up to perhaps as large a current as about threeamperes, if the work is turned out at a steady rate, or as large asperhaps twice this amount if the output of work is variable and theplating plant only intermittently used, is a form of the Lalandebattery manufactured by Messrs. Umbrcit and Matthes of Leipzig.This refers to the cases most unfavourable to the employment otprimary batteries, namely, when either cheap electrical or cheap mecha-nical power, or both, is to be easily obtained. Under other circum-stances, where neither electrical nor mechanical power is to be had,the importance of this form of primary battery is greatly increased,and it may be employed with advantage under the most favourablecircumstances for currents up to as large as 20 or perhaps 30 amperes.In connection with these statements it may be remarked that 3amperes is a current sufficiently large to plate satisfactorily about 500square inches of surface with gold, or as much as about 100 to 300square inches with silver, or to electrotype with copper, surfaces aslarge as about 30 to 40 square inches. A fuller discussion of thequestion as to the best form of current generator to employ underdifferent conditions is given at the end of the next chapter, after allthe available current generators have been considered and theirefficiency, prime cost, and upkeep noted.
It is now necessary to describe the various forms of primary electricbatteries which are available for electro-plating and oiher electro-metallurgical work. In the writer's opinion, none of the primarybatteries, except the modified Lalande cell already mentioned, should befor a moment considered for practical work, but oAving to tho fact thatthis form of cell is of very recent introduction, and as in the largerpart of the text of this book other forms of battery are continuallyreferred to, it is necessary, in order that the reader may clearly follow
2 PRIMARY AND SECONDARY CATTERIKS.
every practical technical worker who is possessed of little or no theory,however successful and excellent he may be in his particular branch ofapplied science, will find himself rendered the more capable in carry-ing out improvements and rectifying difficulties the greater the amountof sound theoretical knowledge lie is able to obtain.
The Electric Current.—For all practical purposes the electriccurrent may be considered as being similar to a current of water, andthe electric conductors in which it can flow as being analogous towater pipes, whilst non-conductors of electricity may be rejiresented,by analogy, by the solid materials forming the walls of the pipethrough which the water flows.
Electro-Motive Force, or Electricity Moving Force.—In orderthat a current of water may flow through a pipe, it is necessary to havea water moving force, such as a pump, or a head of water, arrangedsomewhere in the course of the tube through which the water flows.And in order that the electric current may flow, it is always necessarythat there shall be an electricity moving force (or as it is frequentlywritten shortty, an e. m. f.) somewhere in the circuit.
The Electric Circuit.—If the reader will consider for one momenthe will find that in all cases where we have a continuous flow of waterthere must be a closed circuit or path, round which this flow takes place.For instance, if a pump and its attached engine (the source of watermoving force) is raising water from a mine, which water, as it escapesfrom the pump, runs back again down the shaft, we have a case of acontinuous circuit. Again, in the case of a river, running continuously(or nearly so) into the sea and continuously supplied at its sources withwater from the clouds (which water has been extracted from the seaby the sun); the sun is the water motive force and the closed path offlow (or the circuit as it is called in the case of electricity) is down theriver bed, into the sea, up through the air from the sea, as watervapour, transport by the winds as clouds, again a downward paththrough the air on to the land, and once more along the river bed. Inthe case of the electric current we have a closely analogous arrange-ment. There must always be a closed circuit, and as electric ity canonly flow in an electric conductor, such as a metal, carbon, or a con-ducting liquid, the circuit throughout must consist of one or more ofthese materials continuously connected ; if at any point the connectionbetween the conductors is broken by a non-conductor, such as air,ebonite, indiarubber, etc., the current must at once cease flowing
Thus the necessary conditions for a continuous flow of electricityare:—
1st. A source of electricity motive force or e. m. f.2nd. A continuous closed conducting path in the course of which
the source of e. m. f. is placed.
MAGNITUDE OP ELECTRO-MOTIVE FORCES OP BATTFRTES. 5
electro-motive force of any generator is measured in terms of the unitof electrical pressure or electro-motive force, which is called the volt.The actual value of the e. in. f. of any single cell of any electricalbattery which is employed in practice varies from the highest value ofabout 2*2 volts in a secondary battery, down to about ro volt in aSmee's cell. It must be understood that the unit of e. m. f., orelectrical pressure, is analogous to the unit of head of water, orpressure of water, which is usually expressed in so many feet of head.The electrical pressure required in electro-plating work varies fromabout 2 volts up to as much as nearly 8 volts, whilst for ordinaryhouso lighting work pressures usually vary from about ioo volts up toas high as 250 volK on the lamps. Most people can hardly feel apressure of roo direct volts*, when applied to the hands across the body,whilst it is unlikely that 250 volts could give a dangerous shock, unlessthe hand* had been previously well soaked in some conducting liquid.h must be remembered, however, that these results only apply to directpressures; alternating pressures at 100 volts may produce very un-pleasant sensations with some persons, and especially if the hands aremoistened with a conducting liquid. These details concerning thevalue of different voltages, are given in order to familiarise the readerwith some practical ideas of the order of the electrical presMires whichare employed for most electro-chemical processes.
ELECTROMOTIVE FORCES OF THE CHIEF CIIOIICU, BATTERIES.
Name of cell. Approximate volts. "Remarks on voltage.Secondary battery . . r8 to 2*2 constant.Lalande (Cupron elcmont) . 0*75 to 0*85 constant.Daniell I*I constant.Bichromate . . . . 2*1 volts fall with use.Leclanchi; . . . . 1*47 volts fall with \\?Q bu t
recover on standing.Smee's . . • 0*5 to ro volts fall with use.Wolla&ton . . . o'sto ro „ ,,Grove i*6 to 1*9 „ ,,Bunsen 1*5 to 17 „ „
Mixmmr ELECTRO-MOTIVE FORCES RFQUIRED FOR ELECTHO-PL.UINQ
REACTIONS.
Brass • . about 4 volts.Copper (acid bath) . . . . . 0*5 to 1 5 ,,
,, (alkaline bath) . . . . 3 to 5 „Gold 0-5 to 1 ,,Iron (steel facing of copper plates) . . 1 to 1*5 ,,Nickel (on various metals). . , . 1*5 to 8 ,,Platinum 4 to 6 „Silver 0*5 to 1 „Zinc (on various metals) . . . . 3 to 8 „
PRIMARY AND SECONDARY BATTERIES.
Mr. Watt's remarks, that a description of the various forms ofbatteries mentioned shall be given here. Moreover, as no doubt manyexperimentalists, amateurs and other*, may have in their possessionsome one or more of the older forms of electric batteries, a few wordson their construction and management may be found useful.
Electric Batteries.—An electric battery depends for its c. m. f.upon a chemical action occurring within it, and must have threeessential parts.
i and 2. Two different conducting bodies, always solid in practiceunless mercury is employed for one.
3. A liquid which can conduct electricity, but whicii is chemicallychanged by the passage of electricity through it. (Such aliquid is known as an electrolyte. This class of liquids isfurther considered on page 3$.)
The liquid is contained in some vesselmade of a material upon which theelectrolyte has no action, and one endof each of the two conducting solids isimmersed in the liquid. The solidsmust be prevented from touching oneanother in the liquid. To each of thetwo ends of the conducting solids or,as they are called, elements of the bat-tery, which are not immersed in theliquid, terminal screws are attached,and these serve to connect the batteryby means of wires to the apparatus,external to the battery, through whichit is desired to pass an electric cur-
rent. Such a simple arrangement of materials, forming a battery cell,as it is called, is shown in Fig. 1, where % denotes a plate ofmetallic zinc, and P is a plate of platinum; these are immersed in asolution of sulphuric acid in water contained in a glass vessel. Thebinding screws are not shown, but the external conductors of copperwire are soldered directly to the ends of the zinc and platinum respec-thely, which emerge from the liquid.
Each particular combination of a pair of solid conductors and elec-trolyte solution give a perfectly definite electricity motive force at anygiven temperature, but if the temperature is altered, the electricitymoving force of the cell is slightly altered; this alteration, however,is very slight compared with the alteration which may occur due tochanging the material of either one or both of the conducting solids andthe electrolyte.
Magnitude of the Electro-Motive Force* of Batteries.—The
Fig 1.-Single Cellb.
POLARITY OF CHEMICAL BATTKR1KS. 7
cell made up with the elements of hydrogen and zinc in dilute sulphuricacid instead of platinised silver and zinc in dilute sulphuric ; it hasalready been stated that the e. m. f. of the coll practically only dependsupon the nature of the elements and the liquid, and the hydrogen andzinc elements in dilute sulphuric have a smaller e. m. f. than theplatinised silver and zinc in the same liquid. Therefore by Ohm's law,as the e. m. f. has been decreased, the current must decreaseproportionately.
2nd. The deposition of the hydrogen upon the platinised silver platecauses the resistance of the cell to be somewhat increased, and thereforeas II is increased, we again see that by Ohm's law C must decrease.This effect no doubt does exist in the Smee cell to some extent, but itis not by any means Mich a powerful factor in reducing the current asthe fiist noticed cause.
The two above-described actions causing the decrease of the currentgiwn by a cell are included in what is known as the polarisation of thecell, a term which has nothing except custom to recommend it, but isalways intended to indicate the actions we have just considered.
3rd. The third cause of the cell's decrease of activity is due to thefact that the chemical or chemicals in the solution of the cell becomechanged. This always occurs to a greater or smaller extent in all cells.For instance, in the Smee cell the dilute sulphuric acid is graduallyconverted into a solution of zinc sulphate. In the Daniell cell thesame action takes place if dilute sulphuric acid is employed, whilst if azinc sulphate solution is used to commence with, this solution becomesmore and more concentrated. In the Bichromate cell this change ofthe character of the solution has a very marked effect, and it is alsoless, but still noticeable, in the Bunsen and in the Grove's cells. Thechange in the chemical character of the solutions alters one of thethree things necessary for a given e. m. f., and therefore, as mighthave been supposed, the e. m. f. itself is altered, and always in allpractical cases it is altered in such a sense as to diminish the e. m. f.This cause of alteration of e. m. f. of a cell is very small in the case ofthe secondary battery and the Daniell cell, it is greater in the Bunsenand the Grove's cells, and is probably most marked in the case of theBichromate cell, whilst in the Smee it has very little effect. It mustbe understood, however, that this does not mean that the Smee cell hasa much more constant e. m. f. than the Bichromate; as a matter offact their rate of fall of e. m. f. may be much the same, but in theSmee it is chiefly due to the polarising hydrogen, whilst in the Bichro-mate cell it is chiefly due to the alteration of the chemical nature of itsexciting fluid.
Polarity of Chemical Batteries.—All the batteries, with theexception of the secondary battery, which have been enumerated in the
6 PRIMARY AND SECONDARY BATTERIES.
It will bo noticed from the above given details that there is no singleroll which ran give the e. m. f., which is required for many electro-plating operations, but this difficulty may be readily overcome byarranging the batteries in series as it is termed. This method ofarrangement will be briefly referred to later on, but in the meantime itmay be noted that by thus arranging a sufficient number of any cellsin series, any desired e. m. f. may be obtained, and such batteries ofcells of even the lowest e. m. f. have been built up until very largee. m. fs. have been obtained, sufficiently high indeed to need greatcaution in dealing with them to avoid a dangerous shock. Forall plating purposes it is therefore clear that it is a very simplematter to connect in series a sufficient number of the single cells to givea battery having an ample e. m. f.
Polarisation of Cells.—Most electrical batteries, when they havebeen connected in a circuit with a fixed resistance, yield a currentwhich, although perhaps of amply sufficient magnitude at first, isgradually found to decrease in strength. In some cases this variationof strength is very marked, and this is the case although the resistanceof the circuit remains constant. Now the current in an electric circuitflows, as is well known, according to Ohm's law, which states thatthe resistance of any circuit, or part of a circuit, is defined as theratio of the total e. m. f. in that circuit, or portion of a circuit, to thecurrent caused to flow in the circuit. That is, if the resistance of acircuit is represented by the letter K, and the e. m. f. by the letter E,
whilst the current is represented by the letter C, then the ratio -^ is
equal to the resistance Rof the circuit, or the relationship is representedby the equation,
"P 7?~ =r K, or, as it may also be written C = -c a
If K is expressed in volts, and C in amperes, R is expressed in ohms.This well known equation enables us to readily calculate out manyuseful problems. For instance, in the present case, to explain thediminution of the current after a cell has been running some little timeon a constant resistance R, we see that the only way to account forthe fall in current is to suppose that the value of the voltage E of thecell has diminished, and this is ]^recisely what investigation shows hasoccurred. This decrease of the current is due to one or all of the threefollowing causes;—
1st. The current given out by the cell causes a chemical action tooccur in the cell, and if the cell is one containing a single fluid, suchas dilute sulphuric acid (as in the case with the Smee cell), hydrogen isdeposited on the platinised silver plate, and this coating of the plateoutside with hydrogen causes it in effect to act with the e. m. f. of a
THE LALANDE CELL. 9
When the cell is first put up it has an e. m. f. of as much as 1*2 voltsThis high voltage is said to be due to the presence of oxygen in thegaseous orm present with the cupric oxide. If the cell is shortcircuited for a minute or two, however, the volts fall rapidly to about0-82 volts, and then remain constant at this value until the cell iscompletely discharged, that is, until nearly all the cupric oxide ibreduced to metallic copper, when the volts fall to slightly under 0*7.
After complete discharge the cupric oxide plate is regenerated byremoving the reduced plate from the cell, washing it with water andleaving it in a dry and warm place, exposed to the air for a period of20 to 24 hours. If a temperature of 8o° to 1500 Centigrade is em-ployed, the copper is fully re-oxidised in from 20 to 30 minutes. Theplate can then be replaced in the battery, and the cell can once more beused. When the caustic solution is exhausted, a yellowish-grey pre-cipitate of zinc hydrate is thrown down. The cell can be workedafter this precipitate is formed, but the e. m. f. is no longer soconstant as before. The exhausted solution, which consists ofcaustic alkali saturated with zinc hydrate, should therefore beremoved and replaced by a fresh solution. The zinc plates, whichmust be kept amalgamated, must from time to time be cleansedfrom the grey deposit which forms upon them.
The resistance of this form of cell is extremely low, the voltage isvery constant (see Figs. 3 and 4), and as it gives of? no noxious orcorrosive fumes, it may be used in any room without any difficulty onthat account. The cell behaves very much like a secondary batterywith respect to its discharge voltage curve. When it is not being used,all chemical action ceases, and in this respect it is far more perfect thana secondary battery, for if the cell is kept closed up, it can be left formonths, and at the end of tf iat time its charge is as large as at thebeginning. The zinc consumption is from 1 '25 to 2 grams per amperehour. The consumption of alkali is about 6 grams of commercial causticpotash, or four grams of commercial caustic soda, per ampere hour, or ifthe chemically pure alkalies are employed, the consumption is only halfthe above weights. If large batteries are employed, and much workdone with this form of cell, the alkaline solutions, when saturatedwith zinc hydrate, need not be thrown away, as is usually done withthe smaller batteries, but may be regenerated by means of the additionof a suitable quantity of sodium or potassium sulphide, according tothe equation—
Nas H2O2 Zn HjO2 -f Na-> S = 2 Na2 H2O> + Zn S.
Although more expensive, it is rather more convenient to employcaustic potash than caustic soda for this battery, for the caustic soda isliable to form crusts of sodium carbonate, which creep up over the
8 PKIMARY AND SECONDARY BATTERIES.
foregoing list contain metallic zinc as one of their elements, and it isuMeful to note that in every ease the terminal of the cell connected tothe zinc i^ the negative terminal, that is to say, that when connected incircuit the current will flow out from the other or positive terminal ofthe cell and back again in at the negative or zinc terminal. As far asthe \\ riter is aware, there is no primary battery in general use whichdoes not contain zinc, and the zinc is always the negative terminal.
In order that the referenced to different batteries in the followingpages may be intelligible, it is necessary to briefly describe the variousforms, but it must be understood that the only essentials in a givenbattery are the nature of its clement* and its exciting fluid or fluids;the particular arrangement or form of the vessels containing the fluids,and the shape and i^xsition of the elements, may be varied almostinfinitely to obtain certain advantages oi packing of cells, or portability,
or cheapness, or low resistance, or thecontrary for special purposes. In aDaniel 1's cell, for instance, it is of onlyminor importance whether the cell is flatand rectangular, or cylindrical in shape,and whether the amalgamated zinc isimmersed in zinc sulphate solution con-tained in the porous pot with a coppersulphate solution outside, in which thecopper is placed, or the reverse arrange -meut is adopted, with the copper plateinside the porous pot containing thesolution of copper sulphate, whilstthe zinc is out.side in the zinc sulphatesolution; in either case the e. in. f. is
the same, and the cell is a Dauiell cell.
Primary Batteries.—The Lalande (Cupron element), the Daniell,the Bunsen, the Grove, the Leelanche, the Smee, the Wollaston, andthe Bichromate cells are all primary batteries, that is to say, they arecells which give an electric current without having* previously had anelectric current passed through them to charge them.
The Lalande Cell (Cupron element).—Thiscell (Fig. 2) consistsof twoamalgamated sheets of zinc, which together form the negative element,immersed in a solution of either caustic soda (170 grams of commercialcaustic soda per litre) or caustic potash (228 grams of commercialcaustic potash per litre). The makers state that caustic potash or sodavolution of about 19° to 2 1° Beaume is employed. The positive plateof the cell is formed of a mass of cupric oxide, and it is in themechanical construction of this plate of copper oxide that the patentfor that form of Lalande cell known as the " Cupron element" exists.
<'J<( 2.—Cupron ElementCell (Lalande Battery).
THE LALANDE CELL. I I
2 . 0
i
o
it
<*
cs
\ •
\
V
s • ^
•*•
"*B
m
•mm
5
tm
•M •M
Ma
r i
tm
-m
wmm s
1
•M
5
mmma
A
/o
MBJ
m
It s.
•a
p€
=
ao
5.B9I • i MM
• •
mm
iF
a n • • •M
• m
M i ss
• • •
3 0
•w •*•• * ,
•Ma
jj
35Tune in Hours
Fig. 3.—Strong Current Discharge Curve.
The following are the diseharofe curves ot a No. 1 " Cupron"element with a nearly constant current of mean value = o* 15 amperes.
The external resistance = 5*34 ohms. The internal resistance = 0*06ohms. The mean terminal voltage = O'So volts. Tlie ampere hourcapacity = 60. The weight of sodium hydrate employed was, of course,the same as in the last case (Fiir. 3).
2.0
15
io
at
Aihaeye 1 1 11 M L
<*
10
a*
too Z50Time in hours
Pig. 4.—"Weak Current Discharge Curve.
1 0 PRIMARY AND SECONDAUY BATTKRJKS.
sides of the cell and tin* plate; if caustic soda it* used, and this incrus-tation is observed, it must be renuned from time to time.
The following table is given by Mcs.sr*. Umbreit and Matthcs ofLeipzig, the makers of this cell, summarising its chief important points,including output, weight, dimensions and price :—
T\ pe ot cell.(Trade numbei). I I .
Electro-motive force in volts . ' 0*85 085Terminal potential difference j
when normal current is taken ' |off '078-0-82 0-78-0-82
Terminal potential differencewhen maximum < urrent is J
1 taken off o'7o-o#75 0-70-0-75Normal current output in am-
j poresMaximum current output in
I amperesCapacity of cell in ampere
1 hours 40-50Internal resistance of cell in
I ohms o 06 o 03Water required in litres . . 12 ' 2*3Caustic soda, weight lequired
f for one charge in lbs. . . . 044 o'88Caustic potash, weight re-
| quired for one charge in lbs. . o"66 j 1-32Number, and dimensions of the
copper oxide plates in inches,J approximate 1 4*75X4) 1(6x6)Length of CPU in inches . . . 7-5 7-5Width of cell in inches . . . 2-25 3-5Height of cell in inches . . . 7*5Weight of cell complete, in lbs. 3-3 5*82Price in German marks (1
mark = 1 shilling, about).
! in.
jI1 0-85
! IV.
I
0-85
0 78-0*82 o'7S-o-S2
0-70-0-75 0-70-0-75
4
8
160-200
0*0015
4'4
1-67
2'42
2(6X6)8
511
n'55
16
8
16
350-400
O'OOOJ$
7
3'3
4'4
2 (8X8)95'513*519-8
27
The following are two discharge curves of a No r "Cupron"element with a nearly constant current, Mhose mean value == 1*55amperes.
The weight of sodium hydrate (commercial) was 200 grams. Theexternal resistance between the cell terminals = 0*43 ohms. Theinternal resistance of the cell = 0-06 ohms. The mean terminal ^o\-tage during discharge = 0-76 volK The ampere hour capacity •= 53 -5.
DANIELL S CELL. 13
and is about 12 inches high, it costs four shillings. The copper cylinderwhich stands inside this outer pot is fourteen inches high, and is madeby bending up a rectangular sheet of metallic copper, measuring 14inches by 22 inches, into a roughly cylindrical form. The thickness ofthe copper sheet need only be sufficiently great to permit it to standstiffly after it is bent up. The cost of this copper, which weighsroughly about 3 lbs., is about two shillings and threepence. Insidethe copper cylinder is placed an unglazed or porous pot, 13 inches high,and having a diameter of about 5 inches. These porous pots costtwelve shillings per dozen. The zinc element which stands inside theporous pot consists of a cylindrical rod of zinc about 12 inches long and2 inches diameter. It weighs about 8*5 pounds, and contains 8 poundsof zinc and 8 ounces of mercury. The mercury is added to the moltenzinc just before casting, but this addition should be made when thezinc is very nearly cold enough to solidify, otherwi.se most of themercury is volatilized and lost. The addition should also be madeunder a chimney hood, so that any mercury vapour formed may asfar as possible be carried off, for it is poisonous. In my opinion themercury can be more easily and safely added to the molten zinc ifbeforehand it is allowed to soak with about a pound of granulatedzinc, which has been moistened with dilute sulphuric acid (one of acidto three or four of water), and after this amalgamation has been fairlycompleted, and the acid poured ofi", and the resulting amalgam thusobtained washed and dried, the dried amalgam can be added to theremaining melted 7 pounds of zinc, at a moderate temperature, with lessdanger of lobs of mercury by volatilization. In any case the mercuryand zinc alloy obtained is eabt into rods of the form above stated. Thecost of the zinc is about one shilling and twopence, and the mercuryabout one shilling and sixpence. The outer glazed pot <ontains asaturated solution of copper sulphate, to which an addition of about2'5 per cent, by volume of sulphuric acid is made, and an equal orrather smaller amount of nitric acid. The amount of this copperBulplmte solution is about 2\ gallons, each gallon contains about 2pounds of cry&tallised copper sulphate, which costs about twopenceper pound. The solution in the porous pot consists of dilute sulphuricacid, one part of acid to ten parts of water. The total cost of thesolutions is about one shilling- and eightpence. The brass terminals, ofwhich one is soldered on to the edge of the copper plate, and the otherhas the zinc cast on to it, coct about one shilling. The total cobt ofthis cell is therefore about fourteen shillings to make and charge com-plete. The resistance of the cell is slightly under 075 ohms. Six ofthese cells in parallel, when short-circuited, give a current of nineamperes. The e. m. f. is of course close to l*i volts, and the maximumcurrent one cell can give is about 1 '5 amperes*. The total weight of
PRIMARY AND SECONDARY BATTERIES.
Daniell's Cell.—This consists of a rod of amalgamated zinc im-mersed iii either dilute sulphuric acid (eight of water to one part acid),or a dilute solution of zinc sulphate contained in a pot of unglazed andporous porcelain. This pot stands in an outer vessel of glazed earthen-ware containing a saturated solution of copper sulphate, which shouldcontain a little free sulphuric acid, and is often provided with a shelfpartially immersed in the liquid, upon which crystals of copper sulphatemay be placed, so that the strength of the copper sulphate solution maybe preserved in spite of the constant removal of copper from it, due tothe action of the cell. A sheet of metallic copper is bent round theporous ]iot, and stands immersed in the copper sulphate solution. Thecell terminal screws are attached to the zinc and copper plates respec-tively, the y'nio being the negative pole. When the cell is not in usefor some time the porous pot should be lifted out. The level of the
zinc sulphate solution or sulphuric acid solution, accordingto which is employed, should be kept an inch or so abovethe lovel of the copper sulphate solution. This cell givesa remarkably constant c. m. f., and therefore a very con-stant current. It does not polarise. The zinc sulphatesolution gradually gets stronger, and must from time totime be diluted by removing some of the liquid, and fillingup with water, or dilute sulphuric acid. The copper sul-phate solution gets weaker in copper, and its strengthmust be kept up by adding fresh crystals of copper sul-phate, either placed on the shelf described above, or bysuspending a muslin bag containing crystals immersed inthe solution near the top. A two-pint cell will at themost give a current of not greater than about J ampere
in practice, even when dilute sulphuric acid is employedwith the zinc. In Fig. 5 is shown a view of a Daniell cell, in whichthe outer glazed earthenware pot, described above, is replaced by asolid copper external pot to which is attached the positive terminalof the cell.
I have been at some pains to find out the particular form of Daniellcell which may be most cheaply and satisfactorily made, in order toascertain how far this form of cell will compare favourably with theCupron element for use in electro-plating, more especially for electro-silvering and gilding. Mr. F. Lyne, silversmith and electro-plater,of 5, Perry Road, Bristol, has shown me a Daniell ccU which he uses,and in my opinion it is as cheap and serviceable a form of Daniell a*can be obtained, and I am indebted to this gentleman for the details asto cost, etc., which are here given. The outer vessel or containing potof the cell is made of a glazed earthenware cylindrical vessel, known inthe pottery trade as a dyer's pot, it has a capacity of about four gallons,
BUNSEN S CELL.
which A n is the bent zinc plate, C C are the platinum plates of thiscell and the next one to it, and Jj is the porous pot On the kft ofFig. " is shown a battery of four of the cells contained in one commonexternal glazed earthenware cell J), the alternate zincs andplatinums being connected by bras** clamps. This cell ha« a highe m. f. of about 1*9 volts; it, however, gradually falls when a currentis generated, owing chiefly to the weakening of the nitric acid in theporous, pot, due to the chemical action taking place The tell ha« alow resistance, and will ghe a larger current per square inch of positive
Fig. 7.—Grove's Cell.
plate than either the Daniell or the Smee The objections to this cellare chiefly that it is expense, it gi\es off corroshe and unpleasantfumes, and the nitric acid if spilt is liable to do much damage to amsubstance on which it falls.
Bunsen's Cell.—This cell is precisely similar in its constituent^to the Grove cell, except that the platinum is replaced by gas retortcarbon, which therefore makes it a much cheaper form of cell. Mr.Watt, in hi1* original edition of the present work, praises it as being"one of the most useful batteries for the practical purposes of the
PRIMARY AND SECONDARY BATTERIES.
the cell complete is over 50 pounds, and its output is less than that oftwo No. I Cuproii element.*,, which have in series a voltage of 1*5 volts,and give a current of alxmt 1*5 amperes, weigh under seven poundscomplete, have an internal resistance (the tw o in series) of under 0*2ohms, and finally take up a space 7*5 inches high and about 7*5 x 5square inches standing room, whereas the Daniell cell just describedtakes up a space of about 144 square inches standing room, and is over12 inches high, whilst finally the Cupron element cells cost (in Ger-many) ten shillings, as against a cost of about fourteen shillings for theDarnell cell, which has, however, a smaller output. There can there-fore be little doubt as to which is the more advantageous cell toemploy.
Smee Cell.—The Since Cell consists of two amalgamated zincplateb arranged on either side of a thin sheet ofplatinised sih er. The zincs are connected togetherto the negative terminal of the cell, and theplatinised silver is connected to the positive ter-minal. There is no porous pot, and the plates,which are supported at the top by a piece ofwood or ebonite, to which they are attached bythe terminal binding serew.s, are separated fromone another l)elow by a wooden frame or distance-piece, and the whole of this arrangement isimniei'bcd in dilute sulphuric acid (eight partswater and one part sulphuric), which is containedin an external glass, or glazed earthenware pot.A form of the cell i& shown in Fig. 6. This cell,which has an e. m. f. varying from 1 volt to 0-5
Fig. 6. volt, has a low internal resistance, and will, forthe same *-ize of po.sithc plate, gi\c a larger
current than the Dauiell, but the current is nothing like so constant.Grove's Cell.— This cell consists of an external flat pot of glazed
earthenware inside which is another cell of a similar shape, but madeof porous or unglazed porcelain. A flat plate of zinc is bent in sucha form that the porous cell may be placed within its folds, by means ofwhich arrangement a surface of zinc is expo.sed to each side of theinner cell. A plate of platinum foil is inserted in the porous pot, andib of sufficient length to be attached to the projecting* end of the zincplate of the next cell (when arranged in a battery), or to a piece ofebonite or pitch-coated wood when used singly, by means of a bind-ing screw or clamp. The inner porous pot, containing the platinumelement, is filled with strongest nitric acid, and the outer, in which thezinc is placed, is filled with dilute sulphuric acid (one pait sulphuricacid to eight parts water). Lu i i g . 7, on thts right, i& bhown a cell in
BICHROMATE CELL.
the fact that though plathmm is cheapest in a thin plate carbon ismost expensive and is much more readily obtained in the form of arectangular rod. The carbon rods are cut tiom retort < arbon, and thisis sometimes rendered still more dense by immersing in .sugar solutionand then heating to a high temperature repeatedly.
The original form of the battery and its dissected parts are shown
Fig 9 —Bunsen's Cell.
in Fi<r. 9 The carbon block in the Bunsen cell is more or lessporous, and absorbs the nitric acid in which it is immersed by capillaryattraction, in the same manner that a lump of sugar sucks up tea orother liquid into which one end is dipped. This arid will act on thebrass clam}) shown at B, Fig. 8, but to prevent this the outer end ofthe carbon may be made hot and then dippedinto hot paraffin wax ; this will block the pores atthe top, but, as the electricity travels along thesolid carbon and not through the pore-*, if theoutside of the block is scraped free from paraffinthe clamp can be screwed on and good metallicconnection obtained. This cell slowly drops it«e. m. f. like the Grove, and due to a similarcause.
Bichromate Cell. — The bichromate cell,Fig. io, is usually met with as a single fluidcell, and consists of two plates of gas retortcarbon forming together the posith e element, andplaced between them, but not touching them, is asingle plate of zinc, which is the negative elementof the cell. The exciting fluid is made by makinga saturated solution of potassium bichromate andadding to io parts by volume of the solution,about i volume of strongest sulphuric acid,added gradually, and with constant stirring, or
C
Fig. io.Bottle form ofBichromate
Battery.
The acid must bethe heat set at
i 6 PRIMARY AND SECONDARY BATTERIES.
electro -metallurgist." One form of this battery is shown iu Fig". 8.In this particular cell the outer \es.sel is a cylindrical stoneware jarcapable of holding about 4 gallons (but, of course, smaller cells aremade), A plate of stout sheet zinc i» turned up in the form of acylinder A, and this is well amalgamated with mercury. A suitablebinding screw is attached to this cylinder to receive the conductingwire. A porous cell about 3J inches in diameter is placed within thezinc, and in this a block of gas retort carbon is stood, and is furnished
Fig. 8 —Bim&eii's Cell.
with a suitable clamp B for attaching a conducting wire. The porouscell is then nearly filled with strong nitric acid, and the outer \essel isfilled to the same height with dilute sulphuric acid—about 1 part of<icid to 8 pait^ of water. Thi« battery, like the Grove, emits noxiousfumes, and must be kept either in a well-ventilated cupboard oroutside the windows if there are any substances, sudi as metals, etc.,which these fumes might damage in the room in which the current isbeing employed. The reason that a cylindrical porous pot is employedin this battery instead of the flat form used in the Grove, is owing to
MANAGEMENT OK PRIMARY BATTERIES. 19
idle, however, for a short time, it quite recovers it<* oriuinal e. m. f.The oxcitiiii? liquid is Imt ssliulitly poisonous, duo to the /me whichili^ohes in it, and it is non-corrosive; it is not, howe\er, very suitablefor any electro-platiug work. All the many forms of what are knownas dry cells arc variations on the Leclanehe cell, in Avhieli the ammo-nium chloride solution is made into a thick paste with some inertpowder, such as plaster of Paris, mixed with some calcium chloride.
Amalgamation of Zinc Plates.—If a plate of ordinary commercialmetallic zinc, coni •lining perhaps* 2 per cent, or so of impurities, is phu edin dilute sulphuric acid, it immediately commences to dissolve, largequantities of hydrogen gas being given oft' at its surface, and zincsulphate is formed which dissolves in the liquid. This chemical actionis due to what is called local action, caused by the presence of the im-purities in the zinc, for if these are removed, and quite pure zinc,obtained by distillation, is used instead of the impure commercial zincno such chemical action occurs, or at any rate it is extremely slow.Perfectly pure zinc may be employed as one of the elements of anyelectric battery, and the battery will act perfectly, but when not in usethe corrosion of the zinc will cease. The cost of this pure zinc is, how-ever, very high, and it has been found that if the surface of impurecommercial zinc is coated with a sheet of mercury, or rather an amalgamof zinc and mercury, the e. m. f. of the battery is not affected, andthe battery acts as satisfactorily as before, but the local action is com-pletely stopped, and when the battery is not being employed to ghccurrent the zinc does not dissolve. The coating of the zinc plateswith mercury, or amalgamation as it i> termed, is performed by rubbingthe plate with, a rag tied on to the end of a ^tick in a little dilute sulphuricacid (one of acid to ten of water), which may conveniently be placed ina deep saucer, and at the bottom of the saucer, under the acid, must beplaced a little mercury, which raibt be pushed up over the acid-cleanedzinc plate: the mercury will be found to wet the zinc, and leave itwith a bright silvered surface of zinc mercury amalgam. Only thesmallest amount of mercury possible to thus completely silver over theplate must be employed, as an excess of mercury merely causes theplate to "become rotten. When in use, if blackish spots appear on thezinc plate it must be again further amalgamated. The mercuryemployed for amalgamating must be kept by itself in a separate jar orbottle, as it contains dissolved zinc, and must be on no account mixedwith mercury it is desired to keep pure. Dirty or blackish zinc platesare conveniently scrubbed with a flat piece of pumice before amal-gamating.
Management of Vrimary Batteries.—The screws and connectionsmust be kept scrupulously clean, and the zinc plates must always beproperly amalgamated. The solutions in the battery must be renewed
i 8 PRIMARY AND SECONDARY BATTERIES.
liberty may crack tlio glass vessel in which the mixture must bemade. The vine plate is attached to a brass rod, which is held inposition by a thumb-screw. When the battery is not in use thisscrew must be slackened and the zinc raised out of the liquid bymeans of the rod, and must be held in this raised position by againtightening" up the thumb-screw. When the battery is being used thezinc must be lowered and the thumb-screw again tightened. Theneglect of this precaution is not infrequently a cause of considerabletrouble, as the battery will then give no current. The bichromatebattery has a high c. m. f., which is fairly constant, but in time falls,owing to the chemical alteration of the exciting fluid. The excitingfluid is, when fresh, of a dark orange colour, but becomes after it hasbeen used of a darker and darker brown, and then greenish browncolour, and finally quite dark green; before this complete changetakes place, however, the e. m. f. of the cell will have fallen con-siderably, and the solution should be renewed. As the solution isaltered it deposits hard dark-coloured crystals of potassium chromealum, which must be removed from time to time. The chemical actionin the battery goes on whether it is being used or not, if the zinc isimmi'isod in the solution, and it is on this account that the zinc plateis so made that it can be readily withdrawn directly the cell is out ofuse. The resistance of a bichromate cell is low, and it will giveabout as large a current as a Bunsen cell for the same area of thepositive element immersed in the exciting fluid. A double fluidbichromate battery is also made, in this the carbon plate is placed alonein the bichromate solution and the zinc clement, which must now beamalgamated, is placed in a separate porous pot with dilute sulphuricacid (one volume of concentrated acid to ten of water). In this formof the cell the zinc need not be withdrawn when the cell is not inuse, but if it is to remain out of use for some time it is better, as inthe Daniell cell, to remove the porous pot and its contents until thecell is again required. One marked advantage of the bichromatecell over other cells having high e. m. f. is due to the fact that it doesnot give off corrosive fumes.
The I*eclanche Cell.—This battery consists of a positive carbonelement surrounded by some paste or conglomerate of manganese dioxideand carbon. The carbon plate and its surrounding carbon and man-ganese composition stands in a solution of ammonium chloride, which iskept nearly saturated. The solution flows freely through the porouspot into contact with the carbon plate and its surrounding manganesedioxide, the cell being a single fluid cell. The negative element of thecell is a zinc rod. This cell gives off no objectionable fumes, and hasa maximum e. m. f. of 1*43 volts about, but after use for a short timeit polarises, and its voltage fallfe considerably; if allowed to remain
BINDING SCREWS* 2 1
plates, and there was in each case the same distance between thepositive and negative plates. The currents obtained for each batteryso arranged were passed through solutions of copper sulphate of thesame strength, with the electrodes of copper of the same size and equaldistances, each during the period of one hour. The following resultswere obtained:—
Grove battery .Daniell battery .Smee batteryWollaston battery
104 grains of copper deposited.3322 „ ,,
Constancy of Batteries.— The activity of most batteries graduallyalters if they are left unadjusted, so that one kind of battery may beuseful for a short period, and another kind if the action is to be sus-tained for any length of time. This is illustrated by the followingtable, showing the weight of copper deposited, the conditions beingthe same as in the last experiment:—
Grove batterySingle-cellDaniell . .Smee . . .Wollaston .
Onehour.
1 0 4
62332 2
18
Twohours.
86
57351614
Threehoui s
665434H15
Fourhours.
6046321 1
1 2
Fivehours.
5439321211
S i xhourb
49293OI I
1 0
Seven T t ,hour* l o t a l -
45 464 grs24 311 n3i 227 „10 s 96 „10 90 ,,
In a second experiment of a similar nature, larger plates were used inthe batteries, and proportionately larger electrodes in the copper sul-phate solution, and each battery was kept in action until one pound ofcopper was deposited, the acid being renewed and the zincs brushedevery twenty-four hours. The time taken to effect this is shown inthe following table:—
, 147 hours.Grove battery .Single-cellDaniell
. 19* hours.• 45. 49
Smee batteryWollaston
Binding Screws.—These useful and necessary appliances areusually made from cast brass, and may be obtained in a great varietyof forms. A few examples are shown in the accompanying engrav-ings. Fig. 11 is used for connecting the platinised silver of a Smeobattery to the wooden cross-bar, or for casting in zinc bars for Darnell'ibattery; Tig. 12 is used as a connection for a zinc or flat carbonplate; l l g . 13 is a binding &crew for zinc plates, or for the cylinder a
20 PRIMARY AND SECONDARY BATTERIES.
from time to time, as they are seen by inspection to be becoming rundown, or if the cell does not act sufficiently energetically. Anotherfrequent cause of a battery's failure to act is the contact, howeverslight, of one of the elements with the other inside or outside theliquid, an accident which is known as a short circuit. A loose orcorroded attachment between the battery terminals and the activeelements, or a loosely screwed up wire in the terminal may also causethe battery to cease to work entirely. In Bunsen batteries the upperends of the carbons and the brass clamps should be coated with varnishafter they have been screwed up, in order to avoid action on the brassby the nitric acid.
The coj>per plates of the Wollaston and the silver plate of the Smtebatteries must be kept clean, and if accidentally spotted with mercuryfrom contact with the amalgamated zinc plates, the sheet of metalshould be heated in a flame to expel the mercury, and then shouldbe pickled in dilute sulphuric acid, and scoured after rinsing. Thozinc elements in Daniell cells should not be permitted to touch thrporous cells at the bottom, or a deposit of copper may take place bothinside and outside the cell and render it useless. Porous cells oftencrack from this cause. "When porous cells have been used, and are laidaside until again required for use, they should first be well rinsed inrain or distilled water, and then filled with distilled water. Theyshould never be allowed to become dry, or otherwise any sulphate of zincor copper remaining in their pores will crystallise, and probably in sodoing crack the pot in many places. If when a porous pot is removedfrom a Daniell cell, in which the acid is weak or is entirely replacedby zinc sulphate, it is rinsed out and stood in hard water, that is watercontaining calcium carbonate, a green deposit, or precipitate of cupric,and lime carbonates will be formed in the pores of the pot, and thisdeposit will, in the course of time, very greatly increase the resistanceof the cell If distilled water or very soft water is used this troublewill not occur, but if hard water is the only available variety, it shouldbe slightly acidified with sulphuric acid before it is poured into thecell, and the cell and contents stood in a sink, then the slow oozing ofthe acid water through the cell's pores will remove the copper and zincsalts without precipitating them. If a cell whose resistance has beenraised by the deposit of the basic carbonates, as described above, iswashed or soaked in dilute sulphuric acid, it is often found that thecell becomes cracked all over and perfectly useless, caused by thechemical action which is set up in its pores.
Relative Activity of Pr imary Batteries.—The following experi-ments roughly indicate the relative activity of different kinds ofprimary batteries. The zinc plates were the same in each battery, andin each battery the positive plates had double the area of the zinc
SECONDARY BATTERIES. 27,
lead and a positive element of lead peroxide, supported on some form otlead frame-work. There is always one more negative plate than thenumber of positive plates present in a cell. The exciting fluid is asolution of sulphuric acid in water, having a specific gravity whichvaries from 1-170 when the cell is discharged, up to 1*215 when it isfully charged.
The voltage of a secondary battery, when fully charged, should be2*2 volts, measured whilst the cell is giving a discharge current ofabout half its normal charging- current, and the cell may be usedwithout re-charging until its voltage drops to not lower than 1 '8 volts,measured whilst the cell is giving a discharge current of about half itsnormal charging current.
The voltage of a secondary battery is for all practical purposes veryconstant, and during the greater part of its discharge is very clo&c to2 volts. The resistance of a secondary cell is very much lower than thatof any other form of cell of equal current output. The current outputof any cell is always stated by the maker, but in each ease the actualcurrent output at which the cell is run must depend upon the number ofhours during wliich it is required to be used ; for instance, a .single plate" Chloride " secondary battery, manufactured by the Chloride ElectricalStorage Syndicate of Clifton Junction, Manchehter, which costs wellunder twenty shillings complete, may be discharged for one hour atthe rate of 30 amperes*, but if it is wished to run it for three hourb ouly15 amperes miibt be taken from it, whilst for a six hours discharge, therate may only be 9 amperes, and if discharged at a uniform rate fornine hourb, the current taken out must not be greater than 6'j amperes.The normal charging current for this cell is stated to be 8 amperes, andthe maximum charging current must not be greater than 15 ainpcio.A six-plate cell of this type ib shown iu Fig. 18, and Figs. 19 and 20give ^ iews of the negative and positive plates respectively ; Fit>\ 2 1gives a \iow of three of the Electric Power Storage Company'^secondary cells arranged in scries on a stand. This particular MZOcontains five positive plates. When the voltage of a secondarybattery cell has fallen to 1*8 volt% as measured by a voltmeterwhilst the cell is discharging at the rate of about oue half itsnormal charging current (that is. to bay, in the chloride cell we havebeen considering above, whilst the cell is discharging at the rate ofabout 4 amperes), the cell must not be used any more until afterre-charge, otherwise it will be more or less permanently damaged.The cell can be re-charged, however, and when its voltas»o has risen toabout 2*2 (as measured with the discharge current stated above), it iscompletely re-charged, and can be used again and again under theseconditions, with alternating charge and discharge, for a very long peiio«iif proper care is taken of it. The chief necessary precautions* which
22 PRIMARY AND SECONDARY BA1TERILS.
of a Bunsen battery; Fig-. 14 i» for uniting the poles of dynamos withleading rods: Figs. 15 and 17, are for connecting flat copper bandb to
Fig. ir. Fig. 12. *3- Fig. 14.
zinc and platinum plates, as in Oro\e's battery; Fig. J6 is a clampfor large carbon blocks, for uniting the zincs of a fcniiee, or the copperplatcb of a Wollaston battery.
Fig. 15. 16. Fig. 17.
General Remarks on Primary Batteries.—With the exception oithe " Cupron element," primary batteries require much more careand attention to keep in proper working condition than any other formof generator. Their resistance is as a rule large, and varies with theiroutput, and, as has just been shown, their activity diminishes veryseriously with the time they are left in circuit. The ordinary forms ofprimary batteries are therefore on all grounds, including cost, the leastadvantageous form of source of e. m. f., and should if possible neverbe employed for electro-technical work ; and, unless already possessedby the experimenter, the writer strongly advises him not to purchasethem, but either to invest in some form of the Lalande or "Cupronelement," cell, or in a dynamo or secondary battery, according to thecircumstances of the work it is desired to undertake, a discussion ofwhich considerations will be found at the end of the next chapter.
Secondary Batteries.—Secondary batteries, which arc made in alarge number of different forms, always consist (at least in all formsused commercially up to the present) of a negative element of metallic
SECONDARY BATTERIES. 25
partially charged condition. That is if it becomes necessary to leave itwithout discharging it for, say, a week, see that it is charged up fullyto begin with, and disconnect all leads from it in order that any leak-age may be as much as possible reduced.
2. Never discharge below the A oltage limit of r S , measured as speci-fied above.
l°ig. 19.—Single Negative Plate of Chloride Secondary Cell.
3. Never allow the acid in the cell to evaporate below the top edgesof the battery platen The acid in a cell always tends to decrease, duepartly to evaporation, and partly to what is called spraying. Sprayingis the name given to the spray carried off by the hydrogen and oxygengases liberated in the liquid Avhen the cell is charged, and is especiallynoticeable towards the end of the charge. In order to replace suchlost acid, the cell must from time to time be filled up with either dis-tilled water or rain water, until the level of the liquid is about one to
PRIMARY AND SECONDARY BATTERIES.
Fig. 18.—Chloride Secondary Cell, having Six Positive Platesiu Glass Box.
miibt be taken in order to keep a secondary cell in good condition areae follow*:—
I. Never leave the cell for auy long period in the discharged, or only
SECONDARY BATTEKIES. 27
acid mu&t be added to make icood the loss. To do this it is advisableto keep a mixture of about 3 parts by volume of sulphuric acid(b. g. — 1*85) with 5 park by \oluuie oi distilled water or rain water.
Thib mixture lias a bpeeifie gia\ity of about 1-28, and wlu-u Uiogravity of the acid in the K-condary eell i> found iiimudiatvl> aftrr ,1full charge to be u» low a> l-iy, the btrou^cr <iud solution mubt be
26 PRIMARY AND SECONDARY BATTERIES.
one aud a-half inches above the top of the edges of the plates. As waterhas a less density than the acid liquid in the eells, the added water willtend to remain ah a layer at the top of the cell, floating" upon theunderlying* denser acid. This weak acid at the top tends to damagethe top.s of the plates, and it is therefore a good practice to mix theliquid in the cell, after adding the water, by blowing through a glasstube, pushed down to the bottom of the cell, and having a piece of india-rubber tubing attached to it for a mouth-piece.
Fig. 20.—Single Positive Plate of Chloride Secondary Cell.
It is perhaps hnrdly necessary to caution the reader against gettingthe acid into the mouth : the result will be disagreeable in the highestdegree. As the spraying of the acid liquid removes not only waterbut acid, and as the directions abo\ e given for the making up the lossonly involve the addition of water, it is clear that the acid liquid inthe cell must gradually become weaker : thi.s weakening certainly doesoccur, but only blowly, and when it becomes detectable sufficient fresh
SECONDARY BATTERIES. 29
each of the sides of the cell, and have a sufficiently strong leather sling-Landle soaked in paraffin wax attached to these. This sling-handlemust be large enousrh to permit of its being readily pushed on one sideto allow the cover of the cell to be removed when desired.
7. Be very careful that in charging a cell you connect the positivepole of the cell to the positive pole of the charge apparatus, andthe negative to the negative. The polarity of the terminals canreadily be found by inspection, for the positive terminal is attached tothe lead peroxide plate, which has always a more or less marked darkchocolate colour, whilst the negative is of a darker or lighter cool greycolour. In cells which are fitted with covers, however, the error ofmistaking the polarity is rather easily made if care is not taken whenthe lid is replaced after inspection or adjustment, for the lid of thesec Us has the polarity marked upon it, and it is sometimes not marked onthe emergent lugs of the plates ; consequently if the lid is placed on inreverse position the poles, as judged by inspection, are apparentlythe reverse of what they really are ; this difficulty can be got over bynever allowing anj^one but a reliable and responsible person to remo\ ethe cover of the cell.
8. Do not short circuit the cell, that is do not place a very small orzero resistance between its poles ; the cell will under these circumstancesgive a very large current and will thereby have its useful life muchshortened. Some people make a practice of what is called sparkinga cell, that is, rapidly drawing a wire attached to one teiminal o\erthe other terminal of the cell in order to sec if a spark is given. Thisspark is taken to indicate by its brightness the more or less completecharge of the cell. The proper test to use to ascertain this, is a smallcell-testing voltmeter. Such an instrument costs only about thirtyshillings, it need not read to higher than about 3 volts, and shouldread with an accuracy of not less tiian o#2 volts per dr\i>ion. A g*oodpocket instrument of this kind (Fig. 23) is put on the market byO. Berend & Co., Dunedin House, Ba^inghall Avenue, London, E.C.,and good forms are male by many other manufacturers of electricalinstruments.
If by any accident any material of any kind falls in between theplates, if it is made of a condiK ting substance, it will probably producea short circuit, and the cell must be taken to pieces to remove it. If,however, it is not of a conducting material and it is desired to removeit, a rod of wood, glass, or other non-conducting material must beemployed to fish it out. A rod of conducting* material must on noaccount be introduced between the plates of a charged cell for arypurpose whatever.
9. To keep cells in good condition it is very advisable to rule out a bookin columns, two columns to each cell, one for the vo'ts and the other
28 PRIMARY AND SECONDARY BATTERIES.
added gradually, a little at a time, until the strength of the acid inthe cell rises to i*2i once more.
4. Never remove the negative, or lead (that is the grey-looking)plates, from their acid solution, or, at any rate, do not let this be donefor more than a very short period when it becomes necessary, as issometimes the case, to straighten plates damaged by accidental shortcircuit or other cause.
5. The positive or reddish-chocolate coloured plates, may be removedfrom the acid safely when necessary, but should not be left out longerthan can be helped. No attempt, however, must be made under anycircumstances, unless the cell has already been accidentally completely
Fig. 22.—E. P. S. Portable Q Type Secondary Battery. (In the particularbattery shown here four separate cells are connected in series, eachseparate cell having three positive plates.)
short circuited, to remove either the positive or negative plates from acell whilst it contains acid, otherwise a serious short circuit will almostcertainly occur. The best method of taking to pieces and overhaulinga cell will be mentioned later on.
6. Be very careful to see that no leakage occurs outside the cell fromthe positive to the negative terminal, a common but often unnoticedcause of leakage is the acid soaked wooden cover of the portable orenclosed form of secondary battery. A partly dissected view of aportable E. P. S. secondary cell is shown in Fig. 22. Do not have ametallic handle on the lid of such a cell, or if it is placed on the cell bythe makers, ask them to remove it and place metallic handles, one on
BUCKLING OP CELL PLATES. 31
popper and, indeed, most other substances, have a very pro judicialeffect upon the buttery action, and all possible sources of contaminationshould be as far as possible avoided.
II. All connections to the battery—as, for instance, JB|brass bolts, nuts, washers, etc.—must be kept carefully PBclean, and when in use must be tightly screwed up. rplDo not clean up the metal parts whilst they are in posi-tion over the acid, for it may thereby be contaminated.
If the secondary battery is necessarily to be carriedabout as, for instance, when it ha* to be charged up onother premises, it is advisable to purchase a portableform of battery, but if the battery can be chargedwhilst in a fixed position it is better not to purchase aportable form of coll. Quite apart from the fact thatportable cells are liable to damage somewhat with car-riage, the non-portable type gives a better cell, forthere is better insulation and therefore less liability ofleakage, which is itself a very fruitful source of de-terioration in a cell.
Buckling of Cell Plates.—If a secondary cell isbadly short circuited, or if discharges are taken from itwhich are above its proper capacity, the plates are liableto buckle or bend, and the paste or plugs of peroxide oflead may fall out, and either or both of these accidentsmay completely short circuit a cell internally. Thiswill become evident by the fact that the voltage of thecell reads zero on the voltmeter and the cell will give nocurrent, nor can it be charged up so as to yield a current.Under these circumstances it is absolutely necessary totake the cell to pieces and bend the plates straight oncemore, or remove the plug of lead peroxide which iscausing the short circuit. This operation may be per-formed as follows : first pull out gently the ebonite,glass or celluloid insulators or combs1, which will befound to be separating the positive plates of the cellfrom the negative ; when these separators are all removedlift out the whole of the positive plates and carefullystraighten them by gentle bending where necessary.This bending must be very carefully performed, and isbest effected by placing a wooden board of suitable thick- Hydrometerness between each two positive plates, and gently press-ing the whole pile until all the plates are bent flat and parallel to oneanother. The negative plates are not often found to bo buckled, butif by any chance they are bent they must be lifted out of the acid and
Fig. 24.Cell-
Testing
30 PRIMARY AND SECONDARY BATTERIES.
for the specific gravity, and record the voltage of each cell (measuredwith the precautions already stated) and the .specific graMty of itssolution about twice a week. Such a record ismo*t useful for referenceand shows at a glance the conditions of the cells. The specific gravityof the solution should be taken by means of a hydrometer (Fig"- 24)such as is sold by most cell manufacturers at a price of about two orthi ee shilling each. In many small secondary batteries it is impossible
Fig. 23.—Portable " Pocket Form " of Cell-Testing Voltmeter.
to use a hydrometer directly in the liquid of the cell, as there is noroom for i t ; under these circumstances a sufficient quantity of theliquid bhould be carefully withdrawn from the cell by means of apipette and transferred to a cylindrical tube of sufficient length andwidth to permit the hydrometer to float.
10. Great care should be taken to prevent any copper or brassmaterial (as, for instance, salts and oxides from corroded connectingscrews) from falling into the battery acid, as the presence of salts of
ELECTROLYTES. 33
If by any chance the electrolyte of the cell is spilt the loss must bemade up, not by the addition of distilled water or rain water, as whenevaporation is to be made good, but a sufficient quantity of cold dilutesulphuric acid of r 10, to 1-21 s. g. must be added.
Correct Acid Strength for Secondary Batteries.—The properstrength of the dilute sulphuric acid to be employed for secondarybatteries is usually stated by the maker of the cell, but it is alwaysclosely in the neighbourhood of 1-21. nu sisiuvd at the ordinary airtemperature. This strength of ncid may be made by gradually pour-ing two parts by volume of strung sulphuric acid (1*85 s. g.) into fiveparts by volume of distilled or rain watt r. Heat is liberated, and theacid must be added in a thin stream to 1he water, which is kept wellstirred by a glass rod or a wooden stick. The mixture is best madein a glass vessel, but care must be taken that the acid is graduallyadded, otherwise the rise of temperature will crack the glass; afterthis mixture has been made it must be allowed to cool, its specificgravity carefully measured and adjusted by the addition of morewater or more acid according as the gravity is above or below thedesired value of 1 *21.
Annual Cost of Secondary Batteries.—If a secondary battery isproperly attended to, it may be taken that the annual charge forinterest, depreciation, and repairs is not less than twenty per cent.,reckoned on the prime cost of the battery, but this charge may be con-siderably increased if proper care is not taken to superintend the cells.A portable battery has usually a higher rate of depreciation than afixed battery. Makers will under certain conditions, which are, how-ever, somewhat strict, enter into maintenance guarantees with pur-chasers of their battery. The Chloride Company, for a fixed battery,will enter into such a contract for five years for an annual payment of12 3 per cent, of the value of the battery, but for longer periods thisfirm requires a larger annual payment, and if we allow interest chargeat 5 per cent, the total charge will not be appreciably less than 20 percent.
Electrolytes.—Liquids may, in so far as their electric behaviour isconcerned, be di\ ided into two main classes, namely: liquids which willallow the electric current to pass through them, and liquids whichwill not allow the current to pass through them. The second of theseclasses, namely, those which will not permit the electric current to nowthrough them, are of course insulating liquids, such as, for instance,paraffin oil, turpentine, resin oil, and generally many organic com-pounds known as hydro-carl ons and fatty acids: with this class wehave practically nothing to do in electrolytic refineries, although it istrue that insulators for stationary secondary batteries, and insulatorsfor the support of electric conductors, are frequently filled with some
D
32 PRIMARY AND SECONDARY BATTERIES.
straightened in the same manner n<* the positives; this operationmust be performed without undue force, but as rapidly as possible,for the exposure to the air damages the negatives, aud the straightenedplates must bo returned into the dilute acid as promptly as possible.The rapidity and violence of the chemical action of the air upon themoist negative plates is shown by the fact that, tutor a very shortexposure to the air, they will become hot and the dilute acid ontheir surfaces will rise in clouds of steam. When the plates have beenstraightened as described above, they are returned to the acid fromwhich, however, any plugs of paste or sediment of lead peroxide shouldbe previously removed. The plates sometimes rest upon glass,celluloid, ebonite, or even wooden racks at the bottom of the cell, andcare must be taken that these are in their proper position when theplates are replaced. The insulators should next be re-insertedbetween the positive and negative plates, the level of the acid made upif necessary with dilute i '2i s. g. acid, and the cell is ready for re-charging. It should be charged for a considerable period with acurrent which should be about that of the minimum charging currentspecified by the makers of the cell. This charge may with advantagelast 30 hours, but usually this is inconvenient, but it should in anycase be made as long as possible. Charging and discharging alter-nately at low rates of current output over long periods of time, andtaking care never to discharge below i-8 volts, is a method of treat-ment which tends to get the plates of a repaired short circuited cellinto good condition.
Treatment of Cells in Bad Condition.—If a cell is found, whencharged in series with others of the same size and make, not to effer-vesce so copiously when the charge is being completed, and if thiscell drops its volts on discharge after it has been in use for a shorttime, whilst similar cells working at the same output keep their voltagefor a longer period, it is clear that the cell in question is getting in anunsatisfactory condition. It is said to have a small ampere hourcapacity. In order to restore it to condition it is advisable to chargeit up with the other cells, but not to discharge it or, at any rate, toonly slightly discharge i t : this treatment continued over some half-a-dozen charges will usually do much to get the cell back into conditiononce more.
If the electrolyte of the cell gets into bad condition by reason ofcopper salts or other contamination finding its way into the liquid itmay become necessary to change the liquid; this may be done bysyphoning it out and having at hand some previously prepared colddilute acid of the correct gravity, which can be rapidly added in orderthat the negative plates may remain uncovered for as short a period aspossible.
CONNECTION OF KATtKRIKS TN SERIES AND PARALLEL. 35
ing", ami in many eases, especially in the ease of a secondary electricbattery, or any cell having a very low internal resistance, or a dynamounder the KUILC condition of low internal resistance, which alwaysexists in (ommenial machines, much damage may be done to thegcneratoi : the< ell or dynamo, as the 1 asc may be, being often ruiiiv d un-less the " short '* lastsa\(ry short time iudced. The darner of such a''short • ir< uif " 01 •( urrinii is avoided a-, far as possible by pln< inyfusible cut-outs in (ir< nit, which will be m< Ited by the cumnt flowingduo to the " short <ircuit " it this iu->t- for more than a very limitedtim.1, thus interrupting the- ".short' ,1 d preventing the elanuc_se tothe HI nerator.
The term "short < iivuif " may also be applied <o the case where acurrent which is nowini>- through, say, an electrolytic bath, by reason,let us im.iu'ine, of MHUC piece of metal falling across the metal terminalsof the bath, flow> through tin's metallic path thus provided, which lias
'i?. 25 —Battery arranged in series
a very low resistance, in^t, ad of through the higher resistance path ofthe electrolyte, in which its function is to produce some (hemicalchange. Thus, whilst this- short circuit lasts the electrolytic vat, whichis short cir< uiHl. is useless-, its duty of providing4 so much metal oroth< r material per hour is completely interrupted until the short(ircuit is removed. Lastly, a current uener.itor may be internally shortcircuited. a*» has been desciibed in the case-of a secondary battery inwhich a pliur of paste has fallen between the posith e and negative plates,thus electrically eonnectinu: them inside the cell terminals. This iscalled an internal short circuit.
Connection of Batteries in Series and Parallel.—As liasalready been remarked, batteries of electrical cells mny be arrangedconnected in serie- to i i \ e a large \oltaore. This arrangement isshown in F!<rs. 2^ and 27, where the positive of one cell is connected tothe neu\tti\e of the n<\t, and so on, until the desired number of < "Us"hn\ e been < onueeted, and the final unconnected positive and negative
34 PR1MAKV AND SKCON1>ARY BATTKK1JKS.
such liquid non-conductor. The first class of liquids, namely, thosewhich permit a current of electricity to flow through them, may beagain divided into two other sub-classes : first, liquids which will permitmi electric current to flow through them, but which suffer no altera-tion of composition or chemical change due to the passage of the cur-rent. Sin h liquids are usually moll en metals or molten allots, such asmercury, or molten iron, brass-, .soldi-]*, dc . The s< < ond sub-class con-sj^N, howe\ir, of liquids which allow tin < HITCHt to flow throughthem, but at the -*ame time the < mrent causes a chemical alteration ordecomposition of the liquid. Such liquids ;ire called electrolytes, andusually consist of an aqueous solution of a salt, an acid, or a base, orconsist of a molten salt, acid, or base. Examples of these electrolytesare :—a solution of copper sulphate or of common salt in water; a solu-tion of sulphuric acid or hydrochloric acid in water; a solution of caustic>oda or potash in water; liquid fused zinc or sodium chlorides ; fusedphosphoric aci 1, or fused sodium or potassium hydrates. The essentialdifference, which theory and many e:\ptrinieiits show e\ists betweenliquids which arc electrolytes and liquids which arc not electrolytes, isthat in the non-electrolyte solution the molecules of matter of whichtho substance dissolved in the liquid is made up are all of the samenature and chemical composition, whilst in an electrolyte thesolution consists of A mixture of two or more different kinds ofmolecules. Thus, although common salt or sodium chloride in itssolid state is probably built up of only one kind of molecule or minuteunit, e.'ich of which molecules consists of the same combination of sodiumwith chlorine, yet if sodium chloride is fused we have a solution of sodiummolecules and of chlorine molecules in asol v out of sodium chloride, whilstif common salt is dissolved in water, we are dealing with a solution ofsodium molecules, and chlorine molecules, and sodium chloride moleculesin water. This is the case with all electrodes, and theclectric current, or atany rate the dec trie difference of pressure atthetwoeleetrodesoreouduct-iug terminals from the current generator, which are immersed in theliquid, simply act by attracting these different molecules, into which theoriginal compound has split up, into different dim tions. The electrodeattached to the negative pole of the generator always attract- themetallic element's molecules in an electrolyte, and these niolc( ules aresometimes known as the cathions1, the electrode which attracts Hum iscalled the cathode. The electrode attached to the positive pole of thegenerator attracts the non-metallic element's molecules from the elec-trolyte ; these molecules' are sometimes called the anions, and theelectrode which attracts them is called the anode.
Short Circuits —"When an electric generator has its terminalsjoined by a conductor possession- very small or negligible resistance,the generator gi\es out the largest current which it is capable of yield-
CONNECTION OF BATTERIES IN SERIES AND PARALLEL. 37
joined together, forming the common negative of the buttery. Thee. m. f. of the battery thus connected is that of only one of the
Fig. 28.—Atkinson'sAmpere-meter or Voltmeter.
Fig. 29.—Atkinson'* Ampere-meter or Voltmeter fitted with
flexible leads and < onn< 1 ting plugs
constituent cells, but it is capable of giving a current which islarger than one cell can give, in proportion to the number ofcells thus connected in parallel. The cells of a battery may be
36 PRIMARY \ND SECONDARY 13 \TTERIES.
of the end cells form the terminals of the battery. The electro-motiveforce of such a battery is equal to the sum of the electro-motive forcesof all the cells in the series. Usually only one kind of cell is thus
Fig. 26.—Diagram of Cells arranged in Parallel.
connected to form a battery, mid if so the c. m. f. of the battery isequal to that of one cell multiplied by the number of cells in theseries.
Fig. 27.—Diagram of Cells arranged in Four Groups in Parallel,each group consisting of three in series.
Ciils m;iy also be (omxrlcd in parallel, as shown dincrrnminntieallyin Fig. 26, where all the positives are joined together, forming thecommon positive terminal of the battery, and also all the negatives are
CHAPTER II.
THERMOPILE? - DYNAMOS.—THE COST OF ELECTRICALINSTALLATIONS OF SMALL OUTPUT FOR
ELECTRO-PLATING, ETC.
The Thermopile.—Tho Giilcher Thermopile.—The Cox Thermopile.—The Claiuond Thermopile.—The Dynamo.—Points to be Con-sidered in Buying a Dynamo.—Care of Dynamo —Driving Belts —Starting and Stopping a Dynamo —Cost of Dynamos.—Cost ofMotor-Dynamos.—Specification for and Choice of Motor-Dynamos.—Safety Precautions with Motors of Motor-Dynamos.—Choice ofElectric Generators of Small Output, under Various Circumstances.—Comparison of Costs of Primary Batteries, Secondary Batteries,Dynamos, and Motor-Dynamos.—Costs of Gas Engines, SteamEngines, Oil Engines.—Gas Engines Run on Producer Gas.—Regulating Resistances.—Determination of Polarity of Generators.
Thermopiles.—The next form of electric generator which we haveto consider is that form of apparatus known as a thermopile. Anapparatus of this nature may be briefly described as one which convertsthe heat-energy of some burning fuel into the energy of the electriccurrent. At one time it appeared us though for all ordinary purposesthis form of apparatus must completely displace the electric battery inwhich chemical reactions are the source of the e. in. f., and, indeed, theundoubted fact that in the thermopile the energy of the heat of combustion of a fuel is directly converted into the energy of the elccti hcurrent without any complicated intermediate apparatus such as thesteam-boiler and the steam-engine, or the gas-engine, with the dynamo,seemed to indicate that the thermopile misrht eventually quite supersedethe dynamo. These attractive dreams have not, however, up to thepresent been realised in practice, owing TO the low efficiency of thethermopile, and chiefly to its high prime cost and the (are norc>s>ary tokeep it in s itisfaetory working order. Until the advent of the'"Cupion element" primary cell the thermopile might probably ha\ehad a fairly largo field for small plating work and especially forlaboratory work, but the present writer considers thai, unless undi rvery special circumstances, the thermopile would be better replaced byeither " Cupron elements," secondary batteries, or dynamos. It is.
3 8 PRIMARY AND SECONDARY BATTEKlKb.
a r r a n g e d p a r t l y h i p a r a l l e l a n d p a r t l y i n s c r i e s ; t h u s F i g . 2 7 s h o w ^a d i a g r a m o f t w e l v e c e l l s a r r a n g e d i n f o u r g r o u p s , e a c h o f t h r e e i n. s e r i e s w i t h e a c h o t h e r , t h e g r o u p s b e i n g t h e n c o n n e c t e d i n p a r a l l e l . I nt h e d i a g r a m s t h e u s u a l c o n v e n t i o n o f a t h i c k l i n e f o r t h e n e g a t i v ec l e m e n t a n d a t h i n l i n e t o d e n o t e t h e p o s i t i v e e l e m e n t i s a d o p t e d .L a r g e a n d s m a l l c e l l s o f a u y u f i v o u k i n d m a y b e a r r a n g e d i n p a r a l l e l
i v i t h e a c h o t h e r , b u t c e l l s o f d i i l ' e r e n t k i n d s s h o u l d n o t b e s o c o n n e c t e d ,t h a t i s , a B u n s e n c e l l s h o u l d n o t b e e m p l o y e d i n p a r a l l e l w i t h aD a n i e l l c e l l . A l s o i n p u t t i n g g i o u p s o f c e l l s i n s e r i e s i n t o p a r a l l e lw i t h e a c h o t h e r , a s i n P i g . 2 ~ t t h e g r o u p s m u s t n o t o n l y b e a l l o ft h e s a m e k i n d o f c d l , b u t e a c h g r o u p m u s t c o n t a i n t h e i s a m e n u m b e ro f c e l l s .
Ampere-meters and Voltmeters.—There is a very large numberof these instruments of very different prices and construction now uponthe market. The great point is that they shall be accurate, and alsothat they &hall be fairly dead beat, that is, that the needles or indicatorsshall not oscillate about much when the current is changed, before theysettle down to the position required by the changed current.
A cheap and rather novel form of ampere-meter and voltmeter whichappears to fulfil these conditions is made by Messrs. Atkinson, ofCardiff. Two vie\v& of this instrument are shown in Figs. 28 and 29.Fig. 29 shows an instrument provided with a flexible lead and plugconnector for connecting on to different points. These ampere-metersand voltmeters are identical in general construction and appearance;they are intended to be attached to the wall, but there is no reason whythey should not be made portable by attaching them to suitable stands.For many purposes, especially in a small electro-plating shop, it is anadvantage, or indeed almost necessary, that the instruments should boportable, that is, that they shall be capable of being moved from onepart of the building to another, and quickly and safely set up at anydesired point. The price of these instruments is about £ 1.
Regulating Resistances.—For adjusting the current to any desiredvalue from any given source of constant e. m. f. it is very desirable tohave some form of regulating resistance. Several forms of this class ofApparatus are described and figured at the end of the next chajDter.
THE GULCHER THERMOPILE.
is listed by Franz Muller —Dr. Geissler'b buecebsor—of Bonn am Rhein,Germany, at a price of 190 marks for the largebt size, with 23 marksextra for a gas prebbure regulator.
Dr G. Langbein, of Leipzig-Scllerhauben, Germany, also libts thibthermopile at the same price, whilbt the same bize of thermopile mayalso l)c purchased of l le^f t . 0. Berend <k Co., of Dunedin Hoube,Busin<rhall A\enue, London, E.G., at a price of £14 5b., or with a gabprocure regulator extra, the eo.st IN £15 15b
It is claimed tor thebe thermopilcb that they may be employed con-tinuoubly, and that their efticiency does not vary, neither docs theapparatus deteriorate. They yield a coiibtant clectro-moti\e forcewliich may be slightly varied by turning the gas up or down, and theinternal resistance of the pile ib not large. A thermopile, of eourbc,causes no polarisation troubles like a primary battery.
The following dctailb as to price, etc., of this typo of generator aregiven by Messrb. 0. Berend & Co.:—
No. ]
Number of elementsE . M . F . i n volts . . . .Current s trength obtainable when
the external resistance is equalt o internal . . . .
In ternal resistance in ohmsI Approximate consumption of gasI in cubic feet per hour
Price of thermopilesPrice of gas regulators
26
0 2 5
503
30*50
No. 3.
66
3o O5
2
710
60
4£12
£1
90
10
10 10
£14£1
6-45
10
I
With reference to the foregoing table it must be remarked that \\ Jit 11the thermopile is running "\\ ith the eurrentb there btated, that is,when the external resistance is equal to the internal rebistance of thegenerator, it is working at its greatest rate, that i^, it is giving outelectrical energy to the outbide circuit at its greatest rate.
The following instructions are gi\en as to the use of this theimo-pile : —
"First phw e the tubular porcelain chimneys in their pLu 1 •>, 011top of the elements, by inserting the projecting mi< a tube in the hokbuntil the porcelain rest.s on the metal : in this position they mustremain. Thereupon connect the thermopile by a rubber tube to theiras supply, open the tap, and after a lapse of about half a minute—the time it A\ ill take for the air to escape from the tubes—set light to
40 THEBMOPILES, DYNAMOS, ETC.
however, desirable to describe tho forms of thermopile at presentemployed, moi'c especially as it is s'till quite possible that cheaper,stronger, and more efficient forms inuy be de\elopul in the future, andif this-. impio\em°nt could be carried sufficiently far, it is eeitainlypossible that the d\namo might be largely or altogether displaced, butup to the present there does not .seem great pxjbabihty of this desirableend being attained.
The thermopile consists essentially of a series ot junctionsol differentmetals, allots, or other conducting" solids, which are kept at a fixedhigh t 'luperature, and another set of alt rnaHy arranged .similarjunctions, which are maintained at a fixed low temperature. The
Fig. 30 — Gulchei'b Thermopile.
theory of the action i.s quite unnecessary for practical purposes, and aswe are here merely considering- the thermopile a.s a curient generatorwe .shall .say nothing-on the theoretical aspects of the matter, winchmay, howc\er, by the aid of a moderate amount of mathematk s, beobtained from most treatises on theoretical electricity.
In all forms of thermopile, then, -with which the author is acquainted,the hot juiu tions are heated by means of a iras burner, or a coke or coalfurnace, and the cool junctions are kept (old citb r simply by directexposmc to the air or by the cm ulutiou of a current of < e»ld water froma neighbouring tap.
The oiilcher Thermopile.—Thih apparatus, a >iew of which isfrhown in Fig. 30, is nuinufac tured by J ulius rintsch, Berlin, and
THE COX THERMOPILE. 43
cold junctions are kept cool by means of a stream of water from theordinary supply tap, whereas in the Guleher pile, air cooling* alone isemployed. The following directions for use arc given by the makersof this thermopile : —
I. Directions for use of smaller-si/ed generator, heated with gasburner, and not supplied with water cooling arrangements-, (Fig.36).
The generator with its ua^ burner should be placed upon someconvenient support, such ih a table or stand, where the apparatusoperated can be com enien Un-placed. Use a sufficient lengthof rubber tube to connect theburner to the nearest gas jet inthe room. See that the de-flectors, which arc shown at Din Fig. 35, arc as nearly as pos-sible in the centre of the gene-rator ; this is necessary in orderthat the heat from the burnershall be supplied equally to allparts of the machine. Theburner may be lighted at eitherthe top of the tube or at thetop of the generator. The de-flectors require to be heated upto a cherry-red heat, and suf-ficient gas must be supplied todo this The gas flame shouldnever impinge upon, or strikeagainst the interior of theelement, that is to say againstthe inside of the disc, which isthe part that produces the elec-
Fig. 32.—Cox Thermopile for pas,fitted with water-jacket and
bracket support.
tricity. This last precautionis extremely important. Th<pile may be run continuously,and provided the uas supply i^ steady, the current will not \ary in theslightest degree, but, it it i> required, the strength of the current maybe increased or decreased by regulating th^ amount of gas supplied.More gas will uive more current, less gas U>> current. Short dicuitingthe generator docs not injure it in any way. It should be rememberedthat the element under working conditions becomes hot, and mustnot be handled without using tho fire-proof asbestos pads provided,or some other suitable means. To stop the pile acting simply turn offthe gas.
THERMOPJI.ES, DYNAMOS, ETC.
the gas escaping from the tubular eli monks at the mouth of the porce-lain ehimuoys. (See thai all tli ' imriKTs are alight to prevent escapeof gas, ami to eiiMire full efh\ leuey of the thermopile.) Wlieu theburners are lighted the thermopile is ready for use, and require** nofurther attention. In 8 to 10 minutes after lighting up, the pile is.sufficiently heated to give oit a perfectly constant c. m.f. The consump-tion of gas given in the table is calculated upon a gas |)re.ssure of30 m m= I *r8 in. water column. Before packing, each thermopile iscarefully tested, and adjusted to the highest admissible ga.s pressure, v i/.,50 m m= 1 '9-6 in. water column. As the gas pressure varies consider-ably, it is strongly advisable to always insert a gas pressure regulatoras quoted in list, but in most instances the gas companies will be able
to inform liters of their normalpressure, and when such normalpressure does not surpass themaximum, it is not necessary touse a regulator. Singly turnoff the gas tap for putting thethermopile out of work.
" CAUTION.—JJo not interferewith the ytii> inlet on the (her'mopile ; any increase of this inletwill ) uin the instrument.
The thermopile must be lipt ina di y place, and should be pro-levied from acid vapours, whichno aid attack the inctoL It isadvisable to fix the pile to the 11 allon a horizontal bracket at a heu/hlsufficient to protect it from inter-
ference. ''
The Cox Thermopile.—This thej mopile, invented byJVLr. I I . Barring'ton Cox, is
manufactured by the Cox Thermo Electric Company, Limited, atthe Cox Laboratory, St. Albany Herts, England.* Several generalviews of this form of thermopile are »ivtn in Fiir-. 31, S2> 33-
The hot juiu tions are hi uteri by means of a Bunsen ga-> flame as inthe Gukher pile, but in the larger si/c s of the Cox thermopile the
* I hear that the English Company has been wound up, but theAmerican business is, I believe, still tairied on at 126, Liberty Stieet,New Yoik.-A. 1-.
Fig. 31.—Cox Thermopile for gaswithout water-jacket.
THE COX THERMOPILE. 45course, mu^t be done when the pile has been lighted up for some tenor fifteen minutes, and ha* had timeto reach its full temperature. Toomuch water is useless. The actualtempc ratine ot the waste water mayof (oui'bC be obtained by placinga thermometer bulb in the l^uinprstream. Ancle<tii< < um nt may betaken fmui tlio pile tlii * < tly itis lighted, but the output steadilyincreases with the time until themaximum is reached in about tenminutes.
To stop the pile, turn oft the gasand water, but do not disconnectthe water pipes. Always allow thewater jacket of the pile to remainfull.
The same precautions in lightingthe gas and regulating the heightof the gas flame apply to the
rig- 34-—Section of Cox Ther-mopile having water-jacket.
Flame burning correctly.
r-jacketed thermopile as to the smaller un jacketed form. Theappearance of the flame should belike that «*ho\Mi in Figs. 34 and36. In Fig. 35 a gas flame isshown burning incorrectly, and insuch a manner as to damage thepile. The correct form of flamecan always be obtained by turningthe gas up or down. The pilemust never be used without thecirculating water running. Theseare the only points which rcquheattention, and by taking theseprecautions the natural life ofthe machine is indefinitely long.Negligence in regard to their obser-vance may spoil the pile in a fewhours. To observe the gas-flame look from the bottom ofthe pile upwards. One form ofthe Cox generator is made to berun with a spirit-burner, Fig. ^.
All forms arc claimed by the makers to be economical and
Fig. 35.—Section of Cox Ther-mopile, showing flame burn-
ing incorrectly
44 THEKMOPILES, DYNAMOS, ETC.
Heat in the form of stored energy will operate the apparatus forhome minutes after the gas is put out. The generator should beallowed to thoroughly cool before it is handled.
2. Directions for installing and using the larger sized generators,heated with gas and supplied with water c in ulator.
Screw the machine upon the wall in a vertical j>osition and in sucha place that it may be as free as possible from draughts of air. Connectthe gas burner A, Figs. 34 and 35, on the pile by means of a rubbertube to a eomenient gas Mipply, also connect the water tubes E E inthe same manner with the water supply, taking care that the waterenters the pile at the bottom opening, following the direction of the
arrows »so as to leave atthe top as shown in thedrawing. Remove thestring and tag which istied about the deflectortripod C at the toj) of themachine, and see thatthe deflector rod D restsin the centre of theburner B. Also notethat all screws are tight,especially the connec-tions. The use of smalllead or eompo piping isrecommended instead ofrubber tubes. A lead oreompo pipe is found tobe more satisfactory,especially if a pipe is
Bgr^yjgF^-- to be kept in constant~ or practically constant
Fig. 33.—Cox Thermopile for Spirit Lamp, U b e
without water-jacket. T o s fca r t t h c gcnenitoTi
turn on the gas andwater and light the gas, the flame from which should aj>pear as inFig 34. Observe that the water is running freely through theapparatus, though only a small current is necessary. The correctquantity is determined by the temperature of the waste water, whichshould be kept at a temperature of from 70' to 8oJ Fahrenheit. Thetemperature must on no account be i>ermitted to exceed 150° Fahr.For ordinary purposes the temperature of the cooling water can bedetermined with sufficient accuracy by placing the hand upon thccasing, which should not feel more than slightly warm. This, of
THE CLAMOND THERMOPILE. 47
The Clamond Thermopile.—This pile was originally made by theThermo Generator Company in or about 1876, and the following aredetails concerning their cost and output:—
Volts.Internal resist-
ance • ohms.1 o1 5*o0 O
12 15
Shoit circuitctinuit.
2 amperes.
2 7
Gas consumption:cubn ft. per hour.
359
Pine.£ «.. d.3 0 04 0 0G 10 o
13 o o32 o o
Piles h.u inUL* a lower resist iig results \\ < re given :—
also made, of which Hie iollow-
Volts.3
10
inUrnalresistance.o"6 ohms.2*0 „
Short en cuitcun cut5 amperes55 s>
Coal jns consump-tion in cubic ieet
per hour.6
i-\
37
Price.£ s. d.8 0 0
20 o o32 o o
The piks were spoken well of by Sir \V. H. Preece, and were by hisdirections employed in the Government Telegraph Service, but owingto the fact that the junctions after a time were found to fuse by cominginto direct contact with the burning gas, and to break by too suddencooling and heating, and also because moisture and products ofcombustion apparently in time corroded the junctions, the use of thepiles was discontinued; but Sir W. H. Preece stated thnt the pileswere far more compact than ordinary telegraph batttiics, andexpressed his belief that the difficulties mentioned above could beovercome. The Company, however, collapsed, and were unable tosupply a complete set of thermopiles contrrn ted for to the Postal Tele-graph I) ^p.irtmcnt in 1876. Whether the pile is manufactured underthe name ot Clamond or any other title the present writer is not aware,but apparently, with a few not very complicated modifications, thispile could be made as successful as any others on the market.
The following is a description of the original Clamond pile sriven byMr La tinier Clark at a meeting of the Society of Electrical Engineerin 1876, an account of which, aceompaniedby an inteicstiug discussion,may l>e tound in the Journal of that Society, vol. v., p. 321, et seq.
Mr. L« 1 tuner Clark states that:—11 The mixture employed by Clamond consists of an alloy of 2 parts
antimony and 1 of zinc for the negative element, and for the positiveelement he employs ordinary tinned sheet-iron, the current flowingthrough the hot junction, from the iron to the alloy. The combina-tion is one of srreat power. Each clement consists of a flat bar of
46 TTIERMOriLFS, DYNAMOS, ETC.
strong. The following* details a^ to price and output have beensupplied :—
Cox Generator for Gas with Water-Jacket.—
VolK on open Shoitcuciut .Approx internalcircuit. em icnt. iw-tinc<.
5O3'5
Trice£
556
10
0
10
0
0
d.
0
0
0
0
Fig 3G —Section of Co\ Themiopile for gas, withoutwater-jac ket
Cox Generator for Gas or Spirit-Burner, without Water-Jacket.—
PIKO, complete ^ithVolt* on open Short u m u t cm rent bmnei, etc
en cuit 111 tinipero» £ ». <i.
r 3 1
Prices for separate item**:—
1 o o100
Element . r<> oDeflectors . . 1 6Spirit or gas-burner and stand 1 0
THE CLAMOND THERMOPILE. 49
screws and rods, so as to consolidate the whole, and in this conditionthe pile is allowed to dry and harden. Looked at from the inside, thefaces of the elements form a perfect cylinder, within which the gas isburned. The inner face of each clement is protected from excessiveheat by a tin is trip or cap of tin bent round i t ; beiore it is embedded inthe cement the projecting .strips of tin from the opposite ends of eachpair of dementis are brought together and soldered with a blowpipeand soft solder. The respective rings are similarly connected, and thewhole pile is complete, except as regards the heating arrangements.The positive pole of these piles is always placed at the top. dimmingwas the first to use this stellar arrangement of couples. Tlu pile i->usually heated by gas mingled with air, on the Bunsen principle ; L;;INis introduced at the bottom of a tube of earth JUW are, which is dosulat the top, and is pierced with a number ot small holes thioughout:its length, corresponding, approximately, in number and portion withthe number of elements employed. Bjforo entering this tube, the g t^is allowed to mix with a regulated proportion of air, by an oiitiee inthe supply tube, the size of which can be adjusted; the mixed ua-M.sescape through the holes in the earthenware tube, and there burn insmall blue jets, the annular space between the gas tube and the ele-ments forming a ehimney to which air is admitted at beittom, thoproducts of combustion escaping at the top. In order to preventinjury from over-heating, and to diminish the consumption of ga^,M. Clamond lias introduced a new form of combustion chamber, bywhich he obtains very great advantages. This form io shown inFig. 39. The mixture of air and gas is burnt in a perforated earihui-waro tube, as before described, but instead of exteneling the wholeheight of the battery, it only extends to about one-half of its height.The earthenware tube is surroundeel by an iron tubeot larger diameter,which extends nearly to the top of tho battery, and ib open at the top.Outsiele this iron tube, and at some distance from it, are arranged theelements in the usual manner. A movable cover fits closely o\ er thetop of the pile, and a chimney is connected to the bottom of the pile..Leading off from the annular space between the iron tube and theinterior faces of the elements, the air enters at the bottom of the hontube, and the heated gases, passing up the tube, curl over at the top,and descend on its outside, escaping eventually by the chimney.The elements are heated partly by radiation from the iron tube, andpartly by the hot gases which pa^s, oid>ide the tube, dowiiwanUtowards the chimney. By this arrangement, not only ib great c<. onomyof gas effected, the consumption, A*. L am informed, being reduced byone-half; but the great advantage i^ obtained that the jets of gascan never impinge directly on the elements, and it is thus scarcelypossible to injure the connections by over-heating, in the event of
48 THERMOPILES, DYNAMOS, ETC.
the alloy from 2 inches to 2} inches in length, and from J to 1 inehin thickness. Their form is .shown in Fig1. 37, by which it will be.seen that, looking- at the plan, they are spindle-shaped or broader inthe middle than at the ends. The sheet-tin is stumped out in theform shown in Fig". 38 ; the narrow j>ortion is then bent in the formsshown, in \\ hich .state they are ready for being" fixed in the mould.The melted alloy is poured in, and, before it has cooled, the mould is-opened and the bars remoxed with th<- lugs securely cast into them.The mould is heated nearly to the melting" point of the alloy, and 10or 12 bars are cast at one time. A little zinc i.s added from time totime to make up for the loss- due to volatilisation. The alloy molts atabout 500° Fahr. ; it expands considerably on cooling. The morefr< quonfly the alloy is recast the more perfect becomes the mixture,so th.'it old piles can be reconverted with ad\antayo and with littleloss beyond that of the labour. The alloy is extremely weak and brittle
Fig. 37.—Elements of Clamond'sThermopile connected in series.
Fig. 38.—Sheet Tin Stamping?for Clamond Thermopile.
and easily broken by a blow in fact, is sear' ely stronger than loafsug"ar.
" The tin lugs are bent into form, and the bars are arranged in aradial manner round a temporary brass cylinder, as shown in Fig. 37,a thin slij) of mica being inserted between the tin lug- and the alloy,to prevent contact, except at the junction. The number of radialbars varies with the size of the pile, but for the usual sizes eight orten are employed. As fast as the bars are laid in position, they aresecured by a paste or cement formed of powdered asbestos and solubleglass, or solution of silicate of potassa ; flat rings are also formed of thesame composition, which possesses considerable tenacity when dry ;and as soon as one circle of bars is completed, a ring of the dry asbestoscement is< placed upon it, and another circle oi elements is built uponthis, and so on until the whole battery is* formed. Cast-iron framesare then placed at top and bottom of the pile, and drawn tog-ether by
THE DYNAMO. 5T
consuming 2 lbs. of coke per hour, will deposit about four times theabove quantities in the same period of time.
Messrs. L. and C. Wray introduced some important improvementsupon the form of Clamond's thermopile as described by Mr. LatimerClark, the descriptions of which were given in the discussion on Mr.Clark's paper (he. cit.), but, as far as I am aware, there are no pub-lished details concerning the output, price, gab consumption, and lifeof any other thermopiles of sufficient magnitude for any electro-chemical work beyond those given above.
The Dynamo.—The third and last, and, for the larger operations,the most important current-generator is the dynamo. As was thecase with the other forms of current-generators, no attempt will bemade here to treat of the theory of the dynamo, nor its construction.The theory is well understood and the art of construction has reacheda high degree of perfection. Particular information on these pointsdoes not concern the electro-metallurgist, who is merely interested inthe cost, efficiency, durability, and method of treatment of the finishedmachines. The large number of modern treatises on the theory andconstruction of the dynamo now available make it an easy matterto obtain all details for those anxious to be acquainted with thesosubject^, but (let it be remembered) such knowledge is in no waynecessary to the practical electro-metallurgist.
The dynamo then, in so far as we are concerned, is, like tho electro-chemical battery and tho thermopile, merely a source of e. m. f.,which when connected up in a conducting circuit will yield a larger orsmaller current according to the largeness or smallness of its c. m. f.and the smallness or largeness of the resistance placed in circuit.
There are several forms of dynamos available for obtaining anelectric current, but there is only one form which is of any practicaluse for the electro-metallurgist, and that is the particular form otmachine known as the shunt wound dynamo. Other forms ofdynamos may po^ibly be employed, but they possess no advantagein cost or efficiency, and even when used by experienced persons forelectro-chemical work, are always liable to cause more or less serioustrouble from time to time. Tho soundest advice, then, to anyone aboutto purchase a dynamo for electro-chemical work of any other formthan the shunt wound machine, is " Don ' t . "
The dynamo is so largely employed nowadays that it is difficult toimagine that anyone who is in any way connected with technical workis not familiar with at least the general appearance of the machine.It is not possible to tell by mere inspection the efficient y and outputof a machine, and the general details of equally good dynamos may bevery different. Every machine, however, must contain the followingten important parts (see Fig. 40):—
5O THERMOPILES, DYNAMOS, ETC.
a bad connection occurring, it is ea.xy to find out the imperfect element,and throw it out of IN1 by short-circiiitint<r it over u ith a piece of wire,and the maker* have no difficulty in cutting out a defective elementand replacing it by a sound one. Coke and charcoal lia\e also )>eenemploye*! as ;i source of heat, with \ery yreat economy and success ;in fact, there are many countries and places where jiiis would not boprocurable, but where charcoal or coke could be readily obtained.
• K 39 —Section oi Clamond's Thermopile.
The tension produced by Clamond'b thermo-elementb is MH h that eachtwenty elementb may bo taken as practically equal to one Daniell'scell, or about one volt "
It is stated that a Clamond pile of roo bars, with the consumptionof 5 cubic feet of gas, deposit^ about i ounce of sil\er per hour, andthe .same machine, arranged in multiple are (that is, for fj/«r»htty) willdeport about I ounce of copper in the same tine ; 400 larg'e bars,
THE PYNXMO. 53
A dynamo is really only a piece of apparatus for converting Hie)chanical energy of some steam- or gas-engine into the energy of the
52 THERMOPILES, DYNAMOS, ETC.
1. Field-magnets, M, made of steel or iron (of almost any shape).2. Meld -magnet windings, M', consisting of inbulatcd copper- wire
coils carried round the field magnets.3. Armature shaft or spindle, E E, which rests on and runs in—4. The armature shaft bearings.5. The armature, A A.—Thio consists of a collection of copper
wires or bars attached to a cylindrical core of iron plates. Thecomplete structure is keyed firmly to the armature shaft.
6. The commutator, c.—This is a cylindrical assemblage of copperor occasionally iron segments, ha\ ing an insulating layer betweeneach segment. It is connected by wires, to the armature, andis keyed on the armature shaft at one end of the armature.
7. The brushes, b b.—These are copper-wire gauze or sometimescarbon blocks, which are held in what are called brush-holders,which in their turn are held on the rocker. There are at leasttwo brushes and may be more, but there is always an evennumber. The brushes are held pressing upon the commutatorby means of hold-on springs, and when the dynamo is run-ning the commutator slides beneath the brushes, with whichit is alw.iys kept in close contact by the brush springs.The brushes are normally held in a fixed position whilst themachine is running, but can, if it is desired, be moved forwardor backward a certain distance by rotating the whole of therocker to which the brushes are attached. The rocker is carried011 one of the fixed bearings of the armature spindle, on which itcan rotate, but it can be fixed at any desired position and ren-dered immovable by means of a pinching or clamping screw.
8. The machine terminals.—These are usually fixed to a smallwooden panel on the side or top of the field-magnets of themachine, and it is from these terminals that the current is takenofl from the machine by means of conductors running to the\ ats direct, or more usually vid a switchboard. The terminals arealso connected one to each of the brushes of the machine, andalso one to each of the ends of the field-magnet windings.
9. The pulley, v.—Jf the machine is belt-driven this is keyed tothe armature shaft at the opposite end of the armature to thecommutator. If the machine is not belt-driven there is acoupling for direct coupling to its engine.
to. In niauy ease** there is also a fly-wheel keyed on to thearmature shaft, especially when very steady speeds are lvquhwl,but thi> fly-wheel may be, and generally i>, absent. A \L\v ofan elect ro-plating dynamo made by the Gem ral Kleotlit Companyfor 10 volts and 280 amperes it, shown in Fig. 41. The price ofthiw machine i- / 40.
THE I>YN\MO. 55
the puichasu to <solect the m ulnue whose puce, output, etc , are bt^tsuited to hi** needs and pocket:—
Details concerning Shunt Dynamos foi •
Pow ci IN ul ihl< to inn dyn uno, • • biake-hoise-power.Cun» nt uquncd not loss than impucs.Volts lequuod, about \oltsSpeed at AN huh diiwncr on_mo luns, rc^ s per mmThe machine must not sp uk imdn my \o id up to full load when
once the blushes aie piopcilj uljustcd
The manuf ictuici is asked to tync the following details concerningthe machine offeied, foi the output abo\c stated —
Volt> on machine on open cucuit at normal speedVolts on in ichme at full lo id cm lent, at noimal speed.Stitc whit full loid (uncut i<*St itc wh< thei \olti_jC of machine can be >ancd by field rheostat,
and, if so, between what limits.St itc noimal speed ot nnohmeSt \tc di imctoi uul w ldth of face of pulley s suppliedStite powti icquucd to d ine djuamo it its lull load at noimal
spc edSt itc powci loquned to dn\e eljnamo, when j?i\ni4 the liuuibci
ot unpcies «4peuhtd as hem_, lequmd, at noun il speedSt itc lcsistance of machine fiom hmsh to brush hotSt itc tcmpei ituic n^e of aim ituu and of field-magnets aftei
iuunin_ foi si\ hom> it the full lo id c uncut at noun il speedSt itc dim tion of lotihonSt t( pure of m i< him dilnoicd at with fast and
le>ose pullcjs, belt foik, md stukin^-i^ear complete, and it ofsi/e lcqiuinifl: ilwnc i\ hoise-powei to dnvo it, aKo «<t itcsepai itd\ e\tia co^t ot foundation iails and belt tigliteiimoscicws and held lhcost it, if the Littei is advisiblc
Othei things bemsc equal, the machine with the smallest resistancefiom biush to biush, and the le 1st diffeicncc between its \olt IJH it/oio lo id and full load will be found the mo4 s*\tist ietoi}, whilst ilow speed and a lai»,c output aic also jjood points whidi, howe\er,uufoitunitdj, usually IUM>1\C coriespondmgl^ uewdpnecs The sameltmaik is tiuo of a low tempeiatuic use of both aimatuic and flcld-magncts aftci a piolonged nui it full lo id (the use should not begieatei than about 70° Fain ), and 1K0 the vmallness of the powerlequiiid b^ the. niaehiuu to dnvt it at full load It is paitiuilaily
54 THMIMOPJLES, DYNAMOS, ETC
electric cm lent, and b) itself can gne out no energy unless it hasmechanical eneigy constantly gi\en to it by some engine, such as aste im-engine, gas-en^ me, oil-engme, electric motor, 01 a watei orwind tuibme In setting up a d>n uno it is therefore nece&sarj to seethi t a souice oi a bumcitnt amount of mechanical energy is firstpioMded
The numbei of in ikeis of good and lehable dynamos now to be foundis 111 ire, and it is difficult to mention any patticulai machine 01 machinesab being special!) Oood In oidei, theiefoie, to purchase md instal asuit tble dynamo and engine for an) purpose in\ oh ing moie than a
Fig 41 — G E C Electro plating Dynamo, 10 \olts, 280 amperes
small outlay, it i«, if the person desnous of obtaining the plant is notan electrical engineer himself, "very desirable to obtain the assistance of aconsulting electucal engineer, who will draw out specifications andobtain tenders for supply, delnery, and erection , by this means usually1 arood deal of money and time is sued, and satisfaction obtained atan outlay of a small peicentage of the total cost of the plant installedFor small plants, howe^ei, and foi persons ha\mg some knowledge ofmedium il if not of eke tin il, engineering, it may be worth whileobtaining the dynamo direct, and in this case it is ad\ isable to write,stating the following details, to a number of films manufacturingdynamos, and fiom then quotations a little consideiation will enable
CARE OF A DYNAMO. 57attendant is able to do this it can be done by seeing that the brushesare carefully filed to a flat bearing surface. For this purpose it isadvisable to make a brush clamp of cost iron, as shown in Fig". 42.
The angle of the slope at the top of the clamp may be set for eachparticular dynamo and particular thickness of brush in the followingmanner : Dr.iw* 1 wo parallel lines on a sheet of paper, Fig. 43, havingthe distance between them equal to the thickness of the brush which is tobe employed. Then take a compass, and with one point at A, set oft'an arc whose radius is equal to the thickness of about i\ to 1 ] com-mutator segments, cutting the other line at the point B. Join A to 13and this line gives the angle ofslope of the top surface of therequired brush filing clamp. Tofile up the brush place it in thegroove G of the clamp and placethe covering piece, C, over thebrush, and then place in a viceand file the top end of thecop}>cr with a fine file with anoutward stroke only, until the(opper surface lies even withthe sloping east-iron surface ofthe top of the clamp. Thebrush is then fastened in thebrush-holder, so that the slopingsurface lies closely on the sur-face of the commutator. If themachine is a two-pole machinethe points of contact of thebrushes are arranged at diame-trically opposite points on thecommutator. The pressure with which the springs hold the brushesin contact with the commutator is usually adjustable, and shouldbe arranged to be not too heavy or the brushes cut the commu-tator severely, and not too light or the "vibration of the runningmachine causes the brushes to jump slightly, thus causing badsparking. When sparking is observed at the commutator the brushrocker must be slowly rotated backwards and forwards until somepoint is found at which the sparking is absent or at a minimum, whichshould mean a very slight amount of sparking indeed. If this is notthe case, at the earliest opportunity the brushes must be removed andtrimmed as already described, and again adjusted. If the sparkingstill continues, and the machine has pre\ iously worked sparklessly, ornearly so, it is probable that either the machine is being overloaded, in
Fig. 42.—Brush Trimming Clamp
56 THERMOPILES, DYNAMOS, ETC.
necessary that the power required by the dynamo to drive it at fullload shall be stated in brake-horse-power, as other units of horse-]>o\ver are misleading. If is desirable that the speed should not begreater than about i,^co J.<T minute.
Care of a Dynamo.- AVI ion onee a dynamo is ereefed and running", itis necessary to understand that by constantly observing eeriain simpleprecautions- (which are much more readily carried out than is the casewith the similar precautions required when employing primary orsecondary batteries, or indeed with thermopiles) the life of thedynamo can be indefinitely extended, and, as a matter of fact, therejmirs and depreciations incidental to running a properly looked afterdynamo is not a quarter of the amount expended on a secondarybattery which is equally carefully attended to, whilst the time andtrouble necessitated in carrying out these precautions with the dynamoit, \ery much less than is the case with cells.
It is, if possible, very desirable that a dynamo employed for electro-plating shall not be used in the same room as that in which the platingtanks are situated, for otherwise the vapours from the vats, moreespecially if tlie^ are run hot, are liable to condense on the machineand rust it, and reduce its insulation resistance until at last someshort circuit of the machine may occur. It must be carefullyremembered that probably the most active agent in deteriorating adynamo i< damp.
The bearings should be kept well oiled, and for small machines a lightmineral oil may be employed : it is, however, necessary to guard againstthe lubricating1 oil creeping over on to the armature and commutator.Thi.s mishap is provided against in well-designed machines by havinga V-shaped ring shrunk on the shaft just outside the journals, which,as the oil creeps over it, throws it off on to a curved oil hood cast on thebearings.
Probably the most important point in the wear and tear of a dynamoi.s that im olved in the commutator, and every effort must be made tokeep this small. The copper brushes bearing on the rapidly rotatingbars of the commutator are gradually worn down, and in their turn thebrushes gradually wear more or less severely the surface of the com-mutator. The wear may be ke|^t small by seeing that the surface ofthe commutator is very lightly coated with a thin film of vaseline, andthe brushes must be carefully trimmed. The most destructive agentin the wear of the commutator is not, however, the friction betweenthe brushes and the commutator surface, but is due to the sparkingwhich occurs at the brushes. This sparking tends to pit the surface ofthe metal where it occurs, and once this ]>itting has taken place theaction proceeds at a constantly accelerating rate. The threat thins**,then, is to avoid as t.ir as possible all s|)arking. As far as the
DRIVING BELTS. 59little milk or soap and water may be used as a lul >rican t. The tool shouldbe constantly re-sharpened. If it is noticed that the commutator is gettingrather rough, but before the trouble has gone so far as to produce realinequalities of any size on its surface, necessitating re-turning to removethem, the roughness may be conveniently removed by means of acylindrical segment cut in a thick piece of board whose internal radiusis equal to the external radius of the commutator. If this cylindricalrecess is lined with a piece of the finest glass paper and the dynamo ir>run at its usual speed, the brushes being removed, then, if the cylin-drical recess lined with glass-paper is pressed lightly upon the revolvingcommutator, it will rapidly smooth it up bright. This treatmentmay also be used after the commutator has been re-turned, in orderto give it a last smooth surface.
The dynamo must be kept as free as possible from dust, and if thepresence of dust is unavoidable, then the dynamo itself must beclosed in in some suitable cover. In any case, dust which graduallycollects, and especially the copper dust arising from the wear of thebrushes and the commutator, may be conveniently removed from theend windings of the armature and other places where it collects, by meansof blowing with a pair of bellows. The foundations of the dynamomust be firm, and the machine bed-plate must not move at all perceptiblywhen the dynamo is being driven.
Driving Belts.—Concerning driving belts Mr. Watt remarks asfollows: Most users of dynamo machines, polishing lathes, and othermachinery driven by steam-power or gas-engines, will have experiencedsome trouble from the breaking, slipping, or slackening of the drivingbelts. Since a few hints upon these matters may prove acceptable, wegive the following extracts from an interesting and thoroughly prac-tical paper, by Mr. John Tullis, of St. Ann's Leather Works,Glasgow.*
" Main Driving Lent her Belts should be manufactured so that whenthe joint is made while the belt is in its place, it ought to present theappearance of an endless belt. After having been taken up once ortwice during the first year, good belts such as these require very littleattention during the subsequent years of their long life. If the beltis driving in a warm engine-room, it ought to get a coating of curriers'dubbing three times a year. All belts having much work to do oughtto present a clammy face to the pulley, and this condition can be bestmaintained by applying one coating of dubbing and three coatings ofboiled linseed oil once a year. Thi« oil oxidises, and the gummy sur-face formed gives the belt a smooth, elastic driving face. A belt lookedafter in this way will always run slack, and the tear and wear will beinconsiderable. On the other hand, dry belts have to be kept tighter,
Scottish Leather Trader, July, 1885.
58 THERMOPILES, DYNAMOS, ETC.
which case sparking is often quite unavoidable, or some breakage hasoccurred in the armature windings. Do not overload a machine so asto cause sparking, for to run a machine with sparking brushes is themost extravagant method of running it possible. But if the sparkingis not due to this, but has set in and cannot be .stopped by aiiy of themean* noted above, call in an electrician to put the trouble right. Somemachines, owing to faulty design, will always .spark, and it is particu-larly necessary in purchasing a machine to ascertain by experimentthat the machine will run at its full or any lower load, with properlyadjusted brushes, without any sparking. If a machine does not spark
at the brushes the commutator quickly assumes adark blackish-brown polished appearance, which isvery characteristic of a properly run dynamo. If inspite of till the precautions mentioned above, orbecause of their neglect, a dynamo which did notspark when first set up commences to spark, and, as
' a result, the commutator gets out of truth and isno longer truly cylindrical, but is worn down atcertain points, either due to the sparking or to thecutting effect of too large a brush pressure, it isadvisable to adjust a slide-rest parallel to the arma-ture spindle, and with a very sharp and fine-nosedtool turn down the surface of the commutator untilit is once more truly cylindrical. Care must betaken in performing this operation : first, that a
I vory light cut is taken ; second, that the rest isFig. 43 parallel to the armature spindle, or otherwise the
Diagram for surface of the commutator, after turning up, will besetting angle of coiji{.a] i l jstcad of cylindrical; third, before starting
Brush Trimming ,, ,. . Pi ,, , ,Clamp. ™1C machine again after turning up the commutator
examine the commutator very carefully to ascertainwhether any metallic copper has dragged across the insulation betweenthe commutator bars. If it has, it must be carefully removed. It isto avoid the danger of this occurring that a sharp cutting tool and alight cut are necessary in the turning operation. Running the dynamowith such a piece of copper connecting two neighbouring commutatorsegments may cause very serious damage indeed to the armature andnecessitate lengthy and expensive repairs. It is only in the case of abad form of dynamo, or very serious neglect of the proper precautions,that it should become necessary to have recourse to turning the surfacetrue again. In any case it is evideut that only just sufficient metalshould be removed by the turuiug process to get to the bottom of thecavities worn in the commutator.
The armature shaft may be rotated by hand during the turning, and a
PIUCES OF SMALL DYNAMOS 6 l
valuable to those who, though constantly using driving bolts, maybe unacquainted with the principles of their action.
To Start the Dynamo.—All that is necessary is to run up thespeed of the engine, see that the brushes of the dynamo are up, andthe switches open, then throw over the belt from the loose to the lixedpulley, and when the machine is running adjust the lubricators togive about three or four drops of oil per minute, or if the lubricatorsar" not sight-feed, but havt? worsteds or other adjustments, see thatthese are properly set; then, having noticed that the machine is runningin the correct direction, which may be done by touching the commutatorwith the finger tip, put down the brushes, and when the machine hasexcited, and the outside circuit is ready, close the switches and thecurrent can then be adjusted to its correct value, either by means of aregulating resistance in series, with thc^machine and the plating baths,or by means of what is occasionally convenient, a regulating resistanceoi" rheostat in the shunt windings of the dynamo, or by both of thesedevices.
To Stop tlie Dynamo.—The main switch is iirst opened, the beltis then thrown on to the loose pulley by the belt fork, and the brushesare raised, and the lubricators stopped running. The brushes shouldalways be raised before the machine comes to rest, but not while run-ning full speed.
Prices of Small Dynamos.—Small dynamos for electro-platingcan be obtained for as low a price as about £ro, up to very largeprices for machines of large output. In order to give some rough ideaof the prices at v»lueh the smallest machines may be purchased, thefollowing details are given of machines listed by the General ElectricCompany, Ltd., 69, Queen Victoria Street, London, E.<\, in 1895.Trices are probably somewhat higher now (1901). One of thesemachines is shown in Fig. 41.
Catalogue No. •Current in amperes . . ,E. M. ¥. in voltsDiameter of pulley in inchesWidth of pulley face in inches .Approx. revs, per minute .Approx. brake-horse-pow or
at lull load . . 0
Price . . . . .
200
32
532
2,400
i£*
201
566
32
1,400
k
£>(>
202
726
32
1,200
i£19
203
9 b642\
1,200 1
i {
£24
204
961 0
43
,000
20s
2 8 0
1 0
64
75O
5
£30 £40
The prices of small dynamos, with .suitable direct current motors fordriving them on the same 4iaft, Fig. 44, 01% as they are called, niotor-dynamos, which are listed by the same hrm in an 1899 ^^> a i ' e «follows:—
6o THERMOPILES, DYNAMOS, ETC.
because they vslip and refuse to lift the work. The friction of therunning1 pulley * burns the life' out of the belt while this slipping* isgoing on."
Finny ihr Brit.—As to which <-ide of the leather ought to be placedni \t the pulley, ]\lr. Tullis siys, " Tt is well known that by runningthe (jmhi or smooth side next the pnlley, there is considerable gain indriving1 power. However, by using l>oiled linseed oil, as before men-tioned, the flesh side will soon become as smooth as the grain, and theflriving* power fully as good. A belt working with the grain sidenext the pulley really has a much shorter life than the belt runningon the flesh side. The reason is, the ono is working against thenatural growth of the hide, while the other is working according tonature. . . . If you take a narrow cutting of belt leather, pull itwell, and lay it down, you will at once observe that it naturallycurves flesh side inwards. Nature, therefore, comes as a teacher, andtells us to run the flesh side next the pulley, and practice proves thisto be correct."
Jointwq Belts.—" Whether the belts are new or old, a properlymade joint is of the first importance to all users of belting. . . . Awell-made butt joint, with the lace holes punched in row of diamondshape, answers the purpose fully as well as any. Care should betaken that the holes do not come in line across the belt. A good lace,properly applied, with all the strands of the lace running lengthwiseof the driving side of the belt, will last a long time and costs little. Tfa lap joint is made, time should be taken to thin down the ends of thelap. Joints of this sort should be made to the curve of the smallestpulley over which the belt has to work."
Accumulation of hum pa on Pulleys and Belts.—*' Dust should never boallowed to gather into a cake either on pulley or belt, for if so, thofibre of the leather gets very much strained. The belt is preventedfrom doiiis? its work because this stranger defies the attempts made bythe belt to get a proper hold of the pulley."
Bells and Hopes coming off Pulleys.—" When a bearing gets heated,the shaft naturally becomes heavy to turn. The belts or ropes, havingalready the maximum of power in hand they are designed to copewith, refuse this extra strain, and Avill leave tho pulleys at once,or break. This accident directs the attention of those in chargeto the belts or ropes, when time is taken n\> in consulting as to what isto be done. Meanwhile the cause of all the trouble gets time to cool,and the source of annoyance is never discovered. Before a now startis made, all bearings are well lubricated. All goes smoothly, yetsome one is blamed for the break down."
The above hints, coming as they do from an experienced manu-facturer of leather, who is also an extensive user of belting, should be
PRICES OF SMALL DYNAMOS. 63
regulated as is the case with the motor-dynamo. In purchasing amachine ot this typi it is important to obtain pie< ise details before-haud of the volts taken by the motor, and the volts delivered by thedynamo portion. AKo the vaiiation in the \oltage ot the dynamoportion fiom zero load right up to the full load < nrrent (whk>h must
Fig. \$.—1 H.P. Dynamotor. For Electro-plating.
always be stated), should bo iruarantecd. When inquiring for a motor-dynamo, the following details, should be given to the manufacturer :—
1. Maximum current required from dynamo armature2. Voltage required.3. Voltage of circuit from which the motor portion of the machine
is to be driven.4. Distance of point at which motor-dynamo is to be installed
from the point where power supply leads enter the building(approximately)
5. Woik which the dynamo is to be employed for, e.g., plating,metal refiimm, etc
The motor-dynamo is not to spark either on the motor or thedynamo tide under any load up to tull load when once the brushes areproperly adjusted. Th<' dynamo side mubt be shunt wound.
THERMOPILES, DYNAMOS, E'IC.
PRIMARIES WOUND FOR IOO, 115, and 230 VOLTS.
Output 111\Olts
80
*75375800
Efficiencyper cent.
40
4 3
5O62
£
17
3O
3655
Price&.
1 0
0
1 0
0
d.
0
0
0
0
Ovei-d 11 dimensions,
14
2 0
2426
in inches.X 9 XX II XX 13 Xx 15 x
79
1 0
i *
Another form of motor-dynamo, known sometimes a& adynainotor, in
Fig. 44 —r H P Mo to 1 -Dynamo
which the motor and dynamo windings arc on the same armature,running- in a single field, Fig. 45, K listed at the following prices:—
Output 111volts.35-42
80
175500
Efficiencyper cent
42
45
52'562
Price.£
1 2
2 2
28
43
b.
IO
O
O
O
d0
0
0
0
Over-all dimensionsin inches.
12 X 9 X16 X 11 X19 x 13 x20 x 15 x
79
1 0
M
The \oliage obtained from the.se motor-dynamo^ or dvnamotors (asthose in which there is a common field-magnet to the motor andthe dynamo armature aie sometimes called) can be made of any \aluedesired by the purchaser for special plating work The dynamotor isnot so suitable for electro-plating work as the motor-dynamo, becausethe voltaire from the dynamo side cannot be so cheaply .«nd readily
PKICES OF SMALL DYNAMOS. 65
with automatic zero current release, Figs. 46 aud 47. It is made at a pricefrom £\ lOs. for \ B. H. P. motors; £2 for i| to 2 B. H. P. motors;£2 lOs. for a 3 B. H. P. motor; £4 for a 5 B. H. P. motor, up to£16 for ii 50 B. H. P. motor.
It is, iu the writer's opinion, quite essential that motor* shall be fur-nished with the safety and starting gear specified above, if trouble withthe motor or the supply mains is to be avoided. The whole cost of thedouble pole switch, double pole fuse holder and fuses, and includingthe starting switch and automatic magnetic zero current cut-out
Fig. 46.—Motor-btarting Switch.
mentioned above, should not cost more than £2 15s. for a \l to 2B. H. P. motor, not including the cost of fixing. For a motor ofabout \ to 1 B. H. P., the cost will be about 10s. less.
Having now considered the various available sources of the ele( tri<current with as full detail as the limits of this treatise permit^, w emust turn to the question of the mo»t suitable source to select undergiven conditions of work, always bearing in mind the importantquestions of prime cost, depreciation, maintenance, and cost of energyper given output of the electric generator.
r
6 4 THERMOPILES, DYNAMOS, ETC.
The manufacturer should be required to give the folio wing details .—
1. Normal .speed at sjDecified voltage of power supply eireuit.2. Normal dynamo voltage at specified normal speed at zero load.3. Normal dynamo voltage, motor being run oif specified power
supply voltage, when the dynamo is loaded to specified full load.4. Normal full load current on motor at specified power supply
voltage.5. Normal full load current from dynamo when run at normal
specified speed.6. Temperature rise of field-magnets and also of the armature
or armatures after the machine has been running at full load forsix hours.
7. Price of motor-dynamo or dynamotor delivered and installed inpurchaser's premises, the price to include starting-gear, switch,and safety cut-outs on the motor side. Full details of thestarting apparatus, main switch, and safety cut-outs, if any,which are included, must be given.
8. State if it is possible to refill; to the voltage of the dynamooutput, and if so, between what hunts ; also state whether theajiparatus necessary for this voltage regulation is included inthe price given under (7), and if not, give the price for thisregulator installed complete, separately.
Other things being equal that motor-dynamo or dynamotor is themost satisfactory which :—
1. Takes the smallest current at full load from the supply main atthe specified power supply voltage.
2. Gives out the lai'gest current from the dynamo side at thespecified plating voltage.
3. Has the smallest variation of volts on the dynamo side as theload is altered from zero to full load.
4. Has the smallest temperature rise under the conditions statedabove.
5. Kuns at the lowest speed.
It is desirable that the bearings shall all be fitted with automaticring lubricators with oil level sight tubes, or in any case sight feedlubricators should be employed.
It is also very desirable that the motor side of the machine shall befitted with a double pole switch, a starting switch, double pole fuses,and also an automatic zero current cut-out. A very convenient andlargely used form of switch, which combines a starting switch and a zerocurrent automatic cut-out, is manufactured and sold by the SturtevantEngineering Company, Limited, of 75, Queen Victoria Street, London,which is known as the Cutler-Hammer Plain Ivlotor-.^tart'iig Rheo^at,
ELECTRIC GENERATORS FOR SMALL OUTPUTS. 67
must be home definite solution of the question us to what particulargenerator to instal. In giving general advice, however, it i&> difficultto consider every possible condition which may arise in practice, and ithas therefore been thought wise to select some few definite cases underdefinite stated conditions, and give the solutions for these, which, inth * writer's opinion, appear most satisfactory, leaving1 to the readertlie task of applying one or other or a combination of any of thesesolutions to his own ease.
It must be borne in mind, that throughout this book the pi ices ofapparatus which are given are only stated in order that some idea ofthe nature of the outlay involved in a given installation may beobtained. Prices vary from year to year, and a correct estimatecan only be made after having obtained a tender to a definite specifi-cation. The prices given here, however, are always taken from somestated list.
Cine I.—No power, either electrical or mechanical, is available, andit is not possible to get secondary batteries charged in the neighbour-hood. Under these circumstances it is probably advisable to employthe " Cupron " element up to a current output as large a& 20 amperesat 5 volts, which will cost probably about £24 ios\, or if the work isnot very steady in character, but is required a good deal at one time,with periods of little or no work intervening, it is probably wise touse the "Cupron" element for currents1 up to as high as even 30amperes at 5 volts. The former battery, costing £24 ios1., may be stillused for this current, as the normal current output of such a batteryis 24 amperes, and the maximum which may be used is 48 amperes,although it is advisable to run the battery with currents as near thenormal as possible, if it is desired to obtain the largest ampere-hourefficiency. If the current required is larger than 30 amperes, thencither a small steam-engine, boiler and dynamo, or a uas-engine anddynamo should be purchased. There is not much difference in theprime cost of such a combination, for small powers, but the roomrequired and also the small attention needed make it desirable to pur-chase the gas-engine combination. The total cost f. o. r. of thedynamo yielding 32 amperes at 5 volts, is listed by the General Elec-tric Company, in 1895, at £8 (see p. 61), and the gas-engines may bepurchased for the following prices, taken from the Stockport Gas-Engine List of 1900.
lirake-horse-power. i\
Price£ s
36 10
2
42
J 2
£5O
i
0£ s.
58 IO
42
68 o
66 THERMOPILES, DYNAMOS, ETC.
By the cost of energy we therefore include the co.st of attendancetogether with the co.st of the chemicals consumed in a battery, thecost of the gas or fu 1 burnt in a thermopile, and the cost of gasburnt in a g.is-eugine, oil in an oil-engine, or coal or other fuel underthe boiler supplying a steam-engine; or lastly the cost at whichelectrical cneryy can be obtained from some .source of electric supply.This s(>ur< e of electric supply is usually the public electric power orliyhl inn* *«upph mains, but may also include electric power obtained froma n igh1 touring premises or the electric power obtained in a charged
V.V.
D.r.Kwitth. I
Fig. 47.—Diagram of Connections of Motor-starting Switch.
becondary battery supplied from some neighbouring generator. Thepossibility of obtaining power from either water or wind turbines is atpresent so limited (and to all appearances will remain so) that thesesources of energy will not be considered in any detail here.
Electric Generators for Small Outputs.— In any particular casewhere it is proposed to set up some form of electric generator for asmall amount of electric current for electro-plating or other smallelectro-metallurgical operations, the circumst;mees under which the.installation is to be made are, of course, definitely known, and there
ELECTRIC OENFR\TORS FOR SMALL OUTPUTS. 69
for reasons already pointed out, that the gas-engine r u n 0 I i town oa
is better for electro-plating factories than a steam-engine of the sameoutput.
Case II.—If, as in the last case, there is no electrical or mechanicalpower available, and no means for charging a secondary battery, andthere is further no supply of coal-gas available, then a steam-enginedynamo combination with boiler may be purchased to yield 32 amperesat 5 volts for about £41, and a similar combination to yield 56 amperesat 5 volts for about £49, and when the current required is under about20 amperes for steady work, or 30 amperes for variable work, the" Cuproii" element should be employed instead of steam-dynamoset.
C<iw ITT.—If sufTuiont power i<« available, a«, for instance, from^f>me cnu'mt' on tlu» premises which is only partially loaded, it isprobably better to purchase a small dynamo costing", say, £8 or £10,when the probable quantity of current required is found to begreater than about 3 or 4 amperes. Remembering that such a dynamowill yield as much as 32 amperes. If a current of le<s than about 3 or4 amperes is required it is probably best to purchase 5 No. I I ." Cupron " element*, costing £2 5s., and yielding, when in scries, 2 to4 amperes at 5 volts. (See p. 11.)
Case IV.—If an electric supply company can supply a continuouscurrent on the premises at any reasonable rate, then it is probablyadvisable to purchase a suitable motor-dynamo or dynamotor directlyit is seen that the current required will be as large as 6 amperes or so,for " Cupron" elements for this output at 5 volts would cost about£S 2s., whilst a dynamotor having an output of 8 amperes would costabout £12. Before, however, deciding to instal an electric motor, aclear understanding mu«t be arrived at as to the conditions of chargefor power under which it will be placed. The charge is reasonablylow, in many cases about 2cl. per Board of Trade unit ; which unit, fora motor-drh ing dynamo, may be looked upon as one horse powor usedthroughout one hour, or half that power u.sed steadily for twice thetime and so on. Bat in some one or two cases with which the writeris acquainted a very largo charge is also made per annum or perquarter by the supply corporation for each lioi\se-power or fraction ofa horse-power of the motor installed. This appears to be an arrange-ment which must, one would imagine, have a good deal of effect indiscouraging the u<e of electricity for small power units, a use whichis generally understood to be the great object of supply companies tofoster in order to increase their dividends. This heavy (harge perb. h. p. of power taken by the motor installed per annum is preciselythe sanie whether an) power is- used or not, and although not usual,must, where imposed, be carefully considered when deciding on the
68 THERMOPILES, DYNAMOS, ETC.
The cost of the necessary water-tankb is included in these prices. Asthese machine^ are fitted for constant .speed for electric lighting with twofly- wheels, it is probable that cheaper engines might be purchased. Thedifference would not, however, be much. The prices also include,.standard-.size pulley, patent anti-pulsating gab bag, exhaubt boxesand the usual bet of .spares with .spanner*. ThebC engines are madeby J. E. H. Andrew & Co., of Reddibh, near Stoekport. A gas-engine dynamo plant therefore, to yield 32 amperes at 5 volts, can bepurchabed for about £44 iOb., exclusive of erecting, and one to yield56 amperes at 5 volts for ^5 2 I O s ? exclusive of erecting. The costof the " Cupron " element for \arioub current output ib worked outin the following table :—
Volts. Current.
i632404856
mum 1632
„ 6480
„ 96,, 112
Price.
£ b.8 216 432 840 1048 1256 14
d.0
0
0
0
0
0
It mubt be remarked that the priceb btated for the '' Cupron " element,as given above, are those given on a German li&t, and they would,no doubt, be more expensive delivered in England. The reason that thewriter would advise a gab-engine dynamo set costing bay £45, andcapable of yielding 32 ampere- at 5 \olt.s, rather than a "Cupron"element set of cells having precisely the same normal output a.s thedxnamo, is because the depreciation and upkeep of the "Cupron"elements would be higher than is the case with a properly looked afterUMs-cngiue and dynamo. A cheap vertical .steam-engine and boiler,p-fked and f. o. r , is listed by the General Electric Company, atthe following prices: —
Brake-horse-power.
Price
I
£\3 £49 £51 £57 £82
It is therefore evident that for \cry small powers the steam-enginehas about the same co^t as the gas-engine, but that as the powers in-crea.se the ga>-engiut has th<> lower prime cost. l<Y>r any powers upto about ten brake-horse-power, the present writer considers, partly
GAS ENGINES RUN ON PRODUCER GAS. 71
Q TYPE PORTABLE SECONDARY BATTERIES.
The prices given below are for cells in lead-lined wooden boxeR.
1De^ciiption of
Cull.
Numberoi
CU1-.
SingleCells.
Number oinegativePlato-.
3 Q Plates5 n7 »
n1521 „
"WorkingRate.
CharareAmi viv^
'512
47
10
to 1-3, 2*6> 4, 6'5
n
> 1 3
INs £-£*t> £•
sS«i"32-646'59
13
'p*
<* ;£
•*» 0
1
7142 1
355070
Appioxim.itel)imuwoiis
ovci handlesand
teiminaK.
,£ 1 •If S>A P-
in>. in-.2 5*2* 5^3g ' 5^5 5S65 5^9 5s
1
_n»^.
9i9i9i9*9i9^
-n
1 iur
<C
ell.
•5
c
'9i*52*2
3'44"56'5
^3
!
§ «*
1 1 > M .
68
1 0 *1621
28
l'uce.
1
. d.6 6« 09 6
12 915 319 0
Case VI.—Supposing that both mechanical power and clectiicalpower are available. Then for «mall currents up to about 10 amperesthe "Cupron" element may be employed, or if cheap secondarybattery charging1 is available, secondary batteries may be convenientlyused probably up to as much as 40 or 50 amperes, but above thisamount there is no doubt but that a motor generator costing £36 10s.and yielding 75 amperes at 5 volts is the best thing to invest in, forthe up-keep and depreciation of a motor generator is very small andthe power used cheap, whilst the up-keep and depreciation of secondarybatteries is about 20 per cent, on their prime co>t per annum, whilstpower obtained by external charging is always expeiw\c.
Th" foregoing discussions of several definite cases, are, however,in< omplete, for they do not and cannot take account of several factorswhich must always be eonMdered when deciding the best courseto pursue. For instance, a very e-scutial point in commencing abusiness may be 10 keep the capital outlay small, and again, theknowledge as to whether a gi\^n output is likely to remain steadyor to increase, or whether the business*, although averaging asteady output during the year, is likely to vary very muchfrom time to time during that year, are all points w ith manyothers to which due weight must be given. It is, how-ever, to be hoped that the cases treated of and the information as toprices given may prove of assistance in guiding an intendingpurchaser of electric generators.
Gas Engines run on Producer Gas.—Nothing has been said
7O THFRMOPILKS, DYNAMOS, ETC.
installation of a dynamo driven by elertric power. The rare requiredto keep a motor-dynamo or dynnmotor running* satisfactorily is slight,and the details are the same as those necessary when running adynamo, described on pages 51 to 61. The cost of about £ 1 10s., orperhaps less, must be added to the above price for the motor-dynamo toinclude a satisfactory arrangement of the main switch, starting" switch,automatic zero current cut out, and fuses, as previously specified forany electric motor. (See p. 64.)
Case V.—If portable secondary cells can be charged in the neigh-bourhood at a moderate rate then the secondary battery is cheaper inprime cost, and probably in depreciation, than the " Cupron " element.For instance, a portable secondary battery cell, manufactured by theElectric Power Storage Co., of 4, Great Winchester Street, E.C., havinga capacity of 50 ampere-hours, and giving a safe maximum dischargeat the rate of 9 ampere?* at 2*2 volts, and which can, therefore, bekept up over 5 hours, weigh* 21 lbs. complete, and costs- 15s., whereas3 No. IV. " Cupron " elements, which give a sate discharge at normalcurrent of 8 amperes and 2*4 volts, can be run for about nine timesthis length of time, namely, about 45 hours, before they require thecopper oxide regenerating. Now each charge of the secondarymay, perhaps be made at is. per charge, and, consequently, the costof the secondary battery and nine charges is 24a., whereas the price ofthe 3 No. IV " Cupron " elements is about £4 5s. The " Cupron "elements can, of course, be regenerated at a small cost, but there canbe no doubt that secondary batteries are cheaper, both in prime cost andup-keep, than "Cupron" element batteries if the battery-chargingcan be performed in the neighbourhood at a reasonable cost and withreasonable care of the cells. It must, indeed, be remembered thatmuch damage may be in time done to secondary batteries by chargingthem with currents much above their specified charging currents, andas the batteries sent in, to anyone undertaking charging, usually varymuch in size and the current they require, there is a good deal oftemptation to connect them in series and charge them all with thesame current. If the maximum current employed, however, is withinthe smallest specified current for any cell in the batch no harm will bedone to any of the cells charged at too small a current, the onlytrouble being that they will require a longer charge
Below is given a table of the details and prices of the ElectricalPower Storage Co.'s Q, type portable cells, also shown in Fig. 22, fromtheir list dated 1898.
REGULATING RESISTANCES. 75
procure on the strip of tin, E, which is let into the board, but doesnot < onto nearer than about 2 to 3 inches from the rack A. The depres-sions in the rack, the number of which may be as large as is desired, butwhich the writer finds may be conveniently two, are made of a curvedoutline, and are meant to take ordinary electric light carbons of from10 to 15 millimetres diameter. A good contact between these carbonsand the metal racks is obtained by means of two cast iron clampingbars, Y F, only one of which is shown in the figure, these are aboutone inch wide. To chimp the carbons annealed copper strips, oneinch wide, s^th of an inch thick, with holes at the ends, are slipped onthe \ inch stud screws o o o o, the carbons aie then laid in positionover these strips, and two more similar strips of copper are placed overthem. The clamps are finally placed in position, and are screAveddown with sufficient pressure by butterfly nuts, screwing on to the
c « |G
Fig. 49.—Adjustable Carbon Kod Resistance
stud screws. The length of all the copper strips between the holes inthese ends is less than the distance measured along the curved surfaceof the iron racks and clamps, and hence these copper strips arepulled into tight contact with the carbon rods when the butterfly nutsare screwed down. The terminals of the resistance are at H H. Theresistance may be either employed horizontally as shown, or may behung on the wall by mirror plates or hooks at K K. This resistance isalso made by Messrs. Parfltt and Webber, of Denmark Street, Bristol.One with four carbons costs 15s. complete, whilst two, with twocarbons each, would cost about 1 is. or 12s. each. The four-carbonform* gives a range from one carbon a foot long as the highest resis-
* The resistance of an electric light carbon, having a diameter ofabout 14 m.m. and not soft cored, I have found to be about 0*142 ohmsper foot length when carrying a current of 30 ampi'res in air. Thetemperature of the carbon under these conditions was just sufficientlyhigh to blacken paper pressed against it.—A. P.
74 THERMOPILES, DYNAMOS, ETC.
together, .ami this is varied by means of the larsre hand escrow at oneend of the apparatus. The cost of siu h a regulatable carbon resistancedepends, of (our.se, upon its size. One which will take 50 amperescontinuously without heating" to redness is made by 3Iessrs. Parfitt &Webber, of Denmark Street, Bristol, for a price of £2. It contains50 carbon plate*, each about 3 ins. .square and ^-in. thick. These areinsulated from the iron rods at the sides and bottom by means of thicksheets of asbestos millboard, A. Similar asbestos sheets protect the castiron end-plates from comi'mr into contact with the carbons or the gunmetal terminal plates, B E. TO these plates the terminals are screwed.
The resistance of such a carbon plate resistance may always be halvedor reduced to any value, at a given tightness of the carbon plates,by means of a simple device—namely, by taking out the gun-metalterminal plate and inserting it between the carbons at any other pointthan the extreme end of the pile where its normal position is. Theresistance, therefore, of this apparatus may be reduced from that ofthe whole pile of carbon plates loosely pressed, together down to thatof one carbon plate only, tightly clipped between the two end or
Adjustable Carbon Plate Resistance.
terminal metal plates of the apparatus. There is no harm whateverto be feared from running such a carbon resistance with a current solarge and for so long a time that the carbon plates are at a dull redheat, provided that the resistance is fixed in such a position that thereis no danger of tire being caused by it. If it is stood on .sheet ironwhich is supported on bricks, there can be no danger at all on thisa 'count, even if the bricks rest upon wood.
Another form of carbon resistance which is a <rood deal cheaper thanthe one last described is made of electric light carbons, and is shown inFig. 49. It fulfils the conditions that such a resistance for electro-plating requires, namely, that it is cheap, strong, of considerable rangeof adjustment, and not easily damaged by moisture and fumes. Itconsists of a fixed rack, A, and a movable rack, B, both of cast iron.The movable rack B, can be moved nearer to or farther from A, andcan be clamped in any position on the board c, by means of a clampingscrew, not shown in the figure, which passes through the hole D inthe metal projection at the right hand side of B. This screw exerts
Fig. 51.—Adjustable ^*ire Kesistancc.
DETERMINATION OF THE POLARITY OF GENERATORS. 77
Adjustable wire resistances, sold by Messrs. 0. Berend & Co., ofDunedin House, Basmghall A\enue, London, are shown in Figs.. 51;uul 5-« These resist-ancds c-o t from 16 to K,shillings each in theform of Fig. 51, carry-iixjr a current of fromI to 15 amperes : whilstresistances of the formshown in Fig 52, inwhich the steps are not K)gradual as in the resist-ances shown in Fig. 51,the price \ aries from 25 toto 45 shillings, accordingto si/e, the current car-ried Miryiiiir al>o from4 amperes in the smallest to 20 amperes in the largest size.
Determination of thePolarity of Generators.—Itis not infrequently necessary toascertain the polarity of adynamo, or even a battery, andthis may "be done, in the caseof a dynamo, either by passinga current from it through asolution of one part of «*tronjrestfeulplmri* acid and three parts ofwater contained in an ordinaryjam jar from terminals of li .idscraped bright. The urcaUMcare must be observed, at leastin testing larger machines inthis way, to pre\tnt the twolead strips coming into con-tact. They may be come-niently lv< pt at a distance ofabout three inches from oneauothei. The lead fetrip at-tached to the positive pole ofthe dynamo will become of adark brown or chocolate colour
in about 5 to 10 minutes. A quicker tost, which maybe used witheither batteries or dvnamos, is to employ pole finding paper made withphenolphthalein. This paper is white, but if it ib moistened and laid
Fig. 5-:.—Adjustable Wirellesibtance.
76 THERMOPILES, DYNAMOS, KTO.
tancc down to four in parallel, which may be shortened up by shiftingthe rack n to a lenirth of not more that about 4 inches. The twodouble-carbon form trives, howe\<r, double this r.msjre, i.e., from amaximum resistance of two foot long carbons in series down to the
same \ alue for low resis-tance as the four-carbonform. The prices givenabove for those resis-tances include shiteboards, which in th.itcase do not require thestrip of tin E, which isintended to protect thewood from the end of thes«rew. Each carbon willcarry about 30 ampereswithout becoming suffi-ciently hot to set light topaper.
A variable liquid re-sistance, sold by theGeneral Electric Com-pany, of G(j, Queen Vic-toria Street, is shown inFisr. 50. It is known asLyons' Variable LiquidResistance, it will carryfrom 50 to 80 ampere-*.It consists of a stone-ware jar 24 inches hitihand 8 inches in diameter.Each jar is in a frame-work, to which is at-tached a raising or low er-ing gear for the purposeof inserting a cone oflead in the so-called non-ascetic liquid of sec 111
Fig 50.—Lyons'Variable Liquid Resistance, composition, piob.ibly asolution of *-CHne neutral
salt The price of the cheapest of these resistances is hiyh, he ins; o\er£6. Cheap adjustable liquid remittances can, howe\er, bo rigged upon a somewhat similar principle for temporary purposes by moansof a lartre jam jar and a couple of lead plates in sodium sulphatesolution.
CHAPTER 111.
HISTORICAL .REVIEW OE ELECTRO-DEPOSITION.
Announcement ot J.icobi's Discuvery.—Jordan'* Proce&a Published.—Jordan'sPioci?v>.-Jspenoei's Paper on the Electrotype Process.—Effect otspencer's Papei.—Vindication ot Joidan's Claim.—Mr. bircks onJoidan's Discovery.—Sir Heniy Besaeiner's Experiments.—Dr. UoldingBird's Experiments—Origin ot the Poious Cell.
LONG before the art of Electro-deposition wab founded upon u prac-tical basis, it was well known, experimentally, tliat several metalscould be deposited from their solutions upon other metals, by simplyimmersing them in such solutions ; but thib knowledge was of littleimportance beyond the interesting nature of the rebultb obtained. Thebchoolboy had been accustomed to amubc himself by producing thee\cr-popular " lead tree," by buspending a piece of zinc attached to acopper-wire in a bolution of bugar of lead, or the " silver tree," witha bolution of nitrate of silver and mercury ; or he would coat the bladeof hib penknife with copper, by dipping it for a moment in a weakbolution of bulphate of copper (bluebtone). But thebe, and the likeinteresting faetb, were of no practical value in the artb. It wab alsoknown that articles of bteel could be gilt by bimple immersion in adilute bolution of chloride of gold (that is gold dibsolved in aqua regia),or btill better, in an ethereal bolution of the chloride, and thib bimpleprocess was sometimes adopted in the ornamentation of cngra\edarticles, in imitation of the procebbof damabcoiwf/. The eyes of needleswore albo gilt by a similar procebb. and "goldui-eyed needles" becamepopular amongst the fair hex. With this exception, however, thedeposition of metals, even by simple immersion in metallic solutions,was regarded as interesting and wonderful, but nothing more.
As far back as about the year 1820, the author's father covered the" barrels " of quill pens with silver, by first steeping them in a solutionof nitrate of silver, and afterwards reducing the metal to the metallicstate in bottles charged with hydrogen gas, the object being to protectthe quillb from the softening influence of the ink.
In the year 1836, Professor Daniellmade known his constant battery,and in the same year, Mr. Dc la Rue constructed a modification of thisbattery, in working which he observed that " the copper-plate is1 also
78 THERMOPILES, DYNAMOS, ETC.
on ,t table, and the two wires from the terminals of the dynamo orbatteiy are pressed upon it at a distance of an inch from each other,a deep crimson stuiu will be shown under the negative wire. This«u tion takes place at once. Such pole papers may be purchased ata cheap rate made up into little books.
General Arrangement of Plating Vats.—Fig. 52A gives ageneral perspective view of two vat- in a plating shop, arranged inparallel, with their ampere-meters and regulating resistances in circuit,
Fig. 52A.—General Arrangement of Electro-plating Vatb
and a shaft along the side of each vat which, by means of eccentrics,moves an oscillating1 frame, causing the work to constantly keep ingentle mo\ ement, a movement which is found to be very conducive touniform plating deposits. A are the anode rods and c the cithodo.
It need hardly be said that these ^ ats are intended for nickel, copperor silver plating, but not for gold work, which is done in nun h small* rvath, usually of stoneware or china. A somewhat similar \icw isshown in Fig. 108.
JORDAN'S PROCESS. 8r
inventions [photographic], it appears that Professor Jacobi, at St.Petersburg, has also made a discovery which promises to be of littleless importance to the arts. He has found a method—if we under-stand our informant rightly—of converting any line, however fine,engraved on copper, into a relief by galvanic process. The Emperor ofRussia has placed at the professor's disposal funds to enable him tocomplete his discovery."
Jordan's Process published.—Having seen a copy of the aboveparagraph in the Mechanic's Magazine, May nth, 1839, !Mr. J. C.Jordan, of London, eleven days afterwards sent a communication tothe editor of that journal, in which he put in his claim—if not topriority, as far as Jacobi was concerned, at least to prove that he hadbeen experimenting in electro-deposition some twelve months beforethe announcement of Jacobi's discovery was published in this country.Indeed, Jordan's communication did more, for it contained a definiteprocess, and since this was undoubtedly the first publication of thekind which had appeared in England, the merit of originality—so faras publication goes—is clearly due to Jordan. As an important itemin the history of electro-deposition, we give the subjoined extractfrom his letter from the Mechanic1 a Magazine, June 8th, 1839. Theletter was headed " Engraving by Galvanism."
Jordan's Frocess.—" It is well known to experimentalists on thechemical action of voltaic electricity that solutions of several metallicsalts are decomposed by its agency and the metal procured in a freestate. Such results are very conspicuous with copper salts, whichmetal may be obtained from its sulphate (blue vitriol) by simpry im-mersing the poles of a galvanic battery in its solution, the negativewire becoming gradually coated with copper. This phenomenon, ofmetallic reduction is an essential feature in the action of sustainingbatteries, the effect in thi» case taking place on more extensive sur-faces. But the form of voltaic apparatus which exhibits this result inthe most interesting manner, and relates more immediately to the sub-ject of the present communication, maybe thus described :—It consistsof a glass tube closed at one extremity with a plug of plaster of Paris,and nearly filled with a solution of sulphate of copper. Thio tube andits contents are immersed in a solution of common salt. A plateof copper is placed in the first solution, and is connected by means ofa wire and solder with a zinc plate, which dips into the latter. Aslow electric action is thus established through the pores of the plasterwhich it is not necessary to mention here, the result of which is theprecipitation of minutely-crystallised copper on the plate of that metalin a. state of greater or less malleability, according to the slowness orrapidity with which it is deposited. In some experiments of thisnature, on removing- the copper thus formed, I remarked that the sur-
8o HISTORICAL REVIEW OF ELECTRO-DEPOSITION.
covered with a coating1 of metallic copper which is continually beingdeposited; and so perfect is the sheet of copper thus formed, that,being* stripped off, it has the counterpart of every scratch of the plateon which it i.> deposited.* Although this interesting observation didnot lead to any direct application at the time, it is but reasonable topresume that in the minds of some persons the important fact whichit disclosed would have suggested the possibility of its being suscep-tible of some practical application. It was not until the followingyear (1837), however, that the electro-deposition of metals, experi-mentally, seriously occupied the attention of persons devoted toresearch, the first of whom was Dr. Golding Bird, who decomposedsolutions of the chlorides of ammonium, potassium, and sodium, and.succeeded in depositing* these metals upon a negative electrode ofmercury,f whereby he obtained their amalgams. From the timewhen his interesting results became known, many persons repeatedhis experiments, while others turned their attention to electrolysis asa new subject of investigation, and pursued it with different objects,as will be shown hereafter.
Mr. G. H. Elkington, in 1836, obtained a patent for "Gilding cop-per, brass, and other metals " by immersing the articles in a boilingalkaline solution containing dissolved gold. This was followed, in1837, by several other patents granted to Mr. H. Elkington for coat-ing metals with gold and platinum, and for gilding and silveringarticles- In 1838, Mr. G. E. Elkington, with Mr. O. W. Barratt,patented a process for coating articles of copper and brass with zinc,by means of an electric current generated by a piece of zinc attachedto the articles by a wire, and immersing them in a boiling neutralsolution of chloride of zinc. This was the first process in which aseparate metal was employed in electro-deposition.
Announcement of Jacobi's Discovery.—About the period atwhich the above processes were being developed, it appears that.several other persons were engaged in experiments of an entirelydifferent character and of far greater importance, as will be seen bythe results which followed their labours. In St. Petersburg, Pro-fessor Jacobi had been experimenting in the deposition of copper uponengraved copper-plates, a notice of which appeared in the Athencenm,May 4 th, 1839. The paragraph ran as follows:—li Galvanic Engraving%n llclief.—While M. Daguerre and Mr. Fox Talbot have been dip-ping their pencils in the solar spectrum,! and astonishing us with their
* Philosophical Magazine, 1836.t " Philosophical Transactions of the Royal Society," 1837.I It was about thin period that the famous Daguerreotype process of portrait-
taking was being developed in England.
SPENCER'S PAPER ON ELECTROTYP1NG. 83
fluids in which the metallic electrodes were immersed were in conse-quence separated by a thick disc of plaster of Paris. In one of thecells was sulphate of copper solution, in the other a weak solution ofcommon salt. I need scarcely add that the copper electrode was placedin the cupreous solution, not because it is direct7// connected with whatI have to lay before the society, but because, by a portion of itsresults, I was induced to come to the conclusion I have done in thefollowing paper. I was desirous that no action should take place on thewire by which the electrodes were held together. To attain this objectI varnished it with sealing-wax varnish ; but, in so doing, I droppeda portion of it on the copper that was attached. I thought nothingof this circumstance at the moment, but put the experiment in action.
' 'The operation was conducted in a glass vessel; I had, conse-quently, an opportunity of occasionally examining its progress."When, after the lapse of a few days, metallic crystals had covered thecopper electrode, icith the inept ion of that portion which had beenspotted with the drops of varnish, I at once saw that I had it in mypower to guide the metallic deposition in any shape or form I choseby a corresponding application of varnish or other non-metallicsubstance.
" I had been long aware of what every one who uses a sustaininggalvanic battery with sulphate of copper in solution must know, thatthe copper plates acquire a coating of copper from the action of thebattery : but I had never thought of applying it to a useful purposebefore. My first essay was with a piece of thin copper-plate, havingabout four inches of superfices, with an equal-sized piece of zinc,connected together with a piece of copper wire. I gave the copper acoating of soft cement consisting of bees-wax, resin, and a redearth—Indian or Calcutta red. The cement was compounded afterthe manner recommended by Dr. Faraday in his work on chemicalmanipulation, but with a larger proportion of wax. The plate re-ceived its coating while hot. On cooling, I scratched the initials ofmy own name rudely on the plate, taking special care that the cementwas quite removed from the scratches, that the copper might bethoroughly exposed. This was put into action in a cylindrical g*lassvessel about half filled with a saturated solution of sulphate of copper.I then took a common gas glass, similar to that used to envelop anargund burner, and filled one end of it with plaster of Paris to thedepth of three-quarters of an inch. In this I put some water, addinga few crystals of sulphate of soda to excite action, the plaster of Parisserving as a partition to separate the fluids, but sufficiently porous toallow the electro-chemical fluid to penetrate its substance.
"I now bent the wires in such a form that the zinc end of thearrangement should be in the saline solution, while the copper end
82 HISTORICAL REVIEW OF ELECTRO-DEPOSITION.
face in contact with the plate equalled the latter in smoothnessand polish, and mentioned this fact to some individuals of myacquaintance. It occurred to me therefore, that if the surface of theplate was atgrand, an imprison might be obtained. This was foundto be the case, for, on detaching the precipitated metal, the more deli-cate and superficial markings, from the fine particles of powder usedin polishing, to the deeper touches of a needle or graver, exhibitedtheir corresponding impressions in rduf with great fidelity. It is,therefore, evident that this principle will admit of improvement andthat casts and moulds may be obtained from any form of copper.
" This rendered it probable that impressions might be obtained fromthose other metals having an electro-negative relation to the zinc plateof the battery. With this view a common printing type was substi-tuted for the copperplate and treated in the same manner. This alsowas successful; the reduced copper coated that portion of the typeimmersed in the solution. This, when removed, was found to bea perfect matrix, and might be employed for the purpose of castingwhen time is not an object.
" It appears, therefore, that this discovery may possibly be turnedto some practical account. It may be taken advantage of in procuringcosts from various metals as above alluded to ; for instance, a copperdie may be formed from a cast of a coin or medal, in silver, typemetal,lead, &c, which may be employed for striking impressions in softmetals. Casts may probably be obtained from a plaster surface sur-rounding a plate of copper; tubes or any small vessel may alsobe made by precipitating the metal around a wire or any kind of sur-face to form the interior, which may be removed mechanically by theaid of an acid solvent, or by heat." [May 22nd, 1839.]
It is a remarkable fact that Jordan's letter, regardless of the valu-able information it contained, commanded no attention at the time.Indeed, the subject of which it treated (as also did Jacobi's announceddiscovery), apparently passed away from public view, until a paper byMr. Thomas Spencer, of Liverpool, was read before the LiverpoolPhilosophical Society on the 12th of September in the same year.Omitting the prefatory observations with which the paper commenced,its reproduction will form a necessary link in the chain of evidencerespecting the origin of the electrotype process, and assist the readerin forming his own judgment as to whom the merit of the discoveryis really due.
Spencer's Paper on the Electrotype Process.— "In September,1837, I was induced to try some experiments in electro-chemistry witha single pair of plates, consisting of a small piece of zinc and an equalsized piece of copper, connected together with a piece of wire of thelatter metal. It was k.tended that the action should be slow; the
SPENCER S PAPER ON ELECTROTYPING. 05
" There was one most important (and, to me, discouraging)circumstance attending" these experiments, which was that when Iheated the plates to get off the covering of cement, the meshes ofcopper net-work invariably came off with it. I at one time imaginedthis difficulty insuperable, as it appeared to me that I had cleared thecement entirely from the surface of the copper I meant to have ex-posed, but that there was a difference in the molecular arrangement ofcopper prepared by heat and that prepared by voltaic action whichprevented their chemical combination. However, I then determined,should this prove so, to turn it to account in another manner, which Ishall relate in a second portion of this paper. I then occupied myselffor a considerable period in making experiments on this latter ^ectiuiiof the subject.
" In one of them I found on examination a portion of the copperdeposition, which I had been forming on the surface of a coin, ad-hered so strongly that I was quite unable to get it off; indeed, achemical combination had apparently taken place. This was only inone or two spots on the prominent parts of the coin. I immediatelyrecollected that on the day I put the experiment in action I had beenusing nitric acid for another purpose on the table I was operating- on,and that in all probability the coin might have been laid down wherea few drops of the acid had accidentally fallen. I then took a pieceof copper, coated it with cement, made a few scratches on its surfaceuntil the copper appeared, and immersed it for a short time in dilutenitric acid, until I perceived, by an elimination of nitrous gas, thatthe exposed portions were acted upon sufficiently to be slightlycorroded. I then washed the copper with water, and put it in action,as before described. In forty-eight hours I examined it, and foundthe lines were entirely filled with copper; I applied heat, and thenspirit of turpentine, to get off the cement; and, to my satisfaction, Ifound that the voltaic copper had completely combined itself with thesheet on which it was deposited.
** I then gave a plate a coating of cement to a considerable thick-ness, and sent it to an engraver ; but when it was returned, I foundthe lines were cleared out, so as to be wedge-shaped, or somewhat inform of a V, leaving a hair line of copper exposed at the bottom andbroad space near the surface ; and where the turn of the letters tookplace, the top edges of the lines were galled and rendered ragged bythe action of the graver. This, of course, was an important objection,which I have since been able to remedy in some respects by alterationin the shape of the graver, which should be made of a shape moreresembling a narrow parallelogram than those in common use;some of the engravers have many of their tools so made. I did notput this plate in action, as I saw that the lines, when in relief, would
84 HISTORICAL REVIEW OP ELECTRO-DEPOSITION.
should be in the cupreous one. The ga> glu^s, with the wire, wasthen placed in the vessel containing1 the .sulphate of copper.
" It was then suffered to remain, and in a few hours I perceivedthat action had commenced, and that the portion of the copperrendered bare by the scratches was coated with a pure bright de-posited metal, whilst all the surrounding portions were not at all actedupon. I now saw my former observations realised ; but whether thedeposition so formed would retain its hold on the plate, and whetherit would be of sufficient solidity or strength to bear working if appliedto a useful purpose, became questions which I now endeavoured tosolve by experiment. It also became a question whether, should I besuccessful in these two points, I should be able to produce linessufficiently in relief to print from. The latter appeared to dependentirely on the nature of the cement or etching ground I might use.
"This last I endeavoured to solve at once. And, I may state,this appeared to be the principal difficulty, as my own impressionthen was that little less than |-th of an inch of relief would berequisite.
" I then took a piece of copper, and gave it a coating of a modifica-tion of the cement I have already mentioned, to about Jth of an inchin thickness; and, with a steel point, endeavoured to draw lines inthe form of net-work, that should entirely penetrate the cement, andleave the surface of the copper exposed. But in this I experiencedmu'li difficulty, from the thickness I deemed it necessary to use;more especially when I came to draw the cross lines of the net-work.When the cement was soft, the lines were pushed as it were into eachother; and when it was made of a harder texture, the interveningsquares of net-work chipped off the surface of the metallic plate.However, those that remained perfect I put in action as before.
(' In the progress of this experiment, I discovered that the solidityof the metallic deposition depended entirely on the weakness orintensity of the electro-chemical action, which I found I had in mypower to regulate at pleasure, by the thickness of the intervening wallof plaster of Paris, and by the coarseness and fineness of the material.I made three similar experiments, altering the texture and thicknessof the plaster each time, by which I ascertained that if the plasterpartitions were thin and. coarse, the metallic depositions proceeded withgreat rapidity, but the crystals were friable and easily separated ; onthe other hand, if I made the partition thicker, and of a little finermaterial, the action was much slower, and the metallic deposition wasas solid and ductile as copper formed by the usual methods, indeed,when the action was exceedingly slow, I have had a metallic depo-sition apparently much harder than common sheet copper but morebrittle.
MR. DIRCKS ON JORDAN^ DISCOVERY. 87
many a youth whose first introduction to chemical manipulation wasthe electro-deposition of copper upon a sealing-wax impression of asignet-ring or other small object, acquired therefrom a taste for amore extended study of scientific matters, which eventually led up tohis devoting himself to chemical pursuits for the remainder of hisdays. At the period we refer to there were but few institutions inthis country for the encouragement of scientific study. One of themost accessible and useful of these, however, was that founded byDr. Birkbeck, the well-known Literary and Scientific Institution atthat time in Southampton Buildings, London.
Vindication of Jordan's Claim.—Although Jordan's letter waspublished, as we have shown, three months prior to the reading ofSpencer's paper in Liverpool, that important communication wasoverlooked, not only by the editor of the journal in which it appeared,but also by the scientific men of the period. Even the late AlfredSince, to whose memory we are indebted for the most delightful workon electro-metallurgy that has appeared in any language, failed torecognise the priority of Jordan's claim. Impelled by a strong sensseof justice, however, the late Mr. Henry Dircks wrote a series ofarticles in the Mechanic's Magazine in 1844, in which he proved thatwhatever merit might have been due to Spencer and Jacobi, Jordanwas unquestionably the first to publish a process of electrotyping.Indeed, he went further, for he proved that the electro -deposition ofcopper had been accomplished practically long before the publicationof any process. Before entering into the merits of Jordan's priority.Mr. Dircks makes this interesting statement:—
Mr. Dircks on Jordan's Discovery.—''The earlie&t applicationof galvanic action to a useful and ornamental purpose that I amacquainted with was practised by Mr. Henry Bessemer, of BaxterHouse, Camden Town, who, above ten years ago [about 1832]employed galvanic apparatus to dei>osit a coating of copper on leadcastings. The specimens I have seen are antique heads in relief, thewhole occupying a space of 3 inches by 4 inches. They have lain asornaments on his mantel-piece for many years, and have been seen bya great number of persons."
Appreciating—from its historic and scientific interest—the impor-tance of the above statement, it occurred to the author that if themeans adopted at so early a period in electro -metallurgical historycould become known, this would form an important link in the chainof research respecting the deposition of metals by electrolysis. He,therefore, wrote to Sir Henry Bessemer, requesting him to furnishsuch particulars of the method adopted by him in depositing copperupon the objects referred to as lay in his power after so long a periodof time. With kind courtesy, and a generous desire to comply with
86 HISTORICAL REVIEW OF ELECTRO-DEPOSITION.
have been broad at the top and narrow at the bottom. I took anotherplate, gave it a coating' of the wax, and had it written on with a merepoint. I deposited copper on the lines and afterwards had it printedfrom.
" I now considered part of the difficulties removed; the principalone that yet remained was to find a cement or etching1-ground, thetexture of which should be capable of being cut to the requireddepth, and without raising what is technically termed a burr, and atthe same time of sufficient toughness to adhere to the jilates wherereduced to a small isolated point, which would necessarily occur inthe operation which wood-engravers term cross-hatching.
1 i I tried a number of experiments with different combinations ofwax, resin, varnishes and earths, and also metallic oxides, all withmore or less success. The one combination that exceeded all othersin its texture, having nearly every requisite (indeed, I was enabled topolish the surface nearly as smooth as a plate of glass), was principallycomposed of virgin wax, resin, and carbonate of lead—the white-leadof the shops. With this compound I had two plates, 5 inches by 7,coated over, and portions of maps cut on the cement, which I hadintended should have been printed off and laid before the BritishAssociation at its meeting."
Effect of Spencer's Paper.—When Spencer's paper was publishedit at once commanded profound attention, and many persons practisedthe new art either for amusement or scientific research, while othersturned their attention to it with a view to m iking it a source of com-mercial j rofit. It was not, however, until Mr. Robert Murray, inJanuary, 1840, informed the members of the Royal Institution,London, that he had discovered a method of rendering non-conduct-ing surfaces—such as wax, kc.—conductive of electricity by employ-ing plumbago, or black lead, that the art became really popular in thefullest sense. This conducting medium was the one thing wanted torender the process facile and complete ; and soon after Mr. Murray'sinvaluable discovery had been made known, thousands of persons inevery grade of life at once turned their attention to the electrotypeprocess until it soon became the most popular scientific amusementthat had ever engaged the mind, we may say, of a nation. The sim-plicity of the process, the trifling cost of the apparatus and materials,and the beautiful results which it was capable of yielding, withoutany preliminary knowledge of science, all combined to render the newart at once popular in every home. Every one practised it, includingthe youth of both sexes.
It is not to be wondered at that an art so fascinating should haveproduced more than an ephemeral effect upon the minds of some ofthose who pursued it. Indeed, it is within our own knowledge that
SIR H. BESSEMER S EXPERIMENTS. 89
coins were in currency in those days] into a basin with water andnitric acid. My early attempt's wore not very successful, for the depo-sited metal could be rubbed off, and was in other ways defective. Inext tried .sulphate of copper, both cold and boiling solutions. Ifound the sulphate much better adapted for the purpose than thenitrate solution. At first I relied on the property which iron has ofthrowing down copper from its solutions, and by combining iron, incomparatively large quantities, with antimony, and using this alloywith tin, bismuth, and lead, I succeeded in getting a very thin, buteven, coating of copper; but it was not sufficiently solid, and easilyrubbed off.
" In pursuing my experiments, I found that the result was muchimproved by using a metallic vesssel for the bath instead of an earthen-ware one, such as a shallow iron, tin, or copper dish, as a slightgalvanic action was set up, but the best results were obtained by usinga zinc tray, on the bottom of which the object was laid, face upwards,and the solution then poured in. By this means a Aery firm and solid(oating was obtained, which could be burnished w ith a steel burnisherwithout giving w ay. By adding to the copper solution a few crystalsof distilled verdigris, I obtained some beautiful green bronze deposits,a colour far more suitable for mcdaUioitb and bubh than the brightcopper coating obtained by the sulphate -when used alone.
4' I cast and coated with green copper a small bust of Shakespeare,which, with many other specimens, I sold to Mr. Campbell, thesculptor, who at that time was modelling a life-si/edbust of Canning :he had arranged that I should cast it from the "lost-wax," anddepoj-dt green copper thereon. Unfortunately Campbell died before hi.smodel was completed. But for this incident I might possibly lm\o(arried the deporting process much further, but at that time my suc-cess in casting, in a very hard alloy, dies used for embossing card-board and leather, ottered a more direct and immediate commercialresult, and thus the artistic branch was lost sight of. I remembershowing some of these castings to my friend the late Dr. AndrewUre, about the year 1835-6, with which he was much pleased. Inreferring to them se\eral years later, in the second edition of hissupplement to his ' Dictionary of Arts and Manufactures,' publishedin 1846, he mentions these castings as had atbtin(j±>, at page 70,under the head of ' Electro-Metallurgy,' which commences in thesewords :—
" ' Lhel) o-Mt taUio gy.—By this elegant art, perfectly exact copies ofany object can be made in copper, silver, gold, and some othermetals, through the agency of electricity. The earliest application ofthis kind seems to have been practised about 1in yea 16 ago, by Mr.
ot Camden Town, London, who deposited a coating of
88 HISTORICAL REVIEW OF ELECTRO-DEPOSITION.
the author's wishes, Sir Henry took the trouble to furnish the infor-mation convoyed in the following interesting* communication, whichcannot fail to be read with much gratification by all who havestudied the art of electro-deposition, either from its scientific or prac-tical aspect. When ^\ c call to remembrance the numerous inventionswith which the active mind of Sir Henry Bessemer has been associateddiu'in jf the greater portion of the present century, culminating in hisremarkably successful improvements in the manufacture of steel, it ispleasing to read that at the youthful age of eighteen—when voltaicelectricity was but little understood, and Daniell's, Grove's, andS'nee's batLrbs unknown- he was engaged in experiments withmetals, which were evidently conducted with an amount of patienceand careful observation which would have been highly creditable in aperson of more advanced years.
Sir Henry Bessemer's Experiments.—Replying to the author'sinquiry of S.r II >nry B senior (in January, 1S85) as to the method h »had adopted in coating with copper the objects- referred to above, SirHenry wrote as follows; and the minuteness of the details, given afterso great a lapse of time, will doubtless strike the reader with sonicastonishment:—
" I have much pleasure in replying to your note of inquhy inreference to the deposition of copper from its solutions on white metalcastings.
"My first experiments began when I was about eighteen years ofage, s<iy in 1831-2. At that period, after much practice, I was mostsuccessful in producing castings of natural objects in an alloy of tin,bismuth, and antimony. In this alloy I cast such things as beetles,frogs, 2>rawn>, &v. ; also leaves of plants, flowers, moss-rose buds;and also medallions, and larger works in basso-relievo. By mysystem of (acting in nearly red-hot metal, the metal was retained forten or fifteen minutes in a state of perfect fluidity in the mould,and hence, by its pressure, forced itself into every minute portion ofthe natural object, whatever it might be; thus every minute thornon the stem of the rose was j roduced like so many fine projectingneedles I exhibited several of these castings, coated with copper, at' Topliss's Museum of Arts and Manufactures,' at that time occupy-ing the site of the present National Gallery, and which museum wasafterwards removed to a large building in Leicester Square, now theAlhambiM Theatre, where I also exhibited them.
" Beautiful as were the forms so produced, they had a commonlead-like appearance, which took much from their vilue and artisticbeauty, and as a remedy for this defect, it occurred to me that it waspossible to give them a thin coat of copper, deposited from its solu-tion in dilute nitric acid. This I made by putting a few pence [copper
DR. GOLDING BIRD S EXPERIMENTS.
The apparatus used on that occasion by myself and others was pre-cisely that recommended by Dr. Bird, consisting of simply any glassvessel capable of holding a solution of common salt, into which is in-serted a gas lamp chimney, having its lower end plugged up by pour-ing into it plaster of Paris ; a solution of sulphate of copper is thenpoured into it, and the whole immersed into the contents of the glass,and tightened with pieces of cork. The result expected from thisarrangement was the deposit of metallic veins of the copper within theplaster diaphragm, independent of any connection with the poles ofthe battery. Dr. Faraday, and every other electrician, expressedsurprise and doubt at the results in this respect said to have beenobtained by Dr. Bird ; and Dr. Faraday particularly urged the neces-sity and importance of caution in receiving as established a result sogreatly at variance with all former experience, and proceeded toexplain a variety of causes tending to lead to fallacious results in thecurious and interesting experiments."
Up to this time, the possibility of obtaining electrical effectsby meaiib of a single metal, in the manner pursued by Dr. Bird,would have been considered theoretically impossible. It must not bewondered at, therefore, that even the greatest of our philosophers—Michael Faraday—should have been sceptical in the matter. It isclear now, however, that Dr. Golding Bird's results were based uponprinciples not then understood, and that to this gifted physician wearc indebted for what is termed the " single -cell " voltaic arrange-ment—the first, and for some time after the only, apparatus employedin producing electrotypes.
Origin of the Vorom Cell.—It appears that while Mr. Dircks wasexperimenting (in 1837) in obtaining crystals of copper by Dr. Bh\T&method, he was frequently in communication with Mr. John Dancer,a philosophical instrument maker in Liverpool, and in October of thefollowing year (1838) that gentleman showed him a " ribbon of copper,thin, but very firm, granular on one side, while it was bright andsmooth, all but some raised lines, on the other." This result, Mr.Dancer informed him, was obtained by galvanic action, observingthat some specimens were as tenacious as rolled copper, while otherswere crystalline and brittle. Mr. Dancer attributed the superiorityof the former to the following cause * *' Having gone to the potteriesto look out suitable jars for sustaining batteries, and having fixed ona lot which he was told would not answer ut» theg were not [/lazed, andwould not hold liquor," it occurred to him that such wtglazcd jarsmight be turned to account, and used instead of bladder, brown paperplaster of Paris, and other porous substances he had previously em-ployed. Having obtained a sample for experiment, he subsequentlyfound that he could obtain a more firm and compact deposit of copper
90 HISTORICAL REVIEW OF ELECTRO-DEPOSITION.
copper upon lead castings so as to produce antique heads, in relief,about three or four inches in size. He contented himself with form-ing a few such ornaments for his mantel-piece, and though he madeno secret of his purpose, he published nothing upon the subject. Aletter of the 22nd of May, 1839, written by Mr. C. Jordan, which ap-peared in the Mechanic's Magazine for June 8th following, containsthe first printed notice of the manipulation requisite for obtainingelectro-metallic casts, and to this gentleman, therefore, the world isindebted for the first discovery of this new and important applicationof science to the uses of life.'
*' The first inception of the idea of coating works of art in metalwith a deposited coating of another metal, if not resting solely withme, at least I certainly was within measurable distance of this greatdiscovery some three or four years before it was brought forward byany other person, but I failed to see its true significance, and conse-quently lost a grand opportunity.
" You are quite at liberty to make any use you like of this informa-tion."
We will now return to Mr. Dircks' vindication of Jordan's claim.Referring to Jordan's letter to the Mechanic's Magazine, Mr. Dircks
says, ' * In particular I would direct attention to the fact of the mainincidents named by Mr. Jordan, published June 8th, 1839, agreeingwith those published by Mr. Spencer, September 12th, 1839, and,curious enough, being called forth by the same vague announcement ofProfessor Jacobi's experiments which was then making the round ofthe periodicals. Both parties described Dr. Golding Bird's .smallgalvanic apparatus; one used a printer's type, the other a coppc rcoin, and both recommend the application of heat to remove the pre-cipitated copper.
*' I was aware of Mr. Jordan's letter at the time of its publication,and have frequently been surprised since, that his name has nottranspired in any discussion I have heard ujxm the subject. Nothingcan be clearer than his reasoning, the details of his experiments, andhis several concluding observations."
Dr. Golding Bird's Experiments.—There can be no doubt what-ever that after Dr. Golding Bird published the results of his interest-ing experiments in 1837, and the means by which he obtained his im-portant results, many scientific men devoted themselves to investigatingthe new application of electricity, amongst whom was Mr. Henry Dircks." It was particularly in September and October, 1837," wrote Mr.Dircks, " that several parties attached to scientific pursuits in Liver-pool, were engaged in repeating the experiments of Dr. Golding Bird,and of which ho gave an ncrnmit before the chemical section of theBritish Asbociation at Liverpool, over which Dr. Faraday presided.
DIRCKS ON SPENCER S CLAIM. 93
in the matter thus : "Lastly, therefore, that through the Mechanic'sMagazine (which Mr. Spencer was regularly taking in) the experimentalresults obtained by Mr. Dancer, and the reports in April and May,1839, in public papers, of Jacobi's experiments, all being broad hints,and abundant assistance to aid Mr. Spencer, that he is rather to bepraised for his expression of what was already known, on a smallerand less perfect scale, than to be adjudged a discoverer, much lessthe father of electro-metallurgy, having a preference to every otherclaimant." Following the paper from which the foregoing extract istaken, is a footnote by the Editor of fixe Mechanic's Magazine, which isimportant as showing how strange it was that Jordan's communicationnot only escaped the attention of scientists, but even that of the con-ductor of the journal in which it appeared : " Mr. Dircks has provedbeyond all doubt that we have made a great mistake in advocating sostrenuously the claims of Mr. Spencer to the invention of eleetro-graphv. No one, however, can suppose that we would intentionallyexalt any one at the expense of our own journal, which we are nowpleased to Hud was the honoured medium of the first distinct revela-tion of this important art to the public, by an old and esteemedeorresp<indent of ours, Mr. Jordan. Whatever Mr. Bessemer, Mr.Dancer. Mr. Spencer, or others, may have previously said or done, itwas in private—made no secret of, perhaps, but still not communicatedto the public at large—not recorded in any printed work for generalbenefit. For anything previously done by any of them, they mightliave still remained in the profoundest obscurity. No public descriptionof an earlier date than Mr. Jordan's can, we believe, be produced;and when we look upon that description, it is really surprising to seewith what fulness and precision the writer predicated of an art nearlyall that has been since accomplished. In supporting, as we did, theclaims of Mr. Spencer to be considered as the first discoverer, we hadlost all recollection of Mr. Jordan's communication. "We have nopersonal acquaintance with either of the gentlemen, and could have nomotive for favouring one more than the other. "We took up the cause)f Mr. Spencer with spontaneous warmth because we thought him tobe a person most unfairly and ungenerously used, as in truth he wasso far as the intention went, by those who, having at the time none ofthose reasons we now have for questioning Mr. Spencer's pretensions,yet obstinately refused to acknowledge them. If it should seem tothe reader more than usually surprising that Mr. Jordan's paperescaped the recollection of the editor, through whose hands it passedto the public, his surprise will be lessened, perhaps, when he observeshow it appears to have escaped notice, or been passed over in silence, byevery one else down to the present moment—even those, not a few, whohave expressly occupied themselves in eleetrography To us,
f)2 HISTORICAL REVIEW OF ELECTRO-DEPOSITION.
than in any previous experiment. To the accidental circumstanceabove referred to, we are undoubtedly indebted for that most import-ant accessory to the single-cell apparatus and the two-fluid battery—the porous cell.
In a letter to Mr. Dircks, relative to Sj">encer's claim to the discoveryof a means of obtaining1 " metallic casts " by electro-deposition, Mr.Dancer says, '' I met Mr. Spencer one morning in Berry Street,Liverpool, and happened to have one of these precipitated copperplates with me, which I showed to him. When I told him how it hadbeen formed he would scarcely believe it, until I pointed out the im-pressions in relief of all the minute scratches that were on the plateagainst which it had been deposited. The surprise that Mr. Spencerexpressed very naturally led me to suppose that it was the first com-pact piece of precipitated copper he had seen." At this early period(1838) Mr. Dancer had not only deposited tough reguline copper, buthe went a step farther. He attached to a copper plate, by means ofvarnish, ' * a letter cut out from a printed bill. The copper precipitatedon all parts of the plate, except where the letter was fixed; when Ipeeled the precipitated copper off, the letter came out, not havingconnection with the outside edge. I also obtained an impression bystamping my name on a copper cylinder, the impression being thereverse way All this happened many months before I wasaware that Mr. Spencer had been engaged in anything of the kind,except that he had Dr. Bird*sexperiments in action. Sometime afterthis Mr. Spencer applied to me for one of my porous jars, and one daytit his house he told me for what purpose he wanted it."
It is perfectly evident that Mr. Dancer's results were obtained longbefore the publication of Spencer's paper, and that both were indebtedto Dr. Golding Bird's simple but ingenious contrivance for prose-cuting their first experiments ; and it is also clear that Dancer'sbrilliant idea of substituting porous earthenware for the crude plasterdiaphragms greatly facilitated experimental researches in thisdirection ; while at the same time it placed within our reach one ofthe most valuable accessories of the two-fluid voltaic battery—theporous cell.
Being desirous of placing Jordan's claim to priority—as the firstto make publicly known the process of electrotyping, or clcctrography,as he termed it—Mr. Dircks followed up the subject in the Mechanic'sMagazine y in a series of papers, in which he not only traced Mr.Spencer's experiments to their true origin, namely, Dr. Bird'sexperiments published two years before, and the hints which he hadderived from Dancer, but he moreover showed that Spencer musthave been aware of Jordan's published process, for he says, insumming up the evidence he had produced against Spencer's position
DIRCKS ON SPENCKR S CLAIM. 95
late Dr. Andrew Ure to Mr. Dircks shows how fully he recognisedthat gentleman's advocacy of Jordan's claim: "I read with greatinterest your narrative of the discovery or invention of the electrotypeart, and am much pleased to see justice done to modest retiring meritin the persons of Mr. Jordan and Mr. Dancer. The jay will feel alittle awkward this cold weather, .stripped of his peacock plumage."
The following letter from Faraday tends to show that the greatphilosopher, in common with most other persons, had, prior to Mr.Dircks' explanation of the facts, believed in Spencer "being the origi-nator of electrotyping : "I am very much obliged by your kindliestin sending me your account of the facts, &c, &c. It is very valuableas respects the fixing of dates, and has rather surprised me." *
It is a pity, but none the less true, that while Jordan's communica-tion received no attention whatever, although published in a well-lvad journal, Spencer's paper—which had merely been read before alocal society in Liverpool, and afterwards printed for private einulattononly—commanded the profoundest attention. In short, to use acommon phrase, it "took the world by storm." The name of"Spencer, the discoverer of Electrotyping," was on every lip, andmen of science of all nations regarded him as one who had madea great addition to the long roll of important discoveries whichscience had placed at the disposal of art. Henry Dircks' champion-ship of Jordan's just claim, however, eventually broke up Spencer'sposition, and to the Jirsl publisher of the electrotype process, Mr. C. J.Jordan, was at last accorded the merit—for he received no other recog-nition—of having published a process, if we may not say discovery,which was destined to prove of inestimable advantage to his fellows,not only in itself, but as being the means by which the minds of menwere directed to the deposition of other metals by electrical agency.It would not be out of place to suggest that in commemoration ofJordan's f/tft to mankind of so useful and valuable a proresH, anappropriate testimonial should be set on foot—if not by the public, atleast by those who have directly gained so much by his initiation ofthe art of electro-deposition.
The success which attended the electrotype process induced manypersons to turn their attention to the deposition of gold and silver, bymeans of the direct current; but up to the year 1840 no really suc-cessful solution of either metal was available. In that year Mr. JohnWright, a surgeon in Birmingham, and Mr. Alexander Parkes, inthe employment of Messrs. Elkington, were engaged in makingexperiments in electro-dex>osition, when the former gentleman hap-
* The thiee foregoing letters, which we transcribed from the originals, arenow, we believe, published for the first time.
94 HISTORICAL REVIEW OF ELECTRO-DEPOSITION.
the most surprising thing of any connected with the case is, thatneither Mr. Jordan himself, nor any of his friends, should hefore nowhave thought it worth while to vindicate his claims to the promulga-tion of an art which justly entitles him to take a high place amongthe benefactors of his age and country.—Ed. M. J / . "
While Mr. Dircks' "Contributions to the History of Electro-Metal -lurgy " were being published in the columns of the Mechanic's Magazine,the arguments and farts which he adduced created a deep impressionin the mindb of scientific men of the day, who had unfortunatelyaccepted Spencer as the originator of electrotypy. Of all men, scien-tists are the most anxious to accord the merit of dtscorcrij to those whoare really entitled to it. Devoting themselves to the investigation ofnatural laws, and their application to the useful purposes of man,they are naturally jealous of any attempt on the part of one to appro-priate the honour—usually the only reward—due to another, ft isnot surprising, therefore, that when it became fully proved thatto Jordan and not S]>onrrr was due the credit of having been the firstto publish a process for the practical deposition of copper by electro-lysis, that such men should frankly acknowledge their mistake.Amongst those who came forward to do justice to Jordan's claimwere the late Professor Faraday, Dr. Andrew lire, and ProfessorBrande, then chemist to the Royal Mint. The latter eminent chemistand author of the best chemical manual in our language, sent thefollowing letter to Mr. Dircks, which clearly acknowledges the errorinto which, in common with others, he had fallen in attributing toSpencer the merit of the electrotype process :—
" I am much obliged by your copy of the Mechanic's Magazine andthe information it contains respecting Mr. Spencer's pretensions. 1certainly always gave him credit for much more merit than he appearsto have deserved."
When Spencer found that his position was so severely shaken byMr Dircks' powerful defence of Jordan's claim to priority, he wroteseveral letters in reply, which appeared in the columns of the abovejournal, witlt a view to refute Ids opponent's arguments, and shakehis testimony; but in this he was unsuccessful, for the facts whichMr. Dircks had made known were absolutely beyond refutation. Itis not often that men of science enter into a controversy of this nature,but silence under such circumstances would have been an act of injus-tice to Jordan, by leaving the question still in doubt.
Amongst those who ascribed to Spencer the discovery of the elec-trotype process was Mr. George Shaw, of Birmingham, in the firstedition of his " Manual of Electro-Metallurgy." In the secondedition of his work, however, he made the amende to Jordan, byfrankly acknowledging Lib mistake. The following letter from the
DIECKS ON SPENCER £ CLAIM. 9 /
copper), under the action of the current the copper-plate became dis-solved as fast as pure copper was deposited upon the mould, wherebythe strength of the solution was kept in an uniform condition. It isthis method which is now almost universally adopted (when dynamomachines are not employed) in practising the art of electrotyping upona large scale.
In 1841, Mr. Alfred Smee published his admirable work on Electro-metallurgy, which at that period proved of the greatest service to allpri'.son.s interested in the new art. In the year following, Mr. J. S.Woolrirh introduced his magneto-electric machine, which for manyyear* after occupied a useful position as a substitute for voltaicbatteries, in several large plating works. In this year also, Dr. II.II. Leeson took out a patent for improvements in electro-depositingprocesses, in which he introduced the important elastic mouldingmaterial, ki guiding wires," keeping articles in motion while in thebath, &c.
In 1843, Moses Poole obtained a patent for the use of a thermo-electric pile as a substitute for the voltaic battery ; but the inventionwas not, however, successful. Many patents were taken out in thefollowing years for various processes connected with electro-deposi-tion , but the next most important improvement was due to Mr. "W.Milward, of Birmingham, who accidentally noticed that after wax-moulds, which had been covered with a film of phosphorus—by apply-ing a solution of that substance in bisulphide of carbon to their surfaces—had been immersed in the cyanide of silver plating bath, the silverdeposit upon other articles, such as spoons and forks, for example,which were afterwards coated in the same bath, presented an unusuallybright appearance in parts, instead of the dull pearly lustre whichgenerally characterises the silver deposit. This incident induced Mr.Milward to try the effect of adding bisulphide of carbon to theplating bath, which produced the desired result. For some time hekept the secret to himself; but finding that it eventually becameknown, he afterwards patented the process in conjunction with a Mr.Lyons, who had somehow possessed himself of the secret. From thattime the addition of bisulphide of carbon to silver baths for the pur-poses of u bright " plating has been in constant use.
In the foregoing sketch of the origin and history of electro-deposi-tion we have endeavoured to give such information as we hoped wouldbe interesting to many who are engaged in the practice of the art, andalso instructive to tho^e who may be about to cuter into a study of thesubject, believing, as we do, that the present volume would be incom-
n
96 HISTORICAL REYIRW OF ELECTRO-DErOSrTTON,
poned to meet with a passage in Seheele's " Chemical Essays,'* iawhich ho found that cyanides of gold, .silver, and copper, weresoluble in an excess of cyanide of potassium. It at once occurred tohim that solutions of gold and silver thus obtained might be employedin electro-deposition, and he then formed a solution by dissolvingchloride of silver in a solution of ferro-cyanide of potassium, fromwhich he obtained, by electrolysis, a .stout and firm deposit of .silver,a result which had never before been obtained. A few weeks after,Mr. "Wright prepared a solution with cyanide of potassium, in.stoad ofthe ferro -cyanide, and although various cyanide solutions of silverand copper had already been employed in the .simple immersionprocess of depositing these metals, there is no doubt that it i^ to Mr.Wright that we are really indebted for the practical application ofcyanide of potassium as a solvent for metallic oxides and other saltsused in electro-deposition. About this time (1840) Messrs. Elkingtonwere preparing to take out another patent, when Mr. "Wright, havingsubmitted his results to them, agreed to include his process in theirpatent, in consideration of which it was agreed that he should receivea royalty of one shilling per ounce for all silver deposited under thepatent: on his decease, which took place soon afterwards, an annuitywas granted to his widow. This patent, with Wright's importantaddition, namely the employment of alkaline cyanides, formed thebasis of the now great art of electro-gilding and plating : but it wassome time before the proper working strength of baths and the pro-portion of cyanide could be arrived at, the deposits being frequently11011-adherent, which caused them to strip or peel off the coated articlesm the process of burnishing. This was afterwards remedied to someextent by dipping the articles (German silver chiefly) in a very dilutesolution of mercury. About this time, the author, in conjunctionwith his brother, Mr. John Watt, introduced electro-gilt and silveredsteel pens, which were sold in considerable quantities.
In the same year, Mr. Murray discovered a means of renderingnon-conducting surfaces, as wax, &c, conductive, by coating themwith powdered plumbago, and this important suggestion proved ofinestimable advantage to those who desired to follow the art ofelectrotyping commercially. Indeed, without the aid of this usefulsubstance, it is doubtful whether the important art would have greatlyexceeded the bounds of experiment. At this period, also, anotherimportant improvement in the electrotype process was introduced byMr. Mason, which consisted in employing a separate battery as a sub-stitute for the " single -cell" process up to that time adopted inelectro typing. By the new arrangement, a copper plate was con-nected to the positive pole of a Daniell Battery, while the mould to becoated with copper was attached to the negative pole. When thesewere immersed in the electrotyping bath (a solution of sulphate of
CHAPTER IV.
ELECTRO -DEPOSITION OF COPPER.
Electrotyping by Single-cell Process.—Copying Coin;, and Medals.—Mould-ing Materials.—Gutta-percha.—Plastic Gutta-pereha.—Gutta-perchaand Marine Glue.—Beeswax.—Sealing-wax.—Steaiine.—Stearic Acid.—Fusible Metal.—Elastic Moulding Material.—Plaster of Paris.
IT may fairly be baid that the discovery of the electrotype pro-cess formed the basis of the whole electrolytic industry ; and, inits applications* to various purposes of the arts and to literature, ithas proved of inestimable value. "While, in its infancy, the electro-type process was a source of scientific recreation to thousands ofpersons of all clashes, many were those who saw in the new process awide field of research, from which much was expected and more hasbeen realised. While Faraday, Becquerel and others were investi-gating the process in its more scientific relations, practical men weretrying to apply it to various art purposes, until, in course of time,electrotyping was added to our list of chemical arts.
The simplest form of arrangement for electrotyping small objectsis known as the " single-cell" process, which it will be well to con-sider before describing the more elaborate apparatus employed forlarger work.
Electrotyping by the Single-cell Process. —In its most simpleform, a small jar, Fig. 53, may be used as the outer\essel, and in this is placed a small porous cell, madeof unglazed earthenware or biscuit porcelain, some-what taller than the containing vessel. A strip ofstout sheet-/inc, with a piece of copper wire attached,either by means of solder or by a proper bindingscrew, is placed in the porous cell. A MUHUIUII solu-tion of sulphate of copper (bluestone), made bydissolving crystals of that substance in hot water,and pouring the liquid, when cold, into the outer cell.The porous cell is then filled to the same height as the coppersolution Avith a solution of sal-ammoniac or common s.ilt. To keepup the strength of the solution win n in HM1 ;I few < vy.st.il> of sulphateof eopper are placed in a muslin bag, which is hooked on to the
go HISTORICAL ltEVIEVV OP ELECTRO-DKPOSITION.
plete without some special reference to the interesting origin of sogroat aud useful an art—an art which has many widespread appli-cations of great commercial and decorative importance.
luirther reference to subsequent inventions connected with electro-deposition and its developments in recent years, will be found in thelater chapters of this vol nine.
COPYING COINS AND MEDALS. I O l
the depositing cell. When unamalgamated zinc is used in the single -cell arrangement the sulphate of copper should be simply a saturatedsolution of the salt without that addition of acid, though a few dropsonly may be added with advantage.
It is of great importance that the sulphate of copper should bepure. The crystals should be of a rich dark blue colour and absolutelytree from greenish crystals {sulphaU of iron), which not unfrequentlytret mixed with the copper salt by the carelessness of the shopkeepers'assistant*.
Copying Coins and Medals.—Before explaining the variousmethods of obtaining moulds from different objects, for the purposeof producing fae-similes in copper, let us see how we may employ theabove apparatus in a more direct way. Suppose we desire to obtain acopy, in reverse, of some medal or old com, or even a bronze penny-piece, having decided which side of the coin it is intended to electro-type—say the ol>ni'\/ or 4*head" s ide-we must first render the^urfaeo clean mid bright. This may be very readily done by meansof rottenstone and a little olive oil, applied with a piece of chamoisleather and briskly rubbed OUT the face of the coin. Tn two or threeminutes the surface will be sufficiently bright, when the oil must bewiped oft' thoroughly either Avith cotton wool or blotting paper. AMiort piece of copper wire is next to be soldered to the back of thecoin, and the polished side is then to be brushed-over with a soft plate-brush and plumbago, or blacklead, which will prevent the depositedcopper from adhering to the medal. In order to prevent the copperfrom being deposited upon the back and rim these parts must becoated with some HowioHdmttny material. For this purpose paraffinwax, applied by gently heating the medal and touching it with thewax, or red sealing-wax, dissolved in spirit of wine or wood spirit(pyroxylie spirit), brushed over the surfaces to be protected, willanswer well; but if the latter is employed it must become thoroughlydry before being placed in the copper solution.
Being thus prepared, the end of the conducting wire is to be in-serted in the binding screw attached to the zinc and securely fixed byturninu" the screw until it grips the wire firmly. The coin must belowered into the solution steadily, with its face towards the porouscell, and it" any air-bubbles appear upon its face they must be re-mouvl by means of a camel-hair brush, or, still better, by blowingupon them through a glass tube. It is a good plan to breathe uponthe face of the coin before placing it in the solution, which, by co\er-ing it with a layer of moisture, effectually prevents the formation ofair-"bubbles.
In about t\vent\ -four hours from the first immersion of the medalthe deposit of copper will generally be sufficiently stout to bear re-
IOO ELECTRO-DEPOSITION OF COPPER.
edge of the vessel by means of a short copper hook, and the bagallowed to dip a little way into the liquid. The prepared mould isconnected to the end of the wire (which is bent in this f) form) andgently lowered into the solution, when the whole arrangement iscomplete. In place of the porous cell the zinc may be wrapped inseveral folds of brown paper, enclosing a little common salt, but theporous cells are so readily obtained that it is never worth while toseek a .substitute for them. This simple arrangement will easily beunderstood by referring1 to the cut.
A more convenient single-cell apparatus is shown in Fig. 54, inwhich the containing vessel, or call, is a glass orstoneware jarcaj)able of holding about three pints.In this is placed a porous cell (p). A bar or plateof zinc (z), with binding screw attached, is de-posited in the porous cell; a short -piece of copperwire (iv), for suspending the mould (w) or object tobe copied, has its shorter end inserted in the holeof the binding-screw. The outer vessel is aboutthree parts filled with a .saturated solution of sul-phate of copper (<), and the porous cell is filled tothe same height with a half-saturated solution ofsal-ammoniac or common salt. If the zinc isamalgamated, however, dilute sulphuric acid is usedinstead of the latter solution in the porous cell, anda small quantity of oil of -vitriol (from half an
ouuee to one ounce of acid to the quart of copper solution) added.Am«ly<hH<ttin<j tin Zuic.—Pour a little dilute sulphuric acid, or un-
diluted muriatic acid, into a dish, and, having tied a piece of flannelto the end of a stick, lay the zinc in the dish and proceed to brush the•icid all over the plate ; now pour a little mercury (quicksilver) onthe plate, and rub it over the zinc with the little mop, when it willreadily spread all over the surface, giving the zinc a bright silverylustre. It is important that the zinc should be thoroughly cleaned bythe acid, otherwise the mercury will fail to amalgamate with themetal, and dark patches of unamalgamated zinc will appear. Theperforated shelf, or tray, in the engraving is a receptacle for crystalsof sulphate of copper, which, being placed upon it, gradually becomedissolved while the deposit of copper is going on, and thus re-supplythe solution as it becomes exhausted, whereby the operation progressesuniformly.
To prepare the copper solution for small experimental purposes,dissolve .ibout 10 ounces of sulphate of copper in 1 quart of hotwater and stir until the crystals are all dissolved ; then set the vesselaside until cold, when thc</<«/ liquor id to be carefully poured into
54
MOULDING MATERIALS.
hours the gutta-percha is found to be kneaded into a perfectly homo-geneous mass, which is rolled or drawn into sheets, hands, &c.
(iutta-pereha becomes vsoft and plastic at the temperature of boilingwater (212° Fahr.), when two pieces may be welded together. It is anon-conductor of electricity, and is indeed one of the best v^Hluthif/materials known : it is impervious to moisture, and is scarcely at allaffected by either acids or alkalies. Owing to its plasticity when soft,it is one of the most useful materials for making1 moulds, yielding im-pressions which are exquisitely sharp in the very finest lines. "Whenused for making moulds from small objects, as coins, medallions, orsealing-wax impressions of seals, a piece of gutta-percha of the re-quired size is placed in hot water (the temperature of which should beabout iGcT Fahr.;, and, when sufficiently soft, it should be rolledwhile still wet in the palms of tho hands until it assumes the form ofa ball; it should then again be soaked in tho hot water for a shorttime, and be again rolled as before, care being taken to observe thatthe surface of the ball exhibits no seams or fissures. "When largerobjects have to be copied stout sheet gutta-percha is used, and apieceof the required size cut from the sheet, which is softened as before,then applied to the object, and the necessaiy pressure given to securea faithful impression.
Plastic Gutta-percha.—When gutta-percha is steeped for a fewhours in benzol or naphtha it becomes considerably swollen ; if after-wards soaked in hot water it is exceedingly plastic, and requires butmoderate pressure to obtain most perfect copies from even such fragileobjects as plaster of Paris models.
Gutta-percha and Marine Glue.—The following has aiso beenrecommended : gutta-percha 2 parts, Jeffrey's marine glue 1 part.Each of the materials is first to be cut up into thin strips ; they arethen to be mixed, placed in a pipkin and heated gently, with con-tinual stirring, until the substances have become well incorporated :tho mixture is now ready for use, and should be rolled into the formof balls before being applied for taking impressions. A very usefulmixture is made by melting thin strips of gutta-percha as before, andadding one-third part of lard, keeping the mixture well stirred. It isapplied by pouring it over flat surfaces, as steel plates, &c.
Beeswax.—This is a very useful material for moulding, and may beapplied either in the form of virgin or white wax, or the ordinarycommercial article—yellow beeswax. Since this substance, however,is very commonly adulterated, it may be useful to know something ofits natural characteristics. At the temperature of 32° Fahr. beeswaxbecomes brittle, at from 8o° to 90° it becomes soft and plastic, and itmelts at about 1550 Fahr. Mr. B. S. Proctor says: " I t becomesplastic or kneadable at about 85° Fahr., and its behaviour while worked
TO2 ELECTRO-DEPOSITION OF COPPER.
moving from tin* original, wiion the extraneous copper, which hasspread round the edge of the deposit, or electrotype, may lie carefullybroken away by means of small pliers ; if the medal be gently heatedover a small lamp, the electrotype will readily become detached,and will present, in reverse, a perfect copy of the original, in whicheven the very finest lines will be accurately reproduced. In itspresent condition the electrotype is hard and brittle, and will, there-fore, require careful handling. To give it the toughness and flexi-bility of rolled copper it is only necessary to heat the electrotype todull redness, which may be conveniently done by placing it on a pieceof sheet-iron, and laying this on the clear part of a fire until red hot,when it must be withdrawn and the " type" set a vide to cool. Ifplaced in a very weak solution of sulphuric acid for a few moments,then rinsed and dried, and afterwards brushed over with a little rougeor whiting, its surface may be readily brightened.
If we desire to obtain a copy in relief from our electrotype (also incopper) we must now treat it as the uwnhh folk.wing the same routineas before in all respects, by which we shall obtain a perfect fac-simileof the original coin, which may be mounted and bronzed by any ofthe processes hereafter given.
Having thus seen what results may be obtained with the mostsimple application of the single-cell process, we will next turn our at-tention to the different methods of obtaining moulds from variousobjects, but, before doing so, it will be necessary to consider thenature of the several substances which are employed in moulding andthe methods of preparing them for use.
Moulding Materials.—The chief substances used in the electro-typing art for making moulds are gutta-percha, wax, and fusiblemetal; other materials, however, are employed in certain cases inwhich the substances named would be inapplicable. The variousmaterials will be considered under their separate heads, as follows :—
Gutta-percha.—This most useful moulding material is the concretejuice of I.soiiandra Gutta, a tree growing only in the Malayan Archi-pelago, and of other species of the same genus. The ntem of thegutta-percha tree, which sometimes acquires the diameter of 5 or 6feet, after being notched yields a milky juice which, when ex-posed to the air for some time, solidifies, and this constitutes thegutta-percha of commerce. As imjiorted, it is in irregular blocks ofsome pounds in weight, and commonly containing a large proportionof impurities in the shape of bark, wood, stones, and earthy matter.To purify the crude article it is first cut in thin slices, which are after-wards torn into shreds by machinery. These are next softened byhot wrater and afterwards kneaded in a masticator, by which the im-purities become gradually washed away by the water. After several
ELASTIC MOULDING MATERIAL. TO5
represent tlie principal formula? tor fusible metal, the last of whichmelts at the low temperature of 151^ Fahr. or 6i° below thf boiling"point of water :—
ozs. ozs. ozs.I. BiMiiuth . 8 II. Bismuth . 8 III. Bismuth 8
Lead . 4 Lead . 5 Lead . 4Tin . 4 Tin . 4 Tin . 2
Antimony 1 Cadmium 2
16 18 iGThe metals are to be put into a crucible or clean iron ladle, and
melted over a low fire; when thoroughly fused, the alloy is pouredout upon a cold surface in small buttons or drops, and these, whencold, are to be again melted and poured out as before, the operationsto be repeated several times in order to ensure a perfect admixture ofthe metals. Another and better plan is to f/iaiudate the metal, orreduce it to small grains in the following way:—Fill a tall jar orother vessel with cold water, and on the surface of the water place alittle chopped straw (about 3 inches in length). When the metal ismelted, get an assistant to stir the water briskly in one direction, thenpour in the metal, holding the ladle at some distance from the .surfaceof the water ; by this means the metal will be diffused and separatedinto a considerable number of small grains. The water is then to bepoured off, and the grains collected, dried, and re-melted, after whichanother melting and granulation may be effected, and the alloy finallymelted and cast into a mould, or simply poured out upon a flat iron orother surface, when it will be ready for future use. By the repeatedmelting, the alloy lo&es a little by the oxidation of the metals ; butsince the heat required to fuse it is less than that of boiling water, theloss is but trifling, as compared with the importance of obtaining apa-fat alloy of the various metals. It should be the practice toremove the crucible or ladle from the fire the moment the alloy beginsto melt, and to depend upon the heat of the vessel to complete thefusion.
Elastic Moulding Material.—For making moulds from objectswhich are much under cut, in which case neither of the foregoing sub-stances would be available, an elastic material is employed which hasthe same composition as that from which printers' rollers arc made,that is to say, a mixture of glue and treacle, the formula for whichit;:—
between the finger and thumb is characteristic. A piece the size ofa pea being worked in the hand till tough with the warmth, thenplaced upon the thumb and forcibly stroked down with the forefinger,curls up, following the finger, and is marked by it with longitudinalstreaks." Its ordinary adulterants are resin, farina, mutton suet,and stearine, though more ponderous substances, such as plaster ofParis, have sometimes been detected. White wax is very commonlyadulterated with spermaceti, sometimes to the extent of two-thirds ofthe latter to one of wax. These sophistications, although not neces-sarily fatal to the preparation of good moulds, are certainly objection-able, inasmuch as it not unfrequently hapjiens that a wax mouldsplits or cracks, not alone from cooling too quickly, but owing to thepresence of foreign substances which impair its toughness.
Sealing-wax.—This substance may be employed for taking impres-sions of seals or crests, and was, indeed, one of the first materials usedin the earliest days of electrotyping. The material, however, shouldbe of good quality, and only sufficient heat applied to melt, withoutinflaming it.
Stearine. Stearic Acid.—The former substance is the solid con-stituent of tallow, and the latter (stearic acid) is the same substanceseparated from fats by chemical processes. Either may be used formaking moulds instead of wax ; but the late C. V. Walker recom-mended the following mixture in preference to either:—
Spermaceti.Wax . . . .Mutton Suet
Another formula consists of :—
White WaxSfearineFlake White or Litharge
ifif
ozs.83
The whole ingredients are put into a pipkin and gently heated overa low fire, with continual stirring, for about half an hour, after whichthe mixture is allowed to rest until the excess of litharge (oxide oflead) has deposited. The clear residue is then to be poured into ashallow dish, and when cold is put aside until required for use.
Fusible Metal.—This alloy, which melts at the temperature ofboiling water, and in some preparations very much below that point,is very useful for making moulds from metallic and some other objects;and since it can be used over and over again, and is capable of yieldingexceedingly sharp impressions, it may be considered one of the mostserviceable materials employed for such purposes. The following
CHAPTER V.
ELECTRO-DEPOSITION OF COPPER {continued).
Moulding in Gutta-percha.—Plumbagoing the Mould.—Treatment of theElectrotype.—Bronzing the Electrotype.—Moulds of Sealing-wax.—Copying Plaster of Paris Medallions.—Preparing the Mould.—Plumba-going.—Clearing the Mould.—Wax Moulds from Plaster Medallions.—Moulds from Fusible Metal.
Moulding in Gutta-percha.—In the former case, we explainedhow a copy of a coin could be obtained, in reverse, by making" theoriginal act as the mould. We will now turn our attention toobtaining fac-simile duplicates in relief, from impressions or moulds ofsimilar objects, from such of the materials described in the lastchapter as will best answer the purpose ; and since the applicationof these materials in the simple way we shall indicate will lead toan understanding* of the general principles of mould-making, it isrecommended that the student should endeavour to acquire adroitnessin taking impressions which will be perfectly sharp and clear, beforehe attempts to obtain metallic deposits of copper upon them.
To obtain a copy of a medal, coin, or other similar object, the mostconvenient material to employ is gutta-percha. Take a small pieceof this substance and place it in hot but not boiling water for a fewminutes, or until it is perfectly soft; while still wet, roll it betweenthe palms of the hands until it assumes the form of a ball: it shouldthen be replaced in the water for a short time, and again rolled asbefore. The coin to be copied is now to be laid, face upward, upon apiece of plate-glass, slate, or polished wood. Xow take the ball ofgutta-percha and place it in the centre of the coin, and press it firmlyall over it, from the centre to its circttinference, so as to exclude the air,and in doing this it may be necessary to occasionally moisten the tip?of the fingers with the tongue to prevent the gutta-percha fromsticking to them. A flat piece of wood may now be laid over theprutta-percha, and if this be pressed forcibly by the hands this willensure a perfect impression. After about a quarter of an hour or so,the gutta-percha mould may be readily removed from the coin, pro-vided that the material has set hard.
Plumbagoing the Mould.—Having1 thus obtained a mould from a
106 ELKCTRO-DEPOSITION OF COPPER.
The glue is first to be covered with cold water and allowed to standfor at least twelve hours, by which time it should be perfetly softthroughout. The excess of water is then to be poured off, and thevessel placed in a saucepan or other convenient utensil, containing- alittle water, and heat applied until the glue is completely melted,which may be aided by frequent stirring. When quite melted, pourin the treacle, and again stir until perfect incorporation of theingredients is effected, when the composition may be set aside to cooluntil required for use. To check evaporation and consequent dryingof the surface, the vessel, when the material is quite cold, may beinverted over a piece of clean paper, by which, also, it will be pro-tected from dust. The compound thus formed is exceedingly elastic,and may readily be separated from models even when severelyundercut. Owing to the solubility of this composition, however, somecare is necessary in using it, otherwise it will become partially dis-solved in the copper solution or bath. This is more likely to occur,however, when the solutions are of less strength than saturated, bywhich term we understand that the wat.r present holds as muchsulphate of copper in solution as it is capable of doing. Variousremedies for overcoming this disadvantage will be given whentreating of the methods of obtaining moulds from the material.
Plaster of Paris.—This substance is also Who! for mould-making,either from metallic or natural objects ; but the plaster should be of thefinest quality, such as is used by Italian image makers for the surfaceof their work, and not the coarse material usually sold in the shops.The planter should ho fresh when purchased and preserved in a closely-covered jar until required for use.
Having thus far considered the materials used in making mouldstor electrotype purposes, we will next explain the methods of applying*them, confining our observations to the more .simple examples in theinitial stages of the process.
BRONZING THE ELECTROTYPE. IO9
glass rod or strip of wood before immersing the mould, especially if ithas been previously used for eleetrotyping; if this is not done, thedeposit may become irregular in thickness. 4. The plumbagoedmould should not be disturbed until its entire surface is covered withcopper. A few moments after immersion, a bright pinkish reddeposit of cspper will be observed at the end of the wire, which in ashort time will radiate in the direction of the plumbagoed surface,and this will gradually extend wherever this conducting medium hasbeen spread with the brush, provided the operation has been con-ducted with proper care, and an uniform coating obtained.
Treatment of the Electrotype.—A sufficiently stout deport ofcopper, upon a gutta-percha mould of a small coin, may generally beobtained in about two days, or even in less time, under the mostfavourable condition* ; but it is not advisable to attempt to separatethe electrotype from the mould while the deposit i>> very thin, other-wise the former may become broken in the operation. Assuming thedeposit to be thick enough, the first thing to do is to cut the end ofthe wire connected t'> the mould wilh a pair of cutting pliers or a file,after which the superfluous copper may be removed from the outeredge by breaking it away with the pliers, taking care not to injurethe " t ype" itself. The mould may then be placed in hot water fora moment, when the electrotype will readily separate from the gutta-percha. In order to give additional solidity to the electrotype, it shouldbe hacked «p with pewter solder, which may easily be done as follows : —Put a small piece of zinc into about a teaspoonful of hydrochloric acid(muriatic acid) ; when the effervescence which takes place has ceased,brush a little of the liquid, which is a solution of chloride of zinc,over the back of the electrotype, and then apply solder by means of amoderately-hot soldering iron, until the entire surface is tumid, as itis called, when a further supply of solder should be run on to theback to give the required .solidity. When this is done, the roughedge of the electrotvpe should be rendered smooth with a keen rile.
Bronzing the Electrotype.—To impart an agreeable bronze ap-pearance to the type, it should first be cleaned by brushing it witha solution of carbonate of potash (about half a teaspoonful in an ounceof water), and applying at the same time a little whiting. Anordinary tooth-brush may be used for this purpose, and after briskrubbing the type must be well rinsed in clean water. The bronzetint may be given by brushing over it a weak solution of chloride ofplatinum (1 grain to an ounce of water) : when the desired tint isobtained, the type is to be rinsed with hot water and allowed to dry.The tone may be varied from a delicate olive-brown to deep black,according to the proportion of platinum salt employed. A few dropsof sulphide ot ammonium in water, or, still better, a few grains of
TOS ELECTRO-DEPOSITION OF COPPER.
material wliich is1 a non-conihutor of electricity, we next proceed togive it a conducting; surface, without which it would be incapable ofreceiving the metallic deposit of copper which constitutes an electro-type. For this purpose, plumbago, or graphite,* is usually employed.To plumbago the surface of the gutta - percha mould proceed asfollows :—Hold the mould between the fingers of the left hand, faceupwards ; now dip a soft camel-hair brush in finely-powdered plum-bago (which should be of good quality) and briskly brush it all overthe surface, every now and then taking up a Iresh .supply of plumbagowith the brush. Care must be taken to well brush the powder intoevery crevice of the impression, and it is better to work the brush Incircles, rather than to and fro, by which a more perfect coating i-obtained. When properly done, the face of the mould has a brightmetallic lustre, resembling a well-polished (that is blacklcadedj .stove.
In order to prevent the deposit of copper from taking place on theupper edge (beyond the actual impression), the plumbago which hasbeen accidentally brushed over this .surface should be removed, whichmay be conveniently done by rubbing it oft' with a piece of damp ragplaced over the forefinger. The mould is now to be attached to theconducting wire by gently heating its longer end in the flame of acandle or ignited match, and then placing it on the edge of the mould,as far as the circumference of the impression; by giving it gentlopressure it will become sufficiently imbedded; the wire must not,however, be below the flat surface of the mould. If held steadilyin the hand for a few moments, or until the wire and gutta-perchahave cooled, the joint will .set, and the mould may then be carefullylaid aside until the point of junction has set firm. A little plumbagomust now be brushed over the joint, so as to ensure a perfect ehctrlealconnection between the wire and the plumbagoed mould.
The mould being attached to the conducting" wire, must now beconnected to the zinc by its binding-screws as before (Fig. 54), and bothshould be immersed at the same time in their respective solutions, butthis must be done with care, otherwise the mould may become separatedfrom the wire. It may be well, in this place, to call attention to certainprecautions which, if carefully followed, will prevent failure, andconsequent disappointment, in electrotyping.
Prwantions.- I. The solution of copper to be used in the single-cellapparatus must be kept as nearly as possible in a sat a ratal condition,which is effected by keeping the shelf or tray constantly supplied withcrystals of Milphate of copper. 2. The superficial surface of zincimmersed in the porous cell should not be much greater than that ofthe mould to be copied. 3. The solution should be stirred with a
* Commonly called blacklead> but in reality carbon in a crude state.
COPYING PLASTER OF PARIS MEDALLIONS. T i l
sulphide of ammonium, and when this has dried, the plumbagoand rouge paste is to be applied as before, and the waxed brush againemployed. If the object be heated after applying the sulphide ofammonium, a black bronze, called " smoky bronze," is produced, andif the high lights be lightly rubbed with a piece of chamois leatherdipped in spirit of wine, a very pleasing effect of contrast is obtained.
Moulds of Sealing Wax.—This material is, as we have said, veryuseful for obtaining impressions of seals, signet rings, and other smallobjects. A simple way of taking an impression in healing-wax is asfollows: Hold a card over a .small bcnzoline lamp, but not touchingthe name ; now take a stick of the best red sealing-wax and allow itto touch the heated part of the paper, working* it round and rounduntil a sufficient quantity of the wax becomes melted upon the card.Now place the card upon the table, and having gently breathed uponthe seal or signet ring, impress it in the usual way. Havingsecured an impression, cut away the superfluous portions of the cardwith a pair of scissors, and moisten the wax impression with a fewdrops of spirits of wine. When this has apparently dried, proceed tobrush plumbago over the surface, using a camel-hairbrush, and whenperfectly coated, gently heat the end of the conducting-wire and applyit to the edge of the sealing-wax, allowing the point of the wire toapproach the edge of the impression. Now brush a little plumbagoon the point, and connect the short end of the wire to the binding-screw.
After having obtained several electrotypes successfully, and therebybecome <tu fiat to the manipulation of the single-cell apparatus, thestudent will naturally desire to extend operations to objects of a moreimportant nature, such as medallions, busts, statuettes, and naturalobjects, as leaves, fishes, kc. But before attempting the more elabo-rate subjects it will be well to select, for our next operation, one of asimpler character, such as a plaster of Paris medallion, an admirablemodel to reproduce in metallic copper.
Copying Plaster of Paris Medallions.—These pleasing works ofart, which may be obtained at small cost from the Italian imagemakers, are specially suited for the elementary study of tl\e electrotypeprocess, while a cabinet collection of such objects reproduced in copperforms an exceedingly interesting record of the manipulator's skill andperseverance. There are several materials from which moulds fromplaster medallions may be obtained ; but we will first describe themethod of preparing a mould with gutta-percha. To render theplaster more capable of bearing the treatment it will have to be sub-jected to, the face of the medallion should first be brushed over withboiled linseed oil, and this allowed to sink well into the plaster. Afterabout two days the oil will have sufficiently dried and hardened upon
n o ELECTRO-DEPOSITION OP COPPER.
sulphide of barium dissolved in water, will give very pleasing bronzetints to the copper surface, the depth of which may be regulated atwill by a longer or shorter exposui'e to the action of the bronzingmaterial. If a solution of sulphide of barium be used, about 5 grainsto the ounce of water will produce a pleasing tone in a few seconds.It is better to immerse the electrotype in the liquid (previouslyfiltered) and to remove it the instant the desired tone is reached, andto place it at once in clean water.
Another method of bronzing electrotypes is by the application ofplumbago, by which very pleasing effects may be obtained with alittle care in the manipulation. The surface of the electrotype is tobe first cleaned with rotten stone and oil; the oil is then to be par-tially removed by a tuft of cotton wool, and the surface is next to bebrushed lightly over with plumbago (a soft brush being used) until aperfectly uniform coating is given. It is next to be heated to a pointthat would singe the hair of the blacklead brush, and then set asideto cool, after which it must be brushed with considerable friction.The tint will depend upon the quantity of oil allowed to remain, thisenabling the surface to retain more of the blacklead, consequently toappear of a darker colour. The effect is very fine, and gives highrelief to the prominent parts, from their getting so much more polishthan the hollows, thus obviating the disagreeable effect which allunbronzed bassi-relievi produce by reason of their metallic glare.—Hoc k hi.
The beautiful red bronze tone which is seen on exhibition and othermedals is produced by brushing over the medal a paste composed ofperoxide of iron (jewellers' rouge) and plumbago, after which thearticle is moderatly heated, and when cold is well brushed until itacquires the necessary brightness and uniformity of surface. Equalparts of fine plumbago and jewellers' rouge are mixed up into anuniform paste with water, and the cleaned medal is then uniformlybrushed over with the mixture, care being taken not to allow thefingers to come in contact with the face of the object. The medal isthen placed on a stout plate of iron or copper, and this i& heated untilit acquires a dark colour ; it is then removed from the fire and allowedto become cold. It is next brushed for a long time, and in alldirections, with a moderatly stiff brush, which is frequently passed overa block of yellow beeswax, and afterwards upon the paste of plum-bago and rouge. The bronzing may also be produced by dipping thecleaned medal in a mixture composed of equal parts of perchlorideand pernitrate of iron; the medal is then to be heated until thesesalts are thoroughly diy. It is afterwards brushed as before with thewaxed brush until a perfectly uniform and bright surface is obtained.
Bronzing may also be effected by dipping the medal in a solution of
CLEARING THE MOULD. I I '
tins Wing- frequently dipped into the plumbago is to be lightly butbriskly applied, special care being' taken t'> well plumbago the hollows.When it is borne in mind that the most delicate line, even if imper-ceptible to the e\e, will be reproduced in the metallic copy, theimportance of not injuring the face of the mould will become at onceapparent. It is also absolutely necessary that the gutta-percha .shouldbe of the best quality, and since the same material may be used overand over again, its tir.st cost is of little consideration.
Clearing the Mould.— The m Mild being well coated with plum-bago, all excess of this material which has become spread over theouter edges, beyond the impression itself, must be wiped away, andthe more completely this is done the less trouble will there be after-wards in clearing away from the electrotype the crystalline depositwhich, under any circumstances, forms around the circumference of theelectrotype. Indeed, when the student has once or twice experiencedthe inconvenience of having to remo\e the superfluous copper fromhis electrotypes, he will not fail to evert his wits to diminish thelabour which this involves as far as practicable, by every possible carebefore the mould goes into the copper bath. "We therefore urge for hisu'uidance, that the removal of the excess <>f plumbago should be deemedone of the important details of his manipulation, and that it should neverbe neglected. After wiping away the excess of blacklead, it will befound a good plan to place a piece of dry rag on the forefinger and torub it on a common tallow candle, so as to make the part slightlygreasy ; if now the edge of the mould (carefully avoiding the impres-sion) be rubbed with the rag-co\ered finger, this will effectuallyprevent the deposit from taking place upon such part; before doingthis, however, the conducting wire should be gently heated and im-bedded in the edge of the mould as before, taking care that the pointof the wire touches the extreme edge of the impression, and a ptrfivtcoihucttOH between the wire and the latter must be secured by apply-ing a little plumbago with a camel-hair brush or the trp of the finger.It is- sometimes the practice to apply varnish of some kind to the edgesof moulds, and also to the conducting wire as far as the joining, butuntil the student has thoroughly mastered the process of copyingsimple objects in the way we have indicated, we do not recommendhim to employ varnishes; indeed not until dealing with objects ofa larger and more elaborate kind.
The mould being now ready, is to be connected to the binding-screwby its wire, and since the material of which it is composed is muchlighter than the copper solution, the wire must be sufficiently rigid,when bent at right angles, as in Fig. 54 to keep the mould well downin the bath. Being placed in the solution, it must be allowed toremain undisturbed until the entire surface of the impression is
112 ELECTRO-DEPOSITION OF COPPER.
the surface to render the plaster less liable to injury. The medallionthus, prepared is next to be provided with a rim or collar of pasteboardor thin sheet tin, "which must be tightly secured round its circumferenceeither by means of thin copper wire, jeweller's " binding -wire," orstrong twine. The rim should project about half an inch above thehighest point on the face of the medallion, and must be on a levelwith it> base ; it is then to be laid upon a perfectly smooth surface untilthe moulding material is ready. We recommend the student to prac-tise upon small medallions at first; say about two inches or two inchesand a half in diameter.
Preparing the Mould.--A lump of gutta-percha is now to be takenof sufficient size to cover the medallion, fill the vacant space up to thetop of the rim, and project above it. The gutta-percha is to besoftened in hot water and rolled up into the form of a ball, as beforedirected, care being taken to obliterate all bcanib or cracks by repeatedlysoaking in the hot water and rolling in the hands. It must on noaccount be applied until it is perfectly smooth, and as soft as hot waterwill make it. To give additional smoothness to the surface of the ball,it may be lightly rolled round and round, with one hand only, for aniii.stant upon a polished table just before being used. Now take theball in one hand and place it in the centre of the medallion ; then pressit firmly from the centre towards the circumference, taking care notto shift it in the least degree. The gutta-percha must be pressed wellinto the cavity, and when this is done, a piece of Hat wood may beplaced on the mass and this pressed with both hands with as muchforce as possible for a few moments, when it may be left until thegutta-percha has set hard. If convenient, a weight may be placedupon the b<>;»rd after having pressed it with the hands. In about half;in hour the board may be removed, and the mould allowed to restuntil quite cold, when the rim may be removed and the mould sepa-rated by gently pulling it away from the medallion. As a precautionagainst breaking the plaster medallion, it may be wrell to suggest thatits back should be examined, and if it be otherwise than perfectly flat,it may be advisable to gently rub it upon a sheet of glass-paper, whichwill readily remove all irregularities from the surface. It is alsoimportant that the surface upon which the medallion is laid, whenapplying the gutta-percha, should be quite level ; and it will bestill better if several folds of blotting-paper are placed between thetable and the medallion before the necessary pressure is given. Thesepoints being attended to, there is little fear of the medallion becomingbroken.
Plumbagoing.—The gutta-percha mould is now to be well plum-bagoed, for which purpose a soft brush, such as jewellers use forbrushing plate and jewellery that has been rouged, may be used, and
WAX MOULDS FROM PLASTER MEDALLIONS. I 15
the top of the rim, if any air-bubbles appear they must bo at oncoremoved with a camel-hair brush kept for this purpose, or the featherend of a quill, or even a strip of paper may be used. The waxmust now be allowed to cool a* slowly as possible, and in order tofavour this gradual cooling", a clean, dry jar may be inverted overthe mould and there left until the wax is quite cold. This precautionwill tend to prevent the wax from cracking", an event which sometimes,but not very frequently, occurs.
When quite cold, the wax mould will generally separate from theplaster by the application of moderate force to pull them asunder. Ifsuch is not the case, however, return the medallion to the plate andpour in a little boiling water. After a few second^ immersion themould will easily come away. If, however, owing to some irregu-larity in the face of the medallion, the mould still refuses to separate,plunge the whole into cold water, and, if necessary, use the edge ofa knife as a lever between the two surfaces and force them asunder.If it be found that small portions of plaster adhere to the mould thesemay be carefully picked out with a fine-pointed piece of wood, andthe mould afterwards very lightly brushed over with a soft plate brush.Should it be found that .some particles still obstinately adhere to thewax, apply a little oil of vitriol with a thin strip of wood to the partsand set the mould aside for about twelve hours, by which time the acid,by attracting moisture from the air, will loosen the plaster, which maythen be brushed away with a soft brush and water. The mould mustthen be put away to dry, or may be laid, face downward, upon a padof blotting-paper or calico.
The mould is now to be plumbagoed with a very soft brush, but,owing to the yielding nature of the wax, the greatest care must betaken not to apply the brush too severely, only sufficient friction beingused to coat the surface uniformly. It is a good plan to sprinkle alittle plumbago over the face of the mould, aud then to work thebrush about in circles, by which means a AVCII plumbagoed surfacemay readily be obtained. This operation being complete, the super-fluous plumbago is to be brushed off, and, by blowing upon the faceof the mould, any plumbago remaining in the crevices may be re-moved. The conducting* wire is to be attached, as in the case ofgutta-percha, by gently wanning the end of the wire ; but, if themould be a tolerably large one (**ay, 3 inches in diameter) it will bewell to bend the end of the wire so as to leave a length of about aninch or more to be embedded in the edge of the mould, by whichmeans it will be more effectually supported than if the point of thewire only were attached. The joint must now be well plumbagoed,and the excess of this material which has been brushed over theedges may easily be removed by scraping" it away with a pen-knife.
ELECTKO-BEPOSITION OF COPPER.
covered. In from two to throo (Lays the deposit should bo of sufficientthickness to allow of its separation from the mould.
For copying small medallions of the size referred to, the single-cellapparatus shown in Fig. 54 may he used, hut for larger sizes or for
depositing upon several moulds at thesame time, the arrangement shown inFig. 55 Avill he most suitable. Thisapparatus consists of a. wood box wellvarnished in the interior, and dividedint) two cells or conrpartments by a2»arfitiim of thin porous wood. Thelarger cell is nearly filled with a satu-rated solution of .sulphate- of copper,and the smaller cell with a half-satu-rated solution of sal-ammoniac;. Aperforated shelf is suspended in thelarger compartment to contain a supplyof crystals of the sulphate. A ])lateof pure zinc, connected by a copperconducting wire, is suspended in thesmaller cell, and the mould connectedto the c>2>posite end of the wire bysuitable binding-screws. In this ar-
rangement neither acid nor mercury are used, and although the actionis not so rapid as in the former arrangements, it is very reliable forobtaining good results.
Wax Moulds from Plaster Medallions. — Beeswax is a veryuseful material for preparing moulds from plaster medallions, thefollowing simple method being adopted:—The medallion, instead ofbeing oiled as in the previous case, is simply soaked in hot water fora short time or until it has become completely saturated. First put asufficient quantity of wax into a pipkin and melt it by a slow fire;when melted, place it on the hob until wanted. Place the medallionface upwards in a plate or large saucer, into which pour boiling wateruntil it reaches nearly half-way up its edge. In a minute or two theface of the plaster will assume a moist appearance, when the excess ofwater is to be poured out of the plate. A rim of card is now to befastened round the edge of the medallion, which maybe secured eitherby means of sealing-wax or a piece of twine. As before, the rimshould extend about half an inch above the most prominent point ofthe image. The medallion being returned to the plate, the wax isnow to be steadily poured on to the face of the object, the lij> of thepipkin being placed near the pasteboard rim and nearly touching it, toprevent the formation of air-bubbles. When the cavity is filled up to
• 55-
MOULDS FKOM FUSIBLE METAL. I I )
has assumed the pasty condition the coin, being held by its gutta-percha handle, is to be promptly and firmly pressed upon the massuntil it is sufficiently imbedded m it. In the course of a minute orso the coin may be withdrawn, when the mould should present aperfect and delicate impression of the original—of course in reverse.Should any faults be visible, owing to want of dexterity on the partof the operator, the metal must be re-melted and the operation con-ducted again. A very little practice will enable the student to pro-duce moulds in this alloy with perfect ease. The coin, in each of theabove cases, should be perfectly cold before applying it to the alloy.Large medals are moulded by simply dropping them—a little side-ways—into the metal when on the point of solidification.
Connecting the Mould to the Wire.—"When a perfect mould isobtained the conducting wire is to be attached, which is done by firstscraping the longer end of the wire so as to render it perfectlyclean ; it is then to be held in the flume of a candle, but at a littledistance from the clean end. The mould being now held in the lofthand, is to be brought near, but not touching, the flame, and, whenthe wire is sufficiently hot, it is to be pressed against the bat I of themould, when it will at once become imbedded in it, and in a fewmoments will be firmly set. A small portion of powdered resinapplied to the spot will assist the union of the two metals. The backand upper edge of the mould must now be coated with sealing-waxvarnish or some other quick-drying varnish, or, if carefully applied,paraffin wax (which melts at u very low heat) may be applied by firstqcntly heating the mould and touching it with a small stick of theparaffin wax. It is well, also, to varnish that portion of the conduct-ing wire aborv the joint which has to be immersed in the copper bath,iu order to prevent it from receiving the copper deposit.
n6 ELECTRO-DErOSITION OF COPPER.
The same precautions must be observed with regard to wax-mouldsas with those made from gutta-percha when immersing them in thebath, otherwise they will, from their exceeding lightness, be disposedto rise out of the solution. In the case of large moulds made fromsuch light materials they require to be weighted in order to keep thembeneath the surface of the copper solution, as we shall explain whentreating of them.
The stearine composition may be employed instead of wax in thepreceding operation, but we recommend the student to adopt the lattermaterial for copying small medallions, since, with a little care, it willanswer every purpose, and needs no preparation beyond melting it.
Moulds from Fusible Metal.—There are many ways of makingmoulds from fusible metal, but, for our present purpose, we will selectthe most simple. To obtain an impression of a coin or medal, melt asufficient quantity of the alloy in a small ladle or iron spoon, then, hold-ing the coin face downward between the forefinger and thumb of theright hand, pour the alloy into the rim oi an inverted cup or basin,and, bringing the coin within a distance of about 2 inches from themolten alloy, allow it to fall flat upon the metal and there leave ituntil cold. If, when the metal is poured out, there is an appearanceof dulness on the surface (arising from oxidation of the metals) apiece of card or strip of stiff paper should be drawn over it, whichwill at once leave the surface bright. As the metal soon cools, how-ever, this may be more conveniently done by an assistant just beforethe coin is allowed to fall. If no other help is at hand a piece ofcard should be placed close to the cup, so that the moment the metalis poured out it may be applied as suggested, and the coin promptlydropped upon the cleaned surface of the alloy. A very little practicewill render the student expert in obtaining moulds in this way, and,considering how very readily the material is re-melted, a few failuresneed not trouble him.
The fusible alloy may also be employed in the form of a paste, but,in this case, it is advisable to have the assistance of another pair ofhands, since, in this condition, it soon becomes solid and therefore un-usable. The coin should first have a temporary handle attached toit, which may readily be done by rolling a small lump of gutta-perchainto the form of a ball: one part of this should now be held in theflame of a candle until the part fuses, when it is to be pressed uponthe back of the coin and allowed to remain until cold. This gutta-percha knob will serve as a handle by which the coin may be heldwhen the impression is about to be taken. The requisite quantity of
fusible alloy is now to be poured upon a piece of board andrked up into a stiff paste by moans of a flat piece of wood—an
operation that only occupies a few moments. The instant the alloy
ARRANGEMENT OF THE BATTLEY.
glass or stoneware, for small operations, is charged with an acid htion of Mil 'hate of copper, which is composed us follows :—
jlu-
vulphate of CopperSulphuric AcidWater (about) .
. lb.
i gallon.
The sulphate of copper, as before, is dissolved in a sufficient quantityof hot water, after which cold water isadded to make up one gallon ; the sul-phuric acid is thon added and the so-lution is set aside until quite cold,when it is to be poured into thedepositing bath, which should be quiteclean. When first placing the mouldto be copied in the bath, a smallsurface only of the copper plate shouldbe immer»ed in the solution, and thismay be gradually increased (by lowering1 the copper plate) as thedeposit extends over the surface of the mould.
In Fig. 54 is shown an arrangement in which several moulds aresuspended by a brass rod laid aeros^ the bath B, the rod being con-nected to the zinc element of the battery, A, by the wire, .»•. Strips otsheet copper are suspended by a brass rod, c, which is connected by abinding-screw to the positive conducting wire, r, of the battery, which
Fig- 56.
\\\ the woodcut represents a Daniell cell. In this arrangement, thesheet copper, by becoming dissolved in the solution during the electro-lytic action, keeps up the normal .strength of the bath, which inthe .sinirlc-cell arrangement is attained by the supply of crystals ofsulphate of copper. It inav be well to mention that it is alwayspreferable, besides being more economical of time, to deposit upon
CHAPTER VL
ELECTRO-DEPOSITION OF COPPER {continued).
Electtotyping by Separate JJuth'ry.—Arrangement of the Battery.—CopyingPla^tei Bints.—Guiding Wires.—Moulding in Placer of Paris.—Copy-ing Animal Substance*.—Electro-coppering Flowers, Insects, &c.—Copy-ing Vegetable Substances.—Depositing Copper upon Glass, Porcelain,&c.—Coppering Cloth.
Electro typing by Separate Battery.—In employing- the single -cell apparatus, we have keen that it is necessary to keep up thestrength of the solution by a constant supply of crystals of sulphate ofcopper, otherwise the solution would soon become exhausted of itsmctiily and therefore useless. If we employ a .separate battenj, however,this method of sustaining the normal condition of the bath is unneces-sary, as we will now endeavour to show ; but in doing so we mustdirect the reader's attention for the moment to the principles ofelectrolysis, explained in a former chapter. The practical applicationof those principles may be readily expressed in a few words : If, in-stead of making the mould, or object to be copied, the )t((/nttie ilenientr,as in the single-cell apparatus, we take a separate battery composed oftwo elements—say, zinc and copper, as in Daniell's battery, we mustthen employ a .separate copper solution or electrolytic b."h, in whichcase the object to be deposited upon must be connected io the zincclement, as before, but the wire attached to the negative clement oftin* battery (the free end of which is the positue electrode) must haveattached to it a plate of sheet copper, which with the mould must beimmersed in the solution of sulphate of copper. By this arrangement,while the copper is being deposited upon the mould, the .sheet copperbecomes dissolved by the sulphuric acid set free, forming sulphate ofcopper, which continued action re-supplies the bath with metal in theproportion (all things being equal) in which it is exhausted by deposi-tion of copper upon the mould.
Arrangement of the Battery.- At Fig. 56 is shown a DaniolPibattery, A, connected, by it> negative <ondu(-ting win* (proceedingfrom the zinc), to the mould, B, with it& f«u e turned towards thecopper plate or anode, c. The depositing vessel, D, which may be oi
COPYING PLASTER BUSTS. 121
Guid'wy Wire*.—The application of additional wires, to facilitatethe deposition of copper in the cavities, or undercut surfaces, ofmoulds was first introduced by Dr. Lee-son. A sufficient number oflengths of fine brass wire are twisted firmly round the main conduct-ing1 wire, at a short distance from its junction with the mould,and these, one by one, are bent in Mich a way that their extremepoints may rest, hnhlhu upon the hollow surfaces of the mould,whereby the current is diverted, to a certain extent, from the main
Fig. 58.
wire to the cavities or hollows, which JUV less favourably situated forreceiving1 the metallic deposit than the piano Mirfa« os. The applica-tion of guiding wires, is more especially necessan when the object tobe copied is of considerable dimensions ; the principle of theirarrangement is shown in Fig. 58.
The mould, prepared as described, i& to be put in connection with
I2O ELECTRO-DEPOSITION OF COPPEB.
several moulds at a time in the bath, and this can be effected even withapparatus of small dimensions. The more extensive arrangements fordepositing upon large object.s by means of powerful battery currentswill be corsidercd in another chapter.
Copying Plaster Busts.—For this purpose, the elastic mouldingm itjrial is usjd. Suppose we desire to obtain an electrotype from asmall planter bust, the object must fii^t be well brushed over withboiled linseed oil, and then .set aside for two or three days to allow +he> nrface t(> harden. In applying the oil, care should be taken not toallow it to t )uch the lower surface surrounding the orifice at its ba.se,over which a pi M-e of stout paper must be pasted to prevent theelastic material from en coring the cavity, but before doing* this partlyJill the cavity with sand, to increase its weight. The bust is next to besuspended, upside down, by means of twine or thin copper wire,inside a jar sufficiently w ide and deep to leave at least half an inch allround and at the bottom. When thus placed in its proper position,the elastic composition (p. J°5\ having been previously melted, ispoured in, and if any air-bubbles appear, these must be removed withthe feather of a quill, when the vessel is allowed to re.st until thecomposition is quite cold.
The vessel is now to be inverted, when the .solidified ma.ss and theimbedded bust will gradually slip out. To facilitate this by prevent-ing the composition from sticking to the jar, it is a good plan toslightly oil the interior of the vessel in the first instance. Havingremoved the mould, it must now be separated from the planter bust.This is done as follow.s :— First place the mould in an erect position,base downward, then, with a thin knife, make an incision from thetop to the base of the mould, at the hmh of the bust. The mould maynow be readily opened where the inci.sion has been made, and whilebeing held oj>en, an assistant should be at hand to gently remo\e thebust, when the mould, owing to ith elasticity, will readily clo.se itselfagain. It must next be .secured in its proper position by beiim1 care-tully bound round with a bandage of tape. The mould is then to beinverted, and returned to the jar. A sufficient quantity of wax ic
now to be melted at the ?ot<ot temperature that will liquefy it, othei -wise it will injure the mould ; it is then to be poured into the mouldand allowed to rest until thoroughly cold. When cold, the elasticmould is to be again removed from the jar. and sejwr.ited by unt\ inirtlie bandages from the wax-casting. This latter must now be wellplumbagoed, a conducting wire attached, and the joint coated wiihplumbago a.s before directed. Since it will be difficult, howe\<T, 1<»obtain an uniform deposit over su< h ;i comparatm'ly large suriare, ifwill be necessary to apply yttuluty wires, as they are called, andto which we must now direct special attention.
MOULDING IN PLASTER OF PAKIS. 123
with a pair of pliers. When the first layer of metal has been liftedfrom the underlying deposit, the remainder may generally be peeledoff with but little trouble, when the electrotype proper will beexhibited, and if success! ully accomplished it will amply reward theoperator for the trouble and care devoted to its production. Thestudent should not, however, undertake the manipulation of theelastic moulding composition until he has acquired a skilful aptness inthe simpler processes of eleetrotyping. It may be well to mentionthat the elastic composition may be re-used several times, provided ithas been kept in a covered vessel, to exclude it from the action ofeither a moist or a very dry atmosphere.
Moulding in Plaster cf Paris.—This material, especially forcopying1 natural objects, Mich as leave^ ferns, fishes, &c, is exceed-ingly useful, and we will, as in former instances, first give the moresimple method of applying it, so that the student may have no diffi-culty in its manipulation. To obtain a plaster mould from a coin ormedal, for example, first oil the face of the object slightly by applyinga single drop of oil, with a tuft of cotton wool, and with a fresh pieceof wool gently rub the coin all over, so as to leave but a trace of oil onthe surface, the most trifling quantity being sufficient to prevent theadhesion of the plaster to the original. A rim of card is now to befixed round the medal, to form a receptacle for the plaster. A littlecold water is then to be poured in a cup, or other convenient vessel,and a small portion oijiiw plaster dropped into the water. The excessof water is now to be poured off and the plaster briskly stirred with aspoon. Now fill the spoon with the plaster (which should be about theconsistency of cream) and pour it carefully over the face of the medal.If any air-bubbles appear, disperse them with a feather or camel-hairbrush, which should be immediately after plunged into cold water, sothat the plaster may easily be removed, and the brush thus left readyfor future use. In about half-an-hour or so, the coin and mould maybe detached, and the latter should then be placed in a moderatelywarm oven until dry. When perfectly dry, the face of the mould isto be well painted over with boiled linseed oil, repeating the operationseveral times ; or the mould may be saturated with wax, by pouring alittle of this substance, in a melted state, over the face of the mould,and then placing it in the oven until the wax becomes absorbed by theplaster. When cold, the mould must be plumbagoed in the ordinaryway, and a copper conducting wire attached by twisting the wireround its circumference, and forming a connection with the plumba-jU'oed siu'f.icr by means of a drop of melted wax, afterwards brushedover with plumbago. That portion of the wire which surrounds themould should be coated with v;miUh to prevent the copper from beingdeposited upon it. The superfluous plumbago should, as in the
1 2 2 ELECTRO-DEPOSITION OF COPPER.
the battery, by suspending* it from the negative eondueting-rod, andthen gently lowered into the coppering bath. In the present case only amoderately stout deposit, or " shell," of copper will be necessary, since,as we shall explain, this deposit will, in the next operation, act thepart of a wotiM, in producing a fac-simile of the original. Whena perfect coating is obtained, of sufficient thickness to bear handling,it is to be removed from the bath, rinsed, and allowed to drain. Itmust then be heated sufficiently to melt the wax, which is allowed torun into any convenient receptacle, and the interior of the electrotype(which now represents a mould) must be cleansed from all adheringwax, by continuing the heat until the last drop ceases to flow. It mustthen be treated with spirit of turpeutine, with the application ofmoderate heat, to dissolve out the remaining wax, the operation being'repeated so as to entirely remove all traces of the wax.
The next operation consists in depositing copj:>er upon the interior ofthe copper mould, which may be readily done in the following way:— Asmall quantity of sweet oil is first to be poured into the mould, whichmust be moved about so that the oil may spread all over the sur-face ; it must then be tilted over a vessel to allow the oil to run out,and next placed upon several folds of blotting-paper before a fire, forseveral hours, until the oil ceases to flow. The mould must now becarefully examined, and if any " pin-holes," as they are called, arevisible, thc*e must be stopped by melted wax dropped upon each spotupon the outside of the mould.
The mould is now to be placed in a jar, in an inverted position, andheld in its place by a padding of paper or rag, wedged aroundits base. The negative electrode (or wire connected to the zinc of thebattery) is now to be connected to the mould, which may convenientlybe done by soldering. A strip of stout sheet copper, attached to thepositive electrode, is then to be suspended in the cavit}r of the coppermould, but not allowed to touch any part of it, and in this position itmust be fixed securely, which may be conveniently done by a piece ofwood laid across the orifice of the mould. The mould is now to befilled with the copper solution last mentioned, and the battery is thento be set in action. In order to obtain a good solid electrotype fromthe copper mould, it will be necessary to renew the copper plate, oranode, from time to time when it becomes worn away, unless it be ofsufficient thickness to render such renewal unnecessary. The strengthoi the battery must also be well kept up by renewing the acid solutionin the porous cell. When a deposit of sufficient thickness is obtained,the conducting wires may be di scon nee ted, the copper solution pouredout, and the interior rinsed with water.
Tho next operation is to remove the shell of copper constituting themould, which is done by breaking it awag—beginning at the base—
COPYING ANIMAL SUBSTANCES. 1 25
metallic lustre of a well-polished fire-stove. The conducting wiremust now be attached, which may be effected in this way : Bend apiece of stout copper wire in the fonn shown in Fig. 50,, and pass themould under the hook at «, and beneath the coil of the wire at b ; theshorter end of wire at a should just touch the edge of the im-pression, near the mouth or tail of the fish. The wire thus adjustedmust be secured firmly in its place, by being bound to the mould withthin copper wire. Before placing the conducting wire in its jiosition,as above described, it will be advisable to wipe away all superfluousplumbago from the face of the mould, carefully avoiding injury to theimpression, and when the conducting wire is adjusted, it is a goodplan to coat the wire at all parts but the extreme point at u withvarnish, or melted paraffin wax, to prevent the copper frombecoming deposited upon it. The end of the wire at <tmust be put in metallic contact^ so to speak, with the plum-bagoed impression, by brushing a little of that substanceover the point of junction. Thus prepared, the long end ofthe conducting wire is to be connected to the negative pole ofthe battery, and the mould gently immersed in the bath, thecopper anode previously being suspended from the positiveelectrode.
The second half mould may now be treated in same wayas the above, and when two perfect electrotypes, or shells,are obtained, the superfluous copper should be removed byaid of a pair of pliers and a file; when this is done theinner edges of each electrotype may be tinned, by firstbrushing a little chloride of zinc round the edge, and thenpassing a soldering iron, charged with pewter solder, overthe surface. When the two halves of the fish are thus ^flprepared, they may be brought together and held in posi- \Jtion by means of thin iron " binding wire." The flame of F#
I(r ^g.a spirit-lamp or a blow-pipe flame may now be applied,which, by melting the solder, will soon complete the union, when aperfect representation of a fish will be obtained. This may after-wards be bronzed, gilt, or silvered by the processes described here-after, and, if desired, mounted upon a suitable stand.
The elastic moulding material may also be used for copying animalsubstances ; in this case, one half of the fish must be imbedded inmoulding sand ; a cylinder of thin sheet tin, bound together with finecopper wire, or by soldering, is then placed round the sand, so a&to enclose it, and the sand is made as level as possible, by gentlypressing it with any convenient instrument. The melted elasticmaterial is now to be poured into the cylinder, which should be abouttv*ro inches higher than the highest part of the object, until it nearly
124 ELECTRO-DEPOSITION OF COPPER.
former cases, be removed, by scraping it away with a knife, leaving*the connection, of course, untouched. The mould is now ready forthe depositing bath, into which it must be gently lowered, so as toavoid breaking the connection between the conducting wire and theplumbagoed surface, a precaution which must in all similar cases bestrictly observed.
Copying Animal Substances.—Suppose we desire to obtain anelectrotype of a small fish (the scaly roach being very suitable), forexample. The object i.s first brushed over lightly with a little linseed oil;we next mix a sufficient quantity of plaster of Paris into a thinnishpaste, and pour this in a shallow rim of metal or stout cardboard placedupon a piece of glass or sheet of paper, previously rubbed over with alittle oil or grease ; before the plaster has time to set, the fish is to beheld by its head and tail, and laid on its side upon the paste, usingsufficient pressure to imbed one half of the fish. To assist this, thesoft plaster may be worked up or guided to its proper places bymeans of a knife-blade, care being taken to avoid spreading the plasterbeyond that part which is to form the jirst half of the mould. Theplaster is now allowed to set hard, which occupies about half an hour.We next proceed to mould the second half of the fish. A small brush,say a painter's sash tool, is dipped in warm water, and then wellrubbed over a lump of soap ; this is to be brushed all over the plaster,but avoiding the fish, and the soap and water applied several times toensure a perfect coating. A rim of greater dejith, say j of an inchdeeper, must be fixed round the mould, in place of the formerrim, and a second quantity of plaster made into a thinnish paste, asbefore, which must then be carefully poured over the fish and uppersurface of the mould, taking care not to let it flow over the rim. Thissecond batch of plaster should be sufficient to form a thick half mould,as in the former case, otherwise it may break when being separatedfrom the first half mould.
When the plaster has set quite hard, the two moulds may be sepa -rated by gently forcing them asunder, the soap and water havingthe effect of preventing the two pjaster surfaces from adhering, whilethe oil applied to the fish also prevents the moulding material fromsticking to it. When the two halves of the mould are separated, thefish is to be carefully removed, and the plaster moulds placed in awarm, but not very hot, oren, and allowed to become perfectly dry.They are then to be placed faced downwards in a plate or other shallowvessel, containing melted bees-wax, and allowed to remain untilsaturated with the material, especially on the faces of the moulds;these are now allowed to become quite oold, when they are ready toreceive a coating of plumbago, which must be well brushed into everypart oi the impression, until the entire surfaces present the bright
ELECTRO-COPPERING FLOWERS. ETC. 127
bisulphide of carbon. This highly volatile and inflammable substancedissolves phosphorus very freely; the solution, known as "Greekfive," is a most dangerous compound to handle, and if any of itdrop upon the skin it may produce sores of a serious nature ; more-over, if it be incautiously allowed to drop upon the clothing-, or uponthe floor, it may afterwards ignite and do much mischief. In employ-ing the solution of phosphorus, therefore, the greatest possible caremust be observed. The object, being attached to a wire, is dipped intothe solution, and after being allowed to rest for a few seconds, is nextimmersed in a weak solution of nitrate of silver, and afterwards allowedto dry in the light. If the object, after being dipped in the phosphorussolution, be allowed to remain in the air for more than a few secondsbefore being placed in the nitrate solution, it is very liable to becomeignited. The solution of phosphorus is prepared by dissolving a smallportion of the substance in bisulphide of carbon, about nno part ofphosphorus by weight being sufficient for the purpo*u in 20 ofbisulphide of carbon.
3. A safer method of producing a conducting surface on these objectsis to employ an alcoholic solution of nitrate of silver, made by addingan excess of powdered nitrate of silver to alcohol, and heating themixture over a hot-water bath. The object is to be dipped in thewarm solution for an instant, and then exposed to the air for a shoi ttime until the spirit has evaporated. If now submitted to the fumesof phosphorus, as before described, the film of nitrate of silver soonbecomes reduced to the metallic state, when the object is ready for thecoppering bath.
To render non-metallic substances conductive, Mr. AlexanderParkes introduced the subjoined ingenious processes.
1. A mixture is made from the following ingredients :—
Wax or tallow 1 ounceIndia-rubber 1 drachmAsphalte 1 ounceSpirit of turpentine ih fl ounce
The india-rubber and asphalte are to be dissolved in the turpentine,the wax is then to be melted, and the former added to it and in-corporated by stirring. To this is added one ounce of a solution ofphosphorus in bisulphide of carbon, in the proportion of one part ofthe former to fifteen parts of the latter. The articles, being attached toa wire, are dipped in this mixture ; they are next dipped in a weak solu-tion of nitrate of silver, and when the black appearance of the silver isfully developed, the article is washed in water ; it is afterwards dippedin a weak solution of chloride of gold, and again washed. Being nowcoated with a film of gold, it is ready for immersion in the copper bath.
126 ELECTRO-DErOSITION OF COPPER.
veaches the top', it is then allowed to rest for at least twelve hours,when the metal vim is to l>e removed and the mould withdrawn ; theobje t is next to he liberated from the mould, and the other halfmoulded in the same way. The wax and .stearine composition isto be poured into each half mould, and from the models thus ob-tained plaster moulds may be procured in the same way as from thenatural object, but in this case the wax models must be well brushedover with plumbago before being* embedded in the plaster. Sinceelectrotypes of fishes look exceedingly well as wall ornaments, it willbe only necessary, for this purpose, to obtain an electrotype of onehalf of the fish, which may, after trimming- and bronzing-, be cementedto an oval board, stained black and polished, and, if desired, mountedin a .suitable frame.
Electro-Coppering Flowers, Insects, &c.—Fragile objects, towhiVh the ordinary methods of plumba going could not be applied,
may be prepared to receive a deposit of copper in the sul-phate bath by either of the following methods :—
i. The object, say a rose-bud or a beetle, for instance,is first attached to a copper wire ; it is next dij>ped in aweak solution of nitrate of silver (about fo2*ty grains of thenitrate dissolved in one ounce of distilled water), and afterbeing allowed to drain, but before it is dry, it is to be ex-posed to the vapour of phosphorus under a bell-glass. Toproduce the vapour a small piece of phosphorus is dissolvedin a little alcohol; this is poured into a watch-glass (chemi-cal *' watch-glasses " are readily procurable), which is thenplaced in a plate containing hot sand. The object being
(3 fixed by its wire in such a position that it cannot shift, the
Fig. 60. bell-glass (an ordinary fern-glass will answer admirably)is to be placed over the whole, and allowed to remain undis-
turbed for about half an hour. The sand should not be hot enoughto endanger the bell-glass. By this process, the silver of the nitrateis reduced to its metallic state, causing the object to become aconductor of electricity ; it is then ready for the copj)ering bath,in which it must be immersed with great care. Since very lightobjects will not sink in the solution bath, it is a good plan to form aloop in the conducting wire, as shown in Fig. 60, to which a piece ofstrong silk thread or twine, having a small leaden weight connected tothe opposite end, may be fastened, as in the sketch. By this simplecontrivance light objects and Jfoating moulds, as those made of gutta-percha, wax, &c, may be easily sunk into the bath, and retainedtherein until sufficiently coated.
2. The most effective application of phosphorus for the above pur-pose consists in dipping the object in a solution of phosphorus in
DEPOSITING COPPF1I UFON GLASS, ETC. I29
from the glass. Porcelain capsules, or evaporating dishes, may receivea coating of copper at the outside, by varnishing this surface, extend-ing the coating to the upper rim of the vessel, then applying theplumbago and depositing a coating of copper of sufficient thickness.Another and more effectual way of obtaining an adhesive depositupon glass or porcelain is to send the article to a glass or porcelaingilder, and have gold burnt into its surface, and then depositing uponthe gold coating in the usual manner. MM. Noualhier and Prevostpatented a process for producing a conducting surface upon glass orvitreous substances, which consists in first coating the object with var-nish or gold size, and then covering it with leaf copper. Bv anothermethod they triturated bronze powder with mercury and common salt,and then dissolved out the salt with hot water, leaving the bronzepowder to settle. When dry, this powder is to be applied to thevarnished object in the same way as plumbago. For this purpose,however, Bessemer bronzes, which are exquisitely impalpable, andproduce a very good conducting surface, may be employed with orwithout being mixed with plumbago.
Coppering Cloth.—In 1843, Mr. J. Schottlaendcr obtained a patentfor depositing either plain or figured copper upon felted fabrics. Thecloth is passed under either a plain or engraved copper roller, immersedhorizontally in a sulphate of copper bath, containing but little freeacid. The deposit takes place upon the roller as it slowly revolves*,the meshes of the cloth are thus filled with metal, and the design ofthe roller copied upon it. The coppered cloth is slowly rolled off andpasses through a second vessel filled with clean water. The rolleris previously prepared for a non-adhesive deposit.
f2O ELEOTRO-DE POSITION OF COPPER.
2. In this process, the solution of phosphorus is introduced into thomaterials US'HI for making the mould, thus : —
Wax and deer'** fat, of each
Melt too-other and thon add :—
Phosphorus . . . .Dissolved in bisulphide of carbon
| pound
10 grains150 „
The wax mixture must be allowed to become nearly cool, when thephosphorus solution is to be added very carefully, through a tubedipping1 under the surface of the mixture : the whole are then to bewell incorporated by stirring1. Moulds prepared from this compositionare rendered conductive by being first dipj^ed in a solution of nitrateof silver, then rinsed, and afterwards dipped in a weak solution ofchloride of gold, and again washed, when they are ready for thecoppering solution.
Copying: Vegetable Substances.—The leaves of plants, seaweeds,ferns, Sec, may be reproduced in electrotype, and form very pleasingobjects of ornament when successfully produced. If we wish tocopy a vine-leaf, for example, the leaf should be laid face down-wards upon a level surface, and its back then covered with severallayers of thin plaster of Paris until a tolerably stout coating is given ,the leaf is then to be inverted and embedded in a paste of plaster,care being taken not to allow the material to spread over the face ofthe leaf. When the plaster has become hard, finely powdered plum-bago is to be dusted over the entire surface from a muslin bag. Arim of pasteboard, slightly greased on one side, is now to be fixedround the outer edge of the plaster, and secured by a piece of twine.To render this more easy, the plaster may be pared away with a knife,so as to leave a broad flat edge for the card rim to rest against.Melted wax is now to be poured into the pasteboard cylinder thusformed, in sufficient quantity to make a tolerably stout mould. Whenthoroughly cold, the rim is to be removed and the mould liberatedcarefully. It is then to be plumbagoed, connected to the negativeelectrode of the battery, and immersed in the copper bath. Theelastic material may also be employed in making moulds from vege-table objects.
Depositing Copper upon Glass, Porcelain, &c.—The articleshould first be brushed over with a tough varnish, such as copal, orwith a solution of gutta-percha in benzol; when dry it is to bewell plumbagoed. In some cases it may be necessary to render thesurface of the glass rough, which is effected by submitting it to thefumes of hydrofluoric acid; this is only necessary, however, when thevessel is of such a form that the deposited copper might slip away
ELECTROTYPING PRINTERS SET-UP TYPE. 131
surface rather than to sink into the substance of the pnper—a factwhich was established by the author's father, the late Mr. CharlesWatt (the inventor of the wood-paper process-), when it was nr^texhibited in London in the year 1853,* in the presence of the presentKarl of Derby and many scientific men and representatives of thepn .s.
Wiih a full belief that the American system of clectrotyping, asapplied to letterprc&s printinir, will eventually bo adopted in thiscountry—at first by the more enterprising members of the printing"community—we propose to explain as concisely as the subject willadmit the method which has been practically adopted in the UnitedStates, and we have to thank the distinguished firm of R. Hoe andCo., of New York, the well-known manufacturers of printing andelectrotyping machinery, for much of the information we desire toconvey, as also for their courtesy in furnishing us, at our request,with electrotypes of their machinery for the purposes of illustration.We are also indebted to Mr. Wahl f for additional information onthis subject.
" A s applied to letterpress printing, electro typing is strictly onAmerican ar t ." This is the claim put forward by the firm referredto, and we freely acknowledge the fact. We gave our cousins the artof elcctrotyping, and in exchange they show us how we may apply itto one of the most useful of all purposes—the production of goodprinting from a more durable metal than cither ordinary type orstereotype metal.
Electrotyping Printers' Set-up Type—In pursuing the art ofclectrotypinif, as applied to letterpress punting*, the coittjwbitor, electro-tt/pery and moiurtw must work with one common object, each having aknowledge of what the other requires to perform his part of the workproperly. In carrying* out the operation on an extensive scale, thedepositing room should be on the ground floor, o\\ ing to the weightof the vats, and the flooring should be cemented and well drained.The apartment should be well lighted, and provided with an amplesupply of water. The depositing vats may be of wood, lined withpitch ; and where a magneto or dynamo-electric machine is employed,this should be fixed at such a distance from the vats as not to be inthe way, but at the same time to be as near to them as possible with-out inconvenience.
* Manufacturers in this country refused to adopt this process. It was,however, u taken up " in America in the same year, where it has been workedever since. It is now used in this country to some extent, as also in manyother parts of the world.
t " Galvanoplastic Manipulations." By W. H. Wahl.
CHAPTER Vll.
ELECTRO-DEPOSITION OF COPPER (continued).
Eiectrotyping Printers' Set-up Type.—Plumbagoing the Forme.—Prepay-tion of the Mould.—Filling the Case.—Taking the Impression.—TheCloth.—Removing the Forme.—Building.—Plumbagoing the Mould.—Knight's Plumbagoing Process.—Wiring.—Hoe's Electric ConnectionGripper.—Metallising the Moulds.—Adams' Process of MetallisingMoulds.—Quicking.—The Depositing Bath.—Bntferies.—Treatment ofthe Electrotype.—Fini&hing.—Electro'\piM_; Wood Engravings, &c.—Tin Powder for Electroh ping.
OF all the purposes to which the art of eiectrotyping is applied,none is of greater importance than its application to letterpress print-ing and the copying of wood engravings to be printed from instead offrom the wooden blocks themselves. Although this latter branch of theart is very extensively adoj>ted in this country, in the reproduction oflarge and small engraved blocks for illustrated works and periodicals,newspaper titles, &c., the application of electro typing as a substitutefor stereotyping in letterpress printing has not, as yet, attained thedignity of an art in England. In America, however, the art of re-producing set-up type in electrotype copper has not only acquired ahigh state of development as a thoroughly practical branch of electro-deposition, but it has almost entirely superseded the process of stereo-typing. There are several reasons why this art has- been more fullydeveloped in the States than here In the fir-bt place our transatlantickindred are more prompt in recognising nnd .adopting real improve-ments ; they are less mindful of cost for machinery when the object tobe attained is an important one ; they are not so much under thoinfluence of so-ealleJ *' practical m c n " as ^° igT^ore scientific help;finally, they do not wait until all their competitors have adopted aprocess before they run the risk of trying it for themselves.
During the past few years we have been much impressed by theextreme beauty of the American printing, and the exquisite brilliancyof their engravings. Being printed from copper surfaces, the inkdelivers more freely than from stereotype metal, while, we believe, asmaller amount of ink is required. Again, the American1:! extensivelyemploy wood pulp in tho manufacture of their paper, and this materialbeing less absorbant than cotton-pulp, causes the ink to remain on the
ELECTROTYPING PRINTERS SET-UP TYPE. 133
great pressure, and the movement of the wax caused by the enteringof the type in taking the impression, or mould, is very likely to dis-place any portions of the forme that may he loose. A proof shouldalways be taken after the forme is locked up for the foundry,and both should be examined to make sure that no part has shifted indriving the quoins. Sometimes the matter is set with high spaces butlow leads, or vice versa, or low spaces but no leads; frequently copper-faced and white-faced type are used in the same forme. None ofthese combinations should be allowed, but the whole forme should beeither high spaces and high leads or low spaces and low leads. Inoffices having no high quads, &c, low material must be used; butgreater care is necessary in preparing the forme, more labour requiredof the electrotyper, and the plate is much less satisfactory than whenhigh material is used. "Woodcuts which are locked up with the typemust be perfectly cleaned with naphtha or benzine, and driedthoroughly before the forme is blackleaded, and great care must betaken not to clog the fine lines of the engraving.
Moulds should not be taken from electrotype cuts, since much betterones can be obtained direct from the woodcut.
Correcting the Matter.—"When necessary to make alterations inelectrotype plates, the matter for corrections should be setup and elec-trotyped, but the compositor should separate each correction by a spaceabout a pica, in order that there may be room to saw between them.If the alteration is but a single letter or short word, it is usual tosolder the type to the plate. By setting up corrections in their regularorder, the labour and cost of plate alterations may frequently be muchreduced.
The above technical hints will aid the electrotyper into whose handsa printers' forme may be placed for reproduction in electrotypecopper.
Plumbagoing the Forme.—The forme of type must fir t becleansed from printing-ink, if very dirty, either with potash ley orbenzine ; or, if not very dirty, with water distributed from a rubberpipe with rose sprinkler, after which it must be dried. The forme isnext to be well brushed over with plumbago, to prevent the wax fromsticking. This is applied with a soft hand-brush, the plumbagobeing made to penetrate every crevice. In doing this, great caremust be taken not to fill up the fine lines of the forme with theplumbago.
Preparation of the Mould.—For this purpose a moulding case(Fig. 61) is employed, which is a flat brass pan about three-sixteenthsof an inch in depth, with two flanges, which fit into the clamps of themoulding press. This is fitted with an *' electric connection gripper."The moulding composition consists of the best pure yellow beeswax, to
ELECTRO-DEPOSITION OF COPF&K*
Preparing the Formes.—When the formes, or pages of set-uptype, have to be electrotyped, it is necessary that great care should beexercised in selecting the types, rules, &c, in justifying the same, andin locking-up the forme. When the art of electrotyping comes to be arecognised substitute for stereotyping, it is probable that some modi-fications in the structure of printers' type may be made to suit morefully the requirements of the electrotyper than the ordinary type.The following suggestions are given relative to the composition of thetype for reproduction in electrotype, and these should be well under-stood by those who may hereafter be called upon to produce electro-types from printers' formes.
Composition.—Every quadrat, space, lead-slug, reglet, or piece of fur-niture should be high. Some leads have one or both edges bevelled ; buteven though the bevel is small it is sufficient to cause considerabletrouble, and such leads should not be used in moulding, as the wax issure to be forced into the space of the bevel, to be broken oft', and torequire extra labour in distributing the type, besides making it neces-sary to scrape the wax from the leads before they can be used again.So far as possible, use thick rules and those having a bevel on eachside of the face. Thin rules make so small an opening in the waxthat there is great difficulty in blackleading the mould, and in thebath the copper may bridge across a small opening, leaving the faceand sides of the rule uncovered, or at most with but a thin, imperfectdeposit that is useless. For this reason, tj'pe having considerablebevel, is best for electrotyping. English type has more bevel thanAmerican. Bevelled rules also make impressions in which the hairsof the blackleading brush can penetrate more deeply. Type-highbearers, or guards, about \ of an inch thick, should be put aroundeach page, and scattered through blank spaces, to prevent the waxfrom spreading while the forme is pressed in it, and also to facilitatethe operation of " backing." If there are several pages in a forme,sejmrate them by two guards ; one guard does not give sufficient roomto saw between the pages and leave enough of the bearer to protectthe edges of the plate in " shaving." When the matter occupies buta portion of a page, or the lines are shorter than the full width of thepage, as in poetry, an em dash or a letter should be placed bottom upin each corner of the page, as a guide to the finisher in trimming thethe plate. When the folio is at one corner, that will answer for oneof the guides. All large blanks, chapter heads, and lines unprotectedby other matter, should have type-high bearers so placed as to guardthe exposed parts from injury.
Locking-up.—The formes must be locked much tighter than forprinting, for, in order that the mould shall be perfect, the wax mustenter and fill solidly all the interstices of the forme. This requires
ELECTROTYPING PEINTEPS SET-UP TYPE. '35means of a hydraulic press, or by the " toggle " press, one form ofwhich, as manufactaied by Hoe & Co., ib shown in Pig-. 63. Thisform of prebb consibts. of a nuibsh e frame, having a planed bed, overwhich is a fixed head. Theie ib a projecting table, on which theioimo and cabe may be arranged before sliding them to receive thepicssuie, which is put upon tl»un by laisiug the bed by means of thehand wheel and sue\\ , and the two toggles In this way enormousprebsure ib obtained with but little manual exertion.
Fig. 63 —Toggle Pre^s foi Electron pe Mould.
The Cloth.—Where low spaces are used, it is customary to make apreliminary invpi ewon with a thin si cct of gum cloth interposed ;this is then umo\ cd and the picssuie put on ugam Where the clothib not used, it is nccossaij to sha\c oft, with a wride, thin knife, theprojecting \ \ a \ ridsres.
Kemcving the Forme.—In case the foime should stick to the wax,it may be relie\ed by touching the chase gently in two or three placeswith a long screw drhcr, taking care not to break the face of the wax.The case ib now to Lu placed upon a table, ready for ihe process ofbuilding.
'34 ELECTRO-DEPOSITION OF COPPER.
which is added from five to twenty per cent, of virgin turpentine, toprevent it from cracking. If the temperature ot the apartment is
from 900 to 950 Fahr., the wax may notrequire any addition. The compositionshould be melted by steam heat.*
Filling the Case.—The moulding casehaving been slightly wanned, on the siefftu-luatuiy table, a, Fig. 6?, is placed on the(di>c-filling table, b, truly levelled, and themelted wax, contained in the small jacketedpan, is poured into it with a clean ironor copper ladle, great care being taken torun the wax entirely o\ er the case whileit is hot, so that it may not, by cooling tooquickly in any part, cause irregularities.
F,g. 61.-Moulding Case. T h e a i r . b u b b l e s w h i c h r i s e t o t h e surface
must be touched with the heated building-von, Fig. 64, when they willdisappear. If, on cooling, the wax shrinks away from the edgesof the case, it can be re-melted there by running the point of theheated building-iron over it, so as to close up any fissure. Whencool, the wax should present a smooth, even surface; if this be not
Fig. 62.—Case-filling and Steam-heating Tables.
the ease it is useless «md must bo put back into the pot and re-molted. The whole surface is now to be caiefully and thoroughlyrubbi d <>\ or "with plimib«i«ro, smd polished with soft h.md-biush , whenthis is effected, the wax is ready to receive the impulsion.
Taking the Impression, or Moulding:.—For this purpose con-siderable and steady pressure is necessary, and thib is given either by
Gutta-percha is seldom used in America for making moulds.
KNIGHT S PLUMBAGOING PKOCESS. 137
excess of plumbago be removed, otherwise a coarse and faultyelectrotype will be obtained.
Owing to the unavoidable dust created bv the dry plumbagoingmachine, by the impalpable graphite powder, some electrotypistsprefer to adopt the a 11 process in\ ented by Mr. Silas> P. Knight, of
• \ \ * \ \
Fig. 65.—Plumbagoing Machine.
the electrotyping department of Messrs. Harper Brothers, NewYork. This process is baid to work more speedily and delicately thanthe former, the moulds being thinly and uniformly coated, neitheromitting the dot of an ?, nor allowing the bridging over of fine lines.
Knight's Plumbagoing Process.—By thib method, the mouldsarc placed upon a shelf, in a suitable receptacle, and a rotary pumpforces an emulsion of plumbago and water over their faces, through atravelling fine-rose nozzle. This process is said to be " rapid, effi-cient, ne.it, and economical."
Wiring. -When the plumbagoing is complete, the workman takesone or more lengths of stout copper wire, the endb of "which aie fir.stcleaned, and then gently heated ; the wires are then embedded in thewax composition on the side of the mould, and the joints are thenplumbagoed with the finger so as to ensure a perfect ihett ual ion)iei txonbetween the wire and the plumbagoed surface. In order to preventthe copper deposit from taking place upon «*uch surfaces beyond the
I36 ELECTRO-DEPOSITION OF COPPER.
Building.—The mould is> now taken in hand by a workman who,with the wide, thin bladed knife, bhaves off the projecting wax ridgesforced up about the edges and low parts of the mould by the press,and which, if not removed, would impede the separation of the " shell''from the face of the mould, when removed from the depositing tank.The operation of " building " is thus performed : the workman takesan implement such as is shown in Fig. 64 (called a " building-iron ") ,
several of which are laid on a rack in a small ovenheated by gas, and applies to it from time to time athin strip of wax, allowing the melted wax to run fromthe point of the tool on to the open spaces or Mauls ofthe mould. The operation requires a skilful and steadyhand of a practised workman. Upon thib point Wahlsays, " I t is essential, in order to avoid the chiseling(routing or deepening of the open spaces) that wouldotherwise be necessary to perform upon the finishedelectrotype, for, unless these open spaces are consider-ably lower than the spaces between the fine lines ofthe subject, they are apt to smut in the printing pro-cess. To cut these out with the chisel, or routing ma-chine, from the finished electrotype would be a difficultand dangerous operation, difficult because of the com-parative hardness of the copper surface, and dangerousbecause the breaking of the continuity of the coppersurface will be liable to curl up on the edge of the cut,and to gradually destroy itb attachment to the stereo-
type metal with which it is backed up." To avoid the necessity ofchiseling, with the risks which it entails, a ridge of wax is built upon those parts of the mould which require to be depressed in thefinished electrotype, but great care is necessary to prevent the waxfrom running where it is not wanted. The wax used for the abovepurpose is cut into strips of six or eight inches in length, and abouthalf an inch in thickness.
Plumbagoing the Mould.—The wax mould being1 prepared asabove, is next coated with plumbago, the material used in Americabeing obtained from Ceylon graphite. The plurnbagoing is generallyjierformed by a machine, the most approved, form of which is repre-sented in Fig. 65, its cover being removed to show its construction.The machine has a travelling carnage, holding one or more forms,which passes to and fro under a laterally-vibrating brush. An apronis placed below to receive the loose plumbago, which is used over andover again. As soon as the mould is sufficiently plumbagoed, it isremoved from the press, and the surplus material is either dislodged bya hand-brush or with broad-nobed bellows. It is esbential that all
Fig. 64.
ADAMS PROCESS OP METALLISING MOULDS. 139
any portion of the surface, after such treatment, remain uncoppcred,the operation is repeated. The excess of copper is washed oft', andthe mould is then ready for the bath." The washing of the mould iseffected by means of a stream of water applied from a rubber hose andpipe, and the mould must be placed in the bath directly after thewashing is complete.
Adams' Process of Metallising Moulds.—This process, whichwas patented in America in 1870, is said to give a perfect conductingsurface to wax moulds with greater certainty and rapidity than anyother, and will accomplish in a few minutes that which plumbagoalone would require from two to four hours. The process is con-ducted as follows : While the mould is still warm in the mouldingcase, apply freely powdered tin (tin bronze powder, or white bronzepowder) with a soft brush until the surface presents a bright, metallicappearance; then brush off the superfluous powder. The forme oftype or wood-cut is then plumbagoed, and an impression or mouldtaken in the wax as before described, the mould being built up andconnected as before. The tin powder is now to be brushed over iteither by hand or machine, and the superfluous tin blown away by thebellows, after which the building-iron is applied for stopping all partbupon which copper is not to be deposited. The mould is then to beimmersed in alcohol, then washed with water "to remove the airfrom the surface," when it is ready to be immersed in a solution pre-pared as follows : Fill a depositing tank nearly full of water, keepingaccount of the number of gallons poured in ; hang a bag of crystalsof sulphate of copper until the water is saturated ; for every gallon ofwater used add from half a pint to three gills of sulphuric acid, andmix the whole thoroughly. In this solution hang a sheet of copper,connected to the positive pole of the battery, and when the solutionbecomes cool and settled, immerse the mould and connect it with thenegative electrode, when the surface of the mould will be quicklycovered with thin copper. Then remove for completion to another andlarger depositing vat, containing a solution made in the proportion ofone pound of sulphate of copper and one gill of sulphuric acid to eachgallon of water. If crystals of sulphate of copper form on the copperplate in the first depositing vat, disconnect it and dissolve them ntf,substituting for it a clean plate.
Since, in the above process, the tin powder becomes dissolved niulenters into the solution, when this liquid becomes saturated with tm,after being long in use, it must be cast aside and replaced by freshsolution. The tin powder may be employed, as a substitute forplumbago, without changing from one bath to another, thus : Afterthe mould has received the desired impression, it is taken to the plum-bago table, and held face downward with one end reRtiug on the
138 ELECTRO DEPOSITION OF COPPER.
face of the mould as may have become coated with the graphite, thoworkman takes his hot building-iron, and passes it over these outlyingparts of the mould so as to destroy the conductibility of the superfluousplumbago ; this is termed stopping.
When moulds of large size have to be treated, it is necessary toplace a series of copper wires on the edges of the mould, by whichmeans the deposit commences uniformly at the several points ofjunction ; these wires are then brought in contact with the slingingwires by which the mould is suspended, and thus receive the currentfrom the conducting rod connected to the dynamo-electric machine orbatteries.
Hoe's Electric Connection Gripper.—A very practical arrange-ment for conducting the current to several points, or parts of themould, is effected by the " electric connection gripper " of Messrs. R.Hoe and Co., which is represented in Fig. 61, as connected to themoulding case. " This arrangement is designed to hold and sustainthe moulding cat e, and at the same time to make an electric connectionwith the prepared conducting face of the mould itself, consequentlyleaving the metal casj itself entirely out of the current (circuit), sothat no copper can be deposited on it."
Metallising the Moulds.—Plumbago being but a moderately goodconductor, many attempts have been made both to improve its con-ductibility, and to prcn ide a substitute for it altogether. With theformer object, we have mixed moderate proportions of Bessemerbronze powder with advantage, as also copper reduced from thesulphate by metallic zinc, and afterwards triturated with honey, animpalpable powder, or h onze, being obtained by washing away thehoney with boiling water, and afterwards collecting \hejine.st particlesof the reduced metal by the process of elutriation; that is, afterallowing the agitated mixture of water and metallic powder to reposefor a few seconds, the liquid, holding the finest particles in suspension,is poured off and allowed to settle, when an exceedingly fine depositof metallic copper is obtained. The process of coppering the mould,devised by Mr. Silas Knight, is generally adopted in America. By thismethod, a thin film of copper is deposited on the mould in a few seconds,the ojioration being conducted as follows : " After stopping out thoseportions of the mould that uiv not to receive the deposit, it is laid in ashallow trough, and a stream of Mater turned upon it from a rose jet,to remove any particles of blacklead that may remain in the lines orletters. The workman then ladles out of a conveniently placed vesselsome sulphate of copper solution, pours it upon the face of the mould,then dusts upon it from a pepper box some impalpably fine ironfilings, and brushes the mixture over the TV hole surface, which thusbecomes coated with a thin, bright, adherent coat of copper. Should
TREATMENT OF THE ELECTROTYPE. 1 4 1
with a Smee battery of ordinary construction. Wahl says that aSmee battery of twenty-six pairs, each 12 by 12 inches, will depositfrom six to six-and-half square feet of copper upon prepared mouldsin four hours. Batteries, however, are not now much used in theStates, having been greatly superseded by the dynamo-electricmachine, whereby the electro typing and electro-depositing arts ingeneral have become enormously increased.
Treatment of the Electrotype.—When the mould has received therequisite deposit, it is to be removed from the bath, and is next to beseparated from the wax composition. This is done by placing themould in an inclined position, and passing a stream of hot water overthe copper surface, which, by softening the wax, enables the coppershell to be stripped off, by raising it from one corner while the hotwater is passing over the mould. The shell should be removed withcare and must not be allowed to bend in the least degree. The thinfilm of wax which adheres to the face of the electro is removed byplacing it upon a wire rack, resting on a vessel containing a solutionof caustic potash, which is poured over the electro by means of a ladle,the liquor returning to the vessel beneath. The potash has the effectof dissolving the wax in a short time, after which the electro is wellrinsed in cold water.
Tinning and Backing the Electrotype.—The first of these opera-tions, tinning, is necessary in order to ensure a perfect union between the"backing-up metal" (stereotype metal)and the electrotype. The back of theelectro is first brushed over with a solutionof chloride of zinc, made by dissolving zincin muriatic acid, and diluting it withabout one-third of water, to which, some-times, a little sal ammoniac is added. Theelectrotype is now laid, face downwards,upon an iron soldering plate, floated on abath of melted stereotype metal, and whensufficiently hot, melted solder, composed ofequal parts lead and tin, is poured over theback, by which it acquires a clean brightcoating of solder. Another method is thefollowing : The shell being placed facedownward, in the backing-pan, is brushedover with the " tinning liquid " as before, and alloyed tin foil is spreadover it, and the pan again floated on the hot backing-up metal until thefoil melts and covers the whole back of the electrotype. When the foilis melted, the backing-pan is swung on to a levelling stand, and themelted backing metal is carefully poured on the back of the shell from
140 ELECTRO-DEPOSITTON OF COPPER.
table, while the other is supported by the hand. It is then struck onthe back several times to loosen the blacklead that is pressed on thewax while moulding, and all the fine dust that may cling to themould must be blown away. After building up and making all con-nections, it is to be placed in the hand-case or plumbagoing machine,and the tin powder applied in the same way as plumbago. Both themachine and hand-case should be kept free from plumbago, thetin powder only being used to metallise the surface of the mould. Ifthe machine bo used, place the mould, or moulds, on the carriage,cover well over with tin powder, close the door, and run once forwardand backward under the vibrating brush ; then turn the moulds round,put on more tin powder, and run through again. It takes threeminutes for the whole operation. The tin powder is to be beaten outon the table used for this powder as before, and then thoroughly wellblown out. Instead of using the building-iron for stopping off, anysuitable varnish, or an alcoholic solution of sealing-wax, may be used.
Quicking.—To prevent the copper deposit from being broken overlines of set-up type, the lines may be wetted with a dilute solution ofnitrate of mercury, or with the cyanide quicking solution used in pre-paring work for plating. A further deposit is then given in the sul-phate of copper bath.
The Depositing Bath.—The solution employed is a saturated solu-tion of sulphate of copper, acidulated with sulphuric acid, and largecopper anodes are suspended in the bath, between which the casescontaining the prepared moulds are suspended, back to back, so that thefaces of the moulds may be directly opposite the anodes. The timeoccupied in obtaining the electro deposit of copper depends upon thepower of the current employed and the thickness of metal desired.For ordinary book or job work, the shell of copper should be about thethickness of good book paper, and this should be obtained in fromthree to five hours. Electros for newspaper, titles, and such blocks asare subjected to much use, should receive a stouter deposit.
Batteries.—Several modifications of the Smee battery have been ex-tensively adopted in the United States, including copper plates,electro-silvered, and platinised ; but the most generally accepted im-provement consists in employing platinised platinum plates for thenegative element instead of platinised silver of the Smco battery. Thebuttery plates, instead of nearly touching the bottom of the cell, as inthe ordinary Smee battery, whereby, after being in use some time,they become immersed in a saturated solution of sulphate of zinc,causing great diminution of the current, only extend to about one-third of the depth of the battery coll. By this arrangement, whichwas devised by Mr. Adams, of America, in 1841, an equal action of thebattery is kept up for a much longer period than would be possible
FINISHING THE ELECTBOTYPE.
it of uniform thickness in all parts. This is offer ted in small estab-lishments by the hand shaving machine, Fig. 68, but since this opera-is the most laborious part of the finishing process, it is far preferableto employ a power machine for this purpose. The plate boinsr nowbrought to nearly its proper thickness, and almost true, is next testedwith a straight-edge, and all unevoniiesses beaten down with a lighthammer and planer, preparatory to the final shaving: the plate i-,then passed through the hand shaving machine, accurately adjusted,and two or three light cuts are taken off. The face is then te.>ted byrubbing with a flat piece of willow charcoal, which, by not blackeningthe low parts, or hollows, enables the workman to see if any suchexist, in which case he putsa corresponding mark toindicate these places on theback with a suitable tool.The plate is then laid, facedownward, and the markedplaces are struck with a ball-faced hammer which forcesup the printing surface be-neath to its proper level.The plate is next subjectedto the hand shaving machine(Fig. 68), by which the backbecomes shaved down to itsproper thickness and ren-dered perfectly level andsmooth. The edges arc nextplaned square and to theproper size, after w hich theyare transferred to the car- Fig. 68.-Hand Shaving Machine,penter, who mounts them,t>/pe-h ujh, on blocks of wood, which mav be either of cherry, mahogan\,or other suitable wood, which is cut perfectly true and square in everydirection. The plates, when mounted, are ready for the printer.
Bookwork is usually not mounted on wood, the plates being left un-mounted, and finished with bevelled edges, by which they are securedon suitable plate blocks of wood or iron, supplied with gripping piece?*which hold them firmly at the proper height, and enable them to beproperly locked up.
Fig. 69 represents Messrs. R. Hoe & Co.'s power planing andsawing machine, which is intended for roughing off plates beforesending them to the shaving machine, and is said to be very simple,quick, and efficient in operation. A circular saw runs in an elevating*
142 ELECTRO-DErOSITION OP COPPER.
an iron ladle, commencing at one of the corners and gradually run-ning" over the surface until it is covered with a backing* of sufficientthickness. A convenient form of backing-pan and stand is shown inFig\ 66. The thickness of the backing- is about one-eighth of an inch,or sufficient to enable the electro, when trimmed and mounted, to with-stand the pressure of the printing press. The backing'-up alloy isvariously composed, but the following* is a g-ood practical formula :—
Finishing.—As they pass from the hands of the " backer,"the plates present a rough and uneven surface on the back, and theblanks are higher than they should be for mounting. It is the finisher's
Fig. 67.—Saw Table, with Squaring Table.
duty to remedy all such defects. If the backed electrotype consists ofseveral pages, it is first taken to the saw table, Fig. 67, where it isloughly sawn apart by a circular saw, the eyes of the workman beingprotected from the particles of flying metal by a square plate of gifts?, asshown in the figure. Each plate is then trimmed all round to removerough edges, and if there are any projections which would prevent itfrom lying flat, these are carefully cut down with a small chisel. Theplate ift next shaved to remo\ e the roughness from the back and make
ELECTROTYPING WOOD ENGRAVINGS. 145
furnish so larjre a number of impressions, equally perfect. Indeed, ifwo take the trouble to examine some of the illustrations of ourperiodical literature which have been produced direct from woodblocks, we cannot fail to notice the gradual depreciation of theoriginal engraved blocks.
In copying an engraved wood block, it is first well brushed overwith plumbago, or simply moistened with water ; it is then placedupon a level bench, and a metal frame somewhat higher than the blockis fastened round it. A lump of softened gutta-percha is then placedin the centre of the engraving, and forcibly spread outward (towardsthe frame), by which air becomes excluded. A plate of cold iron isnow placed over the gutta-percha, with gentle pressure, which isafterwards gradually increased, by means of a press, as the gutta-percha becomes harder. When the mould ha*> cooled, it i.s carefullyseparated from the block, and well plumbagoed, after which tin* con-necting wire and " guiding wires " are attached ; it is then ready forthe depositing bath, where it is allowed to remain until a shell ofsufficient thickness is obtained, which will depend upon the size ofthe mould and the strength of the current employed. Under favour-able conditions, a shell of copper, say, of about one square foot ofsurface, will be obtained in about eight or ten hours, or even less ; itis commonly the practice to put a series of moulds in the bath towardsthe evening, and to leave them in the bath all night; on the followingmorning the deposit is found to be ready to separate from the mould.In electrotype works where magneto or dynamo machines are em-ployed (as in some of our larger printing establishments), a good shellis obtained in from three to five hours,* according to the dimensionsof the mould. After removing the mould from the hath, it is rinsedin water, and the shell carefully detached, and the electrotype isnext backed-up with solder or a mixture of type metal and tin, theback of the electrotype being first brushed over with a solution otchloride of zinc. The edsres of the electrotype are next trimmed witha circular saw, and are afterwards submitted to the planing machine,by which the backing metal is planed perfectly level and flat; the edircsare then bevelled by a bevelling machine, when the plate is readyfor mounting on a block of cedar or mahogany, which is ef¥e< ted by
* An American electrotypist, on a visit to London, told the author, aboutflve years ago, that, having adopted the Weston dynamo machine in place ofvoltaic batteries, he could deposit a shell of copper upon fifteen moulds,each having about two square feet of surface, in about two and a half hours ;that is to say, by the time the fifteenth or last mould was put into thebath the one which had first been immersed was sufficiently coated forhacking up.
T 44 ELECTRO-DEPOSITION OF COPPER.
table at one corner, for squaring* up, and an outside cutter, withsliding- table, is attached for squaring up metal bodies, &c.
Electrotyping from Plaster Moulds.—Plaster of Paris may be em-ploye d for making electrotype moulds instead of wax, in which casethe plaster mould is first soaked in. wax ; it is then coated with a mix-ture composed as follows : nitrate of silver i gramme, dissolved inwater, 2 grammes ; to this i& added 2 J grammes of ammonia, and then3 grammes of absolute alcohol. The mould is then to be exposed to
Fig. 69.—Power Planing and Sawing Machine.
sulphuretted hydrogen ga^ - made by poui'ing dilute sulphuric acid onpowdered sulphide of iron.
Electrotyping Wood Engravings, <fcc.—One of the most usefulund extensive applications of electrotyping is in the copying of woodengravings in electrolytic copper, to form metallic printing surfaces inlieu of printing from the less durable material, wood. The value andimportance of electrotype blocks to the proprietors of illustratedpublications—many of which have an enormous sale—will be at oncerecognised when we state that the electrotype heading of The Timesnewsj>aper is reputed to have produced no less than twenty millions ofcopies or impressions before it required renewal. It would be difficultto estimate how many wood blocks would have been required to
CHAPTER VIII.
ELECTRO-DEPOSITION OF COPPER {continued).
Deposition of Copper by Dynamo-electricity.—Copying Statues, <kc.—Lenoir'aProcess.—Deposition of Copper on Iron.—-Coppering Printing Rollers.—Schlumberger's Process.—Producing Printing Rollers by Electricity.—Coppering Cast Iron.—Coppering Steel Wire for Telegraphic Purposes.—Coppering Solutions.—Dr. Eisner's Solution.—Walenn's Process.—Gulensohn's Process.—Weil's Coppering Process.—Electro-etching.—Glyphography.—Making Copper Moulds by Electrolysis.—Making Electrotype Plates from Drawings.—Coppering Steel Shot.—CopperingNotes.
Deposition of Copper by Dynamo-electricity.—Within the pastfew years, owing to the great advance made in the production ofpowerful and reliable magneto and dynamo-electric machines, the re-duction of copper by electrolysis in the various branches of electro-deposition has assumed proportions of great magnitude ; and whilenickel-deposition—which fifteen years ago was a comparatively un-developed art—has quietly settled down into its legitimate position asan important addition to the great electrolytic industry, the electro-deposition of copper, and its extraction from crude metal, have pro-gressed with marvellous rapidity, both at home and abroad, but moreespecially so within the past five or six years, and we may safelypredict from our knowledge of the vast number of magneto anddynamo machines which are now being constructed, under specialcontracts, that in a very short time the electrolytic reductionof copper will reach a scale of magnitude which will place itamongst the foremost of our scientific industries in many parts ofthe world. Before describing the processes of copj)ering large metallicobjects, we must turn our attention to the production of electrotypesof larger dimensions than those previously considered. At a very earlyperiod of the electrotype art, Russia, under the guidance of the famousProfessor Jacobi, produced colossal statues in electrolytic copper, whichat the time created profound astonishment and admiration. About thesame period our own countrymen directed their attention to this appli-cation of electrotypy, and at subsequent periods electrotypes of con-siderable dimensions were produced not only in this country but onthe Continent. Some exceedingly fine specimens have been producedby Messrs. EUdngton & Co., one of the most notable of which is
I46 ELECTRO-DEPOSITION OF COPPER.
means of small iron pins driven into the bevel edges of the backingmetal. When complete, the block, with its mounted electrotype,should be exactly type high. Respecting electrotypes from woodengravings, or "electros/' as they are commonly called in the print-ing trade, we may mention that many of our larger illustrationsare produced from electrotypes. Engraved steel plates are copied inthe same way as above, and their reproduction in copper by the elec-trotype process is extensively practised.
Tin Powder for Electrotyping.—Grain tin may be reduced to animpalpable powder by either of the following methods :—1. Melt thegrain tin in an iron crucible or ladle, and pour it into an earthenwaremortar, heated a little above its melting point, and triturate brisklyas the metal cools. Put the product in a muslin sieve and sift outthe finer particles, and repeat the trituration with the coarser par-ticles retained in the sieve. To obtain a still finer product place thefine powder in a vessel of clean water and stir briskly ; after a fewseconds' repose, pour off the liquor in which the finer particles aresuspended, and allow them to subside, when the water is to be againpoured off and a fresh quantity of the powder treated as before. Theimpalpable powder is finally to be drained and dried, and should bekept in a wide-mouthed stoppered bottle for use. 2. Melt grain tinin a graphite crucible, and when in the act of cooling, stir with aclean rod of iron until the metal is reduced to a powder. The powdershould then either be passed through a fine sieve or ihUnniul as abovedescribed, which is by far the best method of obtaining an absolutelyimpalpable product. In using this powder for electrotyping pur-poses in the manner previously described, it must not be forgottenthat the tin becomes dissolved in the copper bath ; it should thereforeonly be employed in a bath kept specially for the purpose, and rotbe suffered to enter the ordinary electrotyping vat.
COPPERING PRINTING ROLLERS. 149
prcssions in gutta-percha of the object in several pieces, which mayafterwards be put together to form a perfect figure ; the inner sur-faces of these impressions, or parts of the mould, are then well coatedwith plumbago. A " d u m m y " of the form of the interior of themould, but of smaller dimensions, is now formed of platinum wire, toact as an anode, and the several parts of the plumbagood gutta-perchamould are put together to form a complete mould all round it. Themould, with its platinum wire core (the anode)—which is insulatedfrom metallic contact with the mould by a covering of india-rubberthread—is then placed vertically in the bath, weights being attachedto allow the mould to sink into the solution. The platinum anodeand the plumbagoed mould are then put in circuit and depositionallowed to progress. To keep up the strength of the copper solutionwithin the mould, in the absence of a soluble anode, a continual nowof fresh copper solution is allowed to enter the mould, from a hole atthe top of the head, which makes its escape through holes in the feetof the mould. When a sufficiently stout deposit is obtained, theflexible wire anode is withdrawn through the aperture in the head,after which the various portions of the gutta-percha mould are re-moved, and the seams at the junctions of the electrotype are clearedaway by appropriate tools.
Deposition of Copper on Iron.—Since iron receives the copperdeposit from acid solutions without the aid of a separate current, andthe deposit under these conditions is non-adherent, it is the practiceto give a preliminary coating of copper to iron objects in an alkalinebath, ordinary cyanide solutions being most generally adopted forthis purpose. Many other solutions have, however, been recom-mended, some of which may deserve consideration. In any case, theiron article is first steeped in a hot potash bath, when the presenceof greasy matter is suspected, and after rinsing, is immersed in apickle of dilute sulphuric acid, \ 1b. of acid to each gallon of water.After will rinsing, the article is scoured with coarse sand and water,applied with a hard brush, and after again rinsing, is immersed in thealkaline bath until perfectly coated with a film of copper. It is thenag.iin rinsed, and at once placed in a sulphate of copper bath, whereit i>; allowed to remain until a sufficiently stout coating of copper isobtained. In some cases, where the object is of considerable propor-tions, it is kept in motion while in the solution, by various mechanicalcontrivances, as in Wilde's process, to be referred to shortly.
Coppering Printing Hollers.—Many attempts have been made,during the past thirty years or so, to substitute for the costly solidcopper Eollers used in ealico-printing, iron rollers coated with a layerof copper by electrolysis. The early efforts were conducted with theordinary/voltuio batteries, but the eosat of the electricity thus obtained
J 4 8 ELECTRO-DE POSITION OF COPPER.
that of the Earl of Eglinton, 13^ feet high and weighing* two tons,while some other equally good specimens of life-size busts and bas-reliefs are to be seen in Wellington College, the House of Lords, k<\The well-known Paris firm, MOSSIN. Christofle <fc Co., huvo alsoproduced colossal electrotype statues, one of -which is 29 feet 6 inchesin height, and weighs nearly three tons and a half ; the completion ofthe deposit occupied about ten weeks.
Copying Statues, Sec.—When very large objects have to be repro-duced in electrotype, the method adopted is usually as follows : Theoriginal, formed of plaster of Paris, produced by the modeller orsculptor, is first brushed all over with boiled linseed oil, until the sur-face is completely saturated witli the drying oil. After standing fortwo or three days, according to the temperature and condition of theatmosphere, the object, which is thus rendered impervious to moisture,and readily receives a coating of plumbago, is thoroughly well brushedover with blacklead until the entire surface is perfectly coated withthe conducting material. The model is next connected to conductingwires, assisted by guiding wires, and placed in a sulphate of copper bath,where it receives a deposit of about one-sixteenth of an inch in thick-ness, or a shell sufficiently stout to enable it to retain its form afterthe inner plaster figure has been removed, which is effected in thisway: the electrotype, with its enclosed model, being taken out of thebath, is first thoroughly well rinsed, the copper shell is then cutthrough with a sharp tool at suitable places, according to the form ofthe original figure, by which these various parts, with their guidingwires attached, become separated ; the plaster figure is then carefullybroken away, and all parts of it removed. After rinsing in hot water,the outer surface of the copper " formes " are well varnished over toprevent them from receiving the copper deposit in the next operation.The formes are next exposed to the fumes of sulphide of hydrogen, ordipped in a weak solution of sulphide of potassium (liver of sulphur),to prevent the adhesion of the copper deposit. These " formes," orparts of the electrotype shell, constitute the moulds upon which thefinal deposit, or electrotype proper, is to be formed, and these are re-turned to the depositing tank and filled with the solution of sulphateof copper, anodes of pure electrolytic copper being suspended in eachportion. Deposition is then allowed to take place until the interiorparts or moulds receive a coating of from one-eighth to one-third ofan inch in thickness. The various pieces are then removed from thebath, and after well rinsing in water, the outer shell, or mould, iscarefully stamped off, and the respective parts of the electrotypefigure are afterwards fixed together when the operation is complete.
Lenoir's Process.—A very ingenious method of electrotyping largefigures was devised by M. Lenoir, which consists in first taking im-
COPPERING PRINTING ROI LERS.
Producing Printing Hollers by IVIagneto-electricity. — JProcess.—It is obvious that the electrical power obtained from mag-neto and dynamo-electric machines is more capable of depositing econo-mically the requi&ito thickness of copper upon cast-iron cylinders to formprinting rollers than could be expected from voltaic electricity, whichnecessarily involves the solution of an equivalent of zinc and the con-sumption of sulphuric acid to deposit a given weight of copper. Itis well known that deposition takes place more freely upon the lowersurfaces of the cathode, and consequently, when the deposited metalis of any considerable thickness, the irregular surface thus producedis often a source of great trouble to the electro-depositor ; in the caseof printing rollers, however, in which a perfectly uniform thicknessof the deposit is absolutely indispensable, some means must be adoptedto render the deposit as uniform as possible from end to end of thecylinder. To accomplish this, Mr. Henry Wilde, of Manchester,effected an arrangement for which he obtained a patent in 1875,which consists in " giving to the electrolyte or depositing liquid inwhich the roller to be coated is immersed, of the positive and nega-tive electrodes themselves, a rapid motion of rotation, in order thatfresh particles of the electrolyte may be brought successively in con-tact with the metallic surfaces. By this,'' says the patentee, "powerfulcurrents of electricity may be brought to bear upon small surfaces ofmetal without detriment to the quality of the copper deposited, whilethe rate of the deposit is greatly accelerated.
" Motion may be communicated to the electrolyte, either by therotation of the electrodes themselves, or when the latter are stationary,by paddles revolving in an annular space between them. The ironroller to be coated with copper is mounted on an axis, the lower endof which is insulated, to prevent its receiving the deposit of copper atthe same time as the roller. The roller, after having received a filmdeposit of copper from an alkaline solution in a manner well under-stood, is immersed in a vertical position in a sulphate solution ofcopper, and a motion of rotation is given to the roller or rollers bymeans of suitable gearing. The positive electrodes are copper rollersor cylinders, of about the same length and diameter as the roller tobe coated, and are placed parallel with it in the sulphate solution.The electrical contacts are made near the upper and lower extremitiesof the electrodes respectively, for the purpose of securing uniformityin the thickness of the deposit. The sulphate solution may be main-tained at an uniform density, from the top to the bottom of the bath,by rotating a small screw propeller, enclosed in a tube communicatingwith the liquid, and driven by the same gearing that imparts motionto the roller."
The electric current employed for depositing copper by the above
r5O ELECTRO-DEPOSITION OF COPPER.
was far too great to admit of the process being- practically successful,while at the same time the operation was exceedingly slow. A methodwhich was partially successful consisted in depositing, in the form ofa flat plate, an electrotype bearing the design, which was afterwardscoiled up in a tubular form, and connected to an iron cylinder or rollerby means of solder, the seam being afterwards touched up by theengraver. A far better system, however, is now adopted, which is inevery way perfectly successful; and printing rollers are produced inlarge quantities by electro-deposition at about one-half the cost ofthe solid copper article. Before describing the methods by whichcast-iron rollers are faced with copper at the present time, it may beinstructive to consider briefly some of the means that have beenadopted to deposit a sufficient thickness of copper upon a oast-ironcore to withstand the cutting action of the engraver's tools.
Schlumberger's Process.—This consists in depositing copper uponpreviously well-cleaned cast-iron cylinders by means of the ''single-cell " process. The solution bath consists of a mixture of two solu-tions composed of (i) Sulphate of copper, I part; sulphate of soda,2 parts ; carbonate of soda, 4 parts ; water, 16 parts. (2) Cyanide ofpotassium, 3 ; water, 12 parts. The interior of the bath is surroundedby porous cells containing amalgamated zinc bars with copper wiresattached, and dilute sulphuric acid. The solution is worked at atemperature of from 590 to 650 Fahr., and the iron cylinder, beingput in contact with the zinc elements, remains in the bath for twenty-four hours, at the expiration of which time it is removed, well washed,rubbed with pumice-powder, again washed in a solution of sulphateof copper having a specific gravity of 1 • 161, containing -rioth part of itsvolume of sulphuric acid ; scraps of copper are kept in the bath, to sup-ply the loss of copper, and prevent the liquid becoming too acid. Thecylinder is then returned to the bath, or placed in a mixture composedof the following two solutions : (1) Acetate of copper, 2 ; sulphate ofso.la, 2 ; carbonate of soda, 4 ; water, 16 parts. (2) Cyanide of po-tassium, 3 ; liquid ammonia, 3 ; water, 10 parts. The cylinders areto be turned round once a day, in order to render the deposit uniform,and the action is continued during three or four weeks, or until thedeposit is -o th of an inch thick.
Another method consists in first coppering the well-cleaned cast-iron cylinder in an ordinary alkaline coppering bath, and then trans-ferring it to an acid bath of sulphate of copper, the cylinder in eachwise being surrounded by a hollow ryliuder of copper for the anode ;the process is allowed to proceed slowly, in order to obtain a goodre*; aline coating, and when this i« obtained of sufficient thickness tobear engraving upon, the surface is rendered smooth by turning atthe lathr
COPPERING CAST IRON. 153
cell" method, for which very large porous cells are employed. Inabout four or five days a sufficiently thick coating" of copper isobtained, when, after rinsing and drying, a bronzed appearance isgiven to the work by the application of a solution of ammonio-acetate of copper. With respect to this process M. Fontaine observes:4' It is evident that a coating of copper so deposited can be possessedof no other solidity than its own, and the latter is entirely dependenton the thickness and tenacity of the deposit M. Oudry was accord-ingly led to etfect depositions having one-half a millimetre on ordinaryobjects, and one millimetre or more on fine works. If to that thick-ness is added those of a layer of plumbago and three layers of insu-lating coating material, it will be readily conceived that .such a systemof coppering is only suitable in the case of very large objects. Inthe case of small objects—such as a bust, for example—the nicety ofthe details would be irretrievably spoiled by these five layers, and itwould amount to sacrificing to too great an extent the artistic worthof the object for the purpose of attaining its preservation. It is,nevertheless, certain that this process has really become a branch ofindustry, and that it is the first one which has been applied on a largescale. All the lamp-posts of the city of Paris, the beautiful fountainsof the Place de la Concorde and of the Place Louvois, and a consider-able number of statues and bas-reliefs, have been coppered at Auteuil,in the inventor's factory." It appears that M. Oudry's son subse-quently modified the above process by substituting for the coatingsof paint and plumbago an immersion of the cast-iron objects in athick paint composed of hot oil and copper-dust suspended in theliquid. The objects, when removed from this bath, are first dried inan oven and then rubbed with a wire-brush and copper dust. Theyare afterwards immersed in a sulphate of copper bath.
It is obvious that in either of the above processes a quantity ofcopper far in excess of what would be required as a protective coatingfor iron—provided it could be deposited dirnC upon the metal—mustfrom necessity be deposited upon the plumbagoed, or copper-dustedsurface ; and it is also clear that since the copper represents merely athin shell upon the surface, that a very moderate amount of roughusage, such as the Parisian (jamb* or London street Arab could inflicton very easy terms, by the simple process of climbiug the lamp-postswith metal-tipped boots, would quickly break this "shel l" and ex-pose the underlying layer of plumbagoed varnish. When all theseobjections are taken into consideration—the partial obliteration ot* theliner details of the object, the Labour, e(*t v>i* material, lite h ngth oftime required to complete a single article before it is ready to be placedin position, and add to this the constant liability to damage fromaccident or mischief, this method of coppering iron doe& not appear tohave much to recommend it.
152 ELECTRO-DEPOSITION OF COPPER.
method may be obtained from Wilde's magneto-electric machine,which has been very extensively adopted for this purpose, or fromany dynamo electric machine capable of yielding an adequate current.Mr. Wilde bays, in the specification above quoted, "Although I haveonly mentioned cast-iron as the metal upon which the copper isdeposited, the process is applicable to rollers made of zinc or othermetals, and their alloys. The method of accelerating the rate of de-posit, by gi\ ing to the electrolyte, or to the electrodes, a motion ofrotation, may be applied to the electrolytic method of refining coj^erdescribed in Mr. J. B. Elkington's patent." Mr. Wilde's system ofcoppering cast-iron rollers was established in 1878, but he subse-quently disposed of his patent rights to the Broughton Co];>perCompany, who carry on the process successfully, and have extendedit to the coating of hydraulic rams, ko.
Company, who, Professor Silliman, of Yale College, U.S.A., states,have acquired "the largest electro-plating establishment in theworld ; yet its capacity is soon to be trebled. The works are em-ployed in coppering steel wire used in the company's system oftelegraphy, and now deposit two tons of pure copper per day. Thesteel core of the wire gives the required tensile strength, while thecopper coating gives extraordinary conducting power, reducing theelectrical resistance enormously. The compound wire consists of asteel wire core weighing 200 lbs. to the mile, and having a tensilestrength of 1650 lbs., upon which copper is deposited, by dynamo-electricity, of any required thickness. Twenty-five large dynamomachines are employed, which deposit collectively 10,000 lbs. ofcopper per day, representing 20 miles of ' compound wire,' carry-ing 500 lbs. of copper to the mile. When the works are completed,three 300 horse-power engines will drive dynamo machines for sup-plying the current to deposit copper upon 30 miles of wire per day.In the process of deposition the wire is drawn slowly over spiral coils,through the depositing vats, until the desired thickness is obtained."The advantages of coppered steel wire over ordinary galvanised ironwire for telegraph purposes cannot well be over-estimated, and ifthe process prove as successful as it is stated to be, it will un-doubtedly be a great electrolytic achievement.
Coppering Solutions.—In preparing alkaline coppering solutions,for depositing a preliminary coating of copper upon iron, and forother purposes of electro-coppering, either of the formulae for brass-ing solutions may be used,* by omitting the zinc salt and doubling thequantity of copper salt; or either of the following formulae may beadopted. As a rule, copper solutions should be worked hot, say at atemperature of about 1300 Fahr., with an energetic current, especiallyfor cast-iron work, since even with the best solution deposition is butslow when these solutions are worked cold. It is important to bearin mind in making up copper solutions—and the same observationapplies with at least equal force to brassing solutions—that commer-cial cyanide of potassium is largely adulterated with an excess of car-bonate of potash, and unless a cyanide of known good quality beemployed, the solution will be not only a poor conductor of the cur-rent, but the anodes will fail to become freely dissolved, whereby thesolution will soon become exhausted of a greater portion of its metalin the process of deposition. The cvanide to be used for making upsuch solutions should contain at least 75 per cent, of real cyanide.
Solution 1.—Dissolve 8 ounces of sulphate of copper in about1 quart of hot water ; when cold, add liquid ammonia of the specificgravity of '88o gradually, stirring with a glass rod or strip of woodafter each addition, until the precipitate which at first forms becomes
* See pp. 374 et seq.
154 ELECTRO-DEPOSITION OF COPPER.
Cold Coppering Solution.—One of the chief reasons why alkalinecoppering solutions seldom work vigorously when used at the ordinarytemperature, is that they are too frequently prepared with cheap com-mercial cyanide, containing but a small percentage of real cyanide, andconsequently overloaded with carbonate of potash, a salt which has nosolvent action on the anode, and is of little or no service in the copper-ing bath. While experimenting in this direction some time since, \wfound that a good coppering solution, to be worked in the cold, couldbe prepared from the following formula ; but it is essential that thecyanide be of good quality. For each gallon of solution required,3 ounces of chloride of copper are to be dissolved in about a pint anda-half of cold water ; 12 ounces of soda crystals are next dissolved inabout a quart of water. The latter solution is then to be graduallyadded to the chloride of copper solution, with gentle stirring after eachaddition, until the whole of the alkaline liquid has been added, whenthe resulting carbonate of copper is allowed to settle. After an hour orso the supernatant liquor is poured off and fresh water added to washthe precipitate, which is again allowed to subside as before, the wash-ings being repeated several times, and the precipitate then dissolvedin a solution of cyanide of potassium composed of six ounces of thecyanide dissolved in about a quart of water, the whole being wellstirred until the copper salt has become dissolved. The solution thusformed is now to be set aside for several hours and the clear liquorthen carefully decanted from any sediment that may be present;water is then added to make up one gallon of bath. This solutionwill coat cast or wrought iron very readily with a current from twoto three Daniells, in series, and may be used to give a preliminarycoating to iron work which is to be afterwards thickly coppered in anordinary sulphate bath. The anode used in this, and all other alkalinecoppering baths, should be of pure electrolytic copper.
Coppering Steel Wire for Telegraphic Purposes.—It hadalways been held that if iron wire could be successfully and economi-cally coated with copper, it would be of incalculable service in tele-graphy; and, indeed, many attempts to accomplish this were made ata period when magneto and dynamo-electric machines were unknown.It soon became apparent, however, that, independent of other difficulties,the object could never be practically attained by means of the voltaicbattery. Now that we are enabled to obtain electricity simply at thecost of motive power, that which was impossible thirty yvnrs ago hasbeen to some extent accomplished, and the coppering" of steel wire fortelegraph purposes forms an extensive branch of manufacture in con-nection with one of the telegraph .systems of America. The manu-facture of " compound wire," as it is called, has been carried out ona very large bcale at Ansonia, Connecticut, by the Postal Telegraph
WALEXNS COPPERING SOLUTIONS. 157
quantity of carbonate of potash. This solution is stated to be appli-cable to coating iron, tin. and zinc articles.*
Walenn's Coppering Solution.—This solution, to be employedfor coppering iron, consists in dissolving cyanide of cupper in a solu-tion composed of equal parts of cyanide of potassium and tartrate ofammonia. Oxide of copper and ammoniuret of copper are added insufficient quantity to prevent the evolution of hydrogen at the surfaceof the work during deposition. The solution is worked at about 1800
Fahr. The current from one Smee cell may be used with this solution.It has been found that lh ounce of copper per square foot will pro-tect iron from rust.
Another process of Mr. Walenn's is as follows :—The first part of this invention u relates to electro-depositing
copper upon iron, or upon similar metals, so that the coatingmay be soft and adherent. This consists in using the solution ata boiling heat, or near thereto, namely, from 1500 Fahr. to theboiling point of the solution. The second part is to prevent theevaporation of a solution which is heated during deposition. Acover, with a long condensing worm tube, is used in the depositingbath ; the other end of the tube opens into a box containingmaterials to condense or appropriate the gases that escape. Theliquids flow back down the tube into the tank. The third partof the invention consists in working electro-depositing solutions in aclosed vessel under known, pressure, being applied by heating thesolution or otherwise. The closed vessel may be used for solutions inwhich there is free ammonia, or where other conditions arihC in whichit is necessary to enclose the solution, although neither appreciableincrease of pressure arises nor is heat applied. If there be much gascoming off, the condensing tube, opening into a box of the secondpart of the improvements, may be employed." The fourth part of theinvention consists in adding to the charged, and fully made, copper,brassing, or bronzing solution, cupric ammonide in the cold, until thesolution is slightly green.
Gulensohn's Process.—A bath is made by first obtaining a solutionof chloride of copper, the metal from which is precipitated in the formof phosphate, by means of pyrophosphate of soda. The precipitateis then thoroughly washed until all traces of the chloride of sodaformed have been removed ; the phosphate of copper is next dissolvedin a solution of caustic soda, and, if necessary, a small quantity ofliquid ammonia is added to assist the solution of the phosphate, andto render the deposit brighter and more solid. The strength of thesolution must be regulated according to the strength of the current
The Chemist, vol. vii. p. 124.
'56 ELECTRO-DEPOSITION OF COPPER.
re-dissolved; dilute the solution by adding I quart of cold water.Now prepare a solution of cyanide of potassium by dissolving" aboutl\ lb. of the salt in 2 quarts of water, and add this gradually to thecopper solution, with stirring, until the blue colour of the ammonio-sulphate entirely disappears ; finally add the remainder of the cyanidesolution, and allow the mixture to rest for a few hours, when theclear liquor may be decanted into the depositing vessel or tank, andis then ready for use. This solution may be used cold, with astrong current, but it is preferable to work it at about no° to 130""Fahr.
Solution 2.—The acetate or chloride of copper may boused insteadof the sulphate in making up a coppering bath, the latter &alt beingpreferable.
Solution 3.—A solution prepared as follows has been recommended :Dissolve cyanide of copper in a solution of cyanide of potassium, con-sisting of 2 pounds of cyanide to 1 gallon of water, then adding about4 ounces more of the salt as free cyanide ; the solution is then ready,and should be worked at a temperature of about 1500 Fahr. Cyanideof copper is not freely soluble in a solution of cyanide of potassium,and the liquid does not readily dissolve the anodes, nor is it a goodconductor. It has also a tendency to evolve hydrogen at the cathode;this, however, may be lessened or wholly prevented by avoiding theuse of free cyanide, employing a weaker current, and adding liquidammonia and oxide of copper. From our own experience, the addi-tion of liquid ammonia tc copper solutions, if not applied in the firstinstance, becomes a necessity afterwards.-^ Solution 4.'—Roseleur gives the following formula for a copperingsolution: 20 parts of crystallised acetate of copper are reduced to apowder, and formed into a paste with water ; to this is added 20 partsof soda crystals, dissolved in 200 parts of water, the mixture beingwell stirred. To the green precipitate thus formed, 20 parts of bisul-phite of sodium, dissolved in 200 parts of Avater, are added, by whichthe precipitate assumes a dirty yellow colour. 20 parts of pure cyanideof potassium, dissolved in 600 parts of water, are finally added, andthe whole well stirred together. If the solution does not becomecolourless, an addition of cyanide must be given. It is said that thissolution may be worked either hot or cold, Avith a moderately strongcurrent.
Dr. Eisner's Solution.—In the preparation of this solution, I partof powdered bitartrate of potassium is boilod in ro parts of water, andas much recently prepared and wet hydrated carbonate of copper,which has been washed with cold water, stirred with it as the abovesolution Avill dissolve. The dark blue liquid thus formed is next fil-tered, and afterwards rendered still more alkaline by adding a small
ELECTRO-ETCHING. -59cases the proportions between the copper and tartaric acid should bemaintained as above, and it is advantageous not to increase to anynotable extent the proportion of the caustic soda.
The object to be coppered is to be cleaned with a scratch-brush andthen placed in the bath, when it will become rapidly coated with anadherent film of metallic copper. As the bath gradually loses itscopper, oxide of copper as above prepared should be added to main-tain it in a condition of activity, but the quantity of copper introducedshould never exceed that above prescribed, as compared with thequantity of tartaric acid the bath may contain. If the copper notablyexceeds this proportion, certain metallic iridescences are produced onthe surface of the object. These effects may be employed for orna-mental and artistic purposes. According to the time of the immersion,the strength of the current, and the proportion of copper to the tartaricacid, these iridescences may be produced of different shades and tints,which may be varied or intermingled by shielding certain parts of theobject by a coating of paraffin or varnish, the iridescent effect beingproduced on the parts left exposed. All colours, from that of brass tobronze, scarlet, blue, and green, may be thus produced at will.
Electro-Etching.—When we bear in mind the fact that, with fewexceptions, the anodes employed in electrolytic processes become dis-solved in the bath during electro-deposition, it is evident that ifcertain portions of an anode were protected, by means of a suitablevarnish, from the solvent action of the solution, that such parts, afterthe plate had been subjected to electro-chemical action in the bath,would, on removal of the varnish, appear in relief, owing to theexposed surfaces having been reduced in substance by being partiallydissolved in the solution. Suppose a smooth and bright plate of cop-per, for instance, were to have a design sketched upon it with asuitable varnish, and the plate then connected to the positive electrodeof a voltaic battery and immersed in a solution of sulphate of copper,a cathode of the same metal being suspended from the negative elec-trode ; if, after a few hours' immersion, the plate be taken from thebath, and the varnish removed, the design will ax">pear in bright re-lief, while the unvarnished parts will have been eaten away, ordissolved, leaving hollows of a comparatively dull appearance ; thedesign now forms a printing surface, from which copies may be im-pressed upon paper in the usual way.
The process of voltaic etching is performed in various ways, but thefollowing will explain the general principle upon which the art is con-ducted. A copper wire is first soldered to the plate, and the back isthen coated with a tough varnish ; when this is dry, the face of theplate is coated with engraver's " etching-ground," a composition ofbeeswax 5 parts, linseed oil 1 part, melted together ; it is sometimes
153 ELECTRO-DEPOSITION OP COPPER.
employed in the deposition. The bath may be used for depositing"upon iron or other metals.
Weil's Coppering Processes.—(1.) For coating large objects, ascast-iron fountains, lamp-posts, &c. M. Weil's patent gives the fol-lowing process : Dissolve in 1,000 parts of water, 150 of sodio-potassic tartrate (Roehelle salt), 80 of caustic soda, containing from50 to 60 per cent, of free soda, and 35 of sulphate of copper. Ironand steel, and the metals whose oxides are insoluble in alkalies, arenot corroded in this solution. The iron or steel articles are cleanedwith dilute sulphuric acid, of specific gravity i'OT4, by immersingthem in that liquid from five to twenty minutes, then washing withwater, and finally with water made alkaline by soda. They arenext cleaned with the scratch-brush, again washed, and thenimmersed in the cupreous bath, in contact with a piece of zincor lead, or suspended by means of zinc wires ; the latter is themost economical way. The articles must not be in contact witheach other. They thus receive a strongly-adherent coating of copper,which increases in thickness (within certain limits) with the dura-tion of immersion. Pure tin does not become coppered by contactwith zinc in this solution ; it oxidises, and its oxide decomposes thesolution, and precipitates red sub-oxide of copper, and by prolongedaction, all the copper is thus removed from the liquid. The ironarticles require to be immersed from three to seventy-two hoursaccording to the colour, quality, and thickness of the required deposit.The copper solution is then run out of the vat, and the coated articleswashed in water, then cleaned with a scratch-brush, washed, dried inhot sawdust, and lastly in a stove. To keep the bath of uniformstrength, the liquid is renewed from below, and flows away in a smallstream at the top. After much use, the exhausted liquid is renewedby precipitating the zinc by means of sulphide of sodium (not inexcess), and re-charging the solution with cupric sulphate. Weilalso supplies to the bath hydrated oxide of copper.
(2.) A coppering bath is prepared as follows : 35 parts of crystal-lised sulphate, or an equivalent of any other salt of copper, areprecipitated as hydrated oxide by means of caustic soda or potash.The oxide of copper is to be added to a solution of 150 parts ofRochelle salt, and dissolved in 1,000 parts of water. To this, 60 partsof caustic soda, of about 70 per cent., is to be added, when a clearsolution of copper will be obtained. Other alkaline tartrates may besubstituted for the Rochelle .salt above mentioned, or even tartaric acidmay be employed ; but in the case of tartaric acid, or acid tartrates,a small additional quantity of caustic alkali must be added, sufficientto saturate the tartaric acid or acid tartrate. Oxide of copper mayalso be employed, precipitated by means of a hypochlorite, but in all
MAKING ELECTROTYPE PLATES FROM DRAWINGS. 161
hands, " by whom it is brought in contact with a substance having achemical affinity for the remaining portions of the composition, bywhom they are heightened, ad libitum. Thus, by careful manipula-tion, the lights of the drawing become thickened all over the plateequally. . . . The dearths of these non-printing parts of the blockmust be in some degree proportionate to their width ; consequentlythe larger breadths of hghtt, require to be thickened on the plate to amuch greater extent. It is indispensably necessary that the printingsurfaces of the block prepared for the press should project in suchrelief from the block itself as shall prevent the inking roller touch-ing the interstices ; this is accomplished in wood engraving by cuttingout these intervening parts, which form the lights of the print, to asufficient depth; but in glyphography the depth of these parts isformed by the remaining portions of the white composition on the plate,analogous to the thickncbs or height of which must be the depth on theblock, seeing that the latter is in fact a cabt or rcirr.sc of the former."The plate, thus prepared, is well plumbagoed all over, and is thenplaced in a sulphate of copper bath, and a deposit of sufficient thick-ness obtained, which, on being separated, will be found to be a perfectcast of the drawing which formed the cliche. The metallic plate thusobtained is afterwards backed up with solder and mounted in thesame way as a stereotype plate, and is then ready for the printing press.
Making Copper Moulds by Electrolysis.—A drawing is madeupon a varnished copper plate, as before described ; the plate is thendipped into a weak ** quicking" solution, and then laid upon a fiatand level surface. The mercury attacks the surfaces exposed by thegraver or etching needle, and takes the iHctusais, or curved form, thatis, the relief is greater as the etching lines are larger; the drawing,therefore, is reproduced in relief by the mercury. The plate is nextcovered with a thin paste of plaster of Paris, and when this hasset, the two moulds are to be separated. A counter mould maynow be taken from this, or it may be prepared in the usual way,and, after being well plumbagoed, receive a deposit of copper. Bythe following plan a mould is produced, which i^ at once readyfor the bath. A copper plate is varnished and etched as before. Aneutral solution of chloride of zinc is then poured upon the plate, andafter this a quantity of fusible metal, which melts at from 1750 to2i2°Fahr. The flowing of the fumble metal over the surface of theplate is aided by the application of a spirit-lamp held beneath theplate, or by spreading the metal over the surface with a hot iron rod.The mould thus obtained may then be reproduced by the ordinaryelectrotype process.
Making Electrotype Plates from Drawings.—Thi^ inventionrelates to an improved process of forming matrices of deMgn& for the
M
i 6 o ELECTftO-DEPOSITION OP COPPEE.
the practice to xmokc the surface, before applying* the etching* needle,in order to render its tracings more visible. The design is thendrawn upon the face of tho pinto, cuffing through to the clean surf/iceof the copper. "When the etching1 is complete, the plate is made theanode in a sulphate of copper bath, while a plate of copper is im-mersed as the cathode. The electric current, passing out of theengraved lines, causes the copper to be dissolved from them, wherebythey become etched, much in the same way, and with the same effect,as when acid is used in the ordinary etching* process. The requiredgradations of light and shade are produced by suspending cathodesof different forms and sizes opposite the plate to be etched, in variouspositions, and at different distances from it, thus causing the plate tobe acted upon in unequal depths in different parts, the deepest actionbeing always at those portions of tiie electrodes which are nearestto each other.
Iitatead of using wax, or other etching-ground, as an insulatingmaterial, the plate may be coated with a film of some metal whichwill not be dissolved in the bath. For example, the plate may be firststrongly gilt by electro-deposition, and the design then produced bymeans of a graver, the tool cutting just sufficiently deep to expose thecopper; if now the plate be used as an anode, the copper will becomedissolved, as before, leaving the gilt surface unacted upon, since thesulphuric acid set free during the voltaic action has no effect upon gold.
Again, the design may be made with lithographic ink or varnish,and the exposed parts of the plate then strongly gilt; if, thereafter,the varnish, or other insulating material be cleaned off the plate, thevoltaic etching will follow the ungilt portions, causing them to be-come hollowed out as before.
The baths used for etching by electrolysis should be composed of thesame metal as that to be etched ; thus, a sulphate of copper bath isemployed for etching copper plates, sulphate of zinc for zinc plates,and gold or silver solutions when their metals are to be treated in thesame way. Copper and zinc plates, however, may be etched bymeans of the voltaic battery, in dilute solutions of nitric, sulphuric,hydrochloric, or acetic acid, a process which is said to be coming verymuch into practice.
Glyphography.—This process was invented by Mr. JE. Palmer, andconsists in first staining copper plate black on one side, over which avery thin layer of a white opaque composition, resembling white wax,is spread. The plate is then drawn upon with various etching needlesin the usual way, which remove portions of the white com|>osition, bywhich the blackened surface becomes exposed, forming a strong con-trast to the surrounding white ground. When the drawing is com-plete, it is carefully inspected, and then j asses into a third person's
COPPERING NOTES. 163
any cavities show signs of being foul, they must be cleared with thesteel point as before. The article should then have a final brushingwith moist sand, and after well rinsing be placed in the alkalinecoppering bath and allowed to remain, with an occasional shifting ofposition, until sufficiently coated. If the piece of work is required tohave a stout coating of copper, it should receive only a moderatedeposit in the cyanide bath, and after being well rinsed suspended inthe sulphate of copper, or acid bath, as it is sometimes termed, andallowed to remain therein until the desired coating is obtained. Tosecure an uniform deposit, however, the object should be occasionallyshifted while in the bath, except when mechanical motion is applied,as in coppering iron rollers and other similar work.
2. Respecting the working of copper solution. , Gore makes thefollowing observations: u If the current is too great in relation tothe amount of receiving surface, the metal is set free as a brown ornearly black metallic powder, and hydrogen gas may even be depositedwith it and evolved. In the sulphate solution, if the liquid is toodense, streaks are apt to be formed upon the receiving surface, andthe article (especially if a tall one) will receive a thick deposit at itslower part, and a thin one at the upper portion, or even have thedeposit on the upper end redissolved. If there is too little water,crystals of sulphate of copper form upon the anode, and sometimesoven upon the cathode, at its lower part, and also at the bottom ofthe vessel. If there is too much acid the anode is corroded whilstthe current is not i>assing. The i>resenee of a trace of bisulphide ofcarbon in the sulphate solution will make the deposit brittle, and thiscontinues for some time, although the solution is continually deposit-ing copper ; in the presence of this substance the anode becomes black,but if there is also a great excess of acid, it becomes extremely bright.Solutions of cupric sulphate, containing sulphate of potassium, andthe bisulphide of carbon applied to them, are sometimes employed fordepositing copper in a bright condition. The copper obtained fromthe usual double cyanide of copper and potassium solution, by a weakcurrent, is of a dull aspect, but with a strong current it is bright."For depositing copper from alkaline solutions, we prefer the Bunsenbatter}' to all others.
3. The anodes used in electrotyping, as also those employed for depo-siting copper generally, should consist of pure electrolytic copper, inpreference to the ordinary sheet metal, which invariably containssmall traces of arsenic and other metals, "which are known to diminishits conductivity considerably. Clippings and other fragments of cop-per from electrotypes may be used up as anodes, cither by suspendingthem in a platinum-wire cradle or in a canvas bag, the fragmentsbeing put in connection with the positive electrode of the battery by
162 ELECTR0-DBP031T10N OF COPPER.
production of electrotype plates directly by the hand of the artist ordesigner, in which the design is produced by means of a pointed toolupon a thin sheet of soft metal supported upon a peculiar backing ofsemi-plastic inelastic material of sufficient body or consistence to sup-port the metal without pressure, but sufficiently yielding to give tothe slightest touch of the artist, and allow the material to be depressedunder the tool for the formation of the lines of design. In carryingout this invention a mixture is made of plaster of Paris I lb., chro-ma te of potassa ] oz., and common salt, I oz., which forms a com-pound that will give the most delicate touch of the artist, and willallow the finest lines to be produced upon the metal by the tool.These ingredients may be mixed in various proportions, which willdepend .somewhat upon the boldness or delicacy of the design to beproduced. The mixture may be brought to a semi-plastic state bythe addition of about I pint of water, or sufficient to bring it to theprimer consistence, and the plasticity of the compound may be modi-fied to suit various requirements by using* more or less water. Thesemi-2>las,tie composition is moulded or otherwi.se formed into a fin ttablet of suitable size, and a sheet of soft metal is carefully secured onthe upper face of same, projecting edges being left, which are after-wards turned down over the sides of the tablet. The metal is thenready for the artist, who, with a pointed tool or tools, 2>voduces therequired design by indenting the lines thereon. Wherever touched bythe tool the metal will be depressed into the backing, which has justsufficient body to sup]X>rt the untouched parts, but yields to theslightest pressure of the tool. When the design is finished, themetal is carefully removed from the backing, having the design inrelief on one side and in intaglio on the other, nnd is ready for theproduction of the electrotype 2>late in the ordinary way, which maybe taken from either side, as circumstances require.
Coppering Steel Shot.- The electro-deposition of copper is beingextensively applied by the Nickel Plating Company, Greek Street,S»»ho, London, to the coating of large and small steel shot with copperfor the Xordenfelt gun.
Coppering Notes.—i. In preparing cast-iron work for electro-coppering*, after the pieces have been })iekled and scoured, they shouldbe carefully examined for sand-holes, and if any .such cavities appearupon the work, they must be well cleared from black or dirty matter,which may have escaped the brushing, by means of a steel 2)t>int. Itmust always be borne in mind thateo2>per, and indeed all other metals,refuse to de2>osit upon dirt. After having cleared out the objectionablematter from the sand-holes, and again well brushed the article withsand and water, it is a good plan to give the pioco a slight coaling ofcopper in the alkaline bath, and then to examine it again, when if
CHAPTER IX.
DEPOSITION OF GOLD BY SIMPLE IMMERSION.
Pivpartion of Chloride of Gold.—Water Gilding.—Gilding l>y Immersion ina Solution of Chloride of Gold.—Gilding by Immersion in an Ktherc.ilSolution of Gold.—Solution for Gilding Brass and Copper.—Solutionfor Gilding Silver.—Solution for Gilding Bronze.—French Gilding forCheap Jewellery.—Colouring Gilt Wmk. Gilding Silver by Hipping,or Simple Immersion.—Preparation of the Work for Gilding.—Gildingby Contact with Zinc, Steele's I'roce^.—Gilding with the Hag,
Preparation of Chloride of Gold.—Since for all gilding' purposesby tlic wit }''«>/, as we nviv term it in contradistinction to the processof mercury gilding, this m<ral requires to be brought to the state ofsolution, it will he well to explain the method of preparing the saltof gold commonly known as the vhlnnde of <jo!<(, but whi'h is, strictlyspeaking, a U rchiorirf/' of the metal, since it contains three equivalentsof chlorine. The most convenient way of dissolving the preciousmetal is to carefully place the required quantity in a gla.s>s fla.sk, suchas is shown in Fig. 70, and to pour upon it a mixture consisting ofabout 2 parts of hydrochloric acid and 1 partnitric acid by mrus/<r<. This mixture of acids wascalled aqua regia by the ancients because it hadthe power of dissolving the king of metals—gold.To dissolve I ounce of gold (troy weight) about4 oimces of aqua rtr/'ta will be required, but thiswill depend upon the strength of the commercialacids. Soon after the mixed acids have beenpoured on the gold, gas is evolved, and thechemical action may be accelerated by placingthe flask upon a sand-bath moderately heated.It is always advisable, when dissolving this orother metal, in order to avoid excess of acid,to apply less of the solvent than the maximumquantity in the first instance, and. when the chemical action hasceased, to pour off the dissolved metal and then add a further portionof the solvent to the remainder of the undissolved metal, and so on
Fig. 70.
164 ELECTRO-DEPOSITION OF COPPER.
means of a stout rod or strip of copper. These make-shift anodes,however, should be used for thickening1 the deposit (if an electrotype)after the mould is completely coated with copper, and not in the earlierstage of the process.
4. When it is desired to obtain an electrotype of considerable thick-ness, this may be hastened in the following way : After the completeshell is obtained, clean copper filing's are to be sifted over the surface,and deposition allowed to proceed as usual, when the newly depositedmetal will unite with the copper filings and the original shell, andthus increase the thickness of the electrotype. By repeated additionsof copper filings, folio ,ved by further deposition of copper, the backof the electrotype may be strengthened to any desired extent.
5. For coating with copper non-conducting substances, such aschina or porcelain, the following process has been adopted in France :Sulphur is dissolved in oil of spike lavender to a sirupy consistence, towhich is added either chloride of gold or chloride of platinum, dissolvedin ether, the two liquids being mixed under gentle heat. The com-pound is next evaporated until it is of the consistency of ordinarypaint, in which condition it is a|)2>Hed with a bru&h to such parts of JIchina or porcelain articlo as it i.> desired to coat with copper : thearticle i^ afterward > hakcl in the usual way, after which it is immei'Miland coated with copper in the ordinary sulphate bath.
SOLUTION FOR GTLDTNO SILVER. 167
solved in 200 parts of water. The mixture was then boiled for twohours, during which period the solution, at fh\>t yellow, assumed agreen colour, when it was complete. To apply the above solution themetal articles, of brass or copper, are first well cleaned and thenimmersed in the solution, which must be hot, for about half a minute.Articles of silver or German-silver to be gilt in this solution must beplaced in contact with either a copper or zinc wire.
Gilding by Immersion in a Solution of the Chloride of Gold.—Articles of steel, silver, copper, and some other of the baser metals,may be gilt by simply immersing them in a weak solution of thechloride of gold ; this is, however, more interesting as a fact than ofany practical value.
Gilding by Immersion in an Ethereal Solution of Gold.—Chloride of gold is soluble in alcohol and in ether. The latter solu-tion may be obtained by agitating a solution of gold with ether, afterwhich the mixture separates into two portions ; the upper stratum,which is of a yellow colour, is an ethereal solution of chloride ofgold, while the lower stratum is merely water and a little hydrochloricacid. Steel articles dipped in the ethereal solution become instantlycovered with gold, and, at one time, this method of gilding steel wasmuch employed for delicate surgical instruments, as also for the orna-mentation of other articles of steel. After being applied, the etherspeedily evaporates, leaving a film of gold upon the object. Ifthe ethereal solution be apx>lied with a camel-hair brush or quill pen,initials or other designs in gold may be traced upon plain steelsurfaces. Or, if certain portions of a steel object be protected bywax or varnish, leaving the bare metal in the form of a design, theethereal solution may then be applied to the exposed surfaces, whichwill appear in gold when the wax or varnish is dissolved or otherwisecleared away. Various ways of .applying this solution for the orna-mentation of steel ^ ill naturally occur to those who may be desirousof utilising it.
Solution for Gilding Brass and Copper.—The following formulahas been adopted for " water-gilding " as it is. termed :—
Fine gold 6^ dwts.
Convert the gold into chloride, as before, and dissolve it in 1 quart ofdistilled water, then add
Bicarbonate o f pota^sa . . . . 1 H>.
and boil the mixture for two hours. Immerse the articles to be giltin the warm solution for a few seconds up to one minute according tothe activity of the bath.
Solution for Gilding Silver.—Dissolve equal parts, by weight, ofbichloride of mercury (corrosive sublimate) and chloride of ammonium
DEPOSITION OF GOLD BY SIMPLE IMMERSTON.
until the entire quantity is dissolved without any appreciable excessof acid, after which the various solutions are to be mixed together.
The solution of chloride of gold is to be carefully poured into aporcelain evaporating dish*" (Fig. 71), and this, placed on a sand-bathor otherwise, gently heated until nearly all the acid is expelled, whenthe solution will assume a reddish hue. At this period the authorprefers to move the evaporating dish round and round gently so as tospread the solution over a large surface of the interior of the vessel:
in this way the evaporation of the acid is hastenedconsiderably. When the solution assumes a blood -red colour the dish should be gently, but repeatedly,moved about as before until the semi-fluid mass—
g. 71. which gradually becomes deeper in colour and moredense in substance—ceases to flow. Towards the end
of the operation the last remaining fluid portion flows torpidly, likemolten metal, until it finally ceases altogether, at which moment thedish should be removed from the sand-bath and allowed to cool. Itis necessary to mention that if too much heat be applied when thesolution has acquired the blood-red colour the gold will quickly becomereduced to the metallic state. If such an accident should occur thereduced metal, after dissolving out the chloride with distilled water,must be treated with a little aqua regia, which will again dissolve it.
The red mass resulting from the above operation (if properly con-ducted) is next to be dissolved in distilled water, in which it is readilysoluble, and should form a perfectly clear and bright solution of abrownish-yellow colour. If, on the other hand, the evaporation hasnot been earned to an extent sufficient to expel all the acid the solu-tion will be of a pure yellow colour. It invariably happens, afterthe chloride of gold is dissolved in water, that a white deposit re-mains at the bottom of the evaporating dish—this is chloride of sileer,resulting from a trace of that metal having been present in the gold.
Water-Gilding.—Previous to the discovery of the electrotype pro-cess and the kindred arts of electro-gilding and silvering to which itgave rise, a process was patented by Mr. G. R. Elkington for gildingmetals by the process of simple immersion or '' dipping,'' and thisprocess, which acquired the name of water-gilding, was carried on byMessrs. Elkington at Birmingham for a f~>nsiderable time with successfor a certain class of cheap jewellery. The solution was prepared asfollows: A strong solution of chloride of gold was first obtained, towhich acid carbonate of potash was added in the proportion of 1 part ofgold, in the form of chloride, to 31 parts of the acid carbonate ; to thismixture was added 30 parts more of the latter salt previously dis-
* Evaporating dishes made from Berlin porcelain are the best for thispurpose, sincft thev are not liable to "rack when heated.
FKK.NCH GILDING. i()Q
The pyrophosphate of soda is generally employed, and tins may beprepared by melting", at a white heat, ordinary crystallised phosphateof soda in a crucible. The quantity of gold given in the aboveformula represents the grammes of the pure metal dissolved by aquaregia. In making up the bath, 9 litres of water are put into a por-celain or enamelled-iron vessel, and the pyrophosphate added, withstirring, a little at a time, moderate heat being applied until all thesalt is dissolved. The solution is then to be filtered and allowed tocool. The chloride of gold must not be evaporated to dryncss, aspreviously described, but allowed to crystallise ; the crystals are to bedissolved in a little distilled water, and the solution filtered to keepback any chloride of silver that may be present in the dissolving fla^k,derived from the gold. The filter is next to be washed with theremainder of the distilled (or rain) water. The chloride solution isnow to be added to the cold solution of pyrophosphate of soda, andwell mixed by stirring with a glass rod. The hydrocyanic acid isthen to be added, with stirring*, and the whole heated to near theboiling point, when the solution is ready for use. If the pyrophos-phate solution is tepid, or indeed in any case, Itoseleur thinks it bestto add the pru^ie acid before the solution of chloride of gold is pouredin. The employment of prussie acid in the above solution is notabsolutely necessary, indeed many persons dispense ^\ith it, but thesolution is apt to deposit the gold too rapidly upon articles immersedin it, a defect which might be overcome by employing a weaker solu-tion. If the solutions are cold when mixed, the liquor is of a yellow-ish colour, but it should become colourless when heated. It sometimeshappens that the solution assumes a wine-red colour, which indicatesthat too little prussie acid has been used ; in this case the acid must beadded, drop by drop, until the solution becomes colourless. An excessof prussie acid must be avoided, since it has the effect of retarding thegold deposit upon articles immersed in the solution. The proper con-dition of the bath may be regulated by adding chloride of gold whenprussie acid is in excess, or this acid when chloride of gold predomi-nates. In this way the bath may be rendered capable of gilding\\ ithout difficulty, and of the proper colour.
"Respecting1 the working of this solution, Roseleur says, ''The bathwill produce very fine gilding upon well-cleaned articles, which mustalso have been passed through a very diluted solution of nitrate ofmercury, without which the deposit of gold is red and irregular, andwill not cover the soldered portions. The articles to be gilded mustbe constantly agitated in the bath, and supported by a hook, or placedin a stoneware ladle perforated with holes, or in baskets of brassgauze, according to their shape or size."
In gilding by dipping, it is usual to have three separate baths
168 DEPOSITION OF GOLD BY STMPLK IMMERSION.
(sal-ammoniac), in nitric acid ; now add some grain gold to the mixtureand evaporate the liquid to half its bulk ; apply it, whilst hot, to thesurface of the silver article.
Solution for Gilding Bronze, &c.—A preparatory film of goldmay be given to largo bronze articles that are to be fully gilt by eitherof the processes hereafter described, or small articles of " c h e a p "work may be gilt by immersing them in the following solution, whichmust be used at nearly boiling heat:—
Caustic potash . . . . 1S0 partsCarbonate o f potash . . . 2 0 „Cyanide o f potassium . . . 9 „Water 1,000 „
Rather more than 1J part of chloride of gold is to be dissolved inthe water, when the other substances are to be added and the wholeboiled together. The solution requires to be strengthened from timeto time by the addition of chloride of gold, and also, after beingworked four or five times, by additions of the other salts in the pro-portions given. This bath is recommended chiefly for gilding,economically, small articles of cheap jewellery, and for giving a pre-liminary coating of gold to large articles, such as bronzes, which areto receive a stronger coating in the pyrophosphate bath describedfurther on, or in cyanide solutions by aid of the battery. In thisbath articles readily receive a light coating of gold, and it will con-tinue to work for a very long period by simply adding, from time totime as required, the proper proportions of gold and the other sub-stances comprised in the formula. By keeping the bath in properorder a very large number of small articles may be gilt in it at theexpense of a very small proportion of gold.
Another method of gilding by simple immersion, applicable to brassand copper articles, is to first dip them in a solution of pro to-nitrate of mercury (made by dissolving quicksilver in nitric acidand diluting with water), and then dipping them into the gildingliquid—this plan being sometimes adopted for large articles. It issaid that copper may be gilded so perfectly by this method as toresist for some time the corrosive action of strong acids. During theaction which takes place, the film of mercury, which is electro-positive to the gold, dissolves in the auriferous solution, and a film ofgold is deposited in its place.
F r e n c h Gilding for Cheap Jewel lery .—The bath for gi lding 1<\dipping, recommended by Roseleur, is composed of—
I'yrophosphate of soda or pota«sa . . 800 grammesHydrocyanic acid of £ (pnisNie acid) . 8 ,,Gold in the form of chloride (crystallised) 20 „Distilled water 10 litres.
FRENCH GILDING. 171
position, and are then placed in a charcoal furnace in which the fuelburns between the sides and a vertical and cylindrical grate, as shownin Figs. 72—3).
The work is placed in the hollow central por-tion where the heat radiates. A vertical sectionof the furnace is shown in Fig. 73. When putinto the furnace, the salts upon the articles firstbegin to dry, after which they fuse, and acquirea dull, yellowish-red colour. On applying- themoistened tip of the finger to one of the pieces,if a slight hissing sound is heard, this indicatesthat the heat has been sufficient, when thearticle^ are at once removed and thrown brisklyinto a very weak sulphuric acid pickle, which ina short time dissolves the salts, leaving the workclear and bright, and of a fine gold colour. Itmust be borne in mind that this " colouring"process has a rather severe action upon gilt work, and should the gild-ing be a mere film, or the articles only gilt in parts, the filled saltswill inevitably act upon the copper of which thearticles are made, and strip the greater portionof the gold from the surface ; as it would be agreat risk to submit a large number of in-differently gilt articles to the colouring processunless it was known that sufficient gold hadbeen deposited upon them, although of inferiorcolour, it would be better to operate upon one ortwo samples first, when, if the result provesatisfactory, the bulk of them may then betreated as above. Some operators, when the" dipping " has not been satisfactory as to colour, give the articles aMomentary gilding with the battery in the usual way.
When it is desired to gild articles strongly by the dipping process,they are gilt several different times, being passed through a solutionof nitrate of mercury previous to each immersion ; the film of mercurythus deposited on the work becomes dissolved in the pyrophosphatebath, being replaced by the subsequent layer of gold. In this wayarticles may be made to receive a substantial coating of gold. InFrance, large articles, such as clocks, ornamental bronzes, &c, aregilt in this manner, by which they acquire the beautiful colour forwhich French clocks and goods of a similar character are so justlyfamed. Roseleur states that he has succeeded in gilding copper bythis method sufficiently strong to resist the action of nitric acid forseveral hours. When articles are >lrongly gilt by the dipping process,
DEPOSITION OF GOLD BY SIMPLE IMMERSION.
placed in succession, and close to each other, all being heated uponthe same furnace by gas or otherwise. The first bath consists of anold and nearly exhausted .solution in which the articles arc firstdipped to free them from any trace of acid which may remain uponthem after being" dipped in aqua fortis. The second bath, somewhatricher in srold than the former, is used for the next dipping1, and thearticles then receive their final treatment in the third bath. Bythus working" the baths in round*, " the fresh bath of to-day becomesthe second of to-morrow, and the second takes the place of the first,and so on. This method of operating allows of much more gildingwith a given quantity of gold than with one bath alone," and con-sequently is advantageous both on the score of economy and con-venience. The gilding is effected in a few seconds, when the articlesare rinsed in clear water and dried by means of hot sawdust, prefer-ably from white woods : they are afterwards burnished if necessary.Roseleur does not approve of boxwood sawdust for this purpose, sinceit is liable to clog the wet pieces of work, besides being less absorbentthan the sawdust of poplar, linden, or fir. The sawdust shouldneither be too fine nor too coarse, and kept in a box with two par-titions, with a lining of zinc at the bottom. The box is supportedupon a frame of sheet-iron or brickwork, which admits, at its lowerpart, of a stove filled with bakers' charcoal, which imparts a gentle anduniform heat, and keeps the sawdust constantly dry. After dryingvery small articles in sawdust, they are shaken in sieves of variousdegrees of fineness, or the sawdust may be removed by winnow-ing.
The above process of gilding by dipping, or "pot gilding," as itwas formerly called, is applied to articles of cheap jewellery, asbracelets, brooches, lockets, <fcc, made from copper or its alloys, andhas been extensively adopted in France for gilding the pretty butspurious articles known as French jewellery.
Colouring Gilt Work.—In working gold solutions employed in thedipping process, it may sometimes occur that the colour of the de-posit is faulty and patchy instead of being of the desired rich goldcolour. To overcome this, certain " colouring salts " are employed,the composition of which is as follows :—
Nitrate of potashSulphate of zincSulphate of ironAlum
Of each equal parts.
These substances are placed in an earthenware pipkin, and meltedat about the temperature of boiling water. When fused, the mixtureis ready for use. The articles are to be brushed over with the com-
GILDING WITH THE RAG. 173
receive u blight coating of gold, and thus save the necessity of 1'e-gilding the whole article. This system of " doctoring- " is sometimesnecessary, but should be avoided if possible, as it is undoubtedly afraud upon the customer, since the doctored spot must, sooner orlater, yield up its film of gold and lay bare the metal beneath.
Gilding with the Rag.—This old-fashioned process, which was atone time mu«'h used for gilding the insides of snuff-boxes, bowls ofmustard and salt spoons, Arc, is conducted as below. Instead offorming the chloride of gold in the ordinary way, the following in-gredients are taken :—
Nitric acid . . . . 5 parts.Sal-ammoniac (chloride of ammonium) . . 2 „Saltpetre (nitrate of pota^a) 1 „
A quantity of finely rolled gold is placed in a glass flask, and theother substances are then introduced ; the flask i.s next heated over asand-bath. During the action which takes place, the nitric acid de-composes the chloride of ammonium, liberating hydrochloric acid,which combines with the nitric acid, forming aqua regia, which dis-solves the gold, forming chloride ; the nitrate of potash remains mixedwith the chloride of gold. The flask is then set aside to cool: when< old, the contents of the flask are poured into a flat-bottomed dish,aud pieces of linen rag, cut into convenient squares, are laid oneabove another in the solution, being pressed with a glass rod, so thatthey may become thoroughly impregnated with the liquid. Thesquares of rag are next taken up, one by one, and carefully drained,after which they are hung up in a dark closet to dry. When nearlydry, each piece of rag. supported upon glass rods, is placed over acharcoal fire until it becomes ignited and burnt to tinder, which ispromoted by the nitrate of potash; the burning rag is laid upon amarble slab until the combustion i.s complete, when the ashes are to berubbed with a muller, which reduces them to a flue powder. Thepowder is now collected and placed between pieces of parchment,round which a wet cloth is to be folded; it is thus left for about aweek, being stirred each day, however, to ensure an equal dampingof the powder by the moisture which permeates the parchment.
To apply the powder, a certain quantity is placed on a slab andmade into a paste with water; the workman then takes up a smallportion with his thumb, "which he rubs upon the cleaned surface of thepart to be gilt; the crevices, fillets, or grooves are rubbed with piecesof cork cut to the shape required for the purpose, and the corners, orsharp angles, are rubbed with a stick of soft wood; such as willow orpoplar. When the articles have been gilt in this way, they arefinished by burnishing in the usual manner. When a red-colouredgold is required, a small portion of copper i^ added t<> the otherIngredients when preparing the salt of gold as above described.
172 DEPOSITION OF GOLD BY SIMPLE IMMERSION.
they may be scratch-brushed, or subjected to the process calledor-moultiiwj described in another place.
Gihlbiy Stiver by IMppiny, or Simple LnMCfsion.—The article1* arefirst cleaned and scratch-brushed, after which they are boiled forabout half an hour in the pyropho.sphate gilding bath, to which a fewextra drops of pmssic acid or .sulphurous acid have been added. Theformer acid dissolves a small portion of .silver from the articles, which isreplaced by an equivalent proportion of gold, while the sulphurous acidacts as a reducing agent in the gold solution, and causes the metalto deposit upon the silver from the affinity existing between the twometals, especially when one of them is in the nascent state, that i*% justdisengaged from a combination. This gilding is very fine, but with-out firmness. The deposit is rendered more rapid and thicker whenthe article* of silver are continually stirred with a rod of copper, /inc,or brass.—Rasihur. The deposition by contact of other metals, is, how-ever, due to voltaic action set up by the pyrophosphate solution, andis altogether different to the action which takes place during thesimple dipping process, in which a portion of the metal of which thearticle is composed is dissolved by the .solution, and replaced by anequivalent proportion of gold.
Preparation of the lf\-r/,- for dihluuj—As a rule, the articles shouldfirst be placed in a hot solution of caustic j>otash for a short time,to remove greasy matter, then well rinsed, and afterwards eitherscratch-brushed, or dipped in aqua fortis or kk dipping acid" for aninstant, and then thoroughly well rinsed. If the articles merelyrequire to be brightened by scratch-brushing, after being gilt, it i-only necessary to put them through the same process before gilding,which imparts to the work a surface which is highly favourable to thereception of the deposit, and which readily acquires the necessnn-brightness at the scratch-brush lathe as a finish. Articles winch areto be left with a dead or fronted surface, must be dipped in dippingacid and rinsed before being placed in the gilding bath. It is com-monly the practice to "quick " the articles, after dipping in acid, byimmersing them in a .solution of nitrate of mercury until they becomewhite ; after this dip, they are rinsed, and at once put into the bath.
Gilding by Contact with Zinc—Steele's Frocess.—In this process,a solution is made by adding chloride of gold to a solution of cyanideof potassium : in this the articles to be gilt are placed, in contact witha piece of zinc, which sets up electro-chemical action, by which thegold becomes deposited upon the articles; but since the metal alsobecomes reduced upon the zinc, the process would not be one to re-commend on the score of economy. In some cases, however, in whichit i« necessary to deposit a film of gold upon some portion of an articlewhich has stripped in the burnishing, a cyanide solution of gold maybe dropped on the spot, and this touched by a zinc wire, when it will
GILDING SOLUTIONS. 175
to gild many metallic surf aces, as tin, lead, Britannia metal, and steel,for example, which he could not accomplish satisfactorily with coldsolutions ; moreover, hot gilding solutions readily dissolve any traceof greasy matter, or film of oxide which may be present on the sur-face of the work, through careless treatment, and thus clean thesurface of the work fur the reception of the gold deposit.
Since told gilding solution* are occasionally used in electro-de-position, these will be treated separately, as also the .special purposesto which they are applied.
Preparation of Gilding Solutions.—In making up gilding bathsfrom either of the following formulae, except in such cases as will bespecified, the gold is first to be converted into chloride, as beforedirected ; but the actual weight of the pure metal required for eachspecified quantity of solution will be given in each case.
Of all the solutions of gold ordinarily employed in the operations ofelectro-gilding by the direct current, the double vyamdi of yold and putub-sitdti, when prepared from pure materials, is undoubtedly the best,and has been far more extensively employed than any other. It isvery important, however, in making up gold solutions, to employ thepurest cyanide that < an be obtained. A very good article, commonlyknown as " gold cyanide." if obtained from an establishment ofknow 11 respectability, is well suited to the purpose of preparing thesesolution^ The following formuhe are those which have been mostextensively adopted in practice; but it may be well to state that somepersons employ a larger proportion of gold per gallon of solution thanthat given, a modification which may be followed according to thetaste of the operator ; but we may say that excellent results havebeen obtained by ourselves when employing solutions containing muchless metal than some extensive firms have been known to adopt.
Gilding Solutions.—I. To make one quart of solution, convert1 \ dwt. of fine gold into chloride as before, then dissol\e the massin about half a pint of distilled water, and allow the solution to rest s(>that any trace of <lilvnd< of sihw present may deposit. Pour theclear liquor, which is of a yellow colour, into a glass vessel of 1011-\enient size, and then dissolve about half an ounce of cyanide in fourounces of cold water, and add this solution, gradually, to the chlorideof gold, stirring with a glass rod. On the fii\st addition of the cyanide,the yellow colour of the chloride solution will disappear, and on freshadditions of the cyanide being made, a brownish precipitate ^ ill boformed, when the cyanide solution must be added, gradually, untilno further precipitation takes place. Since the precipitate is freelysoluble in cyanide of potassium, great care must be exercised not toadd more of this solution than is nercss.irv to throw down the nicHlin the turm of cyanide of yold. To determine the right point at which
CHAPTER X.
ELECTRO-DEPOSITION OF GOLD.
Gilding by Tirect Current, or Klectro-Gilding.—Preparation of Gilding Solu-tions.— Gilding Solutions: Becqiierel's.— Fizeau's.—Wood's.—M. deBriant's. — French Gilding Solutions. — Gilding Solutions made bythe Battery Process.—De Ruol/s.—Cold Electro-Gilding Solutions.—Observations on Gilding in Cold Baths.—Ferrocyanide Gilding Solu-tion.—Watt's Gilding Solution.—Kecoid'b Gilding Bath.
Gilding by Direct Current, or Electro-gilding.—Iu gilding bydipping, or .simple immersion, it is obvious that, as a rule, only alimited amount of gold can be deposited upon the work, and thatthe application of this method of gilding, therefore, must be confinedto cheap classes of A\ ork, or to articles which will not be subjected tomuch friction in use. In gilding by the separate current, on the otherhand, we are enabled to deposit the precious metal not only of anyrequired thickness, but also upon many articles which it would bepractically impossible to gild properly by simple immersion in a solu-tion of gold.
Electro-gilding is performed either with hot or cold solutions ; butfor most practical purposes hot solutions are employed. When goldis deposited from void solutions, the colour of the deposited metal isusually of a yellow colour, and not of the rich orange -yellow tintwhich is the natural characteristic of fine gold. the deposit, more-over, is more crystalline, and consequently more porous in cold thanhot solutions, and is therefore not so good a protective coating to theunderlying metal. The gold deposited from hot solutions is not onlyof a superior colour and of closer texture, but it is also obtained withmuch greater rapidity ; indeed, from the moment the articles are im-mer.sed in the gilding bath, all things being equal, the colour, thick-ness, and rapidity of the deposit are greatly under the control of theoperator. In a few seconds of time an article may be gilded of thefinest gold colour, with scarcely an appreciable quantity of theprecious metal, while in the course of a very few minutes a coating ofsufficient thickness may be obtained to resist a considerable amountof wear.
The superior conductivity of hot gilding solutions enables the operator
FRENCH GILDING SOLUTIONS. •77
IV. FizcaiCs Solutions. — (i.) i part of dry chloride of gold isdissolved in 160 parts of distilled water ; to this is added, gradually,solution of a carbonated alkali in distilled water, until the liquidbecomes cloudy. This solution may be used immediately. (2.) 1gramme of chloride of gold and 4 grammes of hyposulphite of sodaare dissolved in 1 litre of distilled water.
V. Wood's Solution. — 4 ounces (troy) of cyanide of potassiumand 1 ounce of cyanide of gold are dissolved in r gallon of dis-tilled water, and the solution is used at a temperature of about 900
Fahr., with a current of at least two cells.VI. M. (h JiruinVs Solution.—The preparation of this solution is
thus described: ''Dissolve 34 grammes of gold in aqua regia, andevaporate the solution until it becomes neutral chloride of gold ; thendissolve the chloride in 4 kilogrammes of warm water, and add to it200 grammes of mngnesia : the gold i.s precipitated. Filter, and washwith pure water; digest the precipitate in 40 parts of water mixedwith 3 parts of nitric acid, to remove magnesia, then wash tl eremaining [resulting] oxide of gold, with water, until the wash-waterexhibits no acid reaction with test-paper [litmus-paper], Nextdissolve 400 grammes of ferrocyanide of potassium [yellow prussiate (fpotash] and 100 grammes of caustic potash in 4 litres of water, addthe oxide of gold, and boil the solution about twenty minutes. Whenthe gold is dissolved, there remains a small amount of iron precipitatedwhich may be removed by filtration, and the liquid, of a fine goldcolour, is ready for use ; it may be employed either hot or cold."
VII . Ftench Gilding Solution*.—The following solutions are recom-mended by Roseleur as those which he constantly adopted in practice—a sufficient recommendation of their usefulness. In the first of theseboth phosphate and bisulphite of soda are employed, with a smallpercentage of cyanide. The first formula is composed of—
Phosphate of soda (crystallised) . 60 partsBisulphite o f soda . . . . 1 0 „Cyanide of potassium (pure) . . 1 partGold (converted into chloride) . 1 „Distilled or rain water . . . 1,000 parts.
The second formula consists of—Phosphate o f soda . . . . 5 0 partsBisulphite of soda . : . . 12A „Cyanide of potassium (pure) . . h partGold 1 „Distilled water . . . . 1,000 parts.
In making up either of the above baths, the phosphate of soda isfirst dissolved in 800 parts of hot water ; when thoroughly dissolved,the solution should be filtered, if not quite clear, and allowed to cool.
i 7 6 ELECTRO-DEPOSITION OF GOLD.
to stop, the precipitate should now and then be allowed to fall, sothat the clear .supernatant liquor may be tested with a drop of thecyanide solution, delivered from one end of the glass rod; or a portionof the clear liquor may be poured into a test tube, or other glass vessel,and then tested with the cyanide. If cyanide has been accidentallyadded in excels, a little more chloride of gold must be added to neutraliseit. The precipitate must be allowed to settle, when the supernatantliquor is to be poui'ed off, and the precipitate washed several timeswith distilled water. Lastly, a little distilled water is to be added tothe precipitate, and a sufficient quantity of cyanide solution poured into dissolve it, after which a little excess of cyanide solution must beadded, and the solution then made up to one quart with distilledwater. Before adding the final quantity of water, however, it is agood plan, when convenient to do so, to pour the concentrated solu-tion into an evaj>orating* dish, and to evaporate it to dryness, whichmay be most conveniently done by means of a sand-bath, after whichthe resulting mass is to be dissolved in one quart of hot distilledwater, and, should the solution work slowly in gilding, a little morecyanide must be added. The solution should be filtered before using,and must be worked hot, that is at about 1300 Fahr.
II . Take the same quantity of gold, and form into chloride asbefore, and dissolve in half a pint of distilled water ; precipitate thegold with ammonia, being careful not to add this in excess. The pre-cipitate i* to be washed as before, but must not be allowed to becomedry, since it will explode with the slightest friction when it is in thatstate. A strong solution of cyanide is next added until the precipi-tate is dissolved. The concentrated solution is now to be filtered, andfinally, distilled water added to make one quart. Of course it willbe understood that the quantity of solution given in this and otherformula? merely rejjresents the basis upon which larger quantities maybe prejNired. This solution must nut be evaporated to dryness.
III. J)tcq(fcrd\s holntivH.—This is composed of—
Chlot ide o f i^old . . . . 1 p a r t
F e r r o c y a n i d e of potass ium . . 10 p a r t s
W a t e r . . . . . . 1 0 0 „
The above salts are first to be dissolved in the water : the liquid isthen to be filtered; 100 parts of a saturated solutiou of ferrocyanideof potafebium are now to be added, and the mixture diluted withonce or twice its volume of water. " I n general, the tone of thegilding varies according as this solution is more or less diluted ; thecolour is most beautiful when the liquid is most dilute, and most freefrom iron [from the ferrocyanide]. To make the surface appearbright, it is sufficient to wash the article in water acidulated withsulphurii- acid, rubbing it gently with a piece of cloth.'*
SOI/TTTOXS MADE BY THE BATTERY PROCESS. 1 7 9
VTTI. Uihhu'f Solutions Made b>j the lhittenj P/v^v.ss.— Tlie systemof forming gold solution*. l>y electrolysis has much to recommend it ;tlie process is simple in itself : it requires but little manipulation, amiin inexperienced hands is less liable to involve waste of gold than theordinary chemical methods of preparing gilding solutions. A tr<*1*1hath made by the battery process, moreover, it' the cyanide be of goodquality, is the purest form of .solution obtainable. To prepare thesolution, dissolve about I pound of good cyanide in i gallon of hotdistilled water. When all is dissolved, nearly till a perfectly cleanand nnv porous cell with the cyanide solution, and stand it upright inthe vessel containing the hulk of the solution, taking care that theliquid stands at the same height in each vessel. Next attach a cleanblock of carbon or strip of clean sheet copper to the negative pole of avoltaic battery, and immerse this in the porous cell. .V irold anodeattached to the positive pole is next to be placed in the bath, and thevoltaic action kept up until about I ounce of gold has been dissolvedinto the solution, which is easily determined by weighing the iruldboth before and after immersion. The solution should be maintainedat a temperature of 1303 to 150" Fahr. while it is under the actionof the current.
Another method of preparing- gold solutions by the battery process,is to attach a large plate of gold to the positive, and a similar plateof gold or block of carbon to the negative electrode, both being im-mersed in the hot cvanide solution as above, and a current from 2Darnell cells parsed through tlie liquid. The negative electrodeshould bo replaced by a clean cathode of sheet Herman silver for a fewmoments occasionally, to ascertain whether the solution i^ richenough in metal to yield a deposit, and when the solution is in a con-dition to yild German silver promptly, with an anode surface of aboutthe same extent, the bath may be considered ready for use. Theproportion of gold, per gallon of solution, may be greatly varied,from -, an ounce, or even less, to 2 ounces of gold per gallon of solutionbeing employed, but larger quantities of cyanide must be used inproportion. While the gold is dissolving into the solution, the liquidshould be occasionally stirred. The bath should be worked at from130' to 150° Fahr., the lower temperature being preferable. Inmaking solutions by the battery process, the position of the anodeshould be shifted from time to time, otherwise it is liable to be cutthrough at the pait nearest the surface of the solution (the waterhne)where the electro-chemical action is strongest. A good way toprevent this is to pun -h a hole at each corner of the gold anode, andalso a hole midway between each of the corner holes, through whichthe supporting hook may be successively passed ; this arrangementwill admit of eight shiftings of the anode. Another plan is to connect
iy8 ELECTRO-DEPOSITION OF GOLD.
The gold having been converted into solid chloride, is next to be dis-solved in ioo parts of water, and the bisulphite of soda and cyanidein the remaining ioo parts. The solution of gold is now to be pouredslowly, with stirring, into the phosphate of soda solution, whichacquires a greenish-yellow tint. The solution of bi&ulphite of sodaand cyanide is next to be added, promptly, when the solution becomescolourless and is ready for use. If the Mention of phosphate of sodais not allowed to become cold before the chloride of gold is added, aportion of this metal is apt to become reduced to the metallic state.Roseleur considers it of irrcut importance to add the various solutionsin the direct order specified.
The first-named bath is recommended for the rapid gilding ofarticles made from silver, bronze, copper, and German .silver, or otheralloys of copper. The second bath is modified so as to be suitable for gild-ing steel, as also cast and wrought iron directly ; that is, without beingpreviously coated with copper. The solutions are worked at a temper-ature of from 122° to 1760 Fahr. In working the first bath, Roseleursays, " Small articles, such as brooches, bracelets, and jewellery-warein general, are kept in the right hand with the conducting wire, andplunged, and constantly agitated in the bath. The left hand holdsthe anode of platinum wire, which is immersed more or less in theliquor according to the surface of the articles to be gilt. Large piecesare su.spended by one or more brass rods, and, as with the platinumanode, arc moved about. The shade of the gold deposit is modifiedby dipping the platinum anode more or less in the liquor, the palertints being obtained when a small surface is exposed, and the darkershades with a larger surface. Gilders of small articles generallynearly exhaust their baths, and as soon as they cease to give satisfac-tory results, make a new one, and keep the old bath for coloured golds,or for beginning the gilding of articles, which are then scratch-brushed and finished in a fresh bath. Those who gild large piecesmaintain the strength of their baths by successive additions ofchloride of gold, or, what is better, of equal parts of ammoniuret ofgold and cyanide of potassium." Articles of copper or its alloys,after being properly cleaned, are sometimes passed through a veryweak solution of nitrate of mercury before being immersed in thegilding* bath.
The above system of working without a gold anode is certainlyeconomical for cheap jewellery, or such fancy articles as merelyrequire the colour of gold upon their surface : but it will be readilyunderwood that solutions worked with a platinum anode would beuseless for depositing a durable coating of gold upon any metallicsurface, unless the addition of chloride of gold were constantlymade.
COLD ELECTRO-GILDING SOLUTIONS. 181
which it readily dissolves, and this may be conveniently done, if alarge filter is Ubed, by pouring it on to the wet precipitate while inthe filter, a portion at a time, until the aurate of ammonia has disap-peared, and the whole of the cyanide solution has passed throughthe filter. This will be a safer plan than removing the precipitatefrom the filter ; or the filter may be suspended in the cyanide solutionuntil the aurate is all dissolved. The solution is finally to be boiledfor about an hour, to drive off excess of ammonia.
After this solution has been worked for some time it is apt tobecome weaker in metal, in which case it must be strengthened byadditions of aurate of ammonia. For this purpose, a concentratedsolution of the gold salt in cyanide of potassium is kept always athand, and small quantities added to the bath from time to time whennecessary. It is preferable to employ good ordinary cyanide inmaking up the bath, and pure cyanide for the concentrated solution.
2. This solution is composed of—
Fine gold . . . .Pure cyanide of potassiumOr commercial cyanide .Distilled water
10 parts20 „30 to 40 parts
. 1,000 parts.
The gold is to be formed into chloride and crystallised, as before,and dissolved in about 200 parts of the water ; the cyanide is next tobe dissolved in the remainder of the water, and, if necessary, filtered.The solutions are now to be mixed and boiled for a short time. Whenthe solution becomes weakened by use, its strength is to be aug-mented by adding a strong solution of cyanide of gold, prepared byadding a solution made from I part of solid chloride dissolved in alittle water, and from I to IT parts of pure cyanide of potassium,also dissolved in distilled water, the two solutions being then mixedtogether.
3. This solution consists of—
Ferrocyanide of pota^ium (yellow prussiate of potash) 20 partsPure carbonate o f pota&h . . . . . 3 0 „Sal-ammoniac . 3 „Gold . . . . . . . . 1 5 „Water 1,000 „
All the salts, excepting the chloride of gold, are to be added to thewater, and the mixture boiled, and afterwards filtered. The chlorideof gold is next to be dissolved m a little distilled water and added tothe filtered liquor. Some persons prefer employing the aurate ofammonia in place of the chloride of gold, and sometimes small
I So ELECTRO-DEPOSITION OF GOLD.
a stout platinum wire or a bundle of fine wires to the anode by meansof gold solder, and to immerse the whole of the anode in the cyanidesolution ; this is a very good plan for dissolving the gold uniformly,since the platinum is not acted upon by the cyanide. Sometimesgold wires are used to suspend the anode, in which case the wireshould be protected from the action of the cyanide by slipping a glasstube or piece of vulcanised india-rubber tubing over it.
IX. De Muolz's Solution.—io parts of cyanide are dissolved in iooparts of distilled water, and the solution then filtered ; I part ofcyanide of gold, carefully prepared and well washed, and dried out ofthe influence of light, is now added to the filtered solution of cyanide.It is recommended that the solution be kept in a closed vessel at atemperature of 6o° to 77° Fahr. for two or three days, with frequentstirring, and away from the presence of light.
X. Cold Electro-gilding Solutions.—The cold gilding bath is some-times used for very large objects, as clocks, chandeliers, &c, to avoidthe necessity of heating great volumes of liquid. As in the case ofhot solutions, the proportions of gold and cyanide may be modifiedconsiderably. Any double cyanide of gold solution may be used cold,provided it be rich both in metal and its solvent, cyanide of potassium,and a sufficient surface of anode immersed in the bath during electro-deposition. For most practical purposes of cold gilding, the followingformulae are recommended by Roseleur:—
Fine gold . 10 partsCyanide of potassium of 70 per cent. . . 30 „Liquid ammonia 50 „Distilled water . . . . . . 1,000 „
The gold is converted into chloride and crystallised, and is then dis-solved in a small quantity of water; the liquid ammonia is now tobe added, and the mixture stirred. The precipitate, of a yellowishbrown colour, is aurate of ammonia, ammoniurct of gold', or fulminatinggold, and is a highly explosive substance, which must not on anyaccount be allowed to become dry, since in that state it would detonatewith the slighcst friction, or an accidental blow from the glass stirrer.Allow the precipitate to subside, then pour off the supernatant liquorand wash the precipitate several times ; since the washing waters willretain a little gold, these should be set aside in order that the metalmay be recovered at a future time. The same rule should apply toall washing waters, either from gold or silver precipitates. Theaurate of gold is next to be poured on a filter of bibulous paper, thatis filtering paper specially sold for such purposes. The cyanideshould, in the interim, have been dissolved in the remainder of thewater. The cyanide solution is now to be added to the precipitate,
OBSERVATIONS ON GILDING IN COLD BATHS. 183
portions of the work appear patchy or spotted, the pieces must beremoved from the hath, rinsed, and well scratch-brushed. As in hotgilding, the plater will find the scratch-brush his best friend whenthe work presents an irregular appearance.
It is not advisable to employ a current of high intensity in coldgilding; the Wollaston or Daniell batteries, therefore, are mostsuitable, and when a series of cells are required to gild large surfacesor a considerable number of objects, the poles of the batteries shouldbe connected in parallel, that is all the positive electrodes should beconnected to the anodes, and all the negative electrodes put in com-munication with the conducting-rod supporting the work in the bath.After deposition has taken place to some extent, an extra cell may N«connected, followed by another, if necessary, and so on; but whileonly a thin coating of gold is upon the work, the strength of thecurrent should be kept low ; deposition takes place more slowly upongold than upon copper or its alloys, therefore an increase of batterypower becomes a necessity after a certain thickness of gold has been de-posited. If the current be too weak, on the other hand, the deposit isapt to occur only at the prominent points of the article, and upon thoseportions* which are nearest the anode. It .sometimes happens, withnewly made baths, that when the articles arc shifted to expose freshsurfaces to the anode, the gold already deposited upon the workbecomes dissolved off: when .such is the case, it generally indicatesthat there is too great an ex< es> of cyanide in the solution, althoughthe same result may occur it' there be too little gold or the current toofeeble.
When the gold deposited in a cold bath is of an inferior colour, thoarticle may be dipped in a weak solution of nitrate of men ury until itis entirely white : it i^ then to be heated to <. \p<.l the nier< ury, andafterwards scratch-brushed. Or the article iu.i\ be brushed <»\ei withthe "green colour,'1 described in another «h.ipUr, and tieated in thesame way as bad-coloured gilding from hot solutions.
XI . 1<t't'ocytuudc (j\Uh)nj Solution.—To a"\oid the use of larii'e quan-tities of cyanide of potassium in gilding solutions, the followingprocess has been proposed: In a vessel, capable of holding 4 litres,are dissolved in distilled water 300 grammes of ferrocyanidc o±potassium, and 50 grammes of sal-ammoniac: 100 grammes of gold,dissolved in aqua regia and evaporated to e\pel the acid as usual,are dissolved in 1 litre of distilled water. Of this solution, 200cubic centimetres are added, little by little, to the ferrocyanide solu-tion, when oxide of iron (from the ferrocyanide) is precipitated.Tho liquid is allowed to cool, and is then filtered and made up to 5litres, when the bath is ready for use. Since it is not a good u>n-ductor, however, and deposits oxide of iron upon the anode, a small
182 ELECTRO-DEPOSITION OF GOLD.
quantities of pruwc acid are added to the bath, to improve the bright-ness of the deposit ; but tlii> acid makes the bath act more slowly.
The deposit of gold from eold solutions varies greatly as to colour.When the bath is in its best working condition, and a brisk currentof electricity employed, the gold should be of a pure yellow colour:sometimes, however, it is several shades lighter, being of a paleyellow; it sometimes happens that the gold will be deposited of anearthy grey colour, in which case the articles require to be eautiouslyscrateh-brushed, and afterwards coloured by the or-moulu process tobe described hereafter. The proportion of cyanide in these bathsshould be about twice that of the chloride of gold; but since thecyanide K of variable quality, it may oft on be necessary to employ anexcess, which is determined by the colour of the deposit: if the goldis in execs-, the deposit m.iv be of a blackish or dark red colour; or if,on the contrary, cyanide preponderates, the operation is slow andthe gold of a dull grey colour, and not unfrequently, when the bathis in this condition, the gold becomes re-dissolved from the work insolution, either entirely or in patches.
When the bath is not in good working order, 1he gold anode mustbe withdrawn from the solution, otherwise it will become dissolved bythe cyanide. It is a <% remarkable phenomenon," s.tvs Koseleur,' ' tha t solutions of cyanide*, even without the action of the electriccurrent, rapidly dissolve in the cold, or at a moderate temperature, allthe metals, except platinum, and that at the boiling point they havescarcely any action upon the metals."
Obscii(itwns o)i (Jihhufj ut fold Baths.—When a pure yellow colouris desired, a newly-prei^ared double cyanide of gold solution, inwhich a moderate excess only of cyanide is present, and containingfrom I to 2 ounces of gold per gallon, will yield excellent results withthe current from a single Wollaston or Daniell battery : but suffi-cient anode must be exposed w (ho soh(/io» to admit of the deposittaking place almost immediately after the article is immersed in thebath. The anode may then be partially raised out of the solution,and the deposition allowed to take place without further interferencethan an occasional shifting of the object to coat the spot where theslinging wire touches. After the article has been in the bath aminute or so, the operator may assure himself that deposition is pro-gressing satisfactorily by di]J>2>ing a piece of clean silvered copper wirein the bath and allowing it to touch the object being gilt, when, ifthe end of the wire becomes coated with gold, he may rest .issiiredthat deposition is proceeding1 favourably. Oarc must be taken, how-ever, tli:il the deposit is not taking place too rapidily, for it is abso-lutely necessary that the action should be gradual, otherwise th<« u«>Mmay strip off under the operation of the scratch-brush. If any
CHAPTER XL
ELECTRO-DEPOSITION OF GOLD {continued).
General Manipulations of Klectro-gilding.—Preparation of the Work.—DeadGilding.—Ctui-es which affect the Colour of the Deposit.—GildingGold Article^—Gilding Insides of Vessels.—Gilding Silver FiligreeWork.—Gilding Army Accoutrement Work.—Gilding German Silver.—Gilding Steel.—Gilding Watch Movements.
General Manipulations of Electro-Gilding.—In small gildingoperations, the apparatus and arrangements arc of an exceedinglywimple character, and need not involve more than a trifling: outlay.A 12-inch Danieil cell, or a Miiall battery (say a half-gallon cell), con-structed as follows, will answer well for gilding such small work asAlbert chains, watch eases, pins, ring's, and other work of smalldimensions. This battery consists of a stone jar,•within which in placed a cylinder of thin sheet -copper, having- a binding screw attached. "Withinthih cylinder is placed a porous cell, furnished witha plate or bar of amalgamated zinc, to the upper endof which a binding screw is connected. A dilutesolution of sulphuric acid is poured into the porous cell, and anearly .saturated solution of sulphate of COJ XT, moderately acidifiedwith sulphuric acid. is. poured into the outer cell. This {simple butter}'costs very little, i» very constant in action, and may readily beconstructed by the amateur or small operator. The gilding bathmay consist of one quart of solution, prepared from any of the for-muhe given ; a square piece of roiled srold, about 2 by 2 inches,weighing about rive pennyweights, or even le&s, will serve for theanode; and an enamelled iron saucepan may be used to contain thesolution. Since gilding" baths require to be used hot (about 130Fahr.), except for special purposes, the solution may be heated bymean.s of a small 4-buraer oil lamp, such as is shown in Fig-. 74,the gilding vessel being* supported upon an iron tripod or ordinary-meat stand.
With this simple arrang'ement, it is quite possible to gild bucharticles as we have named, besides smaller articles, such as broofhoslockets, and fccarf-pin> ; and provided the gold anode be replaced; at
184 ELECTRO-DEPOSITION OP GOLD.
quantity of cyanide is added, but not sufficient to evolve hydrocyanicacid on boiling. The bath should be worked at from ioo° to 1500
Fahr. When the bath ceases to yield a good deposit, 200 c.c. of thegold solution must be added gradually, as before; if it is desired toincrease this proportion of gold, one-tenth of the quantity of theother salts must also be added to the bath.
Xlf. IFatCs Gilding Solution.—A gilding solution which the authorhas use 1 very extensively, and which he first adopted about the year1838, is formed as follows : 1} pennyweight of fine gold is convertedinto chloride, ns before described, and afterwards dissolved in about] pint of distilled water. Sulphide of ammonium is now addedgradually with stirring, until all the gold is thrown down in the formof a brown precipitate. After repose the supernatant liquor is pouredoff, and the precipitate washed several times with distilled water ; itis then dissolved in a strong solution of cyanide of potassium, amoderate excess being added as free cyanide, and the solution thusformed is diluted with distilled water to make up one quart. Beforeusing this solution for gilding it should be maintained at the boilingpoint for about half an hour, and the loss by evaporation made upby addition of distilled water. This bath yields a fine gold colour,and if strengthened from time to time by a moderate addition ofcyanide, will continue to work well for a very considerable period.; itshould be worked at about 1300 Fahr. The above solution gives verygood results with a Daniell battery, and the articles to be gilt do notrequire qnu'lun/, as the deposit is very adherent.
XIII. lieeonVs (iihlini/ Jl«th.—This solution, for which a patent wasobtained 111 1884, is formed by combining nickel and gold solutions,by which, the patentee avers, a considerable saving of gold is effected.To make this solution, lie dissolve^ 5 ounces of nickel salts in about2 gallons of water, to which 12 ounces of cyanide of. jxitassium isadded, " so that the nickel salt* may be taken up quite clear." Thesolution is then boiled until the ammonia contained in the nickel saltsis entirely tvajx>rated. This solution is then added to the ordinarygold solution containing 1 ounce of gold. The proportions given an.preferred, but may be varied at will.
ELECTRO-GILDING. .37
in the accompanying engraving", Fig. 75. The gilding bath restsupon a short-legged iron tripod, beneath which is a perforated gasburner, supplied with gas by means of flexible india-rubber tubingconnected to an ordinarygas-burner. Perforatedburners are readily pro-curable, and are of triflingcost. For brighteningsmall articles the handscratch-brush referred to(Fig. ;0) may be used,
Fig- 75-but, for the convenienceof handling, it should betied to a stick, to prevent it from bending in the hand. The brushis to be dipped in soap-suds or stale beer frequently while being ap-plied to the work.
In gilding upon the above moderate scale, however, the lathescratch-brush, described further on, will be as necessary as in stilllarger operations: an ordinary foot lathe, such as is used in silverplating (which see), is the machine generally used for thispurpose, and is of very simple construction. Such lathes, ortheir chief parts, may often be procured second hand for avery moderate sum. As in scratch-brushing electro-silveredor plated work, stale beer is employed to keep the brushesconstantly wet while the lathe is being used, and the worki-> pressed very lightly against the revolving brushes. It isimpoitant, however, when the scratch-brushes are new,that they should have some hard metallic surface pressedagainst them while in brisk motion for a few minutes, tospread them well out or make them brushy, and to reduce jthe extreme harshness of the newly-cut brass wire ; if thisprecaution be not followed, the gold, if the coating bethin, may become partially removed from the gilt article, renderingit> surface irregular and of an indifferent colour, necessitating regild-inir and scratch-brushing.
Preparation of the Work.—In electro-gilding watch chains ofvarious kinds, brooches, lockets, scarf-pins, and other small articles*of jewellery, it is generally sufficient to well scratch-brush and rinsethem, after which they are at once put into the bath. A preparatorydip in a hot potash bach, however, may be resorted to. After scratch-brushing, a short length of copper ' 'slinging" wire i& attached tothe article, and the free end is connected to the negative electrode ofthe battery by dimply coiling it around the stouter wire several time^the ends of both wires, however, should previously be cleaned by
jr. 76.
iS6 ELECTRO-DEPOSITION OP GOLD.
it becomes "worn a w a y " in use, and the solution kept up to itsnormal height by additions of distilled water to make up for loss byevaporation, the same bath will be capable of gilding a good amountof small work. The bath will, however, require small additions ofcyanide every now and then, that is when it shows signs of workingslowly, or yields a deposit of an indifferent c Aouv; the batteiy, also, willneed proper attention by renewal of the dilute acid occasionally. Inworking on the small scale referred to, in the absence of a proper scratch -brush lathe, the hand " scratch-brush," Fig. 76, may be resorted to :this consists simply of a single scratch-brush, cut o])cn at one end, andspread out before using, by well brushing it against some hard metalsubstance : to mollify the extreme harshness of the newly cut brasswire, of which the brush is composed, it may advantageously be rubbedto and fro upon a hard flagstone, after which it should be rinsed beforeusing. To apply the hand scratch-bru.sh, prc2>are a little warm soapand water, into which the brush must be dipped frequently while beingused. In brushing Albert chains or similar work, the swivel may behooked on to a brass pin, driven into the corner of a bench or table,while the other end of the chain is held in the hand ; while thusstretched out, the moistened brush is dipped in the suds, and lightlypassed to ami fro from end to end, and the position of the article mustbe reversed to do the opposite side ; to brush those parts of the link*,which cannot be reached while the chain is outstretched, the chain isheld in the hand, and one part at a time passed over the first finger, bywhich means the unbrightened parts of the links may be readilyscratch-brushed. It is important, in scratch-brushing, to keep thebrush constantly and freely wetted as abo\ e.
Gilding on a somewhat larger scale- say with our or two gallonsof gold solution—may be pursued without any very great outlay, andyet enable the gilder to do a considerable amount of wm-k <>f variouskinds and dimensions in the course of an ordinary working day. Thearrangement we would suggest may be thu.- briefly explained: forthe battery, a one-gallon Bunsen, or Smec, or an 18-inch Daniellcell; for the anode, two or more ounces of fine gold rolled to about6 by 3 inches, to which a stout piece of platinum wire, about 4 inchesin length, should be attached by means of gold solder. A smallbinding screw may be employed to connect the platinum wire withthe positive electrode of the battery. The object of using platinumwire is to enable the ivholc of the anode to be immersed in the solutionwhen a large surface is necessary, and which could not be properlydone if copper wire were used, since this metal (unlike platinum,which is not affected by the solution) would become dissolved by thebath, and affect the colour of the deposit. A simple method of heat-ing tlie gilding solution and keeping it hot while in u&e will be seen
CAUSES WHICH AFFECT THE COLOUR OF THE DEPOSIT. 189
quicking bath immediately after they have been rinsed from the aciddip.
The surface of articles may be rendered still more dead, or frosted,by slightly brushing them over with finely powdered pumice, or, stillbetter, ordinary bath brick reduced to a powder. By this means theextreme point of dulness, or deadness, may be reached with very littletrouble. Work which requires to be burnished after gilding shouldfirst be steeped in the potash bath, and after rinsing be well scratch -brushed, or scoured with silver sand, soap, and water, when, afteragain rinsing in hot water, it is ready for the bath. In scouring thework with sand and soap, it is necessary to use warm water freely ;the soap may be conveniently applied by fixing a large piece of thismaterial—say X lb. of yellow soap—to the scouring-board by meansof four upright wooden pegs or skewers, forming a square aboutl\ inches each way, within which the soap may be secured firmly,and will retain its position until nearly used up. By this simple planthe soap, being a fixture, may be rubbed with the scouring-brush, asoccasion may require, without occupying a second hand for thepurpose.
Causes which Affect the Colour of the Deposit.—In the opera-tion of gilding, the colour of the deposit may be influenced almostmomentarily in several ways. Assuming that the current of elec-tricity is neither too strong nor too weak, and the bath in perfectorder, if too small a surface of anode is immersed in the bath, thegold deposit will be of a pale yellow colour. Or, on the other hand,if too large a surface of anode is exposed in solution, the depositmay be of a dark brown or "foxy" colour, whereas the mean be-tween these two extremes will cause the deposit to assume the richorange-yellow colour of fine or pure gold. Again, the colour ofthe deposit is greatly affected by the motion of articles while inthe bath : for example, if the gilding be of a dark colour, by brisklymoving the articles about in the bath, they will quickly assume theproper colour. The temperature of the solution also affects the colourof the deposit, the tone being deeper as the solution becomes hotter,and vice versa. The colour of the gilding is likewise much affectedby the nature of the current employed. A weak current from aWollaston or Daniell battery may cause the deposit to be of a palercolour than is desired, whereas a Smee, Grove, or Bunsen (but moreespecially the latter) will produce a deposit of a far richer tone. Thepresence of other metals in the solution, but copper and silver moreparticularly, will alter the colour of the deposit, and therefore it isof the greatest importance to keep these metals out of the ordinarygilding solution by careful means. When gilding in various coloursis needed, recourse must be had to the solutions described elsewhere,
iS8 ELECTRO-DEPOSITION OF GOLD.
means of a piece of emery cloth. When the articles are first dippedinto the solution, they should be gently moved about, so that thedeposit may be regular. Chains should be shifted from their positionoccasionally, so that those portions which are in contact with eachother may become gilt; this may generally be done by giving thechain a brisk shake from time to time, and also by slipping the chainthrough the loop of the slinging wire. If brooches and other similararticles are slung by a loose loop of wire, gentle shaking is all that isnecessary to shift their position on the slinging wire.
Some operators, when gilding metal chains or other work manufac-tured from copper or its alloys—brass, gilding metal, and Germansilver—prefer to quick them after steeping in the potash bath andscratch-brushing. In this case it will be necessary to have a quickingbath or "mercury dip " always at hand. The mercury dip consistsof a very dilute solution of nitrate or cyanide of mercury, and afterthe articles have been whitened in this bath, they must be well rinsedin clean water before being immersed in the gilding bath. The objectof mercury dipping is to ensure a perfect adhesion of the gold deposit.The author has never, either in electro-gilding or silvering, found itnecessary to apply the quicking process, but the solutions both ofgold and silver were not prepared in the same way as those ordinarilyadopted by the trade. The solutions which the author worked for agreat number years without the aid of the mercurial coating are men-tioned in the chapters describing the preparation of gilding andsilvering baths.
Dead Gilding.—There are several methods of preparing the work sothat the deposit instead of being more or less bright when removed fromthe gilding-bath,may present a dead or fi'osted appearance, which is notonly exceedingly beautiful in the rich dulness of its lustre, but isabsolutely necessary for certain classes of work, portions of which arerelieved by burnishing. To obtain a deposit of a somewhat deadlustre, copper and brass articles are dipped for a moment in a mixtureof equal parts of oil of vitrol and nitric acid, to which is added asmall quantity of common salt. The articles are slung on a stout wire,coiled into a loop, and dipped in the nitro-sulphuric acid " dip " foran instant, and immediately rinsed in clean water, kept in a vesselclose to the dipping acid : if not sufficiently acted upon during thefirst dip, they must be again steeped for a moment, then rinsed inseveral successive waters, and at once put into the gilding bath.There should be as little delay a possible in transferring the articlesto the gold bath, after dipping and rinsing, since copper and its alloys,after being cleaned by the acid and rinsed, are very susceptible ofoxidation, even a very few moments being sufficient to tarnish them.If the mercury dip is employed, the work must be dipped in the
GILDING IXSIDES OF VESSELS. IOI
in whose hands such work may sometimes be placed for restorationor recolouring.
Gilding Gold Articles.—Although **painting1 the lily" wouldnot be a very profitable or succcs.>ful operation, articles made frominferior gold alloys are frequently .sent to the electro-gilder tobo »* coloured," that is to receive a .slight film of pure gold, tomake them look like gold of a superior (quality, like rohttre/f f/o/d,in fact. Although such an imposition I1* a positive fraud upon thepurchaser, the electro-gilder has little choice in the matter; if hisnatural scruples would tempt him to refuse such unfair work, as itmay be called, he knows full well that others will readily do the workand "ask no questions;" he must therefore undertake it or lose acustomer—perhaps an important one. Albert chains, rings, pins,brooches, and a host of other articles manufactured from gold alloysof very low standard, are frequently " coloured " by electro-deposition,simply because the process of colouring by means of the '* colouringsalts " would rot them, if not dissolve them entirely.
Gilding Znsides of Vessels.—Silver or electro-plated cream ewers,sugar-basius, mugs, \.<\, are electro-gilt inside in the following wav:The inside of the vessel is first well scratch-brushed, for which pur-pose a special scratch-brush, called an end-brush, is used. Or thissurface may be scoured with soap andwater with a piece of stout flannel; thevessel, after well rinsing, is then placedupon a level table or bench ; a goldanode, turned up in the form of ahollow cylinder, is now to be connectedto the positive electrode of a battery, andlowered into the vessel, and supported inthis position, care being taken that itdoes not touch the vessel at any point.
Fig. 77.
The negative electrode isto be placed in contact with the vessel (Fig. 77). and hot gold solu-tion then carefully poured in, up to its extreme inner edge, belowthe mount, if it have one. A few moments after pouring in thegold solution, the anode should be gently moved to and fro, withoutcoming in contact with the vessel itself, so as to render the depositmore uniform ; it may then be allowed to remain without interruptionfor a minute or so, when the gentle movement of the anode may berenewed for a few moments, these alternations of motion and reposebeing kept up for about five or six minutes—or perhaps a little longer—by which time a sufficiently stout coating is generally obtained.Moving the anode occasionally has the effect of rendering the depositmore regular, while it also exposes fresh surfaces of the solu-tion to the metal surfaces under treatment ; great care, how-
190 FLFCTRO-DEPOSITION OP GOLD.
but on no account should the gilding bath used for ordinary work beallowed to become impregnated with even small quantities of anyother metal. When we .state that trifling canoes will sometimes inter-fere with the natural beauty of the pure gold deposit, the importanceof preserving the bath* from the introduction of foreign matters willbe at once apparent. Another thing that atVeets the colour of thegilding is the accumulation of urytmtc m«iin\ that is, vegetable oranimal matter, which is introduced into the bath by the articles im-mersed in i t : thus, greasy matter from polished work, and beer fromthe scratch-brush, will sometimes lodge in the interstices of hollowwork, and escape into the bath even after the articles have beenrinsed; each in their turn convey organic matter to the gold solution,by which it acquires a darkened colour ; indeed, we have known solu-tions acquire quite a brovni colour from these causes. In our expe-rience, however, the presence of a entail amount of such foreignmatter, in moderation, has often proved of advantage, especially inthe gilding of insides of vessels, when a rich and deep-toned gildingis required : a solution in this condition we should prefer, for insidesof cream ewers, sugar-bowls, and goblets, to a newly-prepared goldsolution ; indeed, when a bath works a little foxy, it is, to our mind,in the be.st condition for these purposes, since the former is apt to yielda deposit which is too yellow for such surfaces. There is an extreme,however, which must be avoided, that is when the bath yields a brown-yellow deposit, which is very unsightly, though not uncommonly to beseen in our shop windows.
"When the gilding upon chains or articles of that class is of a deepbrownish-yellow colour when removed from the bath, it will, whenscratch-brushed, exhibit a fine gold appearance, specially suited tothis class of work, and more like jewellers' " wet colour work " thanelectro-gilding-, which will render it more acceptable to those whoare judges of gold colour. Indeed, when the electro-gilding processwas first introduced, it was a general complaint amongst shopkeepersthat electro-gilding was too yellow, and that electro-gilt work couldeasily be distinguished from coloured gold in consequence, which wasadmitted to be a serious defect, since a person wearing a gilt articlewould naturally wish it to be assumed by others to be of gold. Ingilding such articles, therefore, the aim of the gilder should be toimitate as closely as possible the colour of gold jewellery, whether itbe dry or wet coloured work. In the latter there is a peculiar depthand softness of tone which is exceedingly pleasing; in dry colouredwork a rich dead surface is produced which it is not so difficult toimitate in electro-gilding. The processes of "colouring" articles ofgold will be given in another chapter, since a knowledge oi theseprocesses is not only useful but often necessary to an electro-gilder,
GILDING ARMY ACCOUTREMENT WORK. 193
again, and then to re-immerse it in the bath. A solution for gildingfiligree work should also be tolerably rich in gold—about 5 penny-weights to the quart of solution being a good proportion, though somegilders use a still larger proportion of metal. In gilding filigree worka rather intense current is necessary ; a Bunsen battery, therefore,should be employed, or two Daniell cells arranged for intensity.
Gilding Army Accoutrement Work.—In the early days ofelectro-gilding, great difficulty was experienced by electro-gilders inimparting to sword-mounts, the threaded ornamentation of scabbards,and other army accoutrements the rich dead lustre, as the French termit, which the mercury gilders produced with bo much perfection, andfor a long period electro-gilders, in their anxiety to obtain contractsfor gilding this class of work, made many unsuccessful attempts andsuffered much disappointment from the repeated rejection of theirwork by the government authorities. At the period referred to, therewas a great desire, if possible, to render the pernicious art of mercurygilding unnecessary, since it was too well known that those engagedin the art suffered severely from the effects of mercurial poisoning, bywhich their existence was rendered a misery to them, and their livesabbreviated to a remarkable degree. It may be stated, however, thatthe operations of gilding with an amalgam of gold and mercury werefrequently conducted with little or no regard to the dangerous natureof the fluid metal which the workpeople were constantly handling, andthe volatilised fumes of which they were as constantly inhaling. Itwas a happy epoch in the gilding art when deposition of gold by elec-tricity rendered so baneful a process, incautiously practised, compara-tively unnecessary. We say comparatively, because amalgam ormercury gilding is still adopted, though with a little better regard tothe health of the workmen, for certain classes of work, for which, evenup to the present period, electro-gilding is not recognised as a perfectsubstitute.
To gild army accoutrement work, so as to resemble, as closely aspossible, mercury gilding, the colour and general appearance of thematted or dead parts must be imitated very closely indeed. There areno articles of gilt work that look more beautiful by contrast thanthose in which dead surfaces are relieved by the raised parts andsurrounding edges being brightened by burnishing, and this effect ischarmingly illustrated in the mountings of the regulation sword of theBritish officer. Indeed this class of work, when properly finished,may be considered the perfection of beauty in gilding.
To give the necessary matted surface to the chased portions of swordmounts, and work of a similar description, these parts should bebrushed over with finely-powdered pumice, or bath-brick reduced to apowder and sifted, the latter substance answers the purpose very
192 ELKCTKO-DEPOSITION OF GOLD.
over, is necessary to avoid driving the solution over the orna-mental mount on the rim of the vessel. The lips of cream ewers,which the gold solution cannot reach when the vessel is filled withsolution, are gilt by conducting the solution to such parts as follows :A small gold anode, with a short piece of copper wire attached,is enclosed in a piece of rag or chamois leather ; the end of this wireis then connected to the positive electrode (the article itself being indirect contact with the negative), and the pad, or "doctor," as it issometimes called, is dipped in the gold solution and applied to the partto be gilt; in this way, by repeatedly dipping the pad in the solutionand conducting it over the surface, this part in a short time becomessufficiently gilt; since the lip of a cream ewer, however, is the mostimportant part of the gilt surface, the application of the pad should becontinued until a proper coating is obtained, and care must be takenthat the point of junction between the two deposits of gold is notvisible when the gilding is complete. We should prefer to gild thelip of such vessels first, and after well scratch-brushing, or scour-ing the interior, and especially the line where the two gildings willmeet, then to gild the interior of the body of the vessel, and finally toscratch-brush the whole surface. In gilding the insidcs of vessels, itis important that the outsides and mounts, or mouldings, should be •perfectly dry, otherwise the gold solution may, by capillary attraction,pass beyond its proper boundary and gold become deposited whereit is not required, thus entailing the trouble and annoyance of re-moving it.
Gilding Silver Filigree Work.—A dead surface of silver is veryapt to receive the gold deposit ununiformly, and this is specially so inthe case of silver filigree work, the interstices of which cannot fullybe reached by the scratch-brush; the surfaces brightened by thescratch-brush readily receive the deposit, while those portions of thearticle which es-cajie the action of the wire brush will sometimes fail to*' take " the gold. "When this is found to be the case, a large surfaceof anode should be immersed in the bath, and the article briskly movedabout until the whole surface is coated, when the anode may be par-tially withdrawn, and a sufficient surface only exposed in the bath tocomplete the article as usual. In gilding work of this description it isnecessary that a fair amount of free cyanide should be in the bath, butthe excess must not be too great, or the deposit will be foxy—a colourwhich must be strenuously avoided, since the brown tint will be visiblemore or less upon those interstices (especially the soldered parts)which the scratch-brush cannot reach. As a rule, filigree workshould not be risked in an old gold solution in which organic matter orother impurities may be present. It is a good plan, after giving thearticle a quick coating in the way indicated, to rinse and " scratch " it
GILDING STEEL. *95
after the article is placed in the bath, but not immediately after itsimmersion. In other words, if the gold is allowed to jump on, it willmost assuredly as quickly jump off when the scratch-brush is applied.
In preparing steel articles for gilding, the author has found that byscratch-brushing the work with vinegar, or very dilute hydrochloricacid, instead of sour beer, a very line coating of copper (derived fromthe brass wire of the brushes*) has been imparted to the articles, towhich the gold deposit, from a weak bath, adhered with greatfirmness.
A very successful method of gilding steel is to first copper or brassthe articles in the alkaline solutions of these metals, as recommendedfor silvering steel and iron.* The brass or copper solutions should beused warm, and be in good working order, so as to yield brightdeposits of good colour. Before electro-brassing the articles, however,they must be thoroughly cleansed by scouring with silver-sand, soapand water, or scratch-brushed. Bright steel articles which are notrequired to have a durable coating of gold, but merely a slight film or"colouring" of the precious metal, generally need no preparationwhatever, but may receive a momentary dip in the gilding bath, thenrinsed in hot water, and at once placed in hot boxwood sawdust. Indoing this cheap class of work, however, it is better to use a copperor platinum anode in place of the gold anode, and to make smalladditions of chloride of gold when the solution shows signs ofbecoming exhausted. It must be remembered, however, that thevery dilute gold solution we have recommended for gilding steel con-tains in reality but very little gold, therefore, as it becomes furtherexhausted by working without a gold anode, additions of the chloride,in very small quantities, will require to be made so soon as the bathexhibits inactivity.
For gilding polished steel, a nearly neutral solution of chloride ofgold its mixed with sulphuric ether, and well shaken ; the ether willtake up the gold, and the ethereal solution float above the denseracid. If the ethereal solution be applied by means of a camel-hairbrush to brightly-polished steel or iron, the ether evaporates, andgold, which adlieres more or less firmly, becomes reduced to themetallic .state on the steel, and may be either polished or burnished.
In gilding upon an extensive scale, where large objects, such astime-pieces, chalices, patens, and other work of large dimensions, haveto be gilt, the depohiting tanks are generally enamelled iron jacketedpans, heated by steam. These vessels are placed in rows near thewall of the gilding-room, in a good light, and suitable iron pipingconveys the steam to the various tanks, each of which is provided witha suitable stopcock to admit or bhut off the steam as required; an exitpipe at the bottom of each "jacket" allows the water from the con-
* See Chaps. XVI., XXIV., and XXV.
194 ELECTRO-DEPOSITION OF GOLD.
well. The application of either of these materials should be confined,as far as is practicable, to the chased parts of the article, so as to avoidrendering the surfaces to be afterwards burnished rough by theaction of the pumice powder. The plain surfaces of the article maythen be scoured with silver-sand, soap and water, or scratch -brushed ; but great care must be taken not to allow the scratch-brushto touch the surfaces that are to be left dead. Sometimes it is thepractice to add a little aurate of ammonia to the gilding solution toproduce a dead lustre in gilt work. When it is preferred to adoptthe quxcking process, in gilding this class of work, the articles, afterbeing quicked in the usual way, are placed in the bath until they havenearly received a sufficient deposit, when they are removed, rinsed,and the chased parts quickly brushed with pumice, as before, afterwhich they are returned to the bath for a short time, or until theproper colour and matted appearance are imparted to the work.
Gilding German Silver.—This alloy of copper, as also brass, willreceive a deposit of gold in strong and warm cyanide solutions of goldwithout the aid of the battery; this being the case, in order toprevent the deposit from taking place too rapidly, when electro-gilding articles made from these alloys, the temperature of thesolution should be kept rather low—that is not beyond 120° Fahr.— -and only sufficient surface of anode immersed in the solution to enablethe article to become gilt with moderate speed when Jlrst placed in thebath. It is also advisable that the gold solution should be weaker,both in gold and cyanide, than solutions which are used for gildingsilver or copper work. If, however, quickmg be adopted, these pre-cautions are not so necessary, since the film of mercury checks therapidity of the gilding. Either method may be adopted according tothe fancy of the gilder ; but for our own part, we would not suffer aparticle of mercury to enter the gilding-room (except upon the amal-gamated plates of a battery) under any circumstances.
Gilding Steel.—The rapidity with which this metal receives adeposit of gold, even with a very weak battery current, in ordinarycyanide solutions, renders it imperative that a separate solution shouldbe prepared and kept specially for steel articles. We have obtainedexcellent results by employing a bath composed of
Ordinary double cyanide of gold solution .Water
i part.4 to 6 parts.
To this weakened solution a small quantity of cyanide of potassiummay be added, and the current employed should be of low tension—aWollaston or Daniell battery being preferable. The temperature ofthe bath should be warm, but not hot. The surface of anode insolution must be just so much as will enable the gold to deposit soon
GILDING WATCH MOVEMENTS. 197
watch parts for a few minutes in an alkaline bolution made of100 parts of water and 10 of caustic soda or potassa, and rinsing themin clean water, which should wet them thoroughly if all the oil hasbeen removed. The articles are threaded upon a brass wire.
3. A few gilders then cleanse them rapidly by the compound acidsfor a bright lustre ; others simply dry them carefully in sawdust fromwhite wood.
4. Holding the Parts.—The parts thus prepared are fastened bymeans of brass pins with flat heads upon the even side of a block ofcork.
5. The parts thus held upon the cork are thoroughly rubbed overarith a brush quite free from greasy matters, and charged with apaste of the finest pumice-stone powder and water. The brush ismade to move in circles in order not to abrade one side more than theother. The whole is thoroughly rinsed in clean water, and no particleof pumice dust should remain upon the pieces of the cork.
6. Afterwards we plunge the cork and all into a mercurial solution,which very slightly whitens the copper, and is composed of—
Water .Nitrate of binoxideSulphuric acid
of mercury. 10 litres*.. 2 grammes• 4 „
The pieces are simply passed through the solution, and then rinsed.This operation, which too many gilders neglect, gives strength to thegraining, which without it possesses no adherence, especially whenthe watch parts are made of white German silver, dignified by thename of nickel by watchmakers, or when the baths contain tin intheir composition.
7. Graining.—In this state the parts are ready for the graining—that is to say, a silvering done in a particular manner.
Nothing is more variable than the composition of the graining pow-ders; and it may be said that each gilder has his own formula, accord-ing to the fineness of the grain desired.
The following formulae are used in the works of M. Pinaire :—
Silver in impalpable powder. . . . 3 0 grammes.Bitartrate of potassa (cream of tartar) finely
pulverised and passed through a silk sieve 300 „Chloride of sodium (common salt) pulver-
ised and sifted as above 1 kilogramme.
It is stated that the majority of operators, instead of preparingtheir graining-silver, prefer buying the Nuremburg powder, which isproduced by grinding a mixture of honey and silver-foil with a muller
196 ELECTRO-DEPOSITION OF GOLD.
densed steam to escape into a drain beneath. Each of these tanks isprovided with the usual conducting rods, and the current, which issometimes derived from a magneto or dynamo machine in large estab-lishments, is conveyed by suitable leading wires or rods, attached tothe wall at a short distance from the series of depositing ves«>els. Ingilding large quantities of small articles, as steel pens, for example, aconsiderable number of gilding tanks, of an oblong form, are placedin a row, at a moderate distance apart, and the pens or other smallobjects are introduced into these as the gilders receive the work pre-pared for them.
Gilding Watch Movements—Continental Method.—The re-markable beauty of the Swiss watch movements has always been thesubject of much admiration, and for a long* period this pleasing indus-try was solely confined to Switzerland; France, however, eventuallygot possession of the method, and the art has been extensivelypractised in that country, but more especially at Besancon and Morez,in Jura, and in Paris. M. Pinaire, a gilder at Besancjon, generouslycommunicated the process to the late M. Roseleur, to whom we areindebted for the process.
Pmaire's Method of Gilding Watch Movements.—In gilding watchparts, and other small articles for watchmakers, gold is seldom applieddirectly upon the copper. In the majority of cases there is a pre-liminary operation, called graining, by which a vary agreeable grainedand slightly dead appearance is given to the articles. If we examinecarefully the inside of a watch we may see the peculiar pointed deadlustre of the parts.
This peculiar bright dead lustre, if it may be so expressed, istotally different from that ordinarily obtained. For instance, it doesnot resemble the dead lustre obtained by slow and quick electro-deposition of gold, silver, or copper, which is coarser and dullerthan that of watch parts. Neither does it resemble the deadlustre obtained with the compound acids, which is the result of amultitude of small holes formed by the juxtaposition, upon a previ-ously even surface, of a quantity of more or less large grain6*, alwaysin >ehcf.
The graining may be produced by different methods, and upongold, platinum, and silver; and since the latter metal is that preferredwe shall describe the process applied to it.
This kind of gilding requires the following successive operations :—r. Pieparation of the Watch Parts. — Coming from the hands
of the watchmaker, they preserve the marks of the file, which areobliterated by rubbing upon a wet stone, and lastly upon an oil-btone.
2. The oil or grease which soils them is removed by boiling the
GILDING WATCH MOVEMENTS. I99
turn in every direction, and no work can be done with them. It is,therefore, absolutely necessary to anneal them more or less upon aneven fire. An intelligent worker has always three scratch-brushesannealed to different degrees : one which is half soft, or half annealed,for the first operation of uncovering the grain ; one harder, or littleannealed, for bringing up lustre ; and one very soft, or fully annealed,used before gilding, for removing the erasures which may have beenmade by the preceding tool, and for scratch-brushing after the gild-ing. Of course the scratch-brushing operation, like the grainingproper, must be done by striking circles, and giving a rotary motionbetween the fingers to the tool. The cork is now and then made torevolve. After a good scratch-brushing, the grain, seen through amagnifier, should be regular, homogeneous, and with a lustre all over.Decoctions of liquorice, saponaire (soapwort), or Panama wood areemployed in this operation.
198 ELECTRO-DEPOSITION OF GOLD.
upon a ground-glass plate, until the proper fineness is obtained. Thesilver is separated by dissolving the honey in boiling water, and wash-ing the deposited metal in a filter until there is no remaining trace ofhoney. The silver is then carefully dried at a gentle heat. Thissilver, like bronze powder, is sold in small packages :—
Or—
Silver powderCream of tartarCommon salt (white and clean)
Silver powderCream of tartarCommon salt
. 30 grammes.120 to 150 „
. 100 „
• 30 ». 100 „
1 kilogramme.
All these substances should be as pure as possible, and perfectlydry. Cream of tartar is generally dry, but common salt often needs,before or after it has been pulverised, a thorough drying in aporcelain or silver dish, in which it is kept stirred with a glass rod ora silver spoon.
The mixture of the three substances must be thorough, and effectedat a moderate and protracted heat.
The graining is the coarser as there is more common salt in themixture; and conversely, it is the finer and more condensed as theproportion of cream of tartar is greater; but it is then more difficultto scratch-brush.
8. The Graining Proper.—This operation is effected as follows : Athin paste of one of the above mixtures with water is spread by meansof a spatula upon the watch parts held upon the cork. The cork itselfis fixed upon an earthenware dish, in which a movement of rotationis imparted by the left hand. An oval brush with close bristles isheld in the right hand, and rubs the watch parts in every direction,but always with a rotary motion. A new quantity of the paste isadded two or three times, and rubbed in the manner indicated. Themore we turn the brush and the cork, the rounder becomes the grain,which is a good quality ; and the more paste we add, the larger thegrain.
The watchmakers generally require a fine grain, circular at itsbase, pointed at its apex, and close—that is to say, a multitude ofjuxtaposed small cones. A larger grain may, however, have a betterappearance, but this depends on the nature and the size of the articlesgrained.
9. When the desired grain is obtained, the watch parts are washedand then scratch-brushed. The wire brushes employed also comefrom Nuremburg, and are made of brass wires as fine as hair. Asthese wires are very stiff and springy, they will, when cut, bend and
ELECTRO-GILDING ZINC ARTICLES. 2Oi
stopped or plugged with easy-running pewter solder, and the spotafterwards touched up so as to resemble the surrounding surface,whether it be smooth or chased. When the whole article has beencarefully examined and treated in this way, it is to be immersed for afew minutes only in a moderately strong potash bath, after which itmust be well rinsed. It is next to be placed in a weak sulphuricacid pickle, consisting of—
Sulphuric acidWater .
10 parts100 „
but should not remain in the acid liquor more than a minute or two,after which it is to be thoroughly well rinsed in clean water. The article,having a copper wire attached, is now to be placed in either a cold orwarm brassing solution or alkaline coppering bath for a short time,or until it is covered with a thin deposit of either metal.* If onremoving it from the brassing bath it is found that the soldered spotshave not received the deposit, and present a blackish appearance, thearticle must be well scratch-brushed all over, and again placed in thebath, which, by the way, will deposit more readily upon the solder ifthe bath be warm, a brisk current employed, and gentle motion givento the article when first placed in the bath. The object, when placedin the bath a second time, should be allowed to remain therein for abouthalf an hour or somewhat longer, by which time, if the solution be ingood order, and the current sufficiently active, it will yield a depositsufficiently thick either for bronzing or gilding. It is a commonpractice to deposit a slight coating of brass or copper upon zinc-workin a warm solution in the first instance, and then to complete theoperation in a cold bath.
When the object is to be left bright, that is merely scratch-brushed,after being coated with copper or brass as above, it is simply gilt inan ordinary cyanide gilding bath, and is then treated in the same wayas ordinary brass or copper work. If, however, the article is to beleft dead, the following method may be adopted: After being wellrinsed, the object is to be immersed in a silvering bath in whichit is allowed to remain until it assumes the characteristic white anddead lustre of electro-deposited silver. When the desired effect isproduced, the article must be well rinsed in warm (not hot) waterand immediately placed in a gilding bath which is in a good conditionfor yielding a deposit of the best possible colour.
Another method, which has been much practised on the Continent,is thus described by Koseleur: *' Add to the necessary quantity ofwater one-tenth of its volume of sulphuric acid, and dissolve in thisacid liquor as much sulphate of copper as it will take up at theordinary temperature. This solution will mark from 200 to 240 Baume
» See Chaps. XXIV. and XXV.
CHAPTER XII.
VARIOUS GILDING OPERATIONS.
Electro-gilding Zinc Articles.—Gilding Metals with Gold Leaf.—Cold Gild-ing.—Gilding Silk, Cotton, <fcc.—Pyro-gilding.—Colour of Electro-deposited Gold.—Gilding in various Colours.—Colouring Processes.—He-colouring Gold Articles—Wet-Colour Process.—French Wet-Colouring.—London Process of Wet-Colouring.
Electro-gilding: Zinc Articles.—About thirty years ago a veryimportant industry was introduced into France, which at once com-manded universal admiration, and a rapid sale for the beautiful pro-ducts which were abundantly sent into the market. We allude to theso-called electro-bronzes. These exquisite works of art, many of whichwould would bear comparison with the finest of real bronzes, were infact zinc castings or copies from original works of high merit, coatedwith brass, or, as it was then called, electro-bronze, and artificiallycoloured, so as to imitate as closely as possible the characteristic toneof real bronze. At the time we speak of, articles of every conceivableform, from the stag beetle, mounted upon a leaf, electrotyped fromnature, and reproduced in the form of a zinc casting, each object being"electro-bronzed, to a highly-finished statuette or massive candelabrum,appeared in our shop windows and show-rooms, and presented a reallybeautiful and marvellously varied and cheap addition to our rathermeagre display of art metal work. It was soon discovered by thosewho had the taste for possessing* bronzes, but not the means to satisfyit, that the imitation bronzes lacked nothing of the beauty of theoriginals, while they presented the advantage of being1 remarkablycheap, and thus within the reach of many. The process by whichthe electro-bronzing upon zinc castings is conducted is considered inanother place, and we will now explain how articles of this description,that is zinc castings, may be electro-gilt, and either a bright or deadsurface imparted to the work according to the artistic requirements ofthe article to be treated.
Preparation of Zinc Castings for Gilding.—In order to obtain the bestpossible results, the zinc casting—presuming it to be a work of artwhich deserves the utmost care to turn it out creditably—should firstbe examined for air or band-holes, and these, if present, must be
GILDING METALS WITH GOLD LEAF. 203
article with the battery, then dip it in the mercury bath, and afterwell ringing, finish the operation by a second deposit of gold. Ineither case, the article is finally well rinsed in warm water, and after-wards dried in hot sawdust or a warm stove. Great care is taken toavoid handling the article so as not to stain it with the fingers, or toscratch it in any way, since the delicate frosted surface is very readilyinjured. It is also very important that the rinsing, after each opera-tion, should be perfectly carried out, and that the final drying iscomplete; for if any of the gold solution remain upon any part of thework, voltaic action will be set up between the zinc and copper at thespot, and the article disfigured by the formation of verdigris. Theforegoing process is specially applied to articles of zinc, such as clock-cases, &c, which are generally kept under glass, but may be appliedto smaller ornamental articles which are not liable to friction in use.
In our own practice we have found when gilding zinc, that the bestresults were obtained when all the various stages of the process, fromthe first pickling to the drying, were conducted with rapidity, thegreatest possible attention being devoted to the various rinsing opera-tions. If all baths are in proper order, the various dtps and electro-deposits should each only occupy from a few seconds to a few minutes,while the drying should be effected with the greatest possible despatch,so that the object, being but thinly coated with metals which areelectro-negative to itself, may not be subjected to electro-chemicalaction in parts owing to the presence of moisture or traces of thegilding solution.
Gilding; Metals witli Gold Leaf.—Articles of steel are heated untilthey acquire a bluish colour, and iron or copper are heated to the samedegree. The first coating of gold leaf is now applied, which must begently pressed down with a burni&her, and again exposed to gentleheat; the second leaf is then applied in the same way, followed by athird, and so on ; or two leaves may be applied instead of one, but thelast leaf should be burnished down while the article is cold.
Cold Gilding.—A very simple way of applying this process is todissolve half a pennyweight of standard gold in aqua regia ; nowsteep several small pieces of rag in the solution until it is all absorbed;dry the pieces of rag, and then burn them to tinder. To apply theashes thus left, rub them to a powder, mix with a little water andcommon salt, then dip a cork into the paste thus formed, and rub itover the article to be gilt.
Gilding Silk, Cotton, &c.—There are several methods by whichtextile fabrics may be either gilt or silvered. One method is tostretch the fabric tightly upon a frame, after which it is immersed ina solution of acetate of silver, to which ammonia is added until the pre-cipitate at first formed becomes dissolved, and a clear solution obtained.
ioi VARIOUS GILDING OPERATIONS.
(about I-1600); now add water to reduce its specific gravity to160 or 18° B. (about r i26o). This galvano-plastic * bath isgenerally contained in large vessels of stoneware, slate, wood, orgutta-percha, and porous cells are immersed in it, which are filledwith a weak solution of sulphuric acid and amalgamating salts. Platesor cylinders of zinc are put into these cells, and are connected withone or more brass rods, which rest upon the sides of the vat, andsupport the articles which are to receive the dead lustre."
The articles of zinc, previously coated with copper or brass in analkaline solution, are suspended in the above bath until they haveacquired the necessary dead lustre, after which they are treated asfollows: After being thoroughly well rinsed, they are immersed fora moment in a bath composed of—
Nitrate of mercurySulphuric acidWater . . . .
1 part2 parts
1,000 „
After again r insing, the articles are steeped in the following* solu-tion :—
Cyanide o f potassium . . . 4 0 partsNitrate of silver 10 „Water 1,000 „
The articles are well rinsed after removal from this bath, and arethen ready for gilding, the solution recommended for which is com-posed of—
Phosphate o f soda . . . . 6 0 partsBisulphite of soda . . . . 10 „Cyanide of potassium . . . 1 to 2 partsNeutral chloride o f gold . . . 2 partsWater 1,000 „
This bath is used at nearly the boiling point, with an intense voltaiccurrent. The anode consists of platinum wire, which at first is dippeddeeply into the solution, and afterwards gradually raised out of thebath, as the article becomes coated with gold, until, towards the endof the operation, but a small surface of the wire remains in the bath.It is said that the colour of the gilding by this method is remarkablefor its " freshness of tone." Some operators first gild the article bythe dipping process before described, and then deposit the requisitequantity of gold to produce a dead surface by the electro process in abath specially suited to the purpose. Other gilders first half-gild the
* This term, though never a correct one, is still generally used on the con-tinent to designate the art of electrotyping, or the deposition of copper fromits sulphate.
GILDING IN VARIOUS COLOURS. 2 0 5
gold may be obtained in an old gold solution, in which organicmatter has accumulated from imperfect ringing of the work afterscratch - brushing, and in which there is a good proportion offree cyanide, by employing a strong current and exposing a largesurface of anode. In this case the dej)osit is of a foxy colour, as it istermed, and when .scratch-brushed exhibits a depth of tone which,while being unsuited for most purposes, may be useful as a variety insome kinds of fancy gilding where a strong contrast of colours is arequisite. The colour of the deposit is also much influenced, as beforeobserved, by the extent of anode surface exposed in the bath during theoperation of gilding; if a larger surface be exposed than is propor-tionate to the cathode biofuce (or work being gilt) the colour is dark,whereas when the anode surface exposed is below the proper propor-tion, the deposit will be of a pale colour. Motion also affects thecolour of the gold depo&it—sometimes in a very remarkable degree—the colour being lujhter when the article is moved about in thesolution, and darker when allowed to rest. These differences are moremarked, however, with old and dark coloured solutions than withrecently prepared solutions, or such as have been kept scrupulouslyfree from the introduction of organic impurities.
For ornamental gilding, as in cases where chased or engraved silveror plated work is required to present different shades of colour on itsvarious surfaces, solutions of gold may be prepared from which goldof various tints may be obtained by electro-deposition. These solu-tions are formed by adding to ordinary cyanide gilding baths vary-ing proportions of silver or copper solution, or both, as also solutionsof other metals; but in order to insure uniformity of results, the solu-tions should be worked with anodes formed from an alloy of the samecharacter ; or at least, if an alloy of silver and gold, for example, isto be deposited, an anode of gold and one of silver should be employedin order to keep up the condition of the compound solution.
Green Gold.—This is obtained by adding to a solution of doublecyanide of gold and potassium a small proportion of cyanide of silversolution, until the desired tint is obtained. The solution should beworked cold, or nearly so.
Bed Gold.—To a solution of cyanide of gold add a small quantityof cyanide of copper solution, and employ a moderately strong current.It is best, in making these additions, to begin low, by adding a very smallproportion of the copper solution at first, and to increase the quantitygradually until the required tone is obtained, since an excess of thecopper solution would produce a deposit of too coppery a hue. Thetint generally required would be that of the old-fashioned gold andcopper alloy with which the seals and watch cases of the last, andearlier part of the present, century were made.
2O4 VARIOUS GILDING OPERATIONS.
After immersion in this solution for an hour or two, the thread orfabric is first dried, and then submitted to a current of hydrogen gas,by which the silver becomes reduced and the surface metallised. Inthis condition it is a conductor of electricity, and may be either gilt orsilvered in any ordinary cyanide solution. By another method, thepiece of white silk is dipped in an aqueous solution of chloride ofgold; it is then exposed to the fumes of sulphurous acid gas, pro-duced by burning sulphur in a closed box, when in a very short timethe entire piece will be coated with the reduced metal.
Tyro-gilding.—This process, which is recommended for coatingiroD and steel, is conducted upon the same principle as pyro-plating,*except that the precious metal is deposited in several layers, insteadof, as in the former case, depositing the required coating in oneoperation. The steel article being prepared as recommended forpyro-plating, first receives a coating of gold in the gilding-bath ; itis next heated until the film of gold disappears ; it is then again gilt,and heated as before, these operations being repeated until the lastlayer remains fully on the surface.
Colour of Electro-deposited Gold.—It might readily be imaginedthat gold, when deposited from its solution upon another metal,would necessarily assume its natural colour, that is, a rich orangeyellow. That such is not the case is well known to all who havepractised the art of gilding, and the fact may easily be demonstratedby first gilding a piece of German silver in a cold cyanide solution ofgold, and then raising the temperature of the solution to about 1300
Fahr. If now a similar piece of metal be gilt in the warm solution,and the two gilt surfaces compared, it will be found that while thedeposit from the cold solution is of a pale yellow colour, that obtainedby the warm solution is of a deeper and richer hue. The colour ofthe deposit may also be influenced by the nature of the current, thesame solution being used. For example, the gold deposited by thecurrent from a Bunsen battery is generally of a finer and deeper colourthan that obtained by the Wollaston battery. In the former case,the superior intensity of the current seems to favour the colour of thedeposit. This difference, however, is not so strongly marked in thecase of some other gold solutions, as that prepared by precipitatinggold with sulphide of ammonium, and redissolving the precipitatewith cyanide, for example, which yields an exceedingly good coloureddeposit with copper and zinc elements ("Wollaston or Daniell). Sincethe colour of the gold deposit is often of much importance to theelectro-gilder, we purpose giving below the various means adoptedfor varying the colour of the deposit to suit the requirements of whatwe may term fancy gilding.
Gilding in Various Colours.—A very deep coloured deposit of
* See p. 274*
RECOLOURING GOLD ARTICLES. 2O7
potash should be added; it should next be brushed with warm soapand water, a soft brush being employed, and again rinsed in hotwater, after which it may be placed in warm box sawdust, beingfinally brushed with a long-haired brush.
I I . When the work is strongly gilt, but of an indifferent colour,the following mixture may be used :—
Powdered alum . . . . 3 ounces„ nitre . . . . 6 „„ sulphate of zinc 3 „„ common salt 3 „
These ingredients are to be worked up into a thickish paste, and thearticles brushed over with i t ; they are then to be placed on a pieceof sheet iron, and heated over a clear charcoal or coke fire until theybecome nearly black ; when cool they are to be plunged into dilutemuriatic or sulphuric acid pickle.
Recolouring Gold Articles.—It not unfrequently happens thatan electro-gilder is required by his customers to renovate articles ofgold jewellery, so as to restore them to the original conditionin which they left the manufacturers. Although it has been thecommon practice, with some electro-gilders, to depend upon theirbaths to give the desired effect to what is called " coloured " jewellery,in some cases it would be better to apply the methods adopted bygoldsmiths and jewellers for this purpose, by which the exact effectrequired can be more certainly obtained. There are two methods ofcolouring gold articles; namely, " dry colouring," which is appliedto articles made from 18-carat gold and upwards, and " wet-colour-ing," which is adopted for alloys of gold below that standard, butseldom lower than 12-carat.
The mixture for dry-colouring is composed of
Kit r e . . . . . . 8 ouncesAlum 4 „Common salt 4 „
Or the following :—
Sal ammoniacSaltpetre .Borax
16 „
4 ounces4 ->4 ,,
The ingredients must first be reduced to a powder, and then putinto an earthen pipkin, which is to be placed over a slow fire to allowthe salts to fuse gradually \ to assist this, the mixture should be
2o6 VARIOUS GILDIXG OPERATIONS.
Pink Gold.—This may be obtained by first gilding the article in theusual way, then depositing a slight coating in the preceding bath, andafterwards depositing a mere pellicle of silver in the silvering bath.The operation requires great care to obtain the desired pink tint.The article is afterwards burnished; but since the silver readilybecomes oxidised (unless protected by a colourless varnish) the effectwill not be of a permanent character.
Pale Straw'Coloured Gold.—Add to an ordinary cyanide solutiona small quantity of silver solution, and work the compound solutioncold, with a small surface of anode and a weak current.
Colouring Processes.—When the gilding is of an inferior colourit is sometimes necessary to have at command some method by whichthe colour may be improved. There are several processes by whichthis may be effected, but in all cases there must be a sufficient coatingof gold upon the article to withstand the action of the materialsemployed. This condition being fulfilled, the artificial colouringprocesses may be applied with advantage, and gold surfaces of greatbeauty obtained. Of the processes given below, the first formulawill be found exceedingly useful, since it may be applied to workwhich, though fairly well gilt, need not be so stoutly coated as isnecessary when employing the second formula. It is specially usefulfor bringing up a good colour upon brooches, albert chains, and smallarticles generally. It is technically known by the name "greencolour," and is composed as follows:—
I. Sulphate of copper .French verdigrisSal ammoniac .NitreAcetic acid (about)
The sulphate of copper, sal ammoniac, and nitre are first to be pulver-ised in a mortar, when the verdigris is to be added and well mixedwith the other ingredients. The acetic acid is then to be poured in,a little at a time, and the whole well worked up together, when athin mass of a bluish green colour will result. The article to becoloured is to be dipped in the mixture and then placed on a cleanpiece of sheet copper, which is next to be heated over a clear fire,until the compound assumes a dull black colour; it is now allowed tocool, and is then plunged into a tolerably strong sulphuric acidpickle, which soon dissolves the colouring salts, leaving the article ofa fine gold colour. It is generally advisable to well scratch-brushthe article before colouring, when it will come out of the pickleperfectly bright. When removed from the pickle, the article mustbe well rinsed in hot water, to which a small quantity of carbonate of
ozs.ooooI
dwts.2
444o
gr3.o
1 2
O
O
O
RECOLOURING GOLD ARTICLES. 2OQ
French Wet Colouring.—The formula for this is:—Saltpetre . . . . . 8 ouncesCommon salt . . . . 4 „Alum . . . . . . 4 „
The ingredients must be finely pulverised, as before, and intimatelymixed ; they are then to be put into a good-sized pipkin or crucible,and sufficient hot water added to form the whole into a thick paste.The mixture should be slowly heated, and stirred with a woodenspoon, when it will soon boil up. The work is then to be immersedfor several minutes, then withdrawn and plunged into boiling water,which, dissolving the salts, will allow the work to be examined, when,if not of a sufficiently good colour, it must be reimmersed for a shorttime. As the mixture thickens by evaporation small quantities ofboiling water must be added occasionally, but only after the work hasbeen withdrawn. On the first immersion the work assumes a blackishcolour, but at each successive immersion it becomes lighter, as thebaser metals become removed from the surface of the work, until itfinally assumes the characteristic colour of fine gold. This processshould be applied to gold of less than 16 carats.
London Process of Wet Colouring.—For gold of not less than 15 caratsthe following mixture is used :—
30The salts are to be powdered, as before ; into a crucible about
8 inches high and 7 inches in diameter, put about two spoonfuls ofwater, then add the salts, place the crucible on the fire, and heatgradually until fusion takes place, keeping the mixture well stirredwith a wooden spoon. The article, which should first be boiled innitric acid pickle, is then to be suspended by a platinum wire, andimmersed in the fused mixture for about five minutes, then withdrawnand steeped in boiling water. The muriatic acid is now to be addedto the mixture, and when it again boils up the article is to be immersedfor about five minutes, then again rinsed in boiling water. A spoon-ful of water is now to be added to the mixture, and the work againput in for about three minutes, and again rinsed ; now add two spoon-fuls of water to the mixture, boil up, and immerse the work for twominutes, and rinse again. Finally, add about three spoonfuls of water,and, after boiling up, put in the work for one minute, then rinse inabundance of clean boiling water, when the work will present a beau-tiful colour. The work should then be rinsed in a very dilute hotsolution of potash, and again in clean boiling water, after which itshould be placed in clean, warm boxwood sawdust.
v
2O8 VAEIOUS GILDING OPEKATIONS.
stirred with an iron rod. When the fused salts begin to rise in thevessel, the pieces of work, suspended by a fine silver or platinum, wire,should be at once immersed, and kept moved about until the liquidbegins to sink in the colouring-pot, when the work must be removed,and plunged into clean muriatic acid pickle, which will dissolve theadhering salts. The colouring' mixture will again rise in the pot,after the withdrawal of the work, when it may be reimmersed (whendry) for a short time, and then pickled as before; it is then to berinsed in a wreak solution of carbonate of soda or potash, and after-wards well washed in hot soda and water, next in clean boiling water,and finally put into warm box sawdust to dry. Previous to colouringthe work, it should be highly polished or burnished, although thelatter operation may be performed after the work has been coloured ;the former method is, however, the best, and produces the mostpleasing effect.
Wet'Colonr'wy Process.—This is applied to gold articles made fromalloys below 18-carat, and though there are many formulae adoptedfor colouring gold of various qualities below this standard, wemust limit our reference to one or two only, and for ample infor-mation upon this subject direct the reader's attention to Mr. Gee'sadmirable Goldsmith's Handbook.* The ordinary "wet colour," asthe jewellers term it, consists chiefly in adding a little water to theingredients formerly given, the proportions of the salts being gene-rally about the same ; that is, nitre 8 ounces, alum and common saltof each 4 ounces. These ingredients being reduced to a fine powderand mixed together, are worked up into a thick paste with a little hotwater in a good-sized pipkin or crucible, which is placed over a slowfire and heated gradually, the mixture being stirred with a woodenspoon until it boils up. The work is now to be introduced as beforeand allowed to remain for several minutes, when it must be withdrawnand plunged into boiling water, which will dissolve the colouringsalts and show how far the colouring has progressed. When themixture exhibits a tendency to boil dry, an occasional spoonful ofhot water must be added to thin it, but never while the work is inthe pot. When the work is first put into the colour it becomes nearlyblack, but assumes a lighter tone after each immersion until thecharacteristic colour of fine gold is obtained. When the operation iscomplete, the work will bear a uniform appearance, though somewhatdead, and may be brightened by burnishing or scratch-brushing.After each dipping the work must be well rinsed in clean boilingwater. It must be finally plunged into hot water, and, after wellshaking, be put into warm boxwood sawdust.
* •• The Goldsmith's Handbook," by George E. Gee. London : CrosbyLockwood and Son.
APPLYING THE AMALGAM. 2 1 1
stirred with a slightly crooked iron rod, the heat being kept up untilthe gold is entirely dissolved by the mercury. The amalgam is now tobe poured into a small dish about three parts filled with water, inwhich it is worked about with the fingers under the water, to squeezeout as much of the excess of mercury as possible. To facilitate this,the dish is slightly inclined to allow the superfluous mercury to flowfrom the mass, which soon acquires a pasty condition capable ofreceiving the impression of the fingers. The amalgam is afterwardsto be squeezed in a chamois leather bag, by which a further quantityof mercury is liberated ; the amalgam which remains after this finaltreatment consists of about 33 parts of mercury and 67 of gold in 100parts. The mercury which is pressed through the bag retains a gooddeal of gold, and is employed in preparing fresh batches of amalgam.It is very important that the mercury employed for this purpose bepure. The gold employed may be either fine or standard, butwater-gilders generally use the metal alloyed either with silver orcopper ; if to be subjected to the after process of colouring, standardalloys should be employed, since the beauty of the colouring processdepends upon the removal, chemically, of the inferior metals, silver,copper, or both, from the alloy of gold, leaving the pure metal onlyupon the surface. The amalgam is crystalline, and produces a peculiarcrackling sound when pressed between the fingers close to the ear.
It is usual to keep a moderate supply of gold amalgam in handwhen mercury-gilding forms part of the gilder's ordinary business,and the compound is divided into a series of small balls, which arekept under water ; it is not advisable, however, to allow the amalgamto remain for a long period before being employed, since a peculiarphenomenon known as liquation takes place, by which the amalgamloses its uniformity of composition, the gold being more dense in someparts than in others.
The Mercurial Solution.—To apply the amalgam, a solution ofnitrate of mercury is employed, which is prepared by dissolving, in aglass flask, 100 parts of mercury in 110 parts of nitric acid of thespecific gravity 1-33, gentle heat being applied to assist the chemicalaction. The red fumes which are given off during the decompositionmust be allowed to escape into the chimney, since they are highlydeleterious when inhaled. When the mercury is all dissolved, thesolution is to be diluted with about 25 times its weight of distilledwater, and bottled for use.
Applying the Amalgam.—The pasty amalgam is spread with theblade of a knife, upon a hard and flat stone called the gilding stone,and the article, after being well cleaned and scratch-brushed, istreated in the following way : the gilder takes a small scratch-brush, formed of stout brass wire, which he first dips in the solution.
CHAPTER XIII.
MERCURY GILDING.
Preparation of the Amalgam.—The Mercurial Solution.—Applying theAmalgam—Evaporation of the Mercury.—Colouring.—Bright and DeadGilding in Parts—Gilding Bronzes with Amalgam.—Ormoulu Colour.-Red-Gold Colour.—Ormoulu. — Red Ormoulu.—Yellow Ormoulu.—
Dead Ormoulu.—Gilders' Wax.—Notes on Gilding.
ALTHOUGH the process of gilding metals with an amalgam of gold andmercury, or quicksilver, is not, strictly speaking, an electro-chemicalart, it is important that this system of gilding should be known tothe electro-gilder for several reasons: it is the chief process by whichmetals were coated with gold before the art of electro-gilding wasintroduced ; it is still employed for certain purposes, and many arti-cles of silver which have been mercury gilt occasionally come into theelectro-depositor's hands for regilding, and which are sometimesspecially required to be subjected to the same process, when the voltaicmethod is objected to.
Mercury-gilding-, formerly called wash-gilding, water-gilding, oramalgam-gilding", essentially consists in brushing over the surface ofsilver, copper, bronze, or brass, an amalgam of gold and quicksilver,and afterwards volatilising the mercury by heat. By repeated appli-cations of the amalgam and evaporation of the mercury, a coating ofgold of any desired thickness may be obtained, and when properlycarried out the gilding by this method is of a far more durablecharacter than that obtained by any other means. As we have beforeobserved, the process, unless conducted with great care, is a veryunhealthy one, owing* to the deleterious nature of the fumes of mer-cury to which the workmen are exposed, if these are not properlycarried off by the flue of a suitable furnace.
Preparation of the Amalgam.—Mercury, as is well known, hasthe peculiar property of alloying or amalgamating itself with gold,silver, and some other metals and alloys, with or without the aid ofheat. To prepare the amalgam of gold for the purpose of mercurygilding, a weighed quantity of fine or standard gold is first put into acrucible and heated to dull redness. The requisite proportion ofmercury—8 parts to I part of gold—is now added, and the mixture is
BRIGHT AND DEAD GILDING IN PARTS. 2 1 3
the water of crystallisation of the latter, after which it is heated upona brisk charcoal fire, without draf t, and moved about until the saltsbecome first dried and then fused ; the article is then plunged into avessel containing a large quantity of cold water, in which the colour-ing salts are dissolved, and the dead or matted appearance of thework becomes at once visible. When applying the amalgam for deadgilding, great care must be exercised to insure a sufficiently stoutcoating of gold upon the work, otherwise the colouring salts willsurely attack the underlying metal. When about to colour the workas above, the operator binds the article by means of iron wire to ashort rod of the same metal; he then either dips the article in thecolouring paste or applies it with a brush, and after gently drying it,holds the piece over the fire until the perfect fusion of the compositionhas taken place, when it is at once dipped in water. The colouredmarks left by the wire are removed by a weak solution of nitric acid.
Bright and Bead Gilding in Farts.—When it is desired to havesome parts of an article burnished and other parts left dead, theformer are protected by a mixture of Spanish white (pure white chalk),bruised sugar candy, and either gum or glue, dissolved in water. Themixture of alum, nitre, and common salt is then applied to the partsto be left dead, the article afterwards dried, and heated over the char-coal fire as before until the dried salts have been fused, when it is atonce plunged into cold water, and subsequently in dilute nitric acid,being finally well rinsed and dried. The protected parts are thensubjected to the operation of burnishing, when the article is complete.
Another method adopted in France, in which electro-gilding takesa part, is described as follows : Those parts which are intended fora dead lustre are first gilt with the amalgam; the article is thenheated, scratch-brushed, and re-heated to the orange-yellow colour.Then, with the battery, a sufficiently strong gold deposit is given tothe whole, without regard to the parts already mercury-gilt. All thesurfaces are next carefully scratch-brushed, and the electro-gilt por-tions are brushed over, first with a thin mixture of water, glue, andSpanish white, and afterwards with a thick paste of yellow clay.After drying, the mercury-gilt portions are covered with the pastefor dead-gilding (alum, nitre, &c), and the article heated until thesalts fuse, when it is plunged into water and treated as above.
Roseleur, however, considers this method open to several objections,among which is, red spots are apt to be produced upon such places asmay have been too much heated, or where the gold has not been suffi-ciently thick. He recommends the following by preference: u Gildwith amalgam, and bring up the dead lustre upon those portionswhich are to receive it, and preserve [protect] them entirely with astopping-off varnish. After thorough drying, cleanse the object by
2 1 2 MERCURY GILDING.
of nitrate of mercury, and then next draws it over the amalgam, bywhich it takes up a small quantity of the composition , he then passesthe brush carefully over the surface to be gilt, repeatedly dipping thebrush in the mercurial solution and drawing it over the amalgamuntil the entire surface is uniformly and sufficiently coated. Thearticle is afterwards well rinsed and dried, when it is ready for thenext operation.
Evaporation of the Mercury.—For this purpose a charcoal fire,resting upon a cast-iron plate, has been generally adopted, a simplehood of sheet iron being the only means of partially protecting theworkmen from the injurious effects of the mercurial vapours. M.D'Arcet, of Paris, invented a furnace, or forge, with an arrangementby which the workman could watch the progress of his work throughglass, and thus escape the injurious effects of the mercury vapours.The difficulty of seeing the process clearly, however, during the moreimportant stages of the operation (owing doubtless to the condensa-tion of the mercurial vapour upon the glass), caused the arrangementto be disapproved by those for whose well-being it was speciallydesigned, and the simple hood, regardless of its fatal inadequacy, isstill preferred by many mercury gilders. When the amalgamatedarticle is rinsed and dried, the gilder exposes it to the glowing char-coal, turning it about, and heating it by degrees to the proper point;he then withdraws it from the fire by means of long pincers or tongs,and takes it in. his left hand, which is protected with a leather orpadded glove, and turns it over the fire in every direction, and whilethe mercury is volatilising, he strikes the work with a long-hairedbrush, to equalise the amalgam coating, and to force it upon suchparts as may appear to require it.
When the mercury has become entirely volatilised, the gilding hasa dull greenish-yellow colour, and the workman examines it to ascer-tain if the coating is uniform ; if any bare places are apparent, theseare touched up with amalgam, and the article again submitted to thefire, care being taken to expel the mercury gradually.
Colouring-—The article is next well scratch-brushed, when itassumes a pale greenish colour ; it is afterwards subjected to anotherheating to expel any remaining mercury, when, if sufficient amalgamhas been applied, it acquires the characteristic orange-yellow colourof fine gold. It is next submitted to the process of colouring. Ifrequired to be bright, the piece of work is burnished in the ordinaryway, or, according to the nature of the article, is subjected to theormoulu process described further on. When the surface is requiredto be dead, or frosted, the article is treated somewhat in the same wayas " dry coloured " gold jewellery work, that is, it is brushed overwith a hot paste composed of common salt, nitre, and alum, fused in
ORMOULU. 215
is heated, and while still hot is suspended by an iron wire, andcoated with gilders' wax, a composition of beeswax, red ochre, ver-digris, and alum. It is then strongly heated over the name of a woodfire; sometimes small quantities of the gilders' wax are thrown intothe fire to promote the burning of the fuel. The object is turnedabout in every direction, so as to render the action of the heat uni-form. As soon as all the wax has become burnt off, the name isput out, and the article plunged into cold water, well washed, andbrushed over with a scratch-brush and pure vinegar. Should thecolour not be uniform or sufficiently good, the article must be coatedwith verdigris dissolved in vinegar, dried over a gentle fire, thenplunged into cold water and brushed over with vinegar; and if thecolour is of too deep a tone, dilute nitric acid may be substituted forthe vinegar. After well washing, the article is burnished, then againwashed, and finally wiped with soft linen rag, and lastly dried at agentle heat.
Ormoulu.—The beautiful surface noticeable on French clocks andother ornamental work is produced by the process called ormoulu.The article is first gilt, and afterwards scratch-brushed. It is thencoated with the thin paste of saltpetre, alum, and oxide of iron beforementioned, the ingredients being reduced to a fine powder, andworked up into a paste with a solution of saffron, annatto, or othercolouring matter, according to the tint required, whether red oryellow. When the gilding is strong, the article is heated until thecoating of the above mixture curls over by being touched with a wetfinger. But when the gilding is only a slight film of gold, the mix-ture is merely allowed to remain upon the article for a few minutes.In both cases, the article is quickly washed with warm water containingin suspension a certain quantity of the materials referred to. The articlemust not be dried without washing. Such parts as may have acquiredtoo deep a colour are afterwards struck with a brush made with longbristles. By a series of vertical strokes with the brush the uniformityof surface is produced. If the firbt operation has not been successful,the colouring is removed by dipping the article in dilute sulphuricacid, and after well rinsing, the operation is repeated until the desiredeffect is obtained.
Red Ormoulu is produced by employing a mixture composed of alumand nitre, of each 30 parts ; sulphate of zinc, 8 parts ; common salt,3 parts; red ochre, 28 parts; and sulphate of iron, 1 part. To thismay be added a small quantity of annatto, madder, or other colouringmatter, ground in water.
Yellow Ormoulu is produced by the following: red ochre, 17 ;potash alum, 50 ; sulphate of zinc, 10; common salt, 3 ; and salt-petre 20 parts, made up into a paste as before.
2 1 4 MERCURY GILDING.
dipping it into acids in the usual manner, and gild in the electro-bath. The varnish withstands all these acids and solutions. Whenthe desired shade is obtained, dissolve the varnish with gazoline orbenzine, which, unless there has been friction applied, do not injurein any way either the shade or velvety appearance of the dead lustre.Wash in a hot solution of cyanide of potassium, then in boiling water,and allow to dry naturally. . . . Gilding with dead lustre, whateverprocess be employed, suits only those objects which will never be sub-jected to friction ; even the contact of the fingers injures it."
Gilding: Bronzes with Amalgam.—The article is first annealedvery carefully, as follows: The gilder sets the piece upon burningcharcoal, or peat, which yields a more lively and equal flame, coveringit up so that it may be oxidised as little as possible, and taking carethat the thinner parts do not receive an undue amount of heat. Thisoperation is performed in a dark room, so that the workman may seewhen the desired cherry-red heat is reached. He then lifts the piecefrom the fire, and sets it aside to cool in the air gradually. Whencold, the article is steeped in a weak sulphuric acid pickle, whichremoves or loosens the coating of oxide. To aid this he rubs it witha stiff and hard brush. When the article has been thus renderedbright, though it may appear uniform, it is dipped in nitric acid andrinsed, and again rubbed with a long-haired brush. After washingin clean water, it is dried in hot sawdust or bran. This treatmentsomewhat reduces the brightness of the surface, which is favour-able to the adhesion of the gold. The amalgam is next applied withthe scratch-brush, as before, and the object then heated to expel themercury. If required to be dead, it is treated with the colouring-salts, as before described.
Ormoulu Colour.—To obtain this fine colour upon bronze or otherwork, the gilt object is first lightly scratch-brushed, and then madeto come back again, as it is termed, by heating it more strongly than ifit were to be left dead, and then allowed to cool a little. The ormoulucolouring is a mixture of hematite (peroxide of iron), alum, and sea-salt, made into a thin paste with vinegar, and applied with a brushuntil the whole of the gilded surface is covered, except such parts asare required to be burnished. The object is then heated until itbegins to blacken, the proper heat being known by water sprinkledover it producing a hissing noise. It is next removed from the fire,plunged into cold water, and washed, and afterwards rubbed with abrush dipped in vinegar if the object be smooth, but if it be chased,dilute nitric acid is employed for this purpose. The article is finallywashed in clean water, and dried at a gentle heat.
Bed Oold Colour.—To produce this colour, the composition knownas gxlderh* wax is used. The article, after being coated with amalgam,
KEEPING THE SOLUTIONS UNIFORM. 21 7
heated for a few hours, it will have lost a considerable proportion oi'its water, which must be made up by adding an equivalent of hotwater. If this is not done, the bath, being stronger than it wasoriginally, will probably yield a non-adhering deposit, and the goldmay strip off the work under the scratch-brush. The solution shouldbe kept up to its standard height in the gilding vessel by frequentadditions of hot water during the whole time it is subjected to evapo-ration by the gas-burner, or other heating medium. The solution-line of the bath should be marked upon the inside of the vessel whenthe liquid is first poured in.
4. Gddwij (hfji rent Metah.—Silver and metal articles should not beslung upon the same wire and immersed in the bath at the same time,since brass, gilding metal, and copper receive the deposit more readilythan silver. The latter metal should first receive a coating, afterwhich, if time is an object, the metal articles may be placed in thebath with the partly-gilt silver articles.
5. Employmoit of Impure Gold.—When it is desired to make up a goldsolution from impure material, as from •' old gold," for instance, thealloy should first be treated as follows : To 1 ounce of the alloyedgold, if of good quality—say 18-carat gold, for example—add 2 ouncesof silver, which should not be below standard; melt them in a cruciblewith a little borax, as a flux. When the alloy is thoroughly meltedit is to be poured into a deep vessel containing cold water, whichmust be briskly stirred in one direction, while the molten alloy is beingpoured in. This operation, termed granulation, causes the metal toassume the form of small lumps, or (/rains, as theyare called. The water is now to be poured off andthe grains of alloy collected and placed in a flask,such as is shown in Fig. 70. To remove the silverand copper from the granulated metal, a mixture oftwo parts water and one part strong nitric acid ispoured into the flask, which is then placed on asand-bath, moderately heated, until the red fumeswhich at first appear have ceased to be visiblein the bulb of the ves.sel. The clear liquid is nowto be carefully poured off into a suitable vessel—aglass "beaker," such as is shown in Fig. 78, being a convenientvessel for the purpose. A small quantity of the dilute acid shouldthen be poured into the flask, and heat again applied, in order toremove any remaining copper or silver. If, on the addition of thefresh acid, red fumes do not appear in the flask the operation is com-plete, and the grains of metal will have assumed a dark brown colour.The acid must now be poured off, and the grains well washed, whiloin the flask, with distilled water. The residuum is pure gold and
Fig. 78.
2 l 6 MERCURY GILDING.
Bead Ormouhi, for clocks, is composed of saltpetre, 37 ; alum, 42;common salt, 12 ; powdered glass and sulphate of lime, 4 ; and water,5 parts. The whole of these substances are to be well ground andmixed with water.
Gilders' Wax, for producing a rich colour upon gilt work, is madefrom oil and yellow wax, of each 25 parts; acetate of copper, 13 parts;and red ochre, 37 parts. The oil and wax are to be united by melt-ing, and the substances, after being well pulverised, added gradually.
Notes on Gilding.—When gilding single small articles, it is agood plan to hold the anode by its conducting wire in the left hand,so as to be able to control the amount of surface to be immersed inthe bath, which must be considerably less (with hot solutionsespecially) than that of the article to be gilt. The object being slungby thin copper wire, the free end of the wire is to be twisted roundthe negative electrode (the wire issuing from the zinc of the battery),and the article then dipped into the bath. The article shouldgradually become coated, that is, in a few seconds, but not immediatelyafter it is immersed. Gentle motion will secure an uniform deposit.After the article has become gilt all over, the anode may be lowered alittle deeper into the bath, and the gentle motion of the article keptup for a short time, say from three to five minutes, or until it appearsto be fairly coated. The length of time the article is to remain in thebath must be regulated by the price to be paid for the gilding. If areally good gilding is required, it may be necessary, after about fiveminutes' immersion, to rescratch-brush the article, dip it in the mer-curial solution for a moment, or until it is white, and then, after wellrinsing, give it a second coating. Ordinary gilding, however, isgenerally accomplished in a single immersion.
r. Gilding Jewellery Articles.—Chains, brooches, rings, pins, andother small articles of silver or metal jewellery should first be slungupon thin copper wire, then dipped for a few moments only in a warmpotash bath. The articles are then to be rinsed in warm water andscratch-brushed, after which they are again rinsed, and at onceimmersed in the gold bath. When sufficiently gilt, the work shouldbe rinsed in a vessel kept specially for the first rinsing, which shouldbe saved, and afterwards in clean water. It is then to be properlyscratch-brushed, and plunged into hot water ; next shaken about toremove as much water as possible, and finally put into warm boxwoodsawdust. After moving it about in the boxdust for a few moments,the article requires to be shaken or knocked against the palm of thehand, to dislodge the sawdust. It is now ready to be wrapped up forthe customer, pink tissue paper being preferable for gilt work, andblue or white tissue paper for silver or plated work.
2. Treatment of Gilding Solutions.—When the gilding bath has been
MANAGEMENT OF GOLD BATHS. 219
while being favourable to certain classes of work which can be readilygot at by the scratch-brush, is very objectionable to articles of jewellerywhich are required to present a clear orange-yellow colour in all parts,including the interstices and soldered joints which cannot be reachedby the lathe-brush. When the solution is in this condition we havefound it advantageous to evaporate it to dryness, then to re-dissolve itin hot distilled water, filter the solution when cold, and add a smallproportion of free cyanide, finally making up the bath to about three-fourths of its original volume. The solution thus treated yields a veryrich colour in gilding. It is necessary to mention, however, that goldsolutions which have been prepared by precipitating the gold from itschloride with ammonia should not be evaporated to dryness, since theexplosive fulminate of gold may be present to some extent, whichwould render the operation hazardous.
9. Management of Gold Bathb.—The colour of the gilding may bevaried from a pale straw or lemon colour to a dark orange-red at the willof the operator; thus, when the solution is cold, a pale lemon-coloureddeposit will be obtained. If the bath be warm, a very small surfaceof anode exposed in the solution, and the article kept in brisk motion,the deposit will also be of a pale colour. If, on the other hand, therebe a large excess of cyanide in the bath, a considerable surface ofanode immersed and a strong current, the gilding will be of a darkred colour, approaching a brown tone, and the article, when scratch -brushed, will assume a rich orange-yellow colour, specially suited tocertain classes of work, as theinsides of cream-ewers, goblets, &c, andchains of various kinds. In order to obtain uniform results in any desiredshade, when gilding a large number of articles of the same class, caremust be exercised to keep the temperature of the bath uniform ; theanode surface immersed in the solution the same for each batch ofwork, consisting of an equal number of pieces of the same dimensions ;the battery current as uniform as possible, and, lastly, fresh additionsof warm distilled water must be added frequently to the bath to makeup for loss by evaporation. If these points be observed there will beno trouble in obtaining uniform results. It is scarcely necessary tostate that a large bulk of gilding solution will keep in an uniformcondition for a longer period than a smaller quantity, since the effectof evaporation is less marked than in the latter case.
10. Worn Anodes.—It is not advisable to employ anodes which havebecome ragged at the edges for gilding the insides of vessels, sinceparticles of the metal are liable to be dislodged during the gildingprocess, and, falling to the bottom of the vessel, protect those partsupon which they drop from receiving the deposit; indeed, the smallerfragments will sometimes become electro-soldered to the bottom of thevessel, causing some trouble to remove them. When the edges of an
218 NOTES ON GILDING.
may be at once dissolved in aqua regia, and treated in the same wayas recommended for ordinary grain gold. The silver may readily berecovered from the decanted liquor, which, owing to the presence ofcopper removed from the original alloy, will be of a green colour, byimmersing in it a strip of stout sheet copper, which in the course of afew hours will reduce the silver to the metallic state, in the form of agrey, spongy mass. When all the silver is thus thrown down, thegreen liquor is to be poured off and the silver deposit well washed withhot water. Being now pure silver, it may be used for making upsolution, or fused with dried carbonate of potash into a button.
6. Gilding Filigree Work.—Silver filigree work which has been an-nealed and pickled assumes a dead-white surface, which does notreadily " take " the gilding unless the bath is rich in gold and freecyanide, and the current strong. If such parts of the article as canbe reached by the scratch-brush are brightened by this means, theinterstices which have escaped the action of the brush will sometimes betroublesome to gild, while the brightened parts will readily receivethe deposit. In this case, if the bath is wanting in free cyanide, anaddition of this substance must be made, and the article must be keptrather briskly moved about in the solution, and a good surface ofanode immersed until the dead-white portions of the article are gilt.The anode may then be raised a little, and the piece of work allowedto rest in the bath, without movement, until the desired colour andthickness of coating are obtained. Some persons prefer dipping thiskind of work in the mercury solution before gilding, by which a moreuniform deposit is obtained. This plan is useful when the gold bathhas been recently prepared. It must not be forgotten, however,that in gilding filigree work the battery current must be brisk.
7. Gilding Insides of Vessels.—It sometimes happens, when gilding theinterior of silver or electro-plated tankards, mugs, &c, which havebeen highly embossed or chased, that the gold, while depositingfreely upon the prominent parts, refuses to deposit in the hollows.To overcome this, and to render the deposit uniform, the solutionshould be well charged with free cyanide; the current must be ofhigh tension (a Bunsen, for example), and the anode should be keptin motion during the first few moments. In this way very littletrouble will be experienced from the causes referred to. It is im-portant, however, that insides of such embossed work should be verythoroughly scratch-brushed in the first instance ; indeed, as a mecha-nical assistant, the scratch-brush lathe is the gilder's best friend.
8. Old Solutions. — When a gold solution has been much usedit acquires a dark colour, from being contaminated by impuritiesas beer from the scratch-brush lathe, &c, and in this conditionis likely to yield a deposit of a dull red-brown colour, which,
STRIPPING GOLD FROM SILVER. 22 1
anode, and to renew the gilding solution as it becomes exhausted ofits metal by fresh additions ot' gold salt. The author has found it avery economical plan to use a coppa anode for gilding" work of thisdescription, and by making small additions of chloride of gold whenthe bath exhibited signs of weakness, he has been able to gild a verylarge number of articles, of a very fine colour, with an infinitesimalamount of the precious metal. The only preparation such workreceived was a good scratch-brushing before gilding, and a veryslight scratch-brushing after. In his experience, although the priceswere very low, the result was exceedingly profitable. Against theemployment of a copper anode, it has been argued that the solutionmust of necessity become highly impregnated with copper. Towhich we may reply that we did not find such to be the ease inpractice.
14. Gilding German Silver.—Since this alloy of copper, &c, will gene-rally receive a coating of gold in ordinary cyanide solution, without theaid of the battery, the solution should be somewhat weaker, and thebattery current also, otherwise the gold will not firmly adhere. Thetemperature of the solution should also be lower than is required forgilding articles of silver or electro-plate. When German silver articlesare first placed in the gilding-bath a small surface of anode only shouldbe immersed, and the deposit allowed to take place gradually. If theseprecautions be not observed the operator may suffer the annoyance offinding the work strip when the scratch-brush is applied, or at allevents under the operation of burnishing.
15. Stripping Gold from Silver.—This may be done by making thearticle the anode in a strong solution of cyanide of potassium, or in anold gold solution containing a moderate amount of free cyanide. Aquicker process, however, consists in immersing the articles in strongnitric acid, to which a little dry common salt is added. Care must betaken not to allow the article to remain in the stripping solution onemoment after the gold has been removed, and the articles should bemoved abovit in the liquid, especially towards the close of the opera-tion, to facilitate the solution of the gold from the surface. The goldmay afterwards be recovered from the exhausted acid bath by im-mersing in it several stout pieces of sheet zinc or iron, which willprecipitate the gold in the metallic state, and this may be collected,dried, and fused with a little dried carbonate of potash. Or theexhausted stripping solution may be evaporated to dryness, and theresiduum fused with dried carbonate of potash or soda, a little nitrebeing added towards the end of the operation, to refine it morecompletely.
16. Spurious Gold—"Mystery Gold."—Many attempts have been madefrom time to time to form an alloy which, having somewhat the colour
2 2 0 NOTES ON GILDING.
anode are very ragged it is well to trim them with shears or a pair ofsharp scissors before using* the anode for gilding- insides. The anodeshould always be formed into a cylinder, and not used as a flat platefor these purposes, otherwise the deposition will be irregular, and thehollow surfaces of chased or embossed work may not receive thedeposit at all.
11. Dr/tct.s in Gilding,—When the gold becomes partially dissolved offportions of an article while in the gilding-bath, it generally indicatesthat there is too great an excess of cyanide in the solution. The samedefect, however, may be caused by the current being too weak, theliquid poor in gold, too small a surface of anode in the solution, orby keeping the articles too briskly in motion in a bath containing alarge excess of cyanide. Before attempting an alteration of the solu-tion, the battery should be looked to, and, if necessary, its excitingliquids renewed. The solution should then be well stirred and triedagain ; if the biime defect is observed an addition of chloride of goldshould be made to the bath to overcome the excess of cyanide. If thedeposit is of a very dark red colour, and of a dull appearance, thismay be caused by employing too strong a current, by excess of cyanide,or too great a quantity of gold in the bath. If from the latter causes,the solution must be diluted ; if from the former, the articles shouldbe suspended by a very thin slinging wire, or the positive elementof the battery partially raised out of the battery-cell.
12. Gilding Pewter Solder.—Common jewellery is frequently repairedwith pewter solder, which does not so readily take the gilding as theother parts. A good plan to overcome this is first to well scratch-brush the articles, after which the solder may be treated as follows :Make a weak acid solution of sulphate of copper, dip a camel-hairbrush into the solution and apply it to the soldered joint, and at thesame time touch the spot with a steel point; in a few seconds thesolder will become coated with a bright deposit of copper. Now rinsethe article, and proceed to the gilding as usual, when it will be foundthat the soldered part upon which the film of copper has been depositedwill readily receive a coating of gold, more readily, in fact, than thebody of the article itself. The article, when gilt, is then scratch-brushed and treated as usual. The copper solution for the abovepurpose may be prepared by dissolving about |oz . of sulphate ofcopper in j pint of water, and adding to the solution about J oz. ofoil of vitriol.
13. Gilding Cheap Jewellery.—This class of work, whether of Frenchor Birmingham manufacture, seldom requires more than a mere dip tomeet the requirements of the customer ; indeed, the prices obtainablefor gilding articles of this character will not admit of gilding in thepioper sense of the term. In France it is usual to employ a platinum
SLINGING WIRES. 223
18. Gilding solutions which have been worked with but a smallexcess of cyanide are apt to deposit more gold than is dissolved fromthe anode, by which the action of the bath becomes lessened, while thecolour of the gilding is indifferent. It must always be borne in mindthat in all cyanide solutions, but more especially such as are workedhot, the cyanide of potassium gradually becomes converted into car-bonate of potassium by the action of the atmosphere, and thereforeloses its solvent power.
19. For producing a dead or matted surface upon brass articles ofjewellery, as brooches, lockets, &c, they are first dipped for aninstant in a mixture composed of equal parts of sulphuric and nitricacids, to which a small quantity of common salt is added, and imme-diately plunged into cold water. After being rinsed in one or twoother waters, they are promptly immersed in the gilding-bath, inwhich, after a moment's immerbion, they acquire the desired colour ofgold. After rinsing in hot water, they are finally dried in hot box-wood sawdust. In treating this class of work, care should be takento avoid handling the pieces ; after they have been removed from thesawdust they should be at once wrapped up ready for delivery.
20. When it is desired to give a stout coating of gold to an article,it should be occasionally removed from the gilding-bath, then scratch-brushed, rinsed, and returned to the bath. If the article were allowedto remain in the bath undisturbed until a thick coating was deposited,the surface would probably be rough and crystalline, and moreoverliable to strip when being scratch-brushed. It is sometimes the prac-tice to dip the article for an instant in the quicking solution aftereach gilding, by which the respective layers of gold are less apt toseparate in scratch-brushing or burnishing.
21. The wires used for slinging articles in the gilding-bath shouldnever be reversed, but one end only employed for suspending thearticles, the other being used for connection with the negative elec-trode of the battery. By adopting this system, the gold depositedupon the ends of the slinging wires is less liable to become wastedthan when both ends of the wires are used indiscriminately. Afterthe slinging wires have been used a few times, and before the goldupon them begins to chip or peel off, they should be carefully laidaside, with all the gilt ends in one direction, so that the gold maybe removed, by stripping, at any convenient time. After stripping offthe gold, the wires should be annealed, then pulled out straight, andplaced in bundles. Before being again used, each end of the bundleof wires should be dipped for a few moments in an old dipping-bath,and then rinsed, when they will be ready for future use. It is better totreat slinging-wires thus carefully than to suffer them—which iscommonly the case—to be scattered about.
2 2 2 NOTES ON GILDING.
of gold, would also withstand the action of the usual test for gold—nitric acid. The introduction of the electro-gilding art greatlyfavoured such unscrupulous persons as desired to prey upon the publicby selling as gold electro-gilt articles, which had not a fraction of theprecious metal in their composition. An alloy of this kind entered themarket many years ago, in the form of watch-chains and other articlesof jewellery, the composition of which was, copper 16 parts, platinum7 parts, and zinc I part. This alloy, when carefully prepared, bearsa close resemblance to i6-carat gold, and when electro-gilt wouldreadily pass for the genuine article. The manufacture of this varietyof spurious gold seems to have received a check for a certain period ;but somewhat recently, in a modified formula, it has reappeared, notonly in the form of articles of jewellery, but actually as current coin,and from its highly deceptive character, being able to resist the usualtest, it has acquired the name of ** Mystery Gold." It appears that,when converted into jewellery, the chief aim of the " manufacturers "is to defraud pawnbrokers, to whom the articles are offered in pledge;and, since they readily withstand the nitric acid test, the " transac-tions " are often successful. According to Mr. W. F. Love, in acommunication to the Chemical News, a bracelet made from an alloy ofthis character had been sold to a gentleman in Liverpool, and whenthe gilding was removed the alloy presented the colour of 9-caratgold. The qualitative analysis proved it to be composed of platinum,copper, and a little silver. A qttantitativc analysis yielded the followingresult:—
Silver .PlatinumCopper (by difference)
2-48
32-02
It was found that strong boiling nitric acid had apparently no effectupon it, even when kept in the acid for some time.
17. Gilding Watch Dials.—To prepare a silver watch dial (for ex-ample) for gilding, it should be laid, face upward, upon a flat pieceof cork, and the face then gently rubbed all over with powderedpumice, sifted through a piece of fine muslin, and slightly moistenedwith water, using the end of the third finger of the right hand for thepurpose. The finger being dipped in the pumice paste, should beworked with a rotary motion over the surface of the dial, so as to pro-duce a perfectly uniform and soft dulness. When this is done, apiece of copper slinging wire is passed through the centre hole ofthe dial, and formed into a loop ; the dial is then to be rinsed, andplaced in the bath, care being taken not to touch the face of thearticle either before or after gilding, except in the way indicated.The dial must afterwards be repainted.
DISCOLOURED SOLUTIONS. 2 2 5
large quantities of solution are employed, this addition need not bemade more than once a day, or at the close of the operation. Withthis exception, a good gilding solution will continue to give uniformlygood results for many days—especially if large in bulk—withoutalteration. When it begins to work tardily, however, which majreadily be soon by the extra anode surface required to gild the article-,promptly, moderate additions of cyanide must be given until the bathacquires its normal activity.
25. After working gilding-baths for a lengthened period, theygenerally assume a brown colour, and the gilding is, under suchcircumstances, of an indifferent colour. The chief causes of this discoloration have been already explained, and can be to a great extentavoided, by thoroughly rinsing the articles before putting them inthe bath. When a solution is in this condition the best remedy is toevaporate it as before, and then redissolve the dried mass in distilledwater, using about one-third less water than the original bulk. Alittli fresh cyanide must also be added, and the solution filtered, afterwhich it will generally yield a deposit of excellent colour. Old solu-tions which give deposits of a greenish-black colour may be improvedby evaporation, but the heating of the dried product should be carriedsomewhat farther than in the former cases. It is better, however, toabandon such a solution altogether and to make a fresh one. The goldfrom the waste solution may afterwards be recovered by the processesgiven in another chapter. When gilding solutions, after being workedsome time, yield a pale straw-coloured gilding, this is attributed bysome to the gradual accumulation of silver from the gold anodes(which always contain a trace e>f silver) : we are, however, disinclinedto accept this view, owing to the exceedingly small quantity of silverpresent in fine gold ; moreover, since silver deposits first, if presentin a gold solution, we doubt its liability to accumulate in the bath.We would rather attribute the paleness of deposit referred to, to oneor both of the following causes : — 1 . To the presence of a large excessof carbonate of potash in the bath from using an inferior cyanide ;2. To the presence of tin derived from pewter soldered articles, imper-fectly prepared for gilding.
26. The Tmiisen battery is most generally used for gilding, andindeed the current from this source produces a golel deposit of vt ryline colour. It must be used with caution, however, when gildingarticles at a low price, since it deposits the metal \ t r y freely from hotsolutions, and would soon yield a coating of gold of greater thicknessthan would pay for ordinary cheap work. In gilding >\ith thisbattery, the regulation of the anode surface hi se>lution should bestr'r tly observed, only a sufficient surface being exposed to enable thearticle to become gilt almost immediately after immersion , the anode
2 24 NOTES ON GILDING.
22. GiM'u/ff Lead, liritanma Mcfaf, $r.—When articles composed oflead, tin, Britannia metal, iron, or steel are required to be gilt, it isbest to give them a preliminary coating" of copper in an alkaline bath,or to electro-brass them, after which they may be gilt with perfectease, and with but little liability to strip when scratch-brushed. Thesofter metals, however, will require to be burnished with great care,owing to their yielding nature under the pressure of the burnishing1
tools. The same observation also applies, inversely, to silvered orgilt steel work, in which case the superior metals, being softer thansteel, become expanded under the influence of the burnishing toolafand are consequently liable to become separated, in blisters, from theunderlying harder metal.
23. Execs* of Cyanide Injurious.—When a newly prepared gildingsolution is fir t used (hot), the deposit is usually of a rich, fine goldcolour, if a sufficient quantity of free cyanide has been employed inits preparation, a proper surface of anode immersed in the solution,and the current brisk. If, on the other hand, the colour is pale—thatis yellow, without the characteristic orange tint—this indicates thatone or other of the above conditions is wanting. Before venturingto increase the amount of free cyanide, the condition of the batteryshould be examined, the temperature of the solution raised a little,and a larger anode surface immersed, when, if the solution still yieldsa light-coloured deposit, an addition of strong cyanide solution mustbe given gradually until the gilding assumes the proper orange-yellowcolour. The addition oi cyanide must always be made with caution,for if too great an excess be applied, the solution is apt to yieldbrown deposits, quite unsuitable for many articles of jewellery ware.This quality of gilding, however, is frequently taken advantage offor articles which are required to have a deep gold colour afterscratch-brushing, as the insides of tankards, &c, and also Albertchains and work of a similar description. If a gold solution isin really good working condition, and the current sufficiently brisk, acopper or brass article should gild readily, in hot solutions, with ananode surface considerably less than that of the cathode, or articlebeing gilt, especially if no motion be given to either electrode. Asilver article, however, would require, in the same bath, a much largersurface of anode, but more especially if the surface were frosted, as infiligree work. In gilding articles of this description it is better toexpose a large anode surface and keep the article in gentle motionwhen first put into the bath, after which a portion of the anodemay be withdrawn, and the object allowed to rest undisturbed untilthe coating is sufficiently thick.
24. In working small baths, additions of hot distilled water mustbe given frequently to make up for the loss by evaporation; but where
CHAPTER XIV.
ELECTRO-DEPOSITION OF SILVER.
Preparation of Nitrate of Silver.—Observations on Commercial Cyanide.—Pieparation of Silver Solutions —Bright Plating —Deposition by SimpleImmersion—Whitening Ai tides by Simple Immersion.—WhiteningBrass Clock Dials, &c.
THE process of " electro-plating- " may be considered the most impor-tant branch of the great art of electro-deposition. Not only is itinvaluable in giving to articles manufactured from German silver,Britannia metal, and other metallic surfaces, a beautifully whitecoating of the precious metal even superior in brilliancy to that ofstandard silver, but old plated and electro-silvered articles, from whichthe silver has worn off, may be resilvered by this process and madeto look nearly equal to new, which there was no practical means ofdoing before the introduction of electro-plating. This term, by-the-byc, though generally used, is erroneous, since the process of platingconsists in attaching two plates, or ingots of metal, and rolling theminto sheets, from which, as in the old manufacture of Sheffield plate,various articles of utility are, or rather were, made.
Preparation of Nitrate of Silver.—Since the silvering or "plat-ing" solutions—with one exception—are prepared from the nitrate ofsitter, it will be necessary to consider its preparation previous toexplaining the various ways in which silver baths are made up fromthis salt of silver. To prepare nitrate of silver, the required quantityof g)ain &\hc? is carefully put into a glass flask* or evaporating dish,the former by preference, since during the chemical action whichensues while the solution of the metal is taking place, a portion of themetal may bo lost by the spitting of the solution when the chemicalaction is at its height. In dissolving silver, take, say—
(jruiii silverPure nitric acidDUtiltud 01 rain water
7 ounces.34 .,
* When dissolving large quantities of silver, a stoneware vessel may beemployed.
2 2 6 NOTES ON GILDING.
may be gradually lowered a little as the deposition progresses. Articlesthat only require to receive a mere colour of gold upon them (as incheap jewellery) should be first scratch-brushed, then well rinsed inhot water; dipped for a moment in the gold bath, then rinsed, andlightly scratch-brushed again, and after again rinsing receive amomentary dip in the gilding bath; they are to be finally rinsed inboiling water, then shaken well, and placed in hot boxwood sawdust,from which they are afterwards removed and well shaken to cleansethem from this material.
COMMERCIAL CYANIDE OF POTASSIUM. 2 2 9
more ; hut for most practical purposes from 1 ?, to 2 ounces will boinite sufficient; indeed, some of our best results have heen obtainedA'ith 1 ounce of silver per gallon.
In ino^t of the formnke given, I gallon of solution will he taken as:he bii>is for making up any required quantity of silvering hath ; andt will be readily understood that when larger proportions of silver to.he gallon are preferred, a proportionate increase of cyanide must 1M1
i<ed, not only to dissolve the precipitated metal, but also to play the part»f ffir vijiinnh in tlic solution. It must he remarked here, that unit ss•he ^ilvering-hath contains an excess of cyanide of potassium, themode, or <h^o]t \mj plate, who^e function it is to resupply the solutionwith silver in the proportion in which it is deposited upon the articles,^vill not keep up the uittullte .stenx/th of the hath, and consequently itv\ 111 deposit the metal slowly. A large excess of cyanide, on the otherhand, is not only unnecessary, but is liable to cause the deposited-ilver to blister and strip, or peel oft* the work under the pressure of:he burnishing tools ; and when very greatly in excess, the coatingwill be so non-adherent that it rnny even yield to the scratch-brush,md separate from the underlying metal.
Observations on Commercial Cyanide of Potassium.—Since:he cyanide of potassium is one of the most important and useful sub-stances that come under the command of the electro-depositor, whilethe success of his operations greatly depends upon its act ire quality, it isulvisable to state that ordinary commercial cyanide varies considerablyn this property ; so much so, indeed, as to render it absolutely neces-sary that the user should be put on his guard, lest in purchasing aiheap and "worthless article, he should commit an error which may?ost him much trouble and annoyance, as also pecuniary loss. Beforenaking up any solution in large quantity, in which cyanide of potas-sium is the solvent, we advise him first to obtain samples of the com-iicreial article, and to test them by either of the processes given inmother chapter.* "We may state that some of the cheap cyanides eon-ain a large exeesr. of carbonate of potash. This substance, while)cing a necessary ingredient in the manufacture, is also frequentlyised greatly in excess to produce a cheap article, and may be calledts natural adulterant. This salt (carbonate of potash), however,mless specifically recommended in the preparation of certain depositingsolutions, is not only useless, but when greatly in excess reduces theconductivity of both silvering and gilding baths.
Preparation of Silver Solutions.—Solution 7. The solutions otdiver most generally used for electro-plating arc those eommonly\nlled '" cyanide solutions," the foremost of which is the double njanult)f silver and potassium, which is prepared as follows : 1 ounce of silvers converted into nitrate, as previously described, and the crystals dis-
* See p. 431, et seq.
228 ELECTRO-DEPOSITION OF STLVER.
Put the silver carefully into the flask, then adJ the water, and lastlythe acid. In a few moments vigorous ebullition takes place, with thedisengagement of red fumes of nitrous gas, which should he allowedto escape through the chimney. When the action begins to quietdown a little, the flask must be j^laced on a warm sand-bath. Forsmall operations, or where a j)roper sand-bath is not 2>i*ovided, anordinary frying-pan nearly half-filled with silver-sand will answerthe purjwse well. The flask should remain irpon the sand-bath untilthe red fumes cease to appear in the bulb, at which period the chemicalaction is at an end. It may be well to mention that, in dissolvingsilver, it is advisable in the first instance to use rather less of the acidth.iu is necessary to dissolve the whole of the silver, and to treat theundissolved portion separately, by which means excess of acid isavoided. The nitrate of silver solution must now be decanted into anevaporating dish and j)laccd in the sand-bath, where it is allowed tolvm-iin until a film or pellicle forms on the surface of the liquor, whentlie vessel must be set aside to cool. A few hours after, crystals ofnitrate of silver will have deposited, from which the remaining liquoris to be poured off, and this again evaporated as before. Instead otcrystallising the nitrate, it may simj)ly be evaporated to nearly dry-ness, by which the free acid will become exjwlled.
Should the nitric acid used in dissolving silver contain even a slightportion of hydrochloric acid, an insoluble white precipitate will befound at the bottom of the flask, which is chloride of silver. This,however, will not be injurious to the plating solution. Sometimes,also, a slight deposit of a brownish-black colour is found at thebottom of the vessel in which silver is dissolved ; this is (/old, left inthe grain silver through inrperfect/w/^y in the refining process. Wehave occasionally discovered more than a mere trace of gold at thebottom of the dissolving flask ; indeed in several instances an appre-ciable quantity.
"When dissolving the crystals of nitrate of silver, for the j^rejxirationof either of the following plating solutions, distilled or rain wateronly should be used, since river water always contains traces of sub-stances which form a white precipitate in the presence of nitrate ofsilver.
In describing the silver solutions, the j^oportion of silver in themetallic slate will be given, and it will be understood that in each casethe weighed metal must be first converted into nitrate. We may alsostate that the proportion of silver to each gallon of solution may be\.tried according to the practice of the |)later, some persons preferringsolutions in -which there is a moderate percentage of the metal, 'whileothei\s employ much greater quantities. The projKU'tioii of silver pergallon of solution ranges from h an ounce to 5 or 6 ounces, and even
PREPARATION OF SILVER SOLUTIONS. 231
Fig. 79.
of the precipitate is dissolved, to allow the vessel to stand for a shorttime, then to pour off the clear liquor—which is now a solution of thedouble cyanide of silver and potassium— and to treat the remainder ofthe precipitate with cyanide solution ; by this means too great anexcess of the solvent is avoided. "When all the precipitated silver isredissolved, add about one-fourth more cyanidesolution than that originally used, and pass thesolution through a filter into the plating vat ordepositing vessel, which may be convenientlydone by means of a piece of unbleached calico(previously washed in lukewarm water toremove the "dressing") stretched over threestrips of wood bound together in the form ofa triangle either with copper wire or string,as in Fig. 79. When all the solution has passed through the filter,this may be washed by pouring a little water over it while restingover the bath. The solution is finally to be made up to the full quan-tity by adding the necessary proportion of water, when its preparationis complete ; it will be better, however, to allow it to rest for twenty-four hours before using it for electro-plating.
Free Cyanide.—This term is applied, as we have before hinted, to amoderate excess of cyanide of potassium which it is always necessaryto have in the bath, to dissolve the insoluble cyanide of silver whichforms on the anode, but since the ordinary commercial article is ofvery variable quality, the addition of this substance must to a greatextent depend upon the judgment of the plater, subject to the precau-tions we have previously given ; from one-fourth to one-half the quan-tity of cyanide used in dissolving the precipitate of cyanide of silver maybe added to the solution as free cyanide, and water then added to makeup 1 gallon. If the cyanide, in the first instance, be dissolved in adefinite measured quantity of water, say at the rate of half a pound toa quart of water (40 ounces), the proportion of cyanide used in each ofthe former cases can be readily ascertained by simply measuring thebalance of the solution and deducting its proportion of cyanide fromthe original weight taken. A fair quality of ordinary commercialcyanide should not contain less than 50 per cent, of pure cyanide, butwe have frequently met with an article which contains a very muchlower percentage, which should never be used for making up platingsolutions, but maybe employed in the less important process of dippingin the preparation of work for nickel-plating. Of course it will beunderstood that when cyanide containing a high percentage of the puresubstance is obtained, a proportionately smaller quantity must be used.
Solution II.—One ounce or more of silver is converted into nitrateas before, and the crystals dissolved in from three to four pints of dis-
230 ELECTRO-DEPOSITION OF SILVER.
solved, with stirring, in about 2 quarts of distilled or rain water, whichmay, in the case of small quantities, be effected in a glass vessel orglazed earthenware pan. For large quantities a stoneware vesselshould be used. When the crystals are all dissolved, a strong solutionof cyanide (about J a pound, dissolved in I quart of water) is added,a little at a time, when a precipitate of cyanide of silver will be formed,which will increase in bulk upon each addition of the cyanide. Eachtime, after adding the cyanide solution, the mixture must be wellstirred with a glass rod or strip of wood free from resin. When it isfound that the addition of cyanide produces but little effect, it mustbe added very cautiously, since an excess will redissolve the precipitate,and cause waste in the after process of washing this deposit. Toavoid adding too much cyanide, the precipitate should be allowed tofall down an inch or so, when a glass rod may be dipped in the cyanidesolution, and the clear liquor touched with this, when if a milkinessis produced, a little more cyanide must be added, and the stirringresumed. After a short repose, the same test may be applied, and soon, until a drop of cyanide solution produces no effect. Great caremust be taken not to add more cyanide than is absolutely necessary tothrow down the silver. As an additional precaution, when nearlythe whole of the silver is precipitated, the vessel may be allowed torest for an hour or so, and the clear liquor then poured off and treatedseparately, by which means the bulk of the precipitate will be savedfrom the risk of coming in contact with an excess of cyanide. If,through accident or faulty manipulation, too much cyanide has beenadded, more nitrate of silver solution must be poured in, which, com-bining with the surplus cyanide, will again produce the characteristicmilkiness ; and if the additions of nitrate are made with care, theclear liquor will be perfectly free from silver, and after allowing thecyanide of silver to deposit, may be poured off and thrown away.
Washing the Precipitate.—In all such cases the precipitate should beallowed fully to settle; the supernatant liquor, or "mother liquor,"is next to be poured off slowly, so as not to disturb the solid matter(cyanide of silver) ; a large quantity of fresh water—which for thispurpose may be common drinking water—is now to be poured on tothe precipitate with brisk stirring, and the vessel again left to rest,after which the clear liquor is to be poured off as before, these washingsbeing repeated three or four times.
Dissolving the Precipitate.—To convert the cyanide oi silver into thedouble cyanide of silver and potassium, the strong solution of cyanidemust be added in moderate portions at a time, constantly stirring asbefore, until the precipitate appears nearly all dissolved, at whichperiod the additions of cyanide must be made with more caution. Inthis case, as in the former, it is a good plan, when nearly the whole
PREPARATION OF SITA'EK SOLUTIONS. 233
redissolve the precipitate. When the precipitation is nearly com-plete, it i-* Letter to allow the vessel to rest, and t'> put n little of theclear liquor in a te^t tube, Flu*. 80, and to add u drop or two of theiodide solution, when if n cloudiness is produced, a moderatequantity of the iodide is to be added to the bulk and v»dlstirred in. The clear liquor should be repeatedly tested in thisway, until a single drop of the iodide solution produces nofuvtlki1 eit'eet upon it. In ease of an accidental addition ofloo much iodide, nitrate of silver solution must be added tom utr.fiiv it. AVh« u the precipitation i^ coiu]>lete, th-> \c-siliMii- t be *>et aside- - in a dark place, since the iodide of silver i^atl'ected by light—for an hour or so, after "which the clearliquor must be poured oft', and the precipitate repeatedly y\{f $a
washed with cold water. Lastly, the iodide of silver is to bedissolved in a solution of cyanide of potassium, and a moderate excessadded as before recommended. In working this solution, whcne\erthe anode becomes coated with a greenish film, an addition of cyanidenni^t be made to the bath.
Since the system of working the above solution differs in severalrespects from that adopted with other solutions, it may be well todescribe our own practice in the treatment of German silver work.The articles are first placed in a warm solution of caustic potash, to"omnve greasy matter, after which they are well rinsed. Each articleis thai -well scoured all over with powdered pumice and water, orKuely powdered bath brick—an excellent substitute for the former—and water. As each article is brushed, it is to be well rhw\l in cleanwater, and is then ready for the plating bath, in which it should be<iimpend' >d without delay.
Solution V.—Mr. Tuck obtained a patent, in 1842, for "improve-ments in depositing silver upon German silver,'1 in which he recom-mend^, for plating inferior qualities of German silver, a liquid com-posed of sulphate of .sihrr dissolved in a solution of carbonate ofammonia. Sulphate of silver is formed by adding ? solution ofsulphate of soda (Glauber's salt) to a solution of nitrate of silver, or}»y boiling silver with its weight of sulphuric acid. For plating thebetter qualities of German silver, cyanide of silver is dissolved in a•- tlution of carbonate of ammonia. The proportions used are : —
Sulphate of silverCarbonate of ammonia (dissolved in distilled water)
Or,
Cyanide of silverCarbonate o f ammoni.i . . . . . .
15O70
13*70
p.nt
232 ELECTRO-DEPOSITION" OF SILVER.
tilled water. A solution of carbonate of potash (salt of tartar), eon-: i-1i 11 u* <>F about six; ov eight ounces of the salt to a pint of water, is tnbe gradually added to the solution of nitrate of silver, with constantsiirrhig, until no further precipitate >n takes place. After settling,the rK-ir liquor is poured off, and the precipitate (carbonate of sih-a*)Av.i hel v/itli water several times, as before directed. A strong1 solu-ti m of cyanide is then to be added until all the precipitate is thoroughlydissolved, when a molorate excess is to be added as free cyanide.The solution should now bo filtered and water added to make up oneL»\ill<»n, •>'.' Mich quantity in the saii\v> proportion of materials as in ly 1><*r |!iii\' I. Tn adding exci .ss of cyanide to this and other solutions, ifi-i al\»*»y^ preferable to add it moderately at fir.st, otherwise the work-is v TV liable to strip. After working* the bath for some time, antt/llition of cyanide maybe made, but so long1 as ihe anode keepsperfectly clean while the work is being plated, the less free cyanidethere is in the bath the better. A solution which has been workedfor a considerable time acquires a g-ood deal of organic matter, becom-ing dark in colour in consequence, and is then capable of bearing,without injury to the work, a larger proportion of free cyanide thannewly prepared solutions.
Solution III.—Mr. Alexander Parkes, in 1871, patented a solutionfor depositing solid articles. One ounce of silver is first convertedinto nitrate, from which the silver is thrown down in the form ofo.>\'f of silver, by means of a solution of caustic potash graduallya Ided, until no further precipitation takes place. After washing theoxide, it is dissolved in 2 gallons of water containing 16 ounces ofcyanide of potassium.
Solution IV.—The best solution for depositing silver upon Grcrmansilver without recourse to the process of " quicking," is one which theauthor employed upon an extensive scale for many years with urreatsuccess; it is composed as follows, and although it is rather moreexpensive in its preparation than many other solutions, it is, so far asho is aware, the best solution in which German silver work may beplated without being previously coated with mercury, as in the" quicking" process hereafter referred to. To prepare the solution,1 ounoe of silver is converted into nitrate and dissolved in two or threepints of distilled water as before. About three ounces of ioiUrfr *fpotassium are next to be dissolved in about half a pint of distilledwater. The iodide solution is to be gradually added to the nitratesolution, the operation being performed in a dark corner of theroom, or preferably by feeble gaslight, when a bright lemon yellowprecipitate Avill be formed. The liquid must be hrihkly stirredupon each addition of the iodide, and care must be taken notto add the latter salt on any account in excess, otherwise it will
PKEPARATION OF SILVER SOLUTIONS. 235
electrode of a strong voltaic battery, and placed in the porous cell.A large sheet of silver is next to be connected to the positive elec-trode, and immersed in the larger vessel. The arrangement is shownin Fig. 81. The weight of the sheet silver being ascertained before-hand, the battery is allowed to remain in action for several hours,when the silver plate may be weighed to determine how much of ithas been dissolved in the solution, and the action is to be kept upuntil the proper proportion has been dissolved by the cyanide in theouter vessel. When this point has been reached the porous cell is tobe removed, and its contents may be thrown away.
Another electrolytic method of preparing a silver bath is the follow-ing :—To make a bath containing, say, one ounce of silver per gallon,the cyanide should be of known strength. Assuming the commercialarticle to contain .50 per cent, of real cyanide, about 3 ounces are tobe dissolved in each gallon of water ; a large silver anode connectedto the positive pole of a battery is to be suspended in the solution,and a smaller plate of silver as a cathode. A strong current shouldbe used, and the anode weighed from time to time until the desiredproportion of silver has become dissolved into the solution. The con-dition of the bath may then be tested by suspending a clean plate ofbrass from the negative rod, at the same time immersing about anequal surface of anode, using a moderate current, when if the solu-tion be in good working order, the cathode will at once receive abright deposit of silver. During the action some caustic potassa isformed in the liquid, which may be converted into cyanide, byadding a moderate quantity of hydrocyanic acid, which must be done,however, with exceeding care, owing to the deadly nature of the acid,the vapour of which must not on any account be inhaled. Respectingthe use of this acid, however, we must strongly recommend that its em-ployment should never, under any circumstances whatever, be placed inthe hands of persons unacquainted with its highly poisonous character.
Besides the foregoing, many other processes for preparing silversolutions have been proposed ; but since they are comparatively oflittle or no practical value, they deserve but a passing reference. Byone of these processes chloride of silver is dissolved in hyposulphite ofsoda. The salt of silver thus formed {hyposulphite of sihcr) is readilyacted upon by light, and the silver, being thus converted into aninsoluble sulphide, gradually becomes deposited at the bottom of thebath. Solutions have also been prepared by employing ferroeyanideof potassium (yellow prussiate of potash) as the solvent of cyanide ofsilver. Again, the silver has been precipitated from its nitrate solu-tion by lime-water, forming oxide of silver ; as also by ammonia,poda, magnesia, &c. ; the various precipitates being subsequently dis-solved in a solution of cyanide of potassium. The ordinary double
234 ELECTRO-DEPOSITION OP SILVER.
The silver salt in each case is boiled with the solution of the car-bonate of ammonia until it is dissolved. For coating common Germansilver, he adds half an ounce of sulphate of silver to a solution con-taining 107 grains of bicarbonate of ammonia.
Solution VI.—For producing very white deposits of silver, thsfollowing may be used :—One ounce of silver is dissolved and treatedas before, and the crystals of nitrate redissolved in about half a gallonof distilled water. A moderately strong solution of common salt isthen prepared, and this is gradually added to the former, when acopious white precipitate of chloride of silver is formed, which must bewell washed with cold water. After pouring off the last wash water,a strong solution of cyanide is to be added to the precipitate until it isall dissolved, when a moderate excess is to be added, and the solutioncarefully filtered through filtering paper, the first runnings to bepassed at least twice through the same filter. Lastly, add water tomake up 1 gallon. The solution may be used immediately, but willwork better after a few hours' rest. This solution is very useful forobtaining delicately white deposits, but is not suitable for ordinaryplating purposes, since the deposited silver is liable to strip under theaction of the burnisher. If used somewhat weaker than in the aboveproportions, with a moderate current and small anode surface, thedeposit will adhere to most metals with tolerable firmness ; it is, how-ever, most suitable for coating articles which are either to be merelyscratch-brushed or left a dead white. Chased figures and cast metalwork receive a brilliant white coating in this solution, but to retaintheir beauty they must be kept beneath a glass case, since the finesilver surface soon discolours in the atmosphere.
Solution VII.—This plating solution, which is one of the best formost purposes, is prepared by dissolving bilver in a solution of cyanide,
by aid of the electric cur-rent. Suppose we wish thesolution to contain [ ounceof silver per gallon. Therequired quantity of wateris first put into the bath,and for each gallon ofliquid about 3 ounces ofgood cyanide is added,and allowed to dissolve.A porous cell is now to benearly filled with this
solution, and stood upright in the vessel containing the bulk ofcyanide solution, the liquid being at the same height in both vessels.A strip of sheet copper is next to *be connected to the negative
Fig. 81.
TVRIGIIT rLVHNG. 237
The solution is then bet aside to rest for about lM hours, when it•will be ready for use About *2 ounces of the clear liquid may beadded to every 20 gallons of ordinary plating solution, and well mixedby stirring-. A small quantity of the brightening solution, or "bright ,"ns it is termed in the plating-room, may be added to the solutionevery day, and the liquid then gently stirred. In course of time thebisulphide soluti-m acquires a black colour, to modify which a quantityof strong' cyanide solution, equal to the brightening liquor whieh hasbeen removed from the bottle, should be added each time. In addingthe bisulphide solution to the plating bath an excels must be avoided,otherwise the latter will be spoilt. Small doses repeated at intervalsis the safer pio'edure, and le>.s risky than the application of largerquantities, which may ruin the bath-
A very simple way to prepare the brightening solution is to putfrom 2 t't 3 ounces of bisulphide of carbon in an ordinary k" Winches-ter " bottle, which holds rather more than half a gallon. Now addto this about 3 pints of old silver solution, and shake the bottle wellfor a minute or so : lastly, nearly fill the bottle with a strong solutionof cyanide, shake well as before, and set aside for at least 24 hour.-,.Add about 2 ounces (not more) of the " b r i g h t " liquor, withoutshaking the bottle, to each 20 gallons of solution in the plating vat.Even at the risk of a little loss from evaporation, it is best to add i\wbrightening1 liquor to the bath the last thing in the evening, whenthe solution should be well stirred so as to thoroughly diffuse theadded liquor. The night's repose will leave the bath in good workingorder for the following morning.
Other substances besides the bisulphide of carbon have been used,or rather recommended, for producing a bright deposit of silver, butup to the present no really successful substitute has been practicallyadopted. Among.st other compounds which have been suggested, area solution of iodine and gutta-percha in chloroform, which i.s said tohave a more permanent effect than the bisulphide ; carbonate, and acidcarbonate of potassium, 1^ ounce of each, added once every nine orten days to a plating solution containing 12 ounces of cyanide and31 ounces of silver per gallon. According to Plante, bright silverdep >sits may be obtained by adding a little sulphide of silver to theplating solution.
Although the solution for kt bright plat ing" is useful for some pur-poses, it i>s not adopted as a substitute for the ordinary cyanide ofsilver bath for the general purposes of electro-plating. For articles•which have deep hollows and interstices which cannot be burnishedwithout considerable difficulty, and for the hwides of tea and c >ilee-pots, mid artich s of a similar description, which are required to bebright, but which cannot be rendered so by mechanical methods, a
2$6 ELECTRO-PErOSITlON OF SILVER.
cyanide of silver and potassium solution, however, will be found mostuseful for the general purposes of electro-plating'.
Bright Plating.—The silver deposited from ordinary cyanide solu-iioiisis of a pearly white or dull white, according to the condition andnature of the silver solution, and the strength of the current; and itivS necessary to brighten the work by scratch-brushing before it issubjected to the operations of burnishing or polishing. It is j>os«tible,however, by adding to the plating-bath a small quantity of bi»ulph\(lcuf nn'ttn//, to obtain dejx>siN of silver which are bmjlit instead of dull,for tin• dw'uvorv of Avhich important improvement we are indebted toMr. W. Milward, of IJirmingham, who made the discovery in the fol-lowing way:—He had observed that when Avax moulds for electro-typing, which had been coated with a film of phosphorus by applyinga solution of that substance in bisulphide of carbon, were put into thecyanide plating1 solution to receive a deposit of silver, that otherarticles—as spoons and forks, for example—silvered in the same solu-tion, assumed a brightness more or less uniform, sometimes extendingall over the articles, and at others occurring in streaks and patches.This led him to try the effect of adding bisulphide of carbon alone tothe j)lating .vdution, which produced very satisfactory results. Theimprovement was woiked as a secret for some time, but eventuallyleaked out, in consequence of which Mr. Milward and a person namedLyons (who had become acquainted with the secret) took out a patentin March, 1847,1*01* bright silver deposition by adding " compoundsof sulphur and carbon," bisulphide of carbon being preferred. Fromthat time the bisulphide of carbon has been constantly employedfor producing1 bright deposits of silver.
To make up the solution for "bright plating," the followingmethods are adopted: 1. "6 ounces of bisulphide of carbon are putinto a stoppered bottle, and 1 gallon of the usual plating solutionadded to i t ; the mixture is first to be well shaken, and then set asidefor 24 hours. 2 ounces of the resulting solution are then added toevery 20 gallons of ordinary plating solution in the vat, and the wholestirred together ; this proportion must be added every day, on accountof the loss by evaporation, but where the mixture has been madeseveral days, less than this may be used at a time. This proportiongives a bright de2>o it, but by adding a larger amount a dead surfacemay be obtained, very different to the ordinary dead surface."
-Another method of preparing a solution for bright plating is thefollowing:—Put 1 quart of ordinary silver plating solution info alarge stoppered bottle; now add 1 pint of strong solution of cyanideand shake well; 4 ounces of bisulphide of carbon are then to be added,as also 2 or 3 ounces of liquid ammonia, and the bottle again wellshaken, which operation must be repeated every two or three hour:?,
WHITENING ARTICLES BY SIMPLE IMMERSION. 2 39
be rinsed in hot water, and shaken up with boxwood sawdust. Thesepreparations are also used for silvering clock-faces, thermometer andbarometer scales, and other brass and copper articles, by being rubbedover the surface to be whitened with a cork.
Another chloride of silver paste, for whitening articles of brass orcopper, may be made by taking chloride of silver and prepared chalk,of each one part, common salt IJ- part, and pearlash 3 parts, madeinto a paste, as before. A third mixture is prepared by takingchloride of silver I part, cream of tartar at least 80 parts, to which issometimes added about 80 parts of common salt. The whole aredissolved in boiling water. This solution acquires a greenish tint,from the presence of copper, which takes the place of the silver in theliquid. In using this solution the articles are introduced by means ofa perforated basket, which is briskly stirred about in the hot liquiduntil uniformly white. Some operators modify the above solution byadding common salt, Glauber's salt, corrosive sublimate, caustic lime,&c, but it is doubtful whether any advantage is derived therefrom.
A process, which is to be applied cold, was proposed by Roseleur.and seems to have worked exceedingly well in his experienced hands.A solution of the double sulphite of silver is formed in the followingway : Four parts of soda crystals are dissolved in five parts of distilledwater, sulphurous acid gas (prepared by heating in a glass retortstrong oil of vitriol with some small pieces of copper wire) is thenpassed through the liquid, by allowing it to bubble through mercuryat the bottom of the vessel, to prevent the exit tube from becomingclogged with crystals; the gas is allowed to pass until the fluidre-dissolves the crystals of bicarbonate, and slightly reddens bluelitmus paper. It is then allowed to repose for twenty-four hours, sothat some of the bisulphite of sodium formed may crystallise. Theliquid portion is then to be poured off, and stirred briskly to expel thecarbonic acid. If alkaline to test paper, more sulphuric acid gasmust be added; or if acid, a little more carbonate of soda. After wellstirring, the solution should only turn blue litmus paper violet, or atmost slightly red. A solution of nitrate of silver is now to be addedto the above liquid, with stirring, until the precipitate at first producedbegins to dissolve slowly, when the bath is ready for use. The solutionthus prepared is said to be always ready for work, and "produces,quite instantaneously, a magnificent silvering upon copper, bronze, orbrass articles which have been thoroughly cleansed, and passed througha weak solution of nitrate of binoxide of mercury, although this isnot absolutely necessary." To keep up the strength of the bath freshadditions of nitrate of silver must be made from time to time, andafter awhile some bisulphite of soda must also be added. In workingthis bath the solution is placed in a copper vessel, which also receives
233 ELECTRO-DEPOSITlON OP SILVER.
slight coating of bright silver is an advantage. A bath of brighteningsolution is usually kept for this purpose, in which the articles, afterbeing plated in the ordinary way, are immersed for a short time, bywhich they receive a superficial coating of the bright deposit. In the" bright solution'' the articles first become bright at their lowersurface, the effect gradually spreading upward, until in a shorttime they become bright all over, when they are removed from thebath and immediately immersed in boiling water, otherwise the silverwould quickly assume a dark colour.
Deposition by Simple Immersion.—Articles of brass and copperreadily become coated with a film of silver, without the aid of thebattery current, in tolerably strong solutions of the double cyanide ofsilver and potassium ; the deposit, however,' is not of such a degree ofwhiteness as to be of any practical use. Other solutions of silver aretherefore employed when it is desired to give a slight coating of thismetal to small brass or copper work which will present the necessarybrilliant white colour. Silver may also be deposited upon thesesurfaces by means of a paste of chloride of silver, to which commonsalt or cream of tartar is added. The following processes are thosemost generally adopted:—
Whitening Articles by Simple Immersion.—For small brassand copper articles, as buttons, hooks and eyes, coffin-nails, &c,silvering by simple immersion is employed; and in order to producethe best possible effect, the solution bath should not only be preparedwith care, but kept as free as possible from contamination by othersubstances. To prepare a bath for this purpose, a given quantity offine grain silver is dissolved in nitric acid. The solution of nitrate ofsilver thus formed is added to a large quantity of water, a strongsolution of common salt is then poured in, which precipitates chlorideof silver in the form of a dense white precipitate. When the wholeof the silver is thrown down (which may be ascertained by adding adrop or two of hydrochloric acid or solution of salt to the clear liquor)the precijntate is allowed to subside, after which the supernatantliquor is to be poured off, and the precipitate washed several times.The last rinsing water should be tested with litmus paper, when, ifthere be the least trace of acid, further washing must be given. Theprecipitate, which is very readily acted upon by sunlight, should beprepared in a dull light, or by gaslight, and, if not required for imme-diate use, it should be bottled and kept in a dark cupboard. Thechloride of silver is to be mixed with at least an equal weight of bi-tartrate of potassa (cream of tartar), and only sufficient water addedto form a pasty mass of the consistency of cream. In this mixturethe articles, having been previously cleaned or dipped, are immersed,and stirred about until thjey are sufficiently white, when they are to
CHAPTER XV.
ELECTRO-DEPOSITION OF SILVER (continued).
Preparation of New Work for the Bath. —Quicking Solutions, or MercuryDips.—Potash Bath.—Acid Dips.—Dipping.—Spoon and Fork Work.—Wiring the Work.—Arrangement of the Plating Bath.—Plating Battery.—Motion given to Articles while in the Bath.—Cruet Stands, vfcc.—Teaand Coffee Services.—Scratch-brushing.
Preparation of New Work for the Bath.—In order to insurea perfect adhesion of the silver deposit to the surface of the articlecoated, or plated, as it is erroneously termed, with this or any othermetal, the most important consideration is absolute cleanliness. By thisterm we do not mean that the article should be merely clean in theordinary sense, but that it must be what is termed chemically clean,that is, perfectly and absolutely free from any substance which wouldprevent the silver from attaching itself firmly to the metal to be coated.As evidence of the extreme delicacy which it is necessary to observe inthis respect, *ve may mention that if, after an article (say a Germansilver spoon, for example) has been well scoured with powderedpumice and water, it be exposed to the atmosphere even for a fewseconds, it becomes coated with a slight film of oxide—owing to therapidity with which copper (a constituent part of German silver)attracts oxygen from the air ; this effect is still more marked in thecase of articles made from copper and brass. Now, this slight andalmost imperceptible film is quite sufficient to prevent perfect contactbetween the deposited metal and that of which the article is composed.This fact, in the early days of electro-plating, created a great deal oftrouble, for it was found that the work, after being silvered, was veryliable to strip under the pressure of the burnisher. To overcome thedifficulty, and to secure a perfect adhesion of the two metals, a thirdmetal—mercury or quicksilver—which has the power of alloying itselfwith silver, gold, German silver, copper, and brass, was employed, andthough the author for many years obtained most successful and per-fectly adherent deposits of silver without its aid, the process ofquicking was, and still is, practised by the whole of the electro-platingtrade. The silver solution which the author employed, however, andwhich is described in the foregoing chapter, was differently prepared
C4O ELECTRO-DEPOSITION OF SILVER.
a deposit of silver. Roseleur states that he used this bath for fiveyears, (luring which period lie daily silvered " as many articles as aman could coirvuiiuitly carry." lie also states that, without the aidof a separate current, the deposit from this solution may become nearlyas thick as desired, and in direct ratio to the time of immersion.
"Whitening Brass Clock-Dials, &c, with the Paste.—For thispurjwso chloride of silver and cream of tartar, with or without theaddition of common salt, is made into a paste, as before described, andthis should be well triturated in a mortar until it is impalpable to thetouch. The paste is then spread, a little at a time, ii]xm the brasssurface—which may be a clock-face or thcrmomcter-scale, for instam e—and rubbed upon the metal surface with a piece of soft cork, or" \ civet " cork as it I*-, called. By thus working- the silver pa'•to overthe metal it soon becomes silvered, and a coating of sufficient thicknessfor its purpose obtained in a very short time, according to the size ofthe object. When the silvering* is compete the article is to be ringedand dried in the hot sawdust. Although a very slight film of .silv< ronly is obtained in this way, its somewhat dull tone is sjxriallv ap-plicable to barometer and u\dvanometer scales (1 >ck-di,ils, and objectsof a similar nature, and, as far as iK won-liability to tarnish is con-cerned, it may be considered superior to all other methods of silvering.
QUICKING SOLUTIONS, OR MERCURY DIPS. 243
immersion ; if the solution be too strong, or too acid (when the nitrateof mercury solution is used), or if the solution has become nearlyexhausted l>y use, when copp< r is dipped it may turn hlmh or darkcoloured instead of white, in which ease the quicking bath must berectitied, otherwise it will be impossible to obtain an adherent coating"of silver upon the article treated in it. As a rule, the article* merelyrequire to become perfectly and uniformly v>hite from the coating* ofmercury, but the practice is to irhe a Mromver nlm to work whit h r-requircel to receive a stout deposit of sil\cr, or gold, a^the case may be."When the mercury dip becomes nearly exhaust( d and the mtruirialcoating", in consequence, becomes dark coloured, the liquor >lu uld bethrown away and replaced by a new solution, which is consider* dbitter than :-trengthening the old liquor ; ineleeel, the small amount otmercury which remains in the bath after having" been freely used is ofso little consideration, that the liquor may he cast aside without sacri-fice the moment it gives evidence of weakness by the dark appearanceof the work instead of the characteristic brightness of metallicmercury.
It is a good plan to keep a quantity of concentrated mercurial solu-tion always in stock, so that when a bath becomes exhausted it maybe renewed in a few minutes by simply throwing away the old liquorand adding1 the due proportions of strong solution and water to makeup a fresh ki elip."
Potash Bath.—To remove greasy matter communicated to the workby the polishing process, all articles to be plated must first be steepedfor a short time in a hot solution of caustic potash, for which purposeabout half a pound of American potash is dissolved in each gallon ofwater required to make up a bath, and as this solution becomes ex-haiii-tcel by use it must receive an addition of the caus-tie alkali. Theworkman may readily determine when the solution has lost its activeproperty by simply dipping the tip of his finger in the solution andapplying it to the tip of the tongue, when, if it fails to tingle or" bite " the tongue, the solution has lost its caustic property, and mayeither be thrown away or strengthened by the addition of more causticpotash. When the bath has been once or twice revived in this wayit is better to eliscarel it altogether, when inactive, than to re\ive it.Indeed, when we consider that the object of the caustic alkali is toconvert the greasy matters on the work into soap, by which tinybecome soluble and easily removed by brushing, it will be apparentthat the bath can only be effective so long as the causticity of thealkali remains. Many persons, from ignorance of this matter, havefrequently used their potash baths long after they have lost theiractivity, nnd as a natural consequence the work has come out of siu hbaths nearly in the same state as they entered it, greasy and dirty.
242 ELECTKO-DETOSITION OF SILVER.
to those ordinarily adopted by the trade. Since the process of"quicking " is generally adopted, it will be necessary to describe it indetail.
Quicking Solutions, or Mercury Dips.— This term is applied, asbefore hinted, to coating articles made of brass, copper, or Germansilver—the metals most usually subjected to the process of chvtro-plating—with a thin film of quicksilver, which may be effected byeither of the following solutions :—Nitrate of Mtrvury JJI/J.—Put anounce of mercury into a gla>s flisk, and pour in an ounce of purenitric acid diluted with three times its bulk of distilled water ; if,when the chemical action ceas.es, a r>mall am junt of uudi&solved mercuryremains, add a little more acid, applying gentle heat, until the wholeis dissolved. The solution is then to be poured iuto about I gallon ofwater, and well mixed by stirring. It is then ready for use, and istermed the quicking solution, or nurcury dip. Articles of brass, copper,or German silver dipped into thi^ solution at once become coated witha thin bright film of mercury.
Cyanide of Mercury Dip.—Dissolve one ounce of mercury as before,and dilute the solution with about I quart of distilled water. Nowtake a solution of cyanide of potassium, and add this gradually,stirring after each addition, until the whole of the mercury isprecipitated, which may be determined by dipping1 a glass rod in thecyanide solution, and applying it to the clear liquor after theprecipitate has subsided a little, when, if no further effect is produced,the precipitation is complete. The liquor is next to be separated In-filtration. When all the liquor has passed through the filter, a littlewater is to be poured on to the mass, and when this has thoroughlydrained off, the precipitate is to be placed in a glass or .stonewarevessel, and strong solution of cyanide added, with constant stirring,until it is all dissolved, when a small excess of the cyanide solution isto be added, as also sufficient water to make up one gallon of solution.
Another mercury dip is made by dissolving red precipitate (red oxideof mercury) in a solution of cyanide, afterwards diluted with water.
Per)iiirate of Mercury Solution.—Tins solution is eonvposed of —
Pernitr.ite of mercurySulphuric acidWater .
1 part.2 parts,
iooo .,
A very good mercury dip may be made by simply dissolving twoounces of mercury in two ounces of nitric acid, without the aid of heat;the solution thus formed is to be diluted with about three gallons ofwater.
The quicking bath should contain just so much mercury in solutionas will render a clean copper surface white almost immediately after
A.CID DIPS. 245
minutes, when they are to be briskly shaken in clean cold water, andif not sufficiently bright must be dipped again. If they becomecovered with a dirty deposit, the articles should be scoured with pumiceand water, then immersed in the dip for a short time and again rinsed.Another method is to first dip the articles in a weak pickle, formed bydiluting old and nearly exhausted nitric acid dip with water for a fewminutes, after which they are to be dipped in the same old acid dip inits undiluted condition, and finally in strong aquafortis for a moment;they are next to be well rinsed in several waters.
Dip for Dead Lustre.—To produce a dead, or matted surface uponcopper, brass, or German silver work, the following mixture is used :—
Brown, or fuming aquafortis (by measure)Oil of vitriol
2 parts.1 part.
To the above mixture a small quantity of common salt is added. Thearticles are allowed to remain for some time in the dip, after whichthey are withdrawn and promptly dipped in the preceding liquid andimmediately well rinsed.
Respecting old aquafortis dips, Gore says these may be " revived toa certain extent by addition of oil of vitriol and common salt; the sul-phuric acid decomposes the nitrate of copper in it, and also the commonsalt, and sets free nitric and hydrochloric acids, andcrystals of sulphate of copper form at the bottomof the liquid. All the nitric acid may be utilised inthis manner." This is perfectly true, but as a ruleacid *' dips '' which have become exhausted seldomproduce the required brilliancy or tone of colour (whenthat is an object), even if strengthened by fresh ad-ditions of the concentrated acids with which they werefir&t prepared. Zinc, tin, and lead, as aLso organicmatter, generally find their way into these dips, andmore or less interfere with the direct action of thenitric acid.
Dipping.—The article to be dipped should be sus-pended by a wire of the same metal, or by a wirecovered with gutta-percha or india-rubber tubing,and after a moment's immersion in the acid solution,promptly plunged into clean cold water; if the desiredeffect—a bright or a dead lustre—is not fully pro-duced by the first dip, the article must be again dipped for amoment and again rinsed. In order to remove the acid effectu-ally, several washing vessels should be at hand, into each of whichthe article is plunged consecutively, but the last rinsing water,more especially, should be renewed frequently. When a number of
Fig. 83.
*44 ELECTRO-DErOSITION OF SILVER.
Those who cannot conveniently obtain caustic potash (American potash,for example) may readily prepare it as follows : Obtain a few lumpsof fresh lime and slake them by pouring water over them, and thencovering them with a cloth ; soon after, the lime will fall into a powder,which must be made into milk of lime, as it is called, by mixing it withwater to the consistence of milk or cream. A solution of pearlash isthen made in boiling water, to which is added the cream oi lime, andthe mixture is to be boiled for at least an hour, in an iron vessel.About half or three-quarters of a pound of pearlash to each gallonshould be employed, and about one-fourth less lime than potash. Ifthe solution is thoroughly causticised, no effervescence will occur in theliquor if a drop or two of hydrochloric acid are added ; if, on the con-trary, effervescence takes place on the addition of the arid, the boilingmust be continued.
Acid Dips.--In the preparation of certain kinds of work, acid solu-tions or mixtures are employed which may be advantageously men-tioned in this place. It is well to state, however, that after dipping thework in acid solutions it should be thoroughly rinsed in clean water, since
the addition of even small quantities of acid to thealkaline plating or gilding baths would seriouslyinjure these solutions. Indeed, careless and im-perfect rinsing must always be avoided in all de-positing operations, otherwise the baths will soonbecome deteriorated ; the rinsing waters shouldbe frequently changed, and the workman taughtthat in this item of his labour his motto shouldbe "water no object."
Nitric Acid Dip.—This is frequently used fordipping copper, brass, and German silver work,
and is the ordinary aquafortis of commerce, or fuming nitric acid, (nitrousacid). Stoneware jugs of the form shown in Fig. 82 are used forconveying strong acids. A dipping acid, composed as follows, is alsomuch used for producing a bright and clean surface upon certainclasses of work :—
Fig. 82.
N i t r i c a c i d , c o m m e r c i a l ( b y m e a s u r e )S u l p h u r i c ac id . . . .W a t e r
1 part.2 parts.2 „
To this mixture some persons add a little hydrochloric acid, and others51 small quantity of nitrate of potassa (nitre).
Dip for Bright Lustre.—To give a bright appearance to copper, &c,the following mixture may be employed:—Old aquafortis, or nitricacid dip which has been much used, 1 part; water, 2 parts ,* muriaticacid, 6 parts. The articles are immersed in this solution for a, few
SPOON AND FORK WORK.247
case, it is usual for the customer to weigh the spoons and forks beforohe sends them to the plater, and again on their return, and he pays somuch per ounce for the silver deposited, allowing a moderate discountfrom the original weight to cover any loss which may be sustained inpreparing the work fur the plating bath. "When the goods, however,
Fig. 87.are merely required to look " marketable," the amount of silverdeposited upon such a class of work often ranges from little or nothingto less, if possible.
Wirutg the Work.—Spoons and forks are first wired, as it istermed. For this purpose copper wire is cut into lengths of about12 inches. A length of the wire is coiled once round the shank or narrowpart of the article, and secured by twisting it several times ; the loopthus formed should be quite loo^e, so that the position of the spoon orfork may be easily reversed or shifted while in the plating vat, toequalise the deposit, and to allow the parts where the wire has beenin contact to become coated with silver. The copper wire used for"slinging" is usually about Ko. 20 B.W.G. (Birmingham WireGauge), which is the gauge most generally adopted in this country.The spoons, Sec., are next placed in the hot potash bath, where theyare allowed to remain for a short time, whenthey are removed, a few at a time, andringed in cold water. They are next to bebrushed or scoured all over with finepumice-powder moistened Avith water, andtin 11 thrown into clean water, where theyremain until a sufficient number havebeen scoured, when these are taken out by their wires and im-mersed in the quicking solution, which, for spoon work, may con-veniently be in a shallow oval pan of the form shown in Fig. 88.After remaining in the quicking bath a short time, they areexamined, and if sufficiently quicked, and uniformly bright, likequicksilver, they are rinsed in water and at once suspended in the
Fie. 38.
246 ELECTRO-DEPOSITION OF SILVER.
small articles require to be dipped, they may be suspended from awire, looped up as in Fig. 8$, or they may \xi placed in a per-forated stoneware basket (Fig*. 84), provided with a handle of thesame material. These perforated baskets are specially manufac-tured at the potteries for acid dipping and other purposes, and ifcarefully treated will last for an indefinite period. The basket con-taining the articles to be dipped is plunged into the dipping acid, andmoved briskly about, so as to expose every surface of the metal to theaction of the acid ; as the vessel is raised the liquid escapes throughthe perforations, and after a brisk shaking the basket and its contents
Fig. 84. Fig. 85.
are plunged into the first washing water, in which it is again vigour-ously .shaken, to wash away the acid as far as possible; it is thentreated in the same way in at least two more rinsing waters. Thedipped articles are then to be thrown into a weak solution of crudebitartrate of potash, called arrjo}, to prevent them from becomingoxidised or tarnished. From this liquid they are removed as required,and again rinsed before being quicked and plated. For dipping1 pur-poses, stoneware and gutta-percha bowls (Fig. 85) are also used, andsometimes platinum wire trays, supported by a hook, as in Fig. 87,are employed for very small articles. Hooks of the same kind, but in
Fig. 86.
various foims, are likewise used for supporting various pieces of workduring the dipping operations. One of these is shown in Fig. 86.
Spoon and Fork Work.—In large establishments this class ofwork may be said to hold the leading position, since, as articles ofdomestic utility, the spoon and fork are things of almost universalrequirement. As in all other kinds of electro-plated ware—and wemay add everything else under the sun—the silvering, or platiiisr, isaccomplished according to the requirement of the customer and theprice to be paid for the work when done. In other words, the actualdeposit of silver which each article receives depends upon whether i'is intended to xvear well, or merely required to all. In the former
ARRANGEMENT OF THE PLATING BATH. 249
swept away with the dirt of the floor. It is more economical toemploy fresh wires for each batch of work, and to strip the silver orother metal from the wires by either of the processes hereafter given,by which not only may all the metal be recovered, but by annealing,cleaning, and straightening the wires, they may be used again andagain. Moreover, a wire that has been twisted once becomes hardenedat that part, and cannot with safety be twisted again without beingannealed.
Arrangement of the Plating Bath.—The size and form of deposit-ing tanks for silver plating vary in different establishments, as alsodoes the material of which they are constructed. For small quanti-ties of silver solution, say from ten up to thirty gallons, oval stone-ware pans may be used, and with ordinary care will labt a greatnumber of years. Wooden tubs, if absolutely clean, may also be em-ployed for small operations, but since that material absorbs the silversolution, such vesselsshould be well soakedwith hot water beforepouring in the solution.Tanks made from slate,with india-rubber joints,have also been muchused in silver-plating.Very good plating tanksmay be made in the sameway as directed fornickel - plating baths,that is, an outer vesselof wood, secured by Fig 90
screwed bolts, lined with sheet lead, and re-lined with matched boai cl-ing. Wrought-iron tanks, lined with wood, are, however, greatly pre-ferred, and when properly constructed and lined, form the most durableof all vessels for solutions of this description. Depositing tanks for largeoperations are usually about six feet in length, three feet in width,and about two feet six inches in depth, and hold from two to threehundred gallons of solution; tanks of greater length are, Lowe\ er,sometimes employed. An ordinary wrought-iron plating tank isshown in Fig. 90, in which also the arrangement of the silver anodesand sundry articles m solution is seen. The upper rim of the tank it>furnished with a flange of wood, firmly fixed in its position, uponwhich rest two rectangles of brass tubing or stout copper rod. Theouter rectangle frequently consists of brass tubing about an inch 111diameter, at one corner of which a binding screw is attached, bymeans of solder, for connecting it with the positive pole of the battery
2 4 8 ELECTBO-DEPOSITION OF S1LVEK.
plating tank, as close together as possible without touching. Whenthe bath is filled with work, the spoons or forks should be turnedupside down by slipping the shank through the loop ; and the work-man who does this must be very careful to handle them as little aspossible, and only to grip them with the fingers by the edges, whichan experienced plater will do with great smartness, and with verytrifling contact with his fingers. The objects of thus changing theposition of the work are twofold, namely, to allow the 11 ire mark tobecome coated with silver, and to equalise the deposit, which alwaystakes place more energetically at the lower end of the article while inthe bath. This system of shifting should be repeatedly effected untilthe required deposit is obtained. When shifting the spoons, &c, allthat is necessary is to raise the straight portion of the suspendingwire which is above the solution with one hand, which brings, say, thehandle of the spoon, out of the solution ; if this be now grippedbetween the finger and thumb of the other hand at its edges, andraised until the bowl end touches the loop, by simply turning thespoon round its bowl will be uppermost, in which position the articleis carefully but quickly lowered into the bath again.
Another method of suspending spoons and forks in the plating bathis the following: Copper wire, about the thickness of ordinary bell
_ wire, is cut up into suitable lengths, and which will dependupon the distance between the negative conducting-rod andthe surface of the silver solution. These wires are next tobe bent into the form of a hook at one end, and at the otherend is formed a loop, as in Fig. 89, leaving an openingthrough which the shank of a spoon or fork may pass intothe ring or loop and be supported by it. To prevent thesilver from being deposited upon the vertical portion ofthe wire, where it would be useless and unnecessary, thisportion of the wire should be protected by means of glass,gutta-percha, or vulcanised india-rubber tubing, which isslipped over the wire before the upper hook is formed.
After being some time in use, the lower ring becomes thickly coatedwith a crystalline deposit of pure silver, when these wires must bereplaced by new ones, and the insulating tubes may be again appliedafter removal from the old wires.
Ordinary slinging wires, as those previously described, should neverbe used more than once, and for this reason : when a certain amountof silver or other metal is deposited upon wire—except under certainconditions—it is invariably more or less brittle, and in attempting totwist it round an article it is very liable to break, often causing thearticle to fall from the hand—perhaps into the bath—and renderingthe silver-covered fragments of wire liable to be wasted by being
Fig. 89.
PLATING BATTERY. 251
0
N!
H
H
11Kin 4
""T
^ 1I1
^ N
£Z
P (. 92.
prevent the zinc from coming in contact with the copper plates, asmall block of wood, having1 a tolerably deep groove of the samewidth as the thickness of the sheet of copper, may be fixed on to eachedge of the pair of plates about midway between the top and the bot-tom. In order to regulate the amount of current in working thesebatteries, it is commonly the practice to drill <t hole in the centre ofthe upper part of the zinc plate, to which a strong cord is attached,and allowed to pass over a pulley, the other end of the cord being con-nected to a counterweight. A windlassarrangement, as in Fig. 92, is albo usedfor this purpose, by which the zincplate can be raised and lowered bysimply turning a handle connected to arevolving spindle, supported by up-rights of wood, round which the cordbecomes wound or unwound accordingto the motion given to the handle.
When the bath is about to be filledwith work, the zinc plate should onlybe lowered a short distance into theacid solution, and the surface is to beincreased as the filling of the bath progresses ; if this precautionis not observed, the deposition will take place too rapidly upon thework, and the deposited metal will assume a grey colour insteadof the characteristic white, besides which the silver will be liable tostrip or separate from the underlying metal in the subsequent pro-cesses of scratch-brushing and burnishing, or even under the less severeprocess of polishing. A very safe way to check the too rapid deport,is to suspend an anode from the negative conducting rod as a cathodewhen the first batch of articles is being placed in the bath. AVheuvervpowerful batteries or dynamo-machines are used, the resistance coil(vide Nickel-plating) must be employed.
Motion given to Articles while in the Bath.—In order to insureuniformity of deposit while employing strong electric power frommagneto or dynamo machines, it has been found that by keeping t)tearticles slowly in motion while deposition is taking place, this desirableend can be effectually attained. There are several ingenious de\icesadopted for this purpose, to several of which we may now directattention. It is a fact that deposition takes place first at the cxtrt mocud of the article in solution—that is the point farthest from the sourceof electricity ; * and this being so, we may be sure that the deposition
* Except in electrotyping, in which case the surface which receives thedeposit (plumbago) is but an indifferent conductor of electricity.
250 ELECTRO-DEPOSITION OF SILVER.
or other generator of electricity. The inner iv t ingle should be ofstout copper rod, or wire—usually about one-half the thickness of theformer, and is also provided with a binding* screw at one corner, toconnect it with the negative pole of the battery. A series of brassrods, from half to one inch in diameter, and each about the length oithe tank's width, are laid across the outer rectangle, and from thesearc suspended the silver anodes ; similar but shorter rods of brassare placed between each pair of anodes, and rest upon the innerrectangle : from these rods the articles to be plated are suspended,as shown in the engraving. Before the respective conductingrods are placed in position, they must be thoroughly well cleanedwith emery cloth, as aLo must be the rectangular conductors andwire holes of binding* screws which are to receive the positive andnegative conducting wires, the ends of which must likewise be cleanedwith emery cloth each time before making connection with thebattery. It may be well here to remark that all the points of connec-tion between the various rods, wires, and binding screws must bekept perfectly clean, otherwise the electric current will be obstructedin its passage. When the conducting rods become foul by beingsplashed with the cyanide solution, they should be well cleaned withemery cloth, and the operation of cleaning these rods shouldalways be performed each morning before the first batch of work isplaced in the solution ; the omery cloth should only be applied whenthe conducting rods are perfectly dry. It is always a characteristic ofa really good plater that all Ids conducting rods are kept bright andclean, and every appliance in its proper place.
Plating Battery.—The most useful form of battery for depositingsilver, either upon a large or small scale, is a modification of the
Wollaston battery shown in Fig. 91. Fordepositing upon a large scale, a stone jarcapable of holding about ten gallons formsthe battery cell. A bar of wood, D, having agroove cut in it, so as to allow a stout plateof zinc to pass freely through it, rotsacross the battery jar, A. TWO sheets ofcopper, B b, connected by strips of the samemetal soldered to the upper corners, are placedover the wooden bar, and a binding screwconnected to one of the copper plate**, eitherby means of solder or by a side screw. The
copper plates should nearly reach to the bottom of the far. A suitablebinding screw is attached to the zinc plate, c, which rnuvt be well amal-gamated. The exciting fluid consists of dilute sulphuric acid, in theproportion of one part of the latter to fifteen parts of cold water. To
Fig. 91.
CRUET STANDS, ETC. 253
tions, quicking, &c, before described, the " wires " of cruet and liqueurstands must be separated from the bottoms, to which they aregenerally connected by small nuts, and these latter should be slungupon a wire and laid aside until the other parts of the article are readyfor plating. A wire is then to be connected to each part of the crueti'rame, and tl.ese are then to be immersed in the hot potash liquor,being left therein sufficiently long to dissolve or loosen any greasymatter which may attach to them. After being rinsed, they are to bewell brushed with powdered pumice and water. The brushes used forthis and similar purposes are made from hog hair, and are suppliedwith one or more rows, to suit the various purposes for which they arerequired ; for example, a one-rowed brush is very useful for cleaningthe joints connecting the rings with the framework of cruet stands, asalso for all crevices which cannot be reached by a wider tool; a two-rowed brush is useful for crevices of greater extent and for hollows ;and three, four, five, and six-rowed brushes for Hat surfaces, embossedwork, and so on. One of these useful tools is shown in Fig. 94.
Fig 94-
After scouring and rinsing, the parts of the cruet stand or liqueurstand are to be immersed in the quicking solution until uniformlywhite in every part, after which they must be well rinsed and immedi-ately put into the plating bath ; after a short immersion, the piecesshould be gently shaken, so as to shift the slinging wire from itspoint of contact, and thus enable that spot to become coated withsilver ; it is always advisable to repeatedly change the position of thewire so as to avoid the formation of what is termed a wire mark,and which is of course due to the deposit not taking place at thespot where the wire touches the article, thereby leaving a depressionwhen the article is fully plated. The flat base of the cruet standshould be suspended by two wires, each being passed through oneof the holes at the corner, and it should be slung sideways andnot lengthwise ; its position in the bath should be reversed occa-sionally, so as to render the deposit as uniform as possible ;the same observation applies to the " wire " part of the cruetstand. "When mounts are sent with the cruet stand, not sepa-rate, but cemented to the cruets, which is often the case, it will bewell, if it can be conveniently done, to remove the pin which connectsthe top or cover with the rim of the mustard mount, so as to platethese parts separately, otherwise the cover will require shifting
2 5 2 ELECTRO-DEPOSITION OF SILVER.
progresses in the same ratio during the whole time the articles arereceiving the deposited metal provided the solution and the workremain undisturbed. Indeed, in the case of table forks, if we sufferthem to remain, with their prongs downward, undisturbed for a con-siderable time, we shall find, on removing them from the bath, thatthe prongs, from the extreme tips upward, will be coated with acrystalline or granular deposit, while the extreme upper portion of thearticle will be but poorly coated. In no case is the fact of the deposittaking place from the lowest part of an article upward more practi-cally illustrated than in the process of "stripping" (to which weshall refer hereafter) or dissolving the silver from the surface of platedarticles, when, after they have been in the stripping solution for sometime, we find that the last particles of silver which will yield to the
Fig. 93.
chemical action of the liquid are the points of the prongs of a fork,the lowest part of the bowl of a spoon, as also (if the articles havebeen duly shifted during the plating) the extreme ends of the handlesof either article.
To keep the articles in gentle motion while in the bath, one methodis to connect the suspending rods to a frame of iron, having fourwheels about three inches in diameter connected to it, which slowlytravel to and fro to the extent of three or four inches upon inclinedrails attached to the upper edges of the tank, the motion, which is bothhorizontal and vertical, being given by means of an eccentric wheeldriven by steam power. By another arrangement, the articles arcsuspended from a frame (as in Fig. 93), and the motion given by theeccentric wheel as shown in the engraving. The simplicity of theformer arrangement, however, will be at once apparent.
Cruet Stands, &c.—Before being submitted to the cleansing opera-
SCEATCH-RRIISHING. 255
\i does not touch in a ay part. The vessel is then to be filled to thetop with silver solution dipped out of the bath with a jug, and thewhole allowed to rest for half an hour or so, at the end of whichtime the interior AN ill generally have received a sufficient coating offcilver.
Scratch brushing.—One of the nio^t important mechanical opera-tions, connected with silver-plating is that of scratch-brushing. Yuvthis purpose skeins of thin brass wire, bound round with stout brass orcoppir wire v l ig. 97), are u^ed. "When the plated articles are removedfrom the bath, they present a pearly white appearance not unlike \ cryfine porcelain "ware, but still morerlosely resembling standard silverthat has been heated and pickledin dilute sulphuric acid, as in theprocess of ultitaauy watch dials.The dead white lustre of electro-deposited silver is due to the metalbeing" deposited in a crystallineform, and the dulness is of sofugitive a nature that even scratch-ing* the surface with the finger nailwill render the part more or lessbright by burnishing the soft anddelicate crystalline texture of thedeposit. The object of scratch -brushing is to obliterate the white" burr," as it is called, before thework is placed in the hands of theburnisher or polisher, otherwiseit would be apt to show in suchparts of the finished article ascould not be reached by the toolsemployed in those operations. As
in the ca«*o of gilding, the revolving scratch-brushes are kept con-stantly wetted by a thin stream of stale beer, or half beer andwater, supplied, by means of a tap, from a small vessel (which mayconveniently be a wooden bucket) placed on the top of the scratch-brush box. A tin can, or other light vessel, stands upon the floor,beneath the box, to catch the beer runnings, which escape througha pipe let into a hole in the bottom of the box. A still more handyplan is to have a small hook fixed below the right-hand corner ofthe scratch-brush box, for supporting a tin can or other vessel: andby giving the box a slight inclination forwards, and towards the right-hand corner, the liquor will now out tlirough a hole at the corner, in
254 ELECTRO-DEPOSITION OF SILVEK.
repeats!Jv in order to allow those parts of the joint which are pro-tected from receiving1 the deposit when the cover is open, to becomeduly coated.
Tea and Coffee Services. Like the foregoing articles*, these areof very variable design, find are either plain, chased and embossed, orsimply engraved. Unless sent direct from the manufacturer in theproper condition for plating—that is, with their handles and coversunfixed—it will be better to remove the pins connecting these partswith the bodies of tea and cotfec pots before doing* anything* else tothem, unless, a*, is sometimes the ea->e, they are .so well riveted a.-, torender their severance a matter of difficulty. The disadvantagesattending* the plating* of these vessels with their handles and lids onare that the solution is apt to g*et inside the sockets of the handles,and to ooze out at the joints when the article is finished, while thejoint which unites the lid with the body can only be properly platedwhen the lid is shut, at which time the interior of the lid canreceive no deposit. When sent to the plater by the manufacturer,the \arious parts are usually either separate, or merely held to-g-ether by long* pins, which may readily be withdrawn by a pair ofpliers, and the parts again put together in the same way when thearticles are plated and finished—that is burnished or polished, as theca.se may be.
In plating work of this description, the articles are potashed, scouredand quicked as before, and when ready for the plating bath, the teaand coffee pots are generally wired by passing the slinging wire throughthe rivet-holes of the joints ; but in order to equalise the deposit *isfar as possible, it is a good plan, after the article has received a certainamount of deposit, to make a loop at one end of a eopjxT wire, andto pass it under one of the feet of the teapot, then to raise the vesselsomewhat, and connect the other end of the wire with the conductingrod ; care must be taken, however, not to let the wire touch the bodyof the vessel, or if it does so, to shift it frequently.
Since deposition always takes place more fully at the points andprojections of an article, it will be readily understood that the inte-riors of vessels—being also cmt of elect) teal s'ujht, so to speak, of theanodes-will receive little if any deposit of silver. This being* ihacase, if we wish to do the work thoroughly well in every part, it v, illbe necessary to deposit a coating of silver upon the inside either beforeor after the exterior has been plated. To do this, the vessel beingwell cleaned inside, is j)laced upright on a level bench, and a wireconnected to the negative pole of the battery is slipped through thejoint as before. A small silver anode, being either a strip of themetal or a narrow cylinder, is to be attached to the positive polo, andihe anode lowered into the hollow of the vessel, care being taken that
PLATINU BY DYNAMO-ELECTRICITY. 257
Plating by Dynamo-Electricity.—In the larger electro-platingestablishments, magneto or dynamo-electric machines are employed,and the current from these powerful machines is conveyed bystout leading wires to the various baths, the force of the currententering the baths being regulated by resistances. In works ofmoderate dimensions, a good machine, either of the magneto ordynamo-electric type, will supply sufficient electricity to work a largebath of each of the following solutions : nickel, silver, brass andcopper, as also a good-sized gold bath. In working with thesemachines, it is of the greatest importance that they should be drivenat an uniform speed ; and though some machines require to bedriven at a higher rate of speed than others, the maximum allowedby the respective makers should never be exceeded, or the machinemay become considerably heated and seriously injured. When start-ing the machine, the number of its revolutions should be ascertainedby means of the speed indicator referred to elsewhere, and as far aspracticable the normal speed should be maintained without sensiblevariation while the current is passing into the vats. Although thisuniformity of speed is more certainly obtained, we belie\e, with gasengines than with steam power, if proper care and attention are given,and frequent examination of the speed of the dynamo-armature made bythe plater, tolerable regularity may be attained from the latter sourceof power. It must always be remembered by the plater, that whenthe engine which drives the dynamo is also employed for drhingpolishing lathes, emery wheels, &c , when very heavy pieces are beingtreated in the polishing shop the speed of the dynamo may be greatlyinfluenced ; indeed we have frequently known the belt to be suddenlythrown off the pulley of a dynamo from this cause, and the machine,of course, brought to a full stop.
2 5 6 ELECTRO-DEPOSITION OF SILVER.
which a short piece of lead pipe should be inserted. By this arrange-ment (Fig. 95), the workman can empty the can into the vessel above,whenever the beer liquor ceases to drip upon the scratch-brushes,without allowing" the driving- wheel to stop. Much time may be savedin this way, especially w hen the liquid happens to run short, at which
time the can requires to be emptiedfrequently. To prevent the beerrunnings from overflowing*, andthus making a mess on the floor,while wasting the liquor, no moreliquor should be put into thecistern above than the vessel be-
°* ' low will contain. A quart orthree-pint can full will be quite sufficient for ordinary work, and avessel of this latter capacity will be quite as large as the workmancan manipulate readily without stopping the lathe.
The lathe scratch-brush consists of a series of six or eight scratch -brushes (according to the number of grooves in the " chuck ") bound
to the chuck by strong cord, as in Fig. 96. Previous tofixing the brushes, the skein of fine brass wire forming asingle scratch-brush, Fig. 97, is to be cut with a pair ofshears or strong scissors. Before applying the compoundbrush—which is connected to the lathe-head by means of itsscrewed socket—to the plated work, the brushes should beopened, or spread, by pressing rather hard upon them, whilerevolving, with a piece of stout metal, or the handle of oneof the cleaning brushes ; this will spread the bundles of wireinto a brush-like form suitable for the purpose to which theyare to be applied. It may be well to state that the revolvingscratch-brush should on no account be applied to the work ina dry state, but only when the beer liquor is running suffi-ciently free to keep the brushes ivel.
In working the scratch-brush, it must be allowed to re-volve to the right of the operator, otherwise the " chuck " willbe liable to come unscrewed ; moreover, this is the most con-venient motion for enabling the workman to guide the articleswithout risk of their being jerked out of his hand—an acci-dent that might readily occur if he inadvertently turned the
pj wheel the wrong way. In scratch-brushing spoons and forks,' a very moderate pressure is all that is necessary to render
the surface bright; a little more pressure, however, is requiredfor the edges of salvers, dishes, handles and feet of cruet stands, andother work in which hollows of some depth form a necessary featureof the ornamental mounts.
REPLATING OLD WORK* 2 5 9
proceeding. Both these metals adhere pretty firmly to zinc, iron,and steel, while silver attaches itself freely to brass and copper.If hot solutions of copper or brass are used, the trifling depositrequired to enable the subsequent coating of silver to adhere to thezinc, &c, can be obtained in a very few minutes. Each opera-tion, however, should follow in quick and unbroken succession, for ifthe brass or copper-coated article be allowed to remain, even for a fewseconds, in the air before being placed in the silver bath, it willrapidly oxidise, and render the deposited silver liable to strip when thearticle is scratch-brushed. Moreover, if the brassed or copperedarticles are allowed to remain for a short time in the air while in amoist condition, voltaic action will be set up between the zinc and themetallic covering, by which the latter will become loosened, and willreadily peel off under the action of the scratch-brush. Each article,after being brassed or coppered, should, after rinsing, be placed atonce in the silvering-bath.
Replating Old Work.—Under this head must be considered notonly the old Sheffield and Birmingham ware, the manufacture ofwhich became superseded by the electro-plating process, but also themore modern article known as " electro-plate " (the basis of which isGerman silver), which has, by domestic use, become unsightly in con-sequence of the silver having worn off the edges and other prominentparts most subject to friction in the process of cleaning. In the busi-ness of replating, there must ever be a constant if not a growingtrade, if we consider the enormous quantity of plated goods whichannually flow into the market, and which must—even the best of it—require resilvering at some time or other, while the inferior classes ofgoods may require the services of the electro-plater at a much earlierperiod than the purchaser of the articles expected.
Preparation of Old "Plated" Ware for Resilvering.—Thesearticles, whether of Sheffield or Birmingham manufacture, have abasis of copper. The better class of plated ware, which was originallysold at about half the price of standard silver, and some of which maybe occasionally met with, though doubtless becoming rarer every year,is of most excellent quality, both as to design and workmanship, andwhen properly prepared for replating, and well silvered and finishedafter, is well worthy of being replaced upon the table by the side ofthe more modern articles of electro-plate. Such articles, however,should never be replated with an insignificant coating of silver, sincethe copper surface beneath would soon reappear and expose the indif-ferent quality of the plater's work. It may be well to state, however,that by far the greater proportion of old " plated*' articles are not ofthe same quality as the old Sheffield plate and the equally admirablework formerly manufactured by the distinguished firm of Boulton and
CHAPTER XVI.
ELECTRO-DEPOSITION OF SILVER {continued).
Plating Britannia Metal, <fcc.—Plating Zinc, Iron, &c—Replating Old Work.--Preparation of Old Plated Ware.—Stripping Silvei from Old PlatedArticles.—Stripping Gold from Old Plated Articles.—Hand Polishing.—Resilvering Electro-plate.—Characteristics of Electro-plate.—Deposit-ing Silver by Weight.—Roseleur's Argyrometric Scale.—Solid SilverDeposits.—On the Thickness of Electro-deposited Silver.—Pyro-plating.—Whitening Electro-plated Articles.—Whitening Silver Work.
Plating Britannia Metal, &c.—It was formerly the practice togive a coating* of coj>per or brass to articles made from Britanniametal, tin, lead, or pewter, since it was found difficult otherwise toplate such metals and alloys successfully, that is without being liableto strip. It is usual now, however, to immerse the articles first in thehot potash solution, and to place tnem, with or without previousrinsing, in the depobiting-bath. Since the potash bath dissolves asmall quantity of metal from the surface of articles made from thesemetals, a favourable surface is left for the reception of the silverdeposit, to which the metal adheres tolerably well—indeed sufficientlyso to bear the pressure of the burnishing tools. Since Britanniametal, pewter, &c, are not such good conductors of electricity asGerman silver, copper, or brass, an energetic current must be appliedwhen the articles are first immersed in the bath, and when the wholesurface of each article is perfectly coafced with silver, the amount ofcurrent may be somewhat diminished for a time, and again augmentedas the deposit becomes stouter ; care being taken not to employ toostrong a current, however, in any stage of the plating process. Itmay be mentioned that articles made from Britannia metal—whichare generally sold at a very low price—are seldom honoured with morethan a mere film of silver, in fact just so much as will render themmarketable, and no more; still, however, a very extensive trade isdone in work of this description, much of which presents an exceed-ingly creditable appearance.
Plating Zinc, Iron, &c.—To coat these metals with silver, it isbest to first give them a slight coating of brass or copper, in an alka-line solution, which does not occupy much time, neither is it a costly
STRIPPING OLD PLACED ARTICLES. 26 l
and the mixture stirred vs ith a Btout glass rod until the salts are dis-solved. The article to be stripped is first slung upon a stout copperwire ; it is then to be lowered in the liquid, being held by the wire,until wholly immersed. Leave the article thus for a few moments,then raise it out of the solution, and observe if the silver has beenpartially removed; then redip the article and leave it in the bath fora short time longer, then examine it again ; if the action appearsrather slow, add a little more nitre, and again immerse the article.When the silver appears to be dissolving oft1 pretty freely, the opera-tion must be watched with care, by dipping the article up and down inthe solution, and looking at it occasionally, and the operation must bekept up until all the silver has disappeared, leaving a bare coppersurface. "When a large number of articles have to be stripped, a goodmany of these may be placed in a hot acid bath at the same time, butsince they will doubtless vary greatly in the proportion of silver uponthem, they should be constantly examined, and those which artfirst stripped, or dcsilvcrcdy must be at once removed and plunged intocold water. When all the articles are thoroughly freed from silver,and well rinsed, they are to be prepared for plating by first huffingthem, as described in the chapter on polisliing, after which they arecleaned and quicked in the same way as new work.
A Cold Stripping Solution, which is not so quick in its action as theformer, is made by putting in a stoneware vessel a quantity of strongsulphuric acid, to which is added concentrated nitric acid in the pro-portion of 1 part of the latter acid to 10 parts of the former (bymeasure). In this mixture the articles are suspended until they givesigns of being nearly deprived of their silver, when they are somewhatmore closely attended to until the removal of the silver is complete,when they are at once placed in cold water. The articles must boperfectly dry when placed in this stripping liquid, since the presenceof even a small quantity of water will cause the acid to attack thecopper, brass, or German silver, of which the articles may be made.The vessel should also be kept constantly covered, since sulphuric acidattracts moisture from the air. The silver may be recovered from oldstripping solutions by either of the methods described elsewhere.
Buffing Old Work after Stripping.—The stripped articles, after beingthoroughly well rinsed and dried, are sent to the polishing shop, wherethey are buffed and finished, and the cavities, caused by the action ofvinegar or other condiments upon the base of cruet stands, as far aspossible removed. Sometimes these depressions are so deep that theycannot be wholly removed without rendering the surface so thin that,in burnishing this portion of the article, it is liable to warp or becomestretched, rendering the flat surface unsightly for ever after. Thoback of the stand, which is usually coated with tin, should be roughly
260 ELECTRO-DEPOSTTTON OF SILVER.
Ur.itt, of Birnnngli ira, aomo specimens of which may also be occa-sionally met with ; but a very inferior class of goods, which maygenerally be recognised by their having lost nearly the whole of theirsilver covering—which was never very much—whereas in the betterclass of old plated ware the silver has worn off chiefly at the extremeedges, while the remainder of the article retains a sound coating of silver.
In preparing old plated cruet frames, &c, for replating, the wires,which are generally attached by soft bolder to the stands, must beseparated by firbt scraping the solder clean, and then applying a hotsoldering-iron (using a little powdered resin), which must be donevery carefully, otherwise the solder which connects the feet of thestand may become melted, causing them to drop off ; it is safer, whenapplying the hot iron, to have an assistant at hand, who with a brushor hare's foot should wipe away the solder from the joint when it ismelted. All the joints being treated in this way, in the first instance,the ground is cleared, when by a fresh application of the soldering-iron the logs of the wire may be loosened, one at a time, until thewhole series have become partially displaced, after which, by againapplying the hot iron, the legs, one after another, may be forced out.If the two parts of the frame are not taken asunder in this cautiousway, the workman may involve himself in much trouble from themelting of the lead mounts (called "silver" mounts), the droppingoff of legs, feet, &c, all of which may be avoided in the way we havesuggested. It must be understood that our suggestions are specialtymade for the guidance of those who, though good platers, may not beexperts in the application of the soldering-iron. It is usually thepractice to remove what silver there may be upon old plated articlesby the process termed " stripping." This consists in immersing thearticle in a hot acid liquid which, while dissolving the silver from thesurface, acts but little upon the underlying metal, whether it be ofcopper, brass, or German silver. The process of stripping being animportant auxiliary in connection with the replating of old work, asalso in cases in which an unsuccessful deposit has been obtained uponnew work, we may advantageously describe the process at once ; butprevious to doing so, we may state that the silver removed by strippingfrom the better class of old plated articles is sometimes an importantgain to the electro-plater, if he be fortunate enough to receive aliberal amount of such work, while, on the other hand, the inferiorqualities of plated ware will yield him no such satisfaction.
Stripping Silver from Old Plated Articles.—A stripping-bath isfirst made by pouring a sufficient quantity of strong oil of vitriol intoa suitable stoneware vessel, which must be made hot, either by meansof a sand bath, or in any other convenient way. To this must beadded a small quantity of either nitrate of potash, or nitrate of soda,
OLD PLATED ARTICLES. 2 6 3
tin ; and if this part of the article is required to be silvered—which issometimes, though not always, the case—the tin should first beremoved by dissolving it in some menstruum which will not dissolvethe copper beneath. For this purpose either hydrochloric acid or asolution of caustic potash may be used. If the former, the inside ofthe vessel should first be filled with a boiling hot solution of potash,and after a time the liquid is to be poured out and thoroughly rinsed.It must then be filled with strong muriatic acid, and allowed to restuntil the upper surface, upon being rubbed with a strip of wood,exposes the copper, when the acid is to be poured out, and the vesselagain rinsed. The inside must now be cleaned by brushing withsilver sand and water as far as the brush will reach, when the bottomand hollow parts of the body may be scoured with a mop made withrag or pieces of cloth and silver sand. If it is preferred to dissolvethe tin from the inside of the vessel by means of potash, the hot liquidmust be poured in as before, and the vessel placed where the heat canbe kept up until the desired object—the removal of the tin—is attained,when the vessel must be cleaned ao before. Dissolving the tin fromthe inside of such old plated articles should be the first preparatoryprocess they are subjected to ; indeed, the interiors of all vessels to beelectro-plated should be attended to first, in all the preliminary opera-tions, but more especially in the operations of scouring, in which thehandling of the outside, though a necessity, is liable to cause the workto strip (especially in nickel-plating), unless the hands are kept wellcharged with the pumice or other gritty matter used in scouring. Toremove tin from copper surfaces, a hot solution of perchlorxde of ironmay also be used, for although this iron salt acts freely upon copper,voltaic action is at once set up when the two metals, tin and copper,come in contact with the hot solution of the perchloride, whichquickly loosens the tin so that it may be brushed away with perfectease. From the rapidity of its action, we should prefer to adopt thelatter mode of de-tinning copper articles, but either of the formerwould be safest in the hands of careless or inexperienced manipu-lators.
Old " plated "—we use the term in reference to Sheffield ware moreespecially—sugar-bowls, cream-ewers, mugs, goblets, &c, which havebeen gilt inside, should have what gold may still remain upon thearticle " stripped off " before other operations are proceeded with ;and since these articles were originally mercury gilt, in which a liberalamount of gold was often employed, it is frequently worth while toremove this by dissolving it from the insides of the vessels ; and thesame practice should be adopted with all silver-gilt articles which aremerely required to be whitened, to which we shall refer in anotherplace.
262 ELECTRO-DEPOSITION OF SILVER.
" bobbed " with sand until all the tin is removed. The next items,which usually give some trouble, are the so-called " silver mounts,"which are commonly of two kinds. The edge, or border of the stand,being originally a shell of silver foil, struck in design, and filled orbacked up with lead or solder, is generally more or less free fromsilver, except in the hollows ; and since the soft metal does not receivethe silver deposit so favourably as the metal of which the rest of thearticle is composed, these edges must receive special treatment, other-wise the silver deposited upon them will be brushed off in the after-process of scratch-brushing. There are several ways of treating "leadedges," as they are properly called. Some persons remove them alto-gether, and replace them by brass mounts, which are specially sold forthis purpose. If this plan be not adopted, we must endeavour toinduce the silver to adhere to the lead mounts by some means or other.The edge of the article, after being cleaned, may be suspended, oneangle at a time, in a brassing bath, or alkaline coppering solution,until a film of either metal is deposited upon the leaden mount, when,after being rinsed, a second angle may be treated in the same way,and so on, until the entire edge is brassed or coppered. The smallamount of brass or copper, as the case may be, which may havedeposited upon the plain portions of the work, may be removed bymeans of a soft piece of wood, powdered pumice, and water. Edgestreated in this way generally receive a good adherent coating ofsilver. Sometimes, but not always, the ordinary '' quicking'' willassist the adhesion of the silver to the lead mounts. Another methodof depositing a firm coating of copper upon lead edges is to put aweak acid solution of sulphate of copper in a shallow vessel, and havinga small piece of iron rod in one hand, to lower one portion of the edgeof the cruet bottom into the solution ; then touching the article underthe liquid, in a short time a bright coating of copper will be depositedupon the leaden surfaces, by means of the voltaic action thus set up,when this portion may be rinsed, and the remainder treated in thesame way. Or take a small piece of copper, and connect it by a wireto the positive electrode of a battery, envelop this copper in a piece ofchamois leather or rag, then put the article in connection with thenegative electrode. By dipping the pad, or "doctor," in either anacid or an alkaline solution of copper, or in a warm brassing solution,and applying it to the part required to be coated, a deposit will atonce take place, which may be strengthened by repeatedly dipping thepad in the solution and applying again. In this way, by moving thepad containing the small anode of copper or brass along the edge, therequired deposit may be effected in a very short time with a battery ofgood power—a Bunsen cell, for example.
Old " plated " tea and coffee pots are invariably coated inside with
HAND POLISHING. 265
assistant, while a sufficient quantity of pitch (previously melted in anearthenware pipkin) is poured in. The candlestick must be left inthe erect position until the filling has nearly set, when the hollowformed by the contraction of this substance must be filled up with thesame material, and the article then left until quite cold, when it maybe handed over to the burnisher. When burnished, the surface of thepitch should be levelled with a hot iron, and then at once brought incontact with a piece of green baize, placed upon a table, and gentlepressure applied to cause the uniform adhesion of the two surfaces.When cold, the remainder of the baize is cut away by means of asharp pair of scissors, when, after being wiped with a clean or blightlyrouged chamois leather, the article is finished.
Hand Polishing.—When the electro-plater is unprovided with aproper polishing lathe and the various appliances ordinarily used inpolishing metals, he must have recourse to the best substitute he cancommand for polishing by hand. To aid those who may be thus cir-cumstanced, and who may have no special knowledge of the meansby which the rough surfaces of old work may be rendered sufficientlysmooth for replating, we will give the following hints : Procure a fewsheets of emery-cloth, from numbers o to 2 inclusive ; one or twolumps of pumice-stone ; a piece of Water-of-Ayr stone, about J inchsquare and 5 inches long ; also a little good rottenstone, and a smallquantity of sweet oil. Suppose it is necessary to render smooth thebase, or stand, of an old cruet frame, deeply marked on its plane sur-face by the corrosive, or, rather, voltaic action of the vinegar droppingfrom the cruets upon the plated surface. The article, after beingstripped, as before, should be laid upon a solid bench, and a lump ofpumice (previously rubbed flat upon its broadest part) frequentlydipped in water and well rubbed over the whole surface, that is, notmerely where the cavities are most visible, but all over. After thusrubbing for some time, the stand is to be rinsed, so that the operatormay see how far his labour has succeeded in reducing the depth ofthe " pit-marks." The stoning must then be resumed, and when thesurface appears tolerably uniform, the article should be well rinsed,dried, and again examined, when if the marks are considerablyobliterated, a piece of No. 2 emery-cloth may be bribkly applied tothe surface by being placed over a large cork or bung, after which afiner emery-cloth should be applied. The article should next bethoroughly rinsed, and brushed with water to remove all particles ofemery ; and while still wet, the Water-of-Ayr stone must be rubbedover the surface. The stone should be held in an inclined position,frequently dipped in water, and passed from end to end of the article.The effect of this will be—and must be—to remove all the scratches ormarks produced by the pumice and emery-cloth. Until these have
264 ELECTRO-DEPOSITION OF SILVER.
Stripping Gold from the Insides of Plated Articles.—Thesugar-bowl or other vessel is placed on a level table or bench, and pufcin connection with the positive electrode of a battery. A strip ofsheet copper or platinum foil is next to be attached to the negativeelectrode, and placed inside the vessel, without touching at any point.By this arrangement the article becomes an anode. The vessel mustnow be filled with a moderately strong solution of cyanide of potas-sium, consisting of about 4 ounces of cyanide to 1 quart of water.Since the metal beneath will also dissolve in the cyanide solution, theoperation must be stopped as soon so the gold has disappeared fromthe surface. The solution should then be poured out, and bottled forfuture use. When the stripping solution, from frequent use, hasacquired sufficient gold to make it worth while to do so, the metal maybe extracted by any of the processes given in another chapter.
Old plated table candlesticks, some of which are of admirable designand well put together, may be occasionally met with, as also a veryinferior article, the parts of which are mainly held together by alining or " filling " of pitch, or some resinous compound. In treatingold plated candlesticks, the removal of the Jilting should be the firstconsideration, since it will give the plater a vast amount of aftertrouble if he attempts to plate them while the resinous or other matterremains in the interior. In the first place, the silver solution will besure to find its way into the hollow of the article, from which it willbe next to impossible to entirely extract it when the article is plated,for the liquid will continue to slowly exude for days, or even weeks,after the article is finished. Again, if the article be plated withoutremoving the filling material, this, being freely acted upon by thecyanide solution, will surely harm it. After removing the socket, thegreen baize or cloth should be removed from the base of the candle-stick, when it should be placed before a fire until the whole of theresinous matter or pitch has run out. To facilitate this, the articleshould be slightly inclined in an iron tray or other vessel, so that theresinous matter may freely ooze out and be collected. In dealing withthe inferior varieties of candlesticks—which may be known by all ornearly all the silver having worn from their surface—the plater mayfind, to his chagrin, that before all the stuffing has run out the candle-stick will have literally fallen to pieces. The various parts, not havingbeen originally put together with solder, but held in position merelyby the filling material, readily come asunder when the internal liningis loosened. In such a case as this he should, without losing histemper (if possible), determine to prepare and plate all the partsseparately (keeping the parts of each "stick" together), and afterscratch-brushing, carefully put them together again. The candlestickshould now be turned upside down, and held in this position by an
CHARACTERISTICS OF ELECTRO-PLATE. 267
sary to strike the article with any hard substance, when a ringing,vibratory sound will be produced in the former case, while a dull,unmusical sound, with but little vibration, will be observed in thelatter.
Characteristics of Electro-Plate.—Electro-plated articles of thebest quality are invariably hard-soldered in all their parts ; the wiresof cruet and liquor frames are attached by German silver nuts to thescrewed uprights, or feet of the wires, instead of pewter solder, as inplated ware, and the bottoms of the stands are coated with silver,instead of being tinned, as in the former case. The mounts are of thesame material as the rest of the article, and the handles and feet ofcream-ewers and sugar-bowls are frequently of solid cast Germansilver. With these advantages the electro-plater should have littledifficulty, if the articles have received fair treatment in use, in re-plating them and turning them out nearly equal to new, which itshould be his endeavour to do. It sometimes occurs that *' ship plate''—that is, plated work which has been used on board ship—when itreaches the hands of the electro-plater exhibits signs of very roughusage ; corner dishes are battered and full of indentations, while theflat surfaces of the insides are scored with cuts and scratches, sugges-tive of their having been frequently used as plates, instead of merereceptacles for vegetables ; the prongs of the forks, too, are frequentlynotched, cut, and bent to a deplorable extent. All these blemishes,however, must be removed by proper mechanical treatment, afterthe remaining silver has been removed by the stripping-bath. It isnot unusual for those who contract for the replating of ship work topay by the ounce for the silver deposited, in which case they will notallow the electro-plater to reap the full advantage of the old silverremoved by stripping, but will demand an allowance in their favour,which, if too readily agreed to by an inexperienced plater, mightgreatly diminish his profit if the cost of buffing the articles happenedto be unusually heavy ; he must, therefore, be upon his guard whenundertaking work of this description for the first time, since, other-wise, he may suffer considerable loss, for which the present rate ofpayment for each ounce of silver deposited will not compensate.
After stripping and rinsing, the articles require to be well polished,or buffed, and rendered as nearly equal to new work as possible; theyare then to be potashed, quicked, plated, and finished in the same wayas new goods. Since there is now a vast quantity of nickel -platedwork in the market, some of which is exceedingly white even for nickel,inexperienced or weak-sighted platers must be careful not to mistakesuch articles for silver-plated work. When in doubt, applying a singledrop of nitric acid, which blackens silver while producing no imme-diate effect upon nickel, will soon set the mind at rest upon this point.
266 ELECTRO-DEFOSITION OF SILVER.
disappeared, the smooth but keenly-cutting stone must be applied.After having rendered the surface perfectly smooth, the article is to beagain rinsed and dried. It must now be briskly rubbed with rotten -stone, moistened with oil, and applied with a piece of buff, or belt(such as soldiers* belts are made of), glued to a piece of wood. Whensufficiently rubbed or buffed with the rottenstone, the surface will bebright, and in order to ascertain how the work progresses, it shouldoccasionally be wiped with a piece of rag. In very old plated articles,the pit-holes are frequently so deep that to entirely obliterate themwould render the metal so thin as to spoil the article. It is better,therefore, not to go too far in this respect, and to trust to the cruets,when in their places, disguising whatever remains of the blemishes,after the foregoing treatment, rather than to endanger the solidity ofthe stand itself. By employing pieces of pumice of various sizes(keeping the flattened piece for plane surfaces), strips of emery-clothfolded over pieces of soft wood, Water-of-Ayr stone, and ordinaryhand " buff -sticks" of various kinds, the "wires*' of old cruetand liqueur frames may be rendered smooth enough for plating. Withperseverance, and the necessary labour, many old articles may be putinto a condition for plating by hand labour with very creditableresults ; and it may be some consolation to those living at a distancefrom large towns, if we tell them that during the first ten years of theelectro-plating art, the numerous host of " small men " had no othermeans of preparing their work for plating than those we have men-tioned, many of whom have since become electro-depositors upon anextensive scale.
Resilvering Electro-plate.—This is quite a distinct class of warefrom the preceding, inasmuch as the articles are manufactured fromwhat is called white metal, in contradistinction to the basis of Sheffieldplate, which, as we have said, is the red metal copper. The betterclass of electro-plate is manufactured from a good quality of the alloyknown as German silver, which, approaching nearly to its whiteness,does not become very distinctly visible when the silver has worn fromits surface. Inferior qualities of this alloy, however, are extensivelyused for the manufacture of cheap electro-plate, which is very littlesuperior, as far as colour goes, to pale brass, while the latter alloy isalso employed in the production of a still lower class of work. Thecomparatively soft alloy, of a greyish-white hue, called Britanniametal, is also extensively adopted as a base for electro-plate of a veryshowy and cheap description, of which enormous quantities enter themarket, and adorn the shop-windows of our ironmongers and otherdealers in cheap electro-plated goods. To determine whether anelectro-plated article has been manufactured from a hard alloy, such asGerman silver, or from the soft alloy Britannia metal, it is only neces-
DEPOSITING SILVER BY WEIGHT. 269
hot water, and placed in boxwood sawdust; they are then lightlybrushed over to remove any sawdust that may adhere to them, andcarefully weighed. If still insufficiently coated the articles are againscratch-brushed, quicked, rinsed, and replaced in the bath ; the re-weighing and other operations being repeated as often as is necessaryuntil the required deposit is obtained. This is a tedious and trouble-some method, and is sometimes substituted by the following : Supposea certain number of spoons and forks have been weighed for theplating-bath, one of these articles is selected as a test sample, and isweighed separately; being placed in the bath with the others, it isremoved from time to time and re-weighed, to determine the amountof bilver it has acquired in the bath. Thua» if 24 dwts. of silver arerequired upon each dozen of spoons or forks, when the test samplehas received about 2 dwts. of silver it is known that the rest havea like proportion, provided, of course, that each time it has beensuspended in the bath the slinging wire and that part of the conduct-ing rod from which it was suspended were perfectly clean; it isobvious, however, that even this method is open to a certain amountof doubt and uncertainty, if the workmen are otherwise than verycareful. To render the operation of depositing by weight more certainand less troublesome, some electro-platers in France adopt what istermed a " plating balance." The articles are suspended from a frameconnected to one end of the beam, and a scale pan, with its weightsfrom the other end ; the balance, thus arranged, is placed in communi-cation with the negative electrode of the electric generator, and theanodes with the positive electrode. When the articles, as spoons andforks, for example, are suspended from the frame, and immersed inthe bath, counter-balancing weights are placed in the scale-pan. Aweight equivalent to the amount of silver to be deposited is then putinto the pan, which, of course, throws the beam out of balance; whenthe equilibrium becomes restored, by the weight of deposit upon thearticles in solution, it is known that the operation is complete. Theplater usually employs scales for each bath, especially when silveringspoons and forks. If preferred, the supporting frame may be circular,so that the soluble anode may be placed in the centre of the bath, andat equal distance from the articles. The centre anode need not preventthe employment of other anodes round the sides of the vessel, so thatthe articles receive the action of the current in front and behind them.A sounding bell may be so connected that it will indicate the precisemoment when the equilibrium of the scale takes place. In workingthe silver baths for this purpose, the anode surface immersed in solu-tion is much greater than that of the articles. When the solutionloses its activity additions of cyanide of silver are given to it, andwhen the cyanide is found to have become partially converted into
2 6 8 ELBCTRO-DE POSITION OF SILVER.
Electro-tinned articles, which very much resemble silvered work, mayalso be detected in this way. We are tempted to make one othersuggestion upon this subject, which may not be deemed out of place,it is this: a considerable quantity of nickel-plated German silverspoons and forks are entering the market, which, should they eventuallyfall into the hands of the electro-plater to be coated with silver, maycause him some trouble if he inadvertently treats them as Germansilver work, which in his haste he might possibly do, and attempts torender them smooth for plating by the ordinary methods of hand orlathe-buffing; the extreme hardness of nickel—even as compared withGerman silver—will render his work not only laborious, but unne-cessary, for if he were aware of the true nature of the surface hewould naturally remove the nickel by means of a stripping solution,and then treat the article as ordinary German silver work. Thestripping solution for this purpose Avill be given when treating ofnickel re-plating. It must be understood that in making suggestionsof this nature, in passing, that they are intended for the guidance ofthose who may not have had the advantages of much practical expe-rience, of whom there are many in every art.
Depositing Silver by Weight.—In this country the silver depositis frequently paid for by weight, the articles being carefully weighedboth before and after being placed in the plater's hands. The pricecharged for depositing silver by the ounce was formerly as high as14s. 6d.; at the present period, however, about 8s. per ounce onlycould be obtained, and in some cases even less has been charged. Butunless dynamo-electricity be employed this would be about as profitableas giving ten shillings for half-a-sovereign. In France electro-platingis regulated by law, all manufacturers being required to weigh eacharticle, when ready for plating, in the presence of a comptrollerappointed by the Government, and to report the same article forweighing again after plating. In this way the comptroller knows toa fraction the amount of precious metal that has been'added, and putshis mark upon tha wares accordingly, so that every purchaser mayknow at a glance what he is buying. In Birmingham there is a classof electro-depositors called '* electro -platers to the trade,'* who workexclusively for manufacturers of plated goods and others who, thoughplaters, send a great portion of their work to the "trade " electro-platers, whose extensive and more complete arrangements enablethem to deposit large quantities of the precious metals with consider-able economy and dispatch.
In depositing silver at so much per ounce, the weighed articles,after being cleaned, quicked, and rinsed, are put into the bath, inwhich they are allowed to remain until the plater deems it advisableto re-weigh them, when they are removed from the bath, rinsed in
ARGYROMETRIC SCALE. 2 7 1
rubber, which, by means of a screw beneath, may be raised or lowered,by which means the mercury in the cup is levelled. A second lateralbinding screw connects the negative electrode of the battery. 3. Acast-iron beam, carrying in its centre two sharp polished steel knives ;at each end are two parallel steel bowls, separated by a notch, intendedfor the kni\ es of the scale pan and of the frame for supporting thearticles. One arm of the beam is furnished with a stout platinumwire, placed immediately above and in the centre of the mercury cup,and as the beam oscillates it dips into, or passes out of, the cup.The scale pan is furnished with two cast-steel knives fixed to themetallic bar, which is connected to chains supporting the lowerwooden box for the tare ; the smaller pan, for the weight representingthe amount of silver to be deposited, is placed between these two.4. The frame for supporting the work is also suspended by two stoelknives, the vertical of which is of stout brass tubing, and is equal insize to the opening of the bath, and supports the rods to which thearticles are suspended. The slinging wires are formed into a loop atone end for supporting the spoons or forks, and the vertical portion ofeach wire is covered with india-rubber tubing, to prevent it fromreceiving the silver deposit.
In adjusting the apparatus, the pillar must be set perfectly uprightby aid of a plumb line ; the clamps are then withdrawn from theJmks, and the beam is carefully put in its place, care being taken toavoid injuring the knives that rest in the bowls in the centre of thepillar. The clamps are now replaced, and the beam should oscillatefreely upon the knives without friction. The knives of the frame arenext put in their places, as also those of the scale pan ; mercury isthen poured into the six bowls, where the knives rest, until all thepolished parts of the latter are covered. The insulated steel cup isthen filled with mercury so high that the point of the platinum wirejust touches it, when the beam is level; the small elastic pocket isused for raising and lowering the mercury cup, so as to place it at theproper height for bringing the mercury in contact with the end of theplatinum wire. When the articles have received the amount of silvercorresponding to the weight in the pan at the opposite side of thebeam, the equilibrium \\ ill be established, and the platinum wire willthen leave the mercury, and thus break the circuit and stop the opera-tion. By this automatic arrangement the operation needs no atten-tion, since the moment the platinum wire loses contact with themercury electricity ceases to pass ; if, however, the articles are allowedto remain in the bath after they have received the proper amount ofsilver, a portion of this metal may be dissolved by the free cyanide inthe solution, in which case the end of the platinum wire would againdip into the mercury and complete the circuit, when deposition would
270 ELECTRO-DEPOSITION OF SILVER.
carbonate of potassa, hydrocyanic acid is added, which combines withcarbonate, and liberates carbonic acid gas. This method is preferredto that of adding fresh cyanide, since an accumulation of the car-bonated alkali retards the conductivity of the solution, as also doesthe hydrocyanic acid when added in excess.
Koseleur's Argyrometric Scale.—This is an automatic apparatusand is designed forobtaining deposits ofsilver i' without super-vision and with constantaccuracy, and whichspontaneously breaks theelectric current when theoperation is terminated."The apparatus is madein various sizes, suitablefor small or large opera-tions ; Fig. 98 repre-sents the apparatus tobe employed for thelatter purposes.
It consists of:—1. Awooden vat, the upperledge of which carries abrass winding rod, hav-ing a binding screw atone end to receive thepositive conducting wire
FiS- 98. of the battery; fromthis rod the anodes are
suspended, which arc entirely immersed in the solution, and commu-nicate with cross brass rods by means of platinum wire hooks. Thesecross rods are flattened at their ends so that they may not roll, and atthe same time have a better contact with the "winding rod." 2. Acast-iron column screwed at its base to one of the sides of the bath,carries near the top two projecting arms of cast iron, the extremitiesof which are vertical and forked, and may be opened or closed by ironclamps, these forks being intended to maintain the beam and preventthe knives from leaving their bowls when the beam oscillates toogreatly. In the middle of the two arms are two bowls of polishedsteel, hollowed out wedge-shaped, to receive the beam knives. Onearm of the pillar has at its end a horizontal iron ring, in which isfixed a heavy glass tube which supports and insulates a polished ironcup to contain mercury; beneath this cup is a small pad of india-
THICKNESS OF ELECTRO-DEPOSITED SILVER. 2 7 3
One great objection to solid electro-deposits of silver (and gold) isthat the articles have not the metallic " ring," when struck with anyhard substance, as silver ware of ordinary manufacture. "Thisdisadvantage," says Napier, " is no doubt partly due to the crystallinecharacter of the deposit, and partly to the pure character of the silver,in which state it has not the sound like standard or alloyed silver.That this latter cause is the principal one appears from the fact thata piece of silver thus deposited is not much improved in sound bybeing heated and hammered, which would destroy all crystallisation."This is quite true, but when electro -deposited silver has been incited,and cast into an ingot, by which its crystalline character is completelydestroyed, and which is only partially affected by simply annealingand hammering, the characteristic " r ing" of the pure metal is re-stored. The absence of a musical ring in electro-deposited silver isnot of much consequence, however, since this method of reproductionwould only be applied to rare works of art, such as antique figures,and richly chased articles kept solely for ornament.
On the Thickness of Electro-Deposited Silver.—This may beconsidered a somewhat delicate theme to expatiate upon when wereflect that some articles of commerce, but more especially exportgoods and articles sold at mock auctions, frequently receive a coatingof silver which not only defies measurement by the most delicatemicrometer, but also renders estimation by any other means all butimpossible. This class of work includes spoons and forks, cruet-frames, toast-racks, &c, manufactured from a very inferior descrip-tion of German silver or brass, while Britannia metal tea services,salt-cellars, and many other articles made from the same alloy enterthe market in enormous quantities, with a mere blush of silver uponthem, the thickness of which might be more readily estimated byimagination than by any practical test. As to the amount of silverwhich should be deposited upon articles of domestic use, to enablethem to withstand ordinary wear and tear for a reasonable period,from 1 to 3 ounces per dozen for spoons and forks may be deposited.Taken as a guide, with the smaller quantity of silver upon them, sucharticles, with careful usage, should present a very creditable appear-ance after five years' use ; with the larger proportion, the articlesshould look well, though probably somewhat bare upon those partsmost subject to friction, at the end of twenty yearb. The same arti-cles, if used in hotels or on board ship, would become unsightly inless than half the periods named. German silver tea and coii'eeservices, to be fairly well plated or silvered, should not have less than2 ounces of silver upon the four pieces, which may be distributed inabout the following proportions: for a 5-gill coffee-pot 12 dwts. ;5-gill teapot 12 dwts. ; sugar-basin 10 dwts. ; cream-ewer 6 dwta.
T
272 ELECTRO-DEPOSITION OF SILVER.
bo renewed and continue until the increased weight of silver againcaused the platinum wire to lose contact with the mercury.
3olid Silver Deposits.—Although it is possible to deposit silver,from a cyanide solution rich in metal (say eight ounces of silver pergallon), upon wax or gutta-percha moulds, this method is not practi-cally adopted. The usual method is to first obtain a copper electro-type mould or shell of the object in the ordinary way; silver is thendeposited within the mould (supposing it to be a hollow object) untilof the required thickness ; the copper is afterwards dissolved from thesilver either by boiling the article in hydrochloric acid, or, still better,a strong solution of perchloride of iron, either of which substanceswill dissolve the copper mould without in any way injuring the silver.The perchloride of iron for this purpose may be readily formed bydissolving peroxide of iron (commercial " crocus ") in hot hydro-chloric acid. The method of dissolving the copper recommended byNapier, is as follows: "An iron solution is first made by dissolvinga quantity of copperas in water; heat this till it begins to boil; alittle nitric acid is then added—nitrates of soda or potash will do ; theiron which is thus peroxidised may be precipitated either by ammoniaor carbonate of soda; the precipitate being washed, muriatic acid isadded till the oxide of iron is dissolved. This forms the solution fordissolving the copper. When the solution becomes almost colourless,and has ceased to act on the copper, the article is removed, and theaddition of a little ammonia will precipitate the iron along with aportion of the copper; but after a short exposure the copper is redis-solvcd. The remaining precipitate is washed by decantation ; a littleammonia should be put into the two first waters used for washing.When washed, and the copper dissolved out, the precipitate is redis-solved in hydrochloric acid, and the silver article returned until thecopper is all dissolved off. It is convenient to have two solutions of per-chloride of iron, so that while the iron in the one is being precipitated,the article is put into the other. The persalt of iron will be found todissolve the copper more rapidly than muriatic acid alone ; persul-phate of iron must not be used, as it dissolves the silver along withthe copper.
" The silver article is now cleaned in the usual way, and heated toredness over a clear charcoal fire, which gives it the appearance ofdead silver, in which state it may be kept, or, if desired, it may bescratched and burnished." A very simple and economical method ofproducing perchloride of iron is to reduce the native peroxide of iron,known as "redding," to a powder, and digest it in hot hydrochloricacid, by which the salt is obtained at a cost but little exceeding thatof the acid employed, the native ore being worth only about 25s. perton.
WHITENING SILVER WORK.. 275
silver has been deposited, Tr'hioh indicates approximately the amountof deposit upon the article itself. The article is then removed andrinsed, and afterwards heated in a furnace until the silver is "driven"into the surface of the metal. If the steel article requires to be tem-pered, it is quenched in water, and then brought to the proper temperin the usual "way.
Whitening Electro-plated Articles. — It is well known thatarticles which have been electro-plated tarnish more rapidly thansilver goods ; and while this has by many persons been attributed tothe extreme purity of the electro-deposited metal, which, it wasbelieved, was more susceptible of being attacked by sulphurous fumesand other impurities in the air, by others it is believed to be due to asmall quantity of undecomposed salt remaining in the pores of thedeposited metal, which undergoes decomposition, and causes the workto tarnish. In order to render electro-plate less liable to discolora-tion, the following method has been adopted, but, as will readily beseen, it could not be applied to all classes of work : The article is firstdipped in a saturated solution of borax and then allowed to dry, whena thin layer of the salt remains upon the surf ace ; the article is thendipped a second or even a third time (drying after each dipping) untilit is completely covered with a layer of borax. When large articlesare to be treated this way, the borax may be applied with a boftbrush. The article is next to be heated to a dull red heat, or untilthe borax fuses. When cold, it is to be put into a pickle of dilute sul-phuric acid, which rapidly dissolves the borax ; after rinsing in hotwater it is* placed in hot boxwood sawdust, and then treated in tbousual way.
Whitening Silver Work.—Articles of silver which in their originalfinished state were left either wholly or in part a dead white, and havelost this pleasing effect by wear or oxidation, may be restored to theiroriginal condition by the process termed whitening. The article is firstbrought to a dull red heat (not sufficient to melt the solder) over acharcoal fire—if it be a brooch, watch-dial, or other small silverarticle, by means of the blowpipe flame, the article being placed on alarge and flat piece of charcoal. When the piece of work has thusbeen heated uniformly all over, it is allowed to become cool, afterwhich it is placed in' a glazed earthenware vessel (an ordinary whitebasin will do), containing a sufficient quantity of very dilute sulphuricacid. In a short time the acid will dissolve the oxide from the surface,together with a small quantity of oxide of copper derived from thecopper with which the silver was alloyed, and which, with the silver,becomes oxidised by the heat and subsequent action of the atmosphere.When the article is removed from the pickle—in which it shouldromain for at least twenty minutes to half an hour—if not of a suffi-
274 ELECTRO-DEPOSITION OF SILVER.
When the same articles are required to be fully well plated, the pro-portions should be about as follows: For coffee and teapot, abouti\ ounce of silver each ; sugar-basin I ounce, and cream-ewer aboutio to 15 dwts.
The proportion of silver which should be deposited per square foot,for plating of good quality, is from 1 to 1 \ ounce. "With the latterproportion the electro-silvered work would nearly approach in qualitythe old Sheffield plate, and would last for a great number of yearswithout becoming bare, even at the most prominent parts, unless thearticle were subjected to very severe treatment in use.
Pyro-plating.—It is well known that when a silver-gilt article—asa watch-chain, for example—has been broken, and afterwards repairedby hard soldering, that the film of gold almost entirely disappearsfrom each side of the soldered spot, under the heat of the blow-pipeflame, to the extent of 1 or 2 inches on either side of the joining. Thefilm of gold has, in fact, sunk into the body of the silver, as thoughit had become alloyed with this metal. By some persons this is reallybelieved to be the case. We are, however, disposed to think that theabsorption of the gold under these circumstances is due, not to anactual alloying of the two metals in the ordinary sense, but to theexpansion of the silver by the heat, by which its molecular structurebecomes disturbed, and the film of gold, being thus split up intoinfinitely minute particles, these become absorbed by the silver as themetal contracts on cooling, and consequently disappear from the sur-face. We hold this view because we do not think that the heat of theblowpipe flame required to fuse the solder would be sufficient to forman alloy in the proper sense; indeed, the heat required to " r u n "silver solder would not be sufficiently high even to " sweat" the silverof which the article is composed. The fact of a film of metal becom-ing absorbed by another metal under the influence of heat has beentaken advantage of, and a process termed " pyro-plating " has beenintroduced, and has been worked to some extent in Birmingham. Theprocess, which has been applied to coating articles—of steel and ironmore especially—with gold, silver, platinum, aluminium, copper, &c,may be thus briefly described : The article is first steeped in a boilingsolution of caustic potash ; it is then brushed over with emery -powder, and afterwards with a steel brush and a-solution of commonsoda, in which it is allowed to remain for some time. It is next con-nected to the negative electrode of a strong battery, and immersed ina hot solution of caustic potash, abundance of hydrogen being evolved,and is allowed to remain until it has a '* silvery " appearance. Afterrinsing, it is suspended in a silver bath, with a previously weighed metalplate of the same amount of surface placed as a cathode by its side ;this plate is taken out and weighed from time to time until sufficient
CHAPTER XVII.
IMITATION ANTIQUE SILVER.
Oxidised Silver.—Oxidising Silver.—Oxidising with Solution of Platinum.—Oxidising with Sulphide of Potassium.—Oxidising with the Paste.—Part-gilding and Oxidising.—Dr. Eisner's Process.—Satin Finish.—Sul-phuring Silver.—Niello, or Nielled Silver.—Pink Tint upon Silver.—Silvering Notes,
Oxidised Silver.—Soon after the art of electro-plating had becomean established industry, the great capabilities of the "electro" pro-cess, as it was called, received the serious attention of the more giftedand artistic members of the trade, who, struck with the great beautyof electro-deposited silver, and the facilities which the process offeredfor the reproduction of antique works, induced some electro-platers ofthe time to make c xperiments upon certain classes of work with a viewto imitate the effects seen upon old silver ; some of the results werehighly creditable, and in a short time after "oxidised " silver becamegreatly in vogue, and has ever since been recognised as one of theartistic varieties of ornamental silver or electro-plated work. Wescarcely think we shall err, however, if we venture to say that muchof the "oxidised " silver-plated work of the present time is far inferiorin beauty and finish to that with which our shops and show-roomswere filled sonic thirty years ago. Indeed, when visiting the ParisExhibition of 1878, we were much displeased with the very slovenlyappearance of some of the plated goods which had been part-gilt andoxidised in the exhibits of some of the larger English and Frenchfirms. The specimens referred to had the appearance of having doneduty as specimens in all the exhibitions since 1851, and had sufferedby being repeatedly " cleaned up " for each occasion ; they were cer-tainly far from being creditable.
" Oxidising" Silver.—This term has been incorrectly applied, butuniversally adopted, to various methods of darkening the surface ofsilver in parts, by way of contrast to burnished or dead-white sur-faces of an article. Oxygen, however, has little to do with thediscoloration, as will be seen by the following processes, which areemployed to produce the desired effect. The materials used are various,and they are generally applied with a soft brush, a camel-hair brush
2j6 ELECTRO-DEPOSITION OF SILVER.
ciently pure whiteness it may be heated and pickled again. Whenthe whitening is properly effected, the surface should present a beauti-ful pearl-white appearance, and be perfectly uniform in its lustrousdulness. Directly the article is removed from pickle, it should berinsed in two separate waters, the last water (which should bedistilled water, by preference) being boiling hot. The article, afterbeing removed from the rinsing-bowl, should be allowed to dry spon-taneously, which it will do if the water is boiling hot. It is not agood plan, though it is frequently done, to put work which has beenwhitened in boxwood sawdust, since if it has been much used it isliable to produce stains.
OXIDISING PROCESSES. 279
which mixture is sometimes added a small quantity of red ochre orjewellers' rouge, to imitate the warm tone sometimes observed in oldsilver articles. The paste is spread over the artic los and allowed todry, after which the article is brushed over with a long-haired softbrush, to remove all excess of the composition. The parts in reliefare then cleaned by means of a piece of rag, or chamois leather, dippedin spirit of wine. This method of imitating old silver is speciallyapplicable to vases, tankards, chandeliers, and statuettes. In case offailure in the manipulation, the dried paste may be readily removedby placing the article in a hot solution of caustic potash or cyanide,when, after rinsing and drying, the paste may be reapplied. To givethe old silver appearance to small articles, such as buttons, for example,they are first passed through the above paste, and afterwards revolvedin a barrel or " tumbler " containing dry sawdust, until the desiredeffect is produced.
Fart-gilding and Oxidising.—To give this varied effect to work,the articles are first gilt all over in the usual way ; certain parts arethen stopped offy as it is termed, by applying a suitable varnish. Whenthe varnish has become dry, the article is placed in the silvering bathuntil a sufficient coating, which may be slight, has been obtained.After rinsing, the object is immersed in a solution of sulphide ofpotassium until the required tone is given to the silvered parts, whenthe article is at once rinsed, carefully dried, and the protecting varnishdissolved off, when it is ready to be finished.
Dr. Eisner's Process.—A brownish tone is imparted to platedgoods by applying to the surface a solution of sal-ammoniac, and astill finer tone by means of a solution composed of equal parts ofsulphate of copper and sal-ammoniac in vinegar. To produce a fineblack colour, Dr. Eisner recommends a warm solution of sulphide ofpotassium or sodium.
Sulphide of Ammonium.—This liquid may also be applied to the so-called oxidation of silver, either by brushing it over the parts to beoxidised, or by immersion. It may also be applied, with plumbago,by forming a thin paste with the two substances, which is afterwardsbrushed, or smeared over the surface to be coloured, and when dry asoft brush is applied to remove the excess of plumbago. If preferred,a little jewellers' rouge may be added to the mixture.
Satin Finish.—This process is thus described by Wahl: The sand-blast is in use in certain establishments to produce the peculiar dead,lustrous finish, known technically as satin Jinish, on plated goods ; atemplet of some tough resistant material, like vulcanised india-rubber,is made of the proper design, and when placed over the article, pro-tects the parts which it is desired to leave bright from the depolishingaction of the sand, while the only open portions of the templet are
2 y g IMITATION ANTIQUE SILVER.
being suitable for small surfaces. In applying* either of the materialsthe article should be quite dry, otherwise it will spread over portionsof the work required to be left white, and thus produce a patchy andinartistic effect. The blackening* substances are generally applied tothe hollow parts or groundwork of the object, while the parts whichare in relief are left dead, or burnished according- to taste.
Oxidising with Solution of Flatinum.—Dissolve a sufficientquantity of platinum in aqua regia, and carefully evaporate the result-ing solution (chloride of platinum) to dryness, in the same way as re-commended for chloride of gold. The dried mass may then be dissolvedin alcohol, ether, or water, according to the effect which it is desiredto produce, a slightly different effect being produced by each of thesolutions. Apply the solution oi platinum with a camel-hair brush, andrepeat the operation as often as may be necessary to increase the depthof tone ; a single application is frequently sufficient. The ethereal oralcoholic solution of platinum must be kept in a well-stoppered bottle,and in a cool place. The aqueous solution of platinum should beapplied while hot.
Oxidising with Sulphide of Potassium.—Liver of sulphur (sul-phide of potassium) is often used for producing black discoloration,erroneously termed oxidising. For this purpose four or five grains ofthe sulphide are dissolved in an ounce of hot water, and the solutionapplied with a brush, or the article wholly immersed if desired. Thetemperature of the solution should be about 1500 Fahr. After a fewmoments the silver surface assumes a darkened appearance, whichdeepens in tone to a bluish-black by longer treatment. When thedesired effect is produced the article is rinsed and then scratch-brushed,or burnished if required, or the blackened hollow surfaces are left deadaccording to taste. When it is desired to produce a dead surface uponan article which has been electro-silvered, the article may be placedin a sulphate of copper bath for a short time, to receive a slight coat-ing of copper, after which it is again coated with a thin film of silverin an ordinary cyanide bath. It has then the dead-white appearanceof frosted silver. Where portions of the article are afterwards oxidiseda very fine contrast of colour is produced. In using the sulphide ofpotassium solution it should be applied soon after being mixed, sinceit loses its activeness by keeping. Fresh solutions always give themost brilliant results. Since the sulphide dissolves the silver, it isnecessary that it should be applied only to surfaces which have receiveda tolerably stout coating of this metal, otherwise the subjacent metal(brass, copper, or Gterman silver) will be exposed after the sulphidesolution has been applied.
Oxidising with the Paste.—For this purpose a thin paste is formedby mixing finely-powdered plumbago with spirit of turpentine, to
NIELLO, OR NIELLED SILVER. 28l
sulphur introduced. It is necessary that the articles to be treated inthis way should be absolutely clean.
Niello, or Nielled Silver.—These terms* are applied to a processwhich is attributed to Maso Finniguerra, a Florentine engraver of thefifteenth century, and somewhat resembles enamelling. It consists,essentially, in inlaying engraved metal surfaces with a black enamel,being a sulphide of the same metal, by which very pleasing effects areproduced. The " nielling " composition may be prepared by makinga triple sulphide of silver, lead, and copper, and reducing the resultingcompound to a fine powder. The composition is made as follows : Acertain proportion of sulphur is introduced into a stoneware retort, ordeep crucible. In a second crucible, a mixture of silver, lead, andcopper is melted, and when sufficiently fused the alloy thus formed isadded to the fused sulphur in the first vessel, which converts themetals into sulphides ; a small quantity of sal-ammoniac is thenadded, and the compound afterwards removed from the retort or cru-cible and reduced to a fine powder. The following proportions aregiven by Mr. Mackenzie :—
Put into the first crucible—Flowers of sulphur .Sal-ammoniac .
Put into the second crucible—Silver . . . .Copper . . . .Lead . . . .
750 parts.75 »
15 parts.40 „80 „
When fused, the alloy is to be added to the contents of the firstcrncible. Roseleur recommends diminishing the proportion of lead,which impairs the blue shade of the nielling, and corrodes too deeply.
To apply the powder, obtained as above, it is mixed with a smallquantity of a solution of sal-ammoniac. After the silver work is en-graved, the operator covers the entire surface with the nielling compo-sition, and it is then placed in the muffle of an enamelling furnace, whereit is left until the composition melts, by which it becomes firmlyattached to the metal. The nielling is then removed from the parts inrelief, without touching the engraved surfaces, which then present avory pleasing contrast, in deep black, to the white silver surfaces."This process, however, is only applicable to engraved work.
Wahl describes a cheaper process of nielling, which consists i* inengraving in relief a steel plate, which, applied to a sheet of silver,subjected to powerful pressure in a die, reproduces a faithful copy ofthe engraving. The silver sheet thus stamped is ready to receive the
The art was formerly called working in niello.
280 IMITATION ANTfQUE SILVER.
exposed to the blast. The apparatus employed for this purpose con-sists of a wooden hopper, with a longitudinal slit below, throughwhich a stream of fine sand is allowed to fall, by opening1 a sliding*cover. Closely surrounding" the base of the hopper is a rectangulartrunk of wood, extending some distance below the base of the hop-per, and tapering towards the bottom, to concentrate the sand-jet.This trunk is closed about the sides of the hopper, and open below,and is designed to direct the stream of sand upon the surface of thearticle presented beneath its orifice. To increase the rapidity of thodemolishing action of the sand, a current of air, under regulated pres-sure, is admitted into the uj per part of the trunk, which, when thesand-valve is opened, propels it with more or less accelerated velocityupon the metallic surface below. For this purpose, either a " blower,"or an air-compressor with accumulator, may be used : and the pressuremay be regulated at will. The sand is thus driven with more or lessvelocity down the trunk by the air-blast admitted above, and, fallingupon the surface of the article presented at the bottom, rapidlydepolishes the exposed parts, while those protected by the templet arenot affected. The articles are presented at the orifice of the trunk bythe hands of the operator, which are suitably protected with gloves;and as rapidly as the depolishing proceeds, he turns the article abouttill the work is done. The progress of the work is viewed through aglass window, set in a horizontal table, which surrounds the apparatusand which forms the top of a large box, into which the sand falls, andwhich is made tight to prevent the sand from flying about. A portionof this box in front, where the workman stands, is cut away, and overthe opening is hung a canvas apron, which the operator pushes asideto introduce the work. The sand that accumulates in the box belowis transferred again to the hopper, as required, and is used over andover again. The satin-finish produced by the sand-blast is exceed-ingly fine and perfectly uniform, and the work is done more rapidlythan with the use of brushes in the usual way.
Sulphuring Silver.—A very fine blue colour, resembling " blued "steel, may be imparted to silver or plated surfaces, by exposing thearticle to the action of sulphur fumes. For this purpose, the articleshould be suspended in an air-tight wooden box ; a piece of slate ora flat tile is laid upon the bottom of the box, and upon this is placedan iron tray, containing a small quantity of red-hot charcoal orcinders; about a teaspoonful of powdered sulphur is now quicklyspread over the glowing embers, and the lid of the box immediatelyclosed. After about a quarter of an hour, the lid may be raised (carebeing taken not to inhale the sulphur fumes) and the article promptlywithdrawn ; if the article is not sufficiently and uniformly blued,it must be again suspended and a fresh supply of hot charcoal and
SILVERING NOTES. ZO6
checked, which may be done by exposing a small surtax of anode insolution or suspending a plate of brass or a small -ilvrr anode as v" stop," or check, to the negative rod, until a sufficient number oiarticles (say spoons or forks, for example) have been suspended, whenthe htop may bo removed and the remainder of the articles immerseduntil the conducting rod is full; the rest ot the su-pendmg rodsshould then be treated in the same way. "When magnet«» or dvnamo-electric machines are employed, the full strength ot the current ischecked by the employment of the resistance cod, a description ofwhich will be found in Chapter I I I A simple way of diminishiii«_ theamount of eiment, when tilling the bath with work, is to interposea thin iron wire between the positive electrode and the suspendingrod, whieh must be removed, however, when the cathode surface(the articles to be plated) in the bath approaches that of the anodesurface.
4. Plating Different Mitch at the Same Time.—It is not good practiceto place articles composed of different metals or alloys indiscriminatelyin the bath, since they do not all receive the deposit with equal facility.For example, if two articles, one copper or brass, and anothor Britanniametal or pewter, be immersed in the solution "simultaneously, theformer will at once receive the deposit of silver, while the lattc r willscarcely become coated at all, except at the extremities. Since thebest conductor receives the deposit most freely, the worst conductor(Britannia metal, pewter, or lead) should first be allowed to becomecompletely coated, after which copper or brass articles may be intro-duced. It is better, however, if possible, to treat the inferior con-ductors separately than to run the risk of a defective deposit.
5. Excess of Cyanide.—When there is a large excess of c\ anide in theplating bath, the silver is very liable to strip, or peel off the workwhen either scratch-brushed or burnished; besides this, the anodesbecome dissolved with greater rapidity than is required to merelykeep up the proper strength of the bath, consequently the solutionbecomes richer in metal than when first prepared. The depositormust not confound the terms "free cyanide" with ' 'excess" ofcyanide : the former refers to a small quantity of cyanide beyond thatwhich is necessary to convert into solution the precipitate thrown downfrom the nitrate, which is added to the solution to act upon anddissolve the anode while deposition is going on; the latter term mayproperly be applied to any quantity of cyanide which is in excess ofthat which is necessary for the latter purpose.
In preparing plating solutions from the double cyanide of silverand potassium, great care must be taken, when precipitating thepilver from its nitrate solution, not to add the cyanide m excess, other-wise a poiuon of the precipitated cyanide of silver will be re-dissolved,
2 o 2 IMITATION ANTIQUE SILVER.
nielling. A large number of copies may be obtained from the samematrix. Such is the method by which a quantity of nielled articles aremanufactured, as so-called Russian snuff-boxes, cases for spectacles,bon-bon boxes, &c.
Roseleur suggests the following to produce effects similar to niel-ling : A pattern of the design, cut out of thin paper, such as lacepaper, is dipped into a thin paste of niellingcomposition, or into a con-centrated solution of some sulphide, and then applied upon the plateof silver, which is afterwards heated in the muffle. The heat destroysthe organic matter of the paper, and a design remains, formed by thecomposition which it absorbed.
A solution of chloride of lime (bleaching powder) will blacken thesurface of silver, as ako will nitric acid. For all practical purposes,however, chloride of platinum and weak solutions of the sulphidesbefore mentioned will be found to answer very well if applied withproper judgment.
Fink Tint upon Silver.—Fearn recommends the following for pro-ducing a fine pink colour upon silver : Dip the cleaned article for afew seconds in a strong hot solution of chloride of copper, then rinseand dry it, or dip it in spirit of wine and ignite the spirit.
Silvering Notes.—I. The anodes, if of rolled silver, should alwaysbe annealed before using them. This may easily be done by placingthem over a clear charcoal, or even an ordinary clear fire, until theyacquire a cherry-red heat: when cold, they are ready for use. Ifconvenient to do so, it is a good plan to hard solder a short length ofstout platinum wire (say about three inches long) to the centre of oneedge of the anode, which may be united to the positive electrode ofthe battery, or other source of electricity, by a binding screw, or bypewter solder. The object of attaching the platinum wire is to enablethe anode to be wholly immersed in the bath, and thus prevent it frombeing cut through at the water line, which is generally the case whereanodes are only partially immersed.
2. Worn Anodes.—When the anodes have been long in use, their edgesfrequently become ragged, and if these irregularities are not removedfragments of the metal will fall into the bath, and, possibly, upon thework, causing a roughness of deposit. It is better, therefore, to trimthe edges of anodes whenever they become thin and present a raggedappearance.
3. Precautions to be Observed when Filling the Bath with Work,—Assum-ing the suspending rods to have been cleaned, the battery connectionsadjusted, and the preparation of the articles to be plated commenced,some means must be adopted to prevent the articles Jirst put into thebath from receiving too quick a deposit while others are being gotready. In the first instance, the full force of the current must be
SILVERING NOTES. 285
This is a practice which should be strictly disallowed, for it is evidentthat the particles of brass, emery, and metallic oxides which becomedislodged by the rubbing process, must enter the solution, and beingmany of them exceedingly light, will remain suspended in the solutionfor a considerable time, and finally deposit upon the articles whenplaced in the vat, while some portions of the dislodged matter willbecome dissolved in the bath. All suspending rods should be cleanedat some distance from the plating vat, and wiped with a clean dryrag after being rubbed with emery cloth before being replaced acrossthe tank.
8. Elcctro-siho ing Pen tcr Solder.—Besides the methods recommendedelsewhere, the following may be adopted : After thoroughly cleaningthe article, apply to the soldered spot with a camel-hair brush a weaksolution of cyanide of mercury ; or if it be a large surface the solderedpart must be dipped for a short time in the mercury solution. Ineither case the article must be well rinsed before being immersed inthe silver bath.
9. Metal Tunis.—When working solutions in iron tanks, the platershould be veiy careful not to allow the anodes, or the work to becoated, to come in contact with the metallic vessel while deposition istaking place, since this will not only cause the current to be divertedfrom its proper course, but will also cause the anodes, especially ifthere be a large excess of free cyanide in the bath, to become eateninto holes, and fragments of the metal will be dislodged and fall to thebottom of the vat, and possibly small particles of the metal will settleupon the work. We remember an instance in which several woodennickel-plating tanks, lined with stout sheet lead, coated with pitch,yielded very poor results from some cause unknown to the plater.Having been consulted on the matter, the author soon discovered thesource of mischief : the copper hooks supporting the heavy anodeshad become imbedded in the pitch, and were in direct communicationwith the lead lining, from which a greater portion of the pitch hadscaled off, leaving the bare metal exposed below the surface of thesolution. Upon applying a copper wire connected to the negativeelectrode of the large Wollaston battery, at that time used at theestablishment, to the leaden flange of each tank the author obtained bril-liant sparks, to the great astonishment of the plater and his assistants,and subsequently caused strips of wood to be placed between the sideanodes and the lead lining, after which nickel-plating proceeded with-out check.
10. Bright Plating.—Even in the most skilful hands the bright bolu-tion is very liable to yield ununiform results. When the solution hasremained for some time without being used it is apt to give patchyresiuts, the work being bright in some parts only ; if the solution is
284 IMITATION ANTIQUE SILVER.
and probably lo*t when decanting the supernatant liquor from theprecipitate When the precipitation is nearly complete, the lastadditions of cyanide solution should be made veiy cautiously, andonly so long as a turbidity, or milkiness, is produced in the clearliquor above the precipitate. Instances have been known in whichnot only silver, but gold precipitates also, have been partially re-dissolved by excess of cyanide and the solutions thrown away b}ignorant operators as waste liquors. If by accident an excess ofcyanide has been used during the precipitation of gold or silversolution*!, the difficulty may be overcome by gradually adding a solu-tion of the metallic salt until, in its turn, it ceases to produce turbidityin the clear supernatant liquor. Again, in dissolving precipitates ofsilver or gold, rare is necessary to avoid using a large excess ofcyanide; a moderate excess only is necessary.
0. AHxch s Falling into the Bath.—When an article falls into the bath,from the breaking of the slinging wire or otherwise, its recoverygenerally causes the sediment which accumulates at the bottom of thevat to become disturbed, and this, settling upon the work, producesroughness which is very troublesome to remove. If not immediatelyrequired, it is better to let the fallen article remain until the rest ofthe work L> plated ; or if its recovery is of immediate importance, thelod containing the suspended articles should be raised every now andthen during about half an hour, in order to wash away any sedimentthat may have settled on the work. By gently lifting the rod up anddown, or raising each piece separately, the light particles of sedimentmay readily be cleared from the surface of the work. When verylarge articles, as salvers, for example, are immersed in the bath, theyshould be lowered very gently, so as not to disturb the sedimentreferred to: if this precaution be not rigidly followed, especially ifUie vat be not a very deep one, the lower portion will assuredlybecome rough in the plating, which the most skilful burnishing willbe incapable of removing. We have frequently known it to be neces-sary to strip and replate articles of this description from the cau^ereferred to It ruu&t also be borne in mind that when anodes becomevery much worn minute particles of silver fall to the bottom of the vessel,which, when disturbed in the manner indicated, rise upward, settleupon the work, and become attached, by what may be termed elect) 0-solderwy, to the work, causing the deposit to be rough, and whensuch surface is afterwards smoothed by polishing, the part exhibitsnumerous depressions, or is " pitted, " as the Sheffield burnishersterm it
7. Clean 1 nn Suspending Bods.—It is a very common practice with care-less- workmen to clean the suspending rods with emery cloth whilethey are in ^heir places across the sides or ends of the plating vat.
SILVERING NOTES. 287
plating operations are often rendered unnecessarily troublesome, whiletheir workshops are as unnecessarily untidy.
14. Battery Connections.—Before preparing work for the bath, thebinding screws, clamps,' or other battery connections should be ex-amined, and such orifices or parts as form direct metallic communicationbetween the elements of the batten* and the anodes and cathodesshould be well cleaned if they have any appearance of being oxidisedor in any way foul. The apertures of ordinary binding screws may becleaned with a small rat-tail file, and the flat surfaces of clampsrubbed with emery cloth laid over a flat file. When binding screws,from long use or careless usage, become very foul, they should bedipped in dipping acid, rinsed, and dried quickly. Previous to put-ting work in the bath, a copper wire should be placed in contact withthe suspending rod and the opposite end allowed to touch the anode,when the character of the spark will show if the current is sufficientlyvigorous for the work it has to do *. if the spark is feeble, the connec-tions should be looked to, and the binding screws tightened, if neces-sary ; the hooks and rods supporting tho anodes should also beexamined, and if dirty, must be well cleaned, so as to insure perfectcontact between the metal surfaces.
15. Gutta-percha Lining for Plating Tanks.—This material shouldnever be used for lining the insides of tanks which are to contain cyanidesolutions, since the cyanide has a solvent action upon it, which, after atime, renders the solution a very bad conductor. The author oncohad to precipitate the silver from an old cyanide solution which hadremained for a long period in a gutta-percha lined bath, and soon afterthe acid (sulphuric) had been applied to throw down the silver, thereappeared, floating upon the surface of the liquid, numerous clot*? of abrown colour, which proved to be gutta-percha, although greatlyaltered from its original ata U>.
286 IMITATION ANTIQUE SILVEE.
disturbed, by taking out work or by putting in fresh work, sometimesthe latter will refuse to become bright, and the remainder of the workin the bath will gradually become dull. To obviate this the bathshould be well stirred over night, and all the work to be plated at onetime put into the bath as speedily as jDossible, and all chances ofdisturbance avoided. When the work is known to have a sufficientcoating of the bright deposit, the battery connection should bo brokenand the articles then at once removed from the bath. On no accountmust an excess of the " bright " liquid be allowed to enter a bath.
ir. Dirty Anodes.—When the anodes, which should have a greyishappearance while deposition is taking place, have a pale greenish filmupon their surface, this indicates that there is too little free cyanide inthe bath, or that the current is feeble; the battery should first beattended to, and if found in good working order, and all the connec-tions perfect, an addition of cyanide should be made; this, however,should only be done the last thing in the evening, the bath then wellstirred and left to rest until the following morning.
12. Bust on the Surface of the Bath.—Sometimes in very windy weatherthe surface of the bath, after lying at rest all night, will be coveredwith a film of dust; to remove this spread sheets of tissue paper, oneat a time, over the surface of the liquid, then take the sheets up one byone and place them in an earthen vessel; the small amount of solutionwhich they have absorbed may be squeezed from the sheets, passedthrough a filter, and returned to the bath, and the pellets of papermay then be thrown amongst waste, to be afterwards treated for therecovery of its metal.
13. Old Slinging Wires.—It is not a good plan to use a slinging wire,one end of which has received a coating of silver or other metal morethan once, without first stripping off the deposited metal, in the firstplace the coated end of the wire becomes very brittle, and is liable tobreak when twisting it a second time, possibly causing the article tofall into the bath, or on a floor bespattered with globules of mercuryand other objectionable matter , again, the broken fragments of silver-covered wire, if allowed to fall carelessly on the floor, get swej>t uj}with the dirt, and the silver thus wasted. The wires which havo boonused once should be laid aside, with the plated ends together, and at aconvenient time these ends should be dipped in hot stripj^ing solution,until all the silver is dissolved off, and after rinsing, the ends shouldbe made red hot, to anneal them; the wires may then be cleaned withemery cloth and put in their proper place to be used a<rain. Theseminor details should always be attended to, since they do not neces-sarily involve much time and are assuredly advantageous from aneconomical view. It is too commonly the practice with careless opera-tors to neglect such simple details, but the consequence is that their
THE DEPOSITING VAT.
j^^Jili.LLMT^HSISNB i^ N H
LLLUirha^,j j j . 0
1 °
ill ! l :
The metals ordinarily coated with nickel by electro-deposition arecopper, brass, steel, and iron, and since these require different pre-paratory treatment, as also different periods of immersion in the nickelbath, they will be treated separately. The softer metals, as lead, tin,and Britannia metal, are not suited for nickel-plating, and shouldnever be allowed to enter the nickel bath.
The Depositing Vat, or Tank.—The depositing vessel may be madefrom slate or wood, but the following method of constructing a vat isthat most generally adopted, and \s hen properly earned out produces avessel of great permanency. The tank is made from 2j-inch deal,planed on both sides, the boards forming the sides, ends, and bottombeing grooved and tongued, soas to make the joint*, when puttogether, water-tight; they areheld together by long bolts,tapped at one end to receive anut. The sides and ends, asalso the bottom, are likewisesecured in their position bymeans of screw-bolts, as seenin Fig. 99. When the tank is Fl«- 99-well screwed together, as in theengraving, the interior is to be well lined with pure thin sheet lead. Itis of great importance that the lead used for this purpose be as pure aspossible, for if it contain zinc or tin it will be liable to be acted upon bythe nickel solution which it is destined to hold, and pin-holes will beformed, through which the solution will eventually escape. The jointsof the leaden lining must not be united by means of solder, but by theautogenous process, or " burning," as it is called, that is, its seams arefused together by the hydrogen flame—an operation with which intel-ligent plumbers are well acquainted. If solder were used for thispurpose voltaic action would soon be set up between the lead and thetin of the solder by the action of the nickel solution, and in time aseries of holes would be formed, followed by leakage of the vat. Whenthe lead lining is complete the vessel must be lined throughout withmatched boarding, kept in its position by a rim of wood fastenedround the upper edge of the tank. These tanks are usually 3 feetwide, 3 feet deep, and about 6 feet long, and hold about 250gallons.
Before using the tank it should be well rinsed with clean water. Itis a good plan to quite fill the tank with water, and allow it to remaintherein for several hours, by which time the pressure of the liquid willsoon indicate if there be a leakage at any part; it should then beemptied and examined, to ascertain if thoroughly water-tight.
u
CHAPTER XVIIL
ELECTRO-DEPOSITION OF NICKEL.
Application of Nickel-plating.—The Depositing Tank.—Conducting Rods.—Preparation of the Nickel Solution.—Nickel Anodes.—Nickel-plating byBattery.—The Twin-Carbon Battery.—Observations on Preparing Workfor Nickel-plating.—The Potash Bath.—Dips or Steeps.—Dipping Acid.—Pickling Bath.
Application of Nickel-plating.—When applied to purposes for"which it is specially adapted, nickel-plating may be considered one ofthe most important branches of the art of electro-deposition. In theearlier days of nickel-plating* too much was promised and expectedfrom its application, and, as a natural consequence, frequent disap-pointments resulted from its being applied to purposes for which itwas in no way suited. For example, it was sometimes adopted as asubstitute for silver-plating1 in the coating of mugs or tankards usedas drinking vessels for malt liquors, but it was soon discovered thatthose beverages produced stains or discolorations upon the polishednickel surface, which were not easily removed by ordinary means,owing to the extreme hardness of the metal as compared with silver orplated goods. Again, nickel-plated vegetable-dishes became stainedby the liquor associated with boiled cabbage or spinach, rendering thearticles unsightly, unless promptly washed after using—a precau-tionary measure but seldom adopted in the best-regulated sculleries.It was also found that polished nickel-plated articles when exposedto damp assumed a peculiar dulness, which after a time entirelydestroyed their brilliant lustre, whereas in a warm and dry situationthey would remain unchanged for years, a fact which the mullers ofour restaurants and taverns which were nickel-plated many years agobear ample testimony at the present day.
While practical experience has taught us what to avoid in connec-tion with nickel-plating, it has also shown how vast is the field ofusefulness to which the art is applicable, and that as a protective andornamental coating for certain metallic surfaces, nickel has at presentno rival. Its great hardness—which closely approximates that ofsteel—renders its surface, when polished, but little liable to injuryfrom ordinary careless usage ; while, being a non-oxidisable metal,it retains its natural whiteness, even in a vitiated atmosphere.
I REPARATION OP NICKEL SOLUTIONS. 29I
being cleaned with a rat-tail file, the hooks were dipped into ordinarydipping* acid (sulphuric and nitric acid) for one instant, and rinsed.One end of each hook was then moistened with chloride of zinc, andimmediately plunged into a ladle containing molten tin or pewtersolder. The tinned hook was next inserted into the hole in the anode,and a gentle tap with a hammer fixed it in its place. The anode beinglaid flat 011 a bench, with a pad of greased rag beneath the hole, thenext thing to do was to pour the molten solder steadily into thehole, and afterwards to apply a heated soldering iron. It is better,however, before pouring in the solder, to heat the end of the anode, soas to prevent it from chilling the metal, and a little chloride of zincsolution should be brushed over the inner surface of the aperture, soas to induce the solder to " r u n " well over it, and thus insure aperfect connection between the hook and the anode. The importanceof securing an absolutely perfect connection between these twosurfaces will be recognised when we state that we have knowninstances in which more than half the number of anodes, in a bathholding 2 50 gallons, were found to be quite free from direct contactwith the supporting hooks, owing to the crystallisation of the nickelsalt within the interior of the perforation having caused a perfectseparation of the hooks from their anodes. It was to remedy thisdefect that the author first adopted the system of soldering the con-nections.
Preparation of the Nickel Solution.—The substance usuallyemployed is the double sulphate of nickel and ammonia (or ** nickelsalts," as they are commonly called), a crystalline salt of a beautifulemerald green colour. This article should be pure. For 100 gallonsof solution the proportions employed are :—
Double sulphate of nickel and ammoniaWater . . . . . .
75 lbs.100 gallons.
Place the nickel salts in a clean wooden tub or bucket, and pour uponthem a quantity of hot or boiling water; now stir briskly with awooden stick for a few minutes, after which the green solution maybe poured into the tank, and a fresh supply of hot water added to theundissolved crystals, with stirring, as before. This operation is to becontinued until all the crystals are dissolved, and the solution trans-ferred to the tank. A sufficient quantity of cold water is now to beadded to make up 100 gallons in all. Sometimes particles of wood orother floating impurities occur in the nickel salts of commerce ; it isbetter, therefore, to pass the hot solution through a strainer before itenters the tank. This may readily be done by tying four strips ofwood together in the form of a frame, about a foot square, over whicha piece of unbleached calico must be stretched, and secured either by
290 ELECTRO-DEPOSITION OF NICKEL.
We will assume that it is desired to make up 100 gallons of nickelsolution—in which case the depositing tank should be capable ofholding not less than 120 gallons, to allow for the displacement ofliquid by the anodes and articles to be immersed, as also to allowsufficient space—say 3 inches—above the solution to prevent theliquid from reaching the hooks by which the anodes are suspended,when the bath is full of work. Although we have taken 100 gallonsof solution as a U<uulanl, we may state that, for large operations,tanks capable of holding 250 up to 500 gallons, or even more, arecommonly employed.
Conducting Rods.—These rods, which are used for supporting thenickel anodes, as also the articles to be nickeled, generally consist ofI -inch brass tubing, with a core of iron rod ; they are commonly laidacross the bath, lengthwise, extending about 3 inches beyond theextreme ends of the vessel. Sometimes, however, shorter rods areemployed, and these are laid across the bath from side to side. For anickel bath of 100 gallons and upwards three such suspending rodsare used, one rod being laid from end to end, close to each side of thetank, upon which the requisite number of anodes are suspended bytheir hooks; a third rod is laid, also longitudinally, along the centre
of the tank, midway betweenthe other two, for suspendingthe articles to be nickeled;the anode rods ar« to be con-nected together by a stoutcopper wire at one end bysoldering. These rods aretermed respectively the posi-tive and negative conductingrods, the former receivingthe anodes, and the latterthe work to b6 nickeled. Fig.100 represents a cast nickelanode and its supporting hookof stout copper wire, whichlatter should not be less than\ inch in thickness. In orderto insure a perfect connection
Fig. 100. between the copper hook and theanode, the author has found it
very advantageous to unite the two by means of pewter solder, in thefollowing way,* and which it may be useful to quote here: The holes
* " Electro-Metallurgy Practically Treated." By Alexander Watt.
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£6s
2Q* ELECTRO-DEPOSITION OF NICKEL.
means of tacks or by simply tying it to each corner of the frame withstring1.
Nickel Anodes.—It is not only necessary that the nickel saltsshould be perfectly pure—which can only be relied upon by purchas-ing them at some well-known, respectable establishment—but it isequally important that the nickel plates to be used as anodes—whichmay be either of cast or rolled nickel—should be of the best quality.A few years ago there was no choice in this matter, for rolled nickelwas not then obtainable. Now, however, this form of nickel can beprocured of almost any dimensions, of excellent quality, and anydegree of thinness, whereby a great saving may be effected in the firstcost of a nickel-plating outfit. Again, some years ago it was im-possible to obtain cast nickel anodes of moderate thickness, conse-quently the outlay for this item alone was considerable. Such anodescan now be procured, however, and thus the cost of a nickel-platingplant is greatly reduced, even if cast anodes are adopted instead ofrolled nickel.
Nickel-plating by Battery.—For working a ioo-gallon bath, fourcells of a 3-gallon Bunsen battery will be required, but only two ofthese should be connected to the conducting rods until the bath is abouthalf full of work, when the other cells may be connected, which shouldbe done by uniting them for intensity; that is, the wire attached to thecarbon of one cell must be connected to the zinc of the next cell, andso on, the two terminal wires being connected to the positive andnegative conducting rods. If preferred, however, the batteries maybe united in series, as above, before filling the bath with work, inwhich case, to prevent the articles first placed in the solution fromli burning,'* as it is termed—owing to the excess of electric power—itwill be advisable to suspend one of the anodes temporarily upon theend of the negative rod farthest from the battery, until the bath isabout half filled with work, when the anode may be removed, and theremainder of the articles suspended in the solution. In workinglarger arrangements with powerful currents—to which we shall here-after refer—resistance coils are employed, which keep back the forceof the electric current while the bath is being supplied with work,and even when such coils are used it is usual to suspend an anode orsome other "stop,'* as it is called, from the negative rod during thetime the work is being put into the solution.
Twin-Carbon Battery.—A very useful modification of the Bunsenbattery, and well suited for nickel-plating upon a small scale, is theAmerican twin-carbon battery, introduced by Condit, Hanson andVan Winkle, of New Jersey, U.S A., which, in its dissected condition,i<* represented in Fig. 101. A pair of carbon plates are united by aclamj), with binding screw attached, as shown at A. A plate of stout
DITS, OR STEEPS. 295
always be kept hot), the work will only require to be immersed for afew minutes, by which time the greasy matter will have become con-verted into soap, and being thus rendered soluble, may easily beremoved by the subsequent operations of brushing with pumice, &c.;but we must bear in mind that the causticity of the solution (andconsequently its active property) gradually becomes diminished, notonly in consequence of the potash having combined with the greasymatter, but also owing to its constantly absorbing carbonic acid fromthe air. When the bath has been some time in use, therefore, it willbe necessary to add a fresh quantity of potash, say about a quarterof a pound to each gallon. It is easy to ascertain if the potash haslost its caustic property by dipping the tip of the ringer in the solu-tion, and applying it to the tongue. As the bath becomes weakenedby use, the articles will require a longer immersion, and, with fewexceptions, a protracted stay in the bath will produce no injuriouseffect. Articles made from Britannia metal, or which have pewtersolder joints, should never be suffered to remain in the potash bathlonger than a few minutes, since this alkali (caustic potash) has thepower of dissolving tin, which is the chief ingredient of both. Again,articles made from brass or copper should never be suspended from thesame rod as steel and iron articles, in case the potash solution shouldhave become impregnated with tin dissolved from solder, &c. ; for ifthis precaution be not observed it is quite likely (as we have frequentlyseen in an old bath) that the steel articles will become coated withtin, owing to voltaic action set vip in the two opposite metals by thepotash solution. Cast-iron work, in which oil has been used in thefinishing, should, owing to its porous character, be immersed in thepotash bath for a longer period than other metals in order to thoroughlycleanse it from greasy matter.
Dips, or Steeps.—Besides the potash solution, certain other liquidsare employed in nickel-plating after the work has been " potashed"and scoured, which may be properly described in this place ; and wemay here remind the reader that the employment of these dips, asthey are called, is based upon the fact that the neutral solution ofnickel has no power (unlike cyanide solutions) of dissolving even slightfilms of oxide from work which, after being scoured, has been exposedto the air and become slightly oxidised on the surface. In order,therefore, to remove the faintest trace of oxidation from the surfaceof the work—the presence of which would prevent the nickel fromadhering—it is usual to plunge it for a moment in one or other of thefollowing auxtures after it has been scoured, then to rinse it, andimmediately suspend it in the nickel bath.
The Cyanide Dip.—This solution is formed by dissolving about halfa pound commercial cyanide of potassium in each gallon of water; for
2 9 4 ELECTRO-DEPOSITION Of NICKEL.
brushing- it with powdered pumice or other material, well cnarfiredwith the substance by dipping* the fingers occasionally in the powder.Before explaining* the operation of scouring, it will be necessary todescribe the various solutions, or "dips,'* as they are termed, inwhich the articles are immersed before and after being scoured. Thefirst and most important of these is the potash bath, in which allarticles to be nickel-plated are immersed before undergoing any othertreatment.
The Potash Bath.—The vessel in which the solution of potash iskept for use generally consists of a galvanised wrought-iron tankcapable of holding from 20 to 150 gallons, according to the require-ments of the establishment. An iron pipe, or worm, is placed at thebottom of the tank, one end of which communicates with a steamboiler, a stopcock being connected at a convenient distance for turn-ing the steam on or off; or the tank may be heated by gas jets, by
F>>. 102.
means of perforated piping fixed beneath it. An ordinary form ofpotash tank is shown at A in Fig. 102, in which the worm-pipe isindicated by the dotted lines, &c, a a, the vertical pipe b, with itsstopcock cf being conveniently placed at one corner of the tank, asshown in the engraving. The waste steam from the worm-pipeescapes into a second tank B, partly filled with water, which thusbecomes heated, and is used for rinsing. A rod of iron, or brass tubewith an iron core, rests upon the bath, longitudinally, for suspendingthe articles in the caustic liquor.
The potash solution is made by dissolving half a pound of Americanpotash in each gallon of water required to make up the bath, and thesolution is always used hot. The object of immersing the work to benickeled in the potash bath, is to render soluble any greasy matterwhich may be present, as, for example, the oil used in the variousprocesses of polishing. In a freshly made solution (which must
DIPPING ACID. 297
plan, in the first instance, to have a couple of wooden hoops, securedby copper rivets, placed over the vessel so as to prevent it from leak-ing in the event of the iron hoops giving way in consequence of thecorrosive action of the acid liquor. Precautions of this nature wiDprevent leakage and the inconvenience which it involves.
Dipping Acid.—This name is given to a mixture which is frequentlyused for imparting a bright surface to brass work, and which isvariously composed according to the object to be attained. "Whenrequired for dipping brass work preparatory to nickel-plating, it iscommonly composed of—
In making up the above mixture, the nitric acid is first added to thewater, and the sulphuric acid (ordinary oil of vitriol) is then to begradually poured in, and the mixture stirred with a glass rod. Whencold, it is ready for use. The mixture should be made, and kept, in astoneu are vessel, which should be covered by a sheet of stout glasseach time after using, to prevent its fumes from causing annoyanceand from injuring brass work within its vicinity. The " dipping"should always be conducted either in an outer yard, or near a fire-place, so that the fumes evolved during the operation may escape,since they are exceedingly irritating when inhaled by the lungs.When it is convenient to do so, it is a good plan to have a hood ofwrought iron, painted or varnished on both sides, fixed above anordinary fireplace in the workshop, and to have a hole made in thebrickwork above the mantelpiece to conduct the fumes into the chim-ney ; this arrangement, however, will be of little use, unless there isa good draught in the chimney. It is well to ascertain this, there-fore, before the dipping is proceeded with, which may be readily doneby holding a large piece of ignited paper above the grate, when, ifthe flame persistently inclines towards the chimney, the draught maybe considered perfect; if, however, it shows any inclination to comeforward, it may be assumed that the draught is imperfect, owing tothe chimney being filled with cold air. In this case lighted papershould be applied as before, until the flame and smoke of the ignitedmaterial have a direct tendency upward, or in the direction of thechimney. We are induced to give these precautionary hints moreespecially for the guidance of those who may be necessitated to workin apartments of limited space. In all cases, a vessel of clean watershould be placed close to the dipping bath, into which the articles areplunged the instant after they have been removed from the dippingacid,
20,6 ELECTRO-DEPOSITION OF NICKEL.
operations on a moderate sc lie, a stoneware vessel capable of holding1
about fifteen gallons may be supplied with about twelve gallons of thesolution. Baths of the form shown in A, Fig. 103, and which are tobe obtained at the Lambeth potteries, are well suited to this purpose.Another form of (stoneware vessel is seen in Fig. 104, which, being
Fig. 103. Fig. 104.
deeper, is useful for certain classes of work. In applying the cyanidedip to articles of great length, it is commonly the practice to employ acommon earthenware jug, kept near the dipping bath ; this, beingfilled with the cyanide solution, is held above the highest point of thearticle (a brass tube, for instance) and tilted so that its contents mayflow downward and pass all over the tube, which is then quicklytaken to the water trough or tray and well rinsed, when it is atonce placed in the nickel bath. On using the cyanide dip, it must beremembered that its only object is to dissolve from the surface of therecently scoured work an almost imaginary film of oxide , therefore themere contact of the cyanide solution is amply sufficient to accomplishthe object; on no account should brass or copper articles be exposedto the action of the dip for more than a few seconds; indeed, if thesolution is in an active condition, the quicker the operation is con-ducted the better. It will readily be understood, however, that theweak cyanide bath will gradually lose its activity, when the dippingmay be effected somewhat more leisurely. It is a common fault,however, to use these dips long after they have yielded up their activepower, and we have frequently known them to be employed, andrelied upon, when they were utterly useless.
The Acid Dip.—This solution, which is used for dipping steel andiron articles after they have been scoured, is composed of hydrochloric(muriatic) acid and water, in the proportion of half a pound of theacid to each gallon of water. The solution is generally contained in ashallow wooden tub, which may conveniently be the half of a brandycask or rum puncheon ; but since the acid eventually finds its wayto the iron hoops by which such vessels are held together, it is a good
CHAPTER XIX.
ELECTRO-DEPOSITION OF NICKEL [continued).
Preparation of Nickeling Solutions.—Adams' Process.—Unwin's Process—Weston's Process.—Powell's Process.—Potth' Proces**.—Double Cyanideof Nickel and Potassium Solution.—Solution for Nickeling Tin,Britannia Metal, &c.—Simple Method of preparing Nickel Salts.—Desmur's Solution for Nickeling Small Articles.
Preparation of Nickeling Solutions.—Although many solutionshave been proposed, we may say, with confidence, that for all prac-tical purposes in the electro-deposition of nickel, a solution of thedouble sulphate of nickel and ammonium, with or without the additionof common salt, will be found the most easy to work and the most uni-form in its results, while it is exceedingly permanent in character ifworked with proper care and kept free from the introduction of foreignmatter. The preparation of a nickel bath from the pure double salt isexceedingly simple, as we have shown, and only needs ordinary care tokeep such a solution in good working order for a very considerable period.In order that the reader may, however, become conversant with thevarious solutions and modifications which ingenious persons have fromtime to time introduced, we will, as briefly as possible, explain suchof these processes as may appear to deserve attention, if not adoption.Boettger's original process having been already referred to, we willnow describe Mr. Adanih' modification of it, for which he obtainedpatents in this country, in France, and the United States, and which,after much costly litigation, and consequent loss to those who hadbecome possessed of them, were proved to be unnecessary to the success-ful deposition of nickel by electrolysis. When the ordinary simplemethods of preparing the double salts of nickel and ammonium are takeninto consideration, it seems marvellous that Adams' exceedingly round-about process—which no one with practical chemical knowledge woulddream of following—should have been considered worth contesting ;not to defend the process as such, which no one infringed, but tosecure the sole right to deposit nickel by electro-chemical means, byany process whatever. And what was the real " bone of contention" ?It was based upon the most absurd " claim " ever allowed to becomeattached to a patent, which runs as follows :—
2 9 8 ELECTRO-DEPOSITION OF NICKEL.
Pickling Bath.—Cast iron, before being nickeled, requires to beplaced in a cold arid solution, or pickle, as it is called, to dissolve orloosen the oxide from its surface. The pickle may be prepared in awooden tub or tank, from either of the following formulae :—
Sulphuric acid (oil of vitriol)W a t e r . . . .
i l b .1 g a l l o n .
Cist-iron work immersed in this bath for twenty minutes to halfan hour will generally have its coating of oxide sufficiently loosenedto be easily removed by means of a stiff brush, sand, and water.
"When it is desired that the articles should come out of the bathbright, instead of the dull black colour which they present whenpickled in the plain sulphuric acid bath, the following formula maybe adopted :—-
Sulphuric acidWater
1 1b.1 gallon.
Dissolve in the above two ounces of zinc, which may be convenientlyapplied in its granulated form. When dissolved, add half a pound ofnitric acid, and mix well.
ADAMS PROCESS. 301
evaporated to dryness. The mass is then again dissolved in water,and a much smaller quantity than before of sulphuric acid is added,and the whole again evaporated to dryness, the temperature beingraised finally to a point not to exceed 650 Fahr. This temperature isto be sustained until no more vapours of sulphuric acid can bedetected. The resulting sulphate of nickel is pulverised, and thoroughlymixed with about one-fiftieth of its weight of carbonate of ammonia,and the mass again subjected to a gradually increasing' tempera-ture, not to exceed 6500 Fahr., until the carbonate of ammoniais entirely evaporated. If any iron is present, the most of it will beconverted into an insoluble salt, which may be removed by nitration.The resulting dry and neutral sulphate of nickel is then dissolved inwater by boiling, and if any insoluble residue remains, the solution isfiltered. From the weight of nickel used before solution, the amountof sulphuric acid in the dry sulphate can be calculated. This amountof sulphuric acid is weighed out and diluted with four times its weightof water, and saturated with pure ammonia or carbonate of ammonia—the former is preferred. This solution, if it is at all alkaline, shouldbe evaporated until it becomes neutral to test-paper. The sulphateof ammonia of commerce may likewise be used, but pure sulphate ofammonia is to be preferred. The two solutions of the sulphate ofnickel and sulphate of ammonia are then united, and diluted withsufficient water to leave 11 to 2 ounces of nickel to each gallon of solu-tion, and the solution is ready for use. The object of twice evaporat-ing to dryness and raising the temperature to so high a degree is, inthe first place, to drive oft' the excess of sulphuric acid ; and secondly,to convert the sulphate of iron, if it exists, into basic sulphate, whichis quite insoluble in water.
'* In order to give the best results, it is necessary that the solutionshould be as nearly neutral as possible, and it should in no case beacid. The inventor prefers to use the solution of a specific gravity ofabout 1-052 (water 1*000), though a much weaker or still strongersolution may be used. At temperatures above the ordinary the solu-tion still gives good results, but is liable to be slowly decomposed.An excess of sulphate of ammonia may be used to dilute the solution,in cases where it is desirable to have it contain much less than 1 ounceof nickel to the gallon.
" In preparing the solution of double chloride of nickel and ammo-nium, the nickel is to be purified and dissolved in the same manner asis described for the previous solution ; and it is to be freed from copperand other foreign matters in the same manner. The solution is thenevaporated to dryness ; it should be rendered as anhydrous as possible.The salt is then placed in a retort, and heated to a bright red heat.The salt sublimes, and is collected in a suitable receiver, the earthy
3°° ELECTRO-DEPOSITION OF NICKEL.
"The electro-deposition of nickel by means of a solution of thedouble sulphate of nickel and ammonia, or a solution of the doublechloride of nickel and ammonium, prepared as [below] described, andused for the purposes [below] set forth, in such a manner as to be freefrom the presence of potash, soda, alumina, lime, or nitric acid, orfrom any acid or alkaline reaction."
According* to this, if any solution of nickel, no matter how pre-pared, which could be proved by analysis to be free from the sub-stances named (not one of which would be a necessary associate ofnickel or of its double salts), such solution, if used in nickel-plating*,would be an infringement of the patent! This we know was theimpression of those who held the English patent, and we vainlyendeavoured to show its fallacy. " Any solution of nickel which isfree from these substances and used for plating purposes is an infringe-ment of our patent." That was the contention, and the owners ofthis patent believed themselves entitled to an absolute monopoly of theright to nickel-plate within the four quarters of the United Kingdom.
Adams' Process.—In preparing the solution, the inventor prefersto use pure nickel, but commercial nickel may be used. " Commercialnickel," says the patentee, " almost always contains more or less ofthe reagents employed in the purification of this metal, such as sul-phate of lime, sulphide of calcium, sulphide of sodium or potassium,chloride of sodium, and alumina. When any of these substances arepresent, it is necessary to remove them. This can be done by meltingthe nickel, or by boiling it in water containing at least I per cent, ofhydrochloric acid. The boiling must be repeated with fresh acid andwater until the wash-waters give no indication of the presence of limewhen treated with oxalate of ammonia. When the metal is purifiedby melting, the foreign substances collect on the top of the metal inthe form of slag, which can be removed mechanically. If the nickelcontains zinc, it should be melted in order to volatilise the zinc anddrive it off. The crucible in such a case must not be closed so tightlyas to prevent the escape of the zinc fumes. If copper, arsenic, orantimony be present in the nickel, they can be removed, after thenickel is dissolved, by passing sulphuretted hydrogen through thesolution. The acid to be used in dissolving the metal consists ofI part strong nitric acid, 6 parts muriatic acid, and I part water.Nitric acid or muriatic acid may be used separately, but the above ispreferred. A quantity of this acid is taken sufficient to dissolve anygiven amount of the metal, with as little excess of the former as pos-sible ; a gentle heat is all that is required. The resulting solution isfiltered ; and to prepare the solution of the double sulphate of nickeland ammonium, a quantity of strong sulphuric acid, sufficient to con-vert all the metal into sulphate, is added, and the solution is then
UNWIN'S PROCESS. 303
stop the addition of the solution of sulphate of ammonia, when suffi-cient has been added to combine with all the sulphate of nickelpresent, but I continue to add a large excess. I do this because Ihave discovered that the double sulphate of nickel and ammonia is farless soluble in the solution of sulphate of ammonia than in purewater, so that it is precipitated from its solution in water 011 addingsulphate of ammonia. I therefore contiuue adding the solution ofsulphate of ammonia, continually stirrinur, until the liquid losesnearly all its colour, by which time the double sulphate of nickel andammonia will have been precipitated as a light blue crystallinepowder, which readily settles to the bottom of the vessel. I thenpour off the liquid from the crystalline precipitate of double .sulphateof nickel and ammonia, and wash the latter quickly with a strong,cold solution of sulphate of ammonia, as often as I consider necessaryfor its sufficient purification ; but I do not throw away this liquidafter use, but employ it at my discretion for combining with freshsulphate of nickel, instead of dissolving a further amount of sulphateof ammonia. If I desire to make a further purification of the doublesulphate of nickel and ammonia, I make a strong solution of it indistilled water, and add to the liquid a strong solution of sulphate ofammonia, by which means the double sulphate is precipitated in avery pure condition, and is separated from the liquid by nitration, orby other convenient means, and then dried, or used direct as may bedesired ; the liquid strained away can be employed, instead of freshsolution of sulphate of ammonia, for combining with more sulphateof nickel, or for washing the precipitate of the double sulphate."
Weston's Process.— Mr. Edward Western, of Newark, N.J.,having observed that boric acid, when added to nickel solutions, pro-duced favourable results in the electro-deposition of nickel, obtaineda patent for " the electro-deposition of nickel by means of a solutionof the salts of nickel containing boric ticid, cither in its free or com-bined state. The nickel salts may be either single or double." Theadvantages claimed for the boric acid are that it prevent* the depositof sub-salts upon the articles in the bath, which may occur when thebath is not in good condition. Mr. Weston further claims that theaddition of this acid, either in its free or combined state, to a solutionof nickel salts renders it less liable to evolve hydrogen when the solu-tion is used for electro-deposition; that it increases the rapidity ofdeposition by admitting the employment of a more intense current,while it also improves the character of the deposit, which is lessbrittle and more adherent. Mr. Wahl, after extended practical trialsof Mr. Weston's formula, states that they have " convinced him of thesubstantial correctness of the claims of the inventor," and he adds,'* Where the double sulphate of nickel and ammonia is used, the addi-
3<D2 ELECTRO-DEPOSITION OP NICKEL.
matter heirn? left behind. The salt, thus purified, is dissolved inwater, and to the solution is added an equivalent quantity of purechloride of ammonium. The solution is then ready for use; it mayhave a specific gravity of 1-050 to i#ioo."*
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