No.239.

LONDON, SATURDAY, MARCH 29. [1827-8.

LECTURES ON CHEMISTRY,

BY

PROFESSOR BRANDE.

Delivered at the Royal Institution of GreatBritain.

LECTURE XXXIII.

On the Oxides, Ores and Salts of Inon.

AT the conclusion of the last lecture, Istated to you that iron combined with twodefinite proportions of oxygen to form a pro-toxide and a peroxide, and I mentioned toyou what these were.Now, the protoxide may be obtained by

precipitating a solution of the sulphate ofiron by potash, by washing the precipitateout of the contact of air, and by drying it ata red heat. This protoxide is of a blackcolour, and is sparingly soluble in ammoniaand the carbonated alkalies. There is a

very beautiful mode of obtaining this oxide,contrived by Dr. Ingenhous, namely, the

burning of iron in oxygen gas, which I shallshow you. Here is a piece of iron-wire, tothe extremity of which a bit of sulphur isattached for igniting it, which must be donejust as you plunge it into the gas, and youshould see that the stopper of the jar is suffi..ciently close to prevent the escape of oxygen.The wire, as you see, soon becomes red-hot,then melts, and vivid scintiilations of metalare thrown off, which become quenched asthey fall into the water beneath. Thisprotoxide was formerly known in pharmacy,under the name of martial aethiops, and wasprocured by moistening iron filings with asmall quantity of water, and exposing themto the air for a day or two, the oxide wasthen separated by washing. This oxide is ofa black colour, is almost insoluble in water,and has little or no taste.Now, to obtain the peroxide, you boil the

protoxide in nitric acid, precipitate the solu-tion by ammonia, and it is then to be washed

and dried at a low heat. This oxide you willrecollect, I stated, was composed of one pro-portional of metal, and of one and a half ofoxygen, and was formerly called saffron ofMars. I need not go into an explanation ofthe reasoning by which this conclusion wasarrived at; but this, I believe to be thefact. It has been supposed, by Gay-Lussac,that there is an intermediate compound be-tween the two I have named ; but the evi-dence upon this point has not been of a verysatisfactory kind, and I am inclined to regardit rather as a mixture of the protoxide andperoxide, than as any definite, compound ofthe metal with oxygen. The native oxidesof iron constitute a very important and ex-tensive class of minerals which vary in co-lour, and this is owing, in some cases, to thedegree of oxidation in which they maybe found, and in other cases, to their meretexture. Some of the native oxides are

magnetic, and those which contain most

oxygen are least attracted by the magnet.The richest ore is the magnetic iron ore foundabundantly in Sweden, where it is used forthe manufacture of the fine bar iron, andparticularly for the manufacture of steel. Itoccurs massive, of a slight metallic lustre,and is sufficiently magnetic to take up aneedle and fine iron filings. A varietyof the native oxide is found crystallised inthe island of Elba, and among the volcanicproducts, and is called iron glance, or mica-ceous iron ore. Near Ulverstone, in Lan-cashire, there is a variety of iron ore calledhrrmatite, or red iron-stone, and it occurs ingreat quantities in that neighbourhood, inglobular and stalactitic masses. Most ofour iron plate and iron wire is made fromthis ore.

Mr. Brande then showed the magneticattraction of the different ores, by exposingthem to a polarised needle; and it wasshown that those ores, which contained least

oxygen, were attracted by the magnet.-Now, when you come to clay iron ore andthe peroxide of iron, these contain little iron,and are, therefore, unimportant sources ofit. Clay iron ore contains not more than25 or 30 per cent of iron, yet it is the oreprincipally worked in this country. You

may ask, why we use this ore when we

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have others so much richer The reason is,that it is found in great quantities in theimmediate vicinity of coal and lime-stone,which are advantages sufficiently great toinduce the manufacturer to work this, com-paratively speaking, poor ore. It may beremarked here, with respect to the twoclasses of the salts of iron, that the salts

containing the protoxide are green, and crys-tallisable ; that they absorb nitric oxidewhen in solution, and absorb oxygen withgreat avidity by exposure to air, and ac-quire, in consequence, a red colour. Theperoxide forms a class of salts with the acids,which are uncrystallisable generally speak-ing, soluble in alcohol, but which do not ab-sorh oxygen from the air or nitric oxidewhen in solution.

This brings us to the chlorides of iron.-Chlorine, like oxygen, combines with themetal in two proportions; forming a proto-chloride and a perchloride. In the proto-chloride the combination takes place in theproportion of 1 of iron 28, and 1 of chlo-rine 36, giving 64 as its equivalent ; and,in the perchloride, there is one proportionaland a half of chlorine 54, combined with oneof iron 88, giving 82 as its equivalent.-Now, with regard to the protochloride, youmay obtain it by dissolving iron in muriaticacid, and evaporating the solution;to drynessout of the contact of air ; the protochloridethen assumes a red colour, and, if intenselyheated, a black colour. You may obtainthe perchloride by burning the metal in chlo-rine, but you generally, at the same time,obtain also a little of the protochloride. Assoon as the gas comes in contact with themetal, it begins to act upon the metal, butnot intensely until heat is applied ; a kindof crystalline substance then arises from thecombustion, which is the perchloride. Ifwe now act upon these two chlorides bywater, we shall obtain, in the one instance,a protomuriate, and, in the other, a permuriateY’ iron, which are both dissolved by thewater. They are difficult to crystallise, butthe protomuTÌate may be obtained in smallgreen crystals, which are not permanent,but, upon exposure to air, fall into powder,and become a permuriate. You may obtainthe same compound by dissolving the pro-toxide of iron in muriatic acid, and evapo-rating it to dryness. The protomuriate ifiron is not a salt of any importance. Now,with regard to the permuriate, or, oxymuriateof iron, as it is sometimes called, it is usedoccasionally in the arts, and sometimes inmedicine. Dissolved in spirits of wine, itfurnishes a good chalybeate preparation,and such is the tinctzera feri-i muriatis of theplarmaeopeeia. The composition of the

protomuriate is 36 of the protoxide, and 37of muriatic acid, or one proportional andone; and the permuriate consists of one

proportional of peroxide 40, and one propor.tional and a half muriatic acid 5.5.5, so thatits equivalent is 95.5 ; and here is the diffi-culty in applying the theory of chemicalproportions to the salts of iron. Iodine andiron combine, and you obtain an iodate andan hydriodate C!f iron, which are of a greencolour.

Iron and nitric acid act very powerfullyupon each other,so powerfully, that you canscarcely obtain a protonitrate of iron. This,which you see here, is a protonitrate of iron,and is composed of one proportional of oxide36, and of one of nitric acid 54; and thepemit1"ate, oroxynitrate, is composed of oneof peroxide 40, and of one and a half ofacid 81. Sitlphui, and iron may be unitedtogether, and two sulphurets of iron may beproduced; they may be easily fused toge.ther, and the trick which you have seen

schoolboys perform of melting a poker, byheating it red hot, and then rubbing it overwith a stick of sulphur, is an example of theformation of a sulphuret of iron ; the sul.phur uniting with the iron to form the blackor protosulphuret. The sulphuret and thebisulphuret are, in their composition, inperfect accordance with the theory of pro.portionals ; the sulphuret being composedof one proportional of metal, and one of sul-phur, and the bisulphuret of one of metaland two of sulphur. The sulphuret is usedin the laboratory for the formation of sul-phuretted hydrogen, and for the produc.tion of the protoxide of iron. The bisul.

phuret, or pyrites, is met with in great abart-dance in Nature, in a great variety of crys-talline forms, of which the cube is the pri.mitive. They are often found in masses,and in detached nodules, and being washedout of the soil, and found upon the surface,are called by the people thunderbolts. Wenever think of obtaining the meta) from theseores. Here are also two sulphates, the onea protosulphate, generally called green vitriol,in the dry and in the crystallised state; inthe dry state, it is in the form of a white

powder, and the crystals are of a green co.

lour, and rhomboidal figure. It consists ofone proportional of protoxide 36, and one ofsulphuric acid 40, so that its equivalent is

76. In the crystallised state, 76 parts ofthe dry salt unite with 7 proportionals ofwater 63, so that its equivalent is then :t.*!9.This salt is soluble in twice its weight ofwater at 60°. It is often called copperas, andis obtained in great quantities, by simplyexposing the sulphurets to air and moisture.It is characterised by its green colour, byits solubility in water, and by its styptictaste. Its solution in water is green, andif you leave a little of the sulphuret fromwhich it has been obtained in the solution,it may be retained in a state of pi-otagul.phate ; bat if you expose it to air, or to any

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oxidizing agents, to light, or to nitric acid,it is readily converted into a persulphate qfiron.Now the persulpÌl.ate of iron is easily ob-

tained. When crystals of the protosulphateare exposed to heat, the water of crystalli-sation first passes off, then sulphurous acid,and then sulphuric acid, and there remainsin the vessel a brown dry powder, calledformerly the colcothar of vitriol, which is theperoxide of iron, and this, if mixed withdiluted sulphuric acid, forms the persul-phate. Sometimes the protosulphate isfound native in mines, that is to say, in si-tuations where the sulphurets have beendecomposed by the action of the air andwater. Some time ago, Mr. Hatchett thoughtthat he had found some crystals of the per-sulphate; but it was afterwards ascertained,that these crystals were compounds of theprotosulphate and ammonia; it was, there-fore, a triple salt, and not, as he supposed,a persulphate of iron. It is divested of theinky taste of the other salts of iron, and,therefore, has been proposed as a substitutefor them in medical practice.

Iron combines with phosphorus ; andboth its oxides unite with phosphoric acid,forming protophosphate and per phosphate ofiron; you may easily obtain them byadding to the solutions of iron a solutionof phosphate of soda. The protophosphateof iron is of a pale blue colour, and the per-phosphate white. The protophosphate is

occasionally found native, in large quantities,in bog earth, in various parts of the king.dom; and at one time a large quantity of itwas dug up, and supposed to-be native Prus-sian blue; but it turned out to be only claycoloured with the protophosphate of iron.It was once conceived to be the colouringmatter of the blood, that is to say, the per-phosphate ; but the colouring matter of theblood appears to depend upon the presenceof some peculiar animal principle, and notupon any combination of iron with theblood, as I shall show you by and by.

Ca)’6<M unites with iron, and forms somevery valuable compounds; all the varietiesof steel are essentially carburets of iron;and when you remember its numerous ap-plications, you may judge of the value ofthis compound. Another compound of ironand carbon is plun2bago, or black lead, as it iscommonly called, which is a very valuablesubstance ; 100 parts of it are composed of95 carbon, and 5 of iron ; and if you reversethis proportion, you will nearly arrive atthe composition of steel, it being composedof 95 iron, and &oacute; carbon. Now, with regardto this substance, grapite or plumbago, itis met with in great quantities at Borrodalein Cumberland, embedded in masses ofslate and grauwacke. It is ground down into

powder, and melted with sulphur for themanufacture of black lead pencils, as theyare called, for carpenters; and a coarser

variety of it is used for the manufacture ofcrucibles and earthenware ; the crucibles

are called black lead crucibles. It is alsoused as an ingredient in compositions forcovering cast iron, and for diminishingfriction in machines. Plumbago is very in-fusible, and is very difficult of combustion,which are curious properties conferred uponthe carbon, by the small quantity of ironwith which it appears to be combined. Insome experiments made by Messrs. Stodartand Faraday on the hardening of steel, a

substance was obtained very analagous toplumbago, but the composition of it wasnever ascertained exactly. I shall post-pone what I have to offer to you, on the

properties and quality of steel, until thenext lecture. When iron is subjected to

the action of carbonic acid, a carbonate ofiron is formed. There are two carbonatesof iron, a protocarbonate, and aperearbonate;and these two salts are very easily dis-

tinguished from each other, by the usualcharacteristics of the proto and the persalts of iron, the first being green, thesecond red. Now, the protocarbonate, ifcollected, washed, and dried, passes intothe state of a percarbonate, but the prepa-ration which we have in the Pharmacapaeia,under the name of ferri carbonas, is littlemore than the protoxide of iron, or iron

having lost its carbonic acid. The proto-carbonate exists in a number of mineralwaters, and it appears to be the best formedicinal purposes; a pint of such waterseldom contains more than a grain or twoof the salt ; but I think, that even thatminute quantity is efficacious, much moreso than the large doses of iron which havebeen attempted to be given. When youwish to imitate mineral water, you shouldalways use the protocarbonate ; if you usethe percarbonate, you will obtain a verydifferent result, which will not at all ap-proach to the character of the natural chaly-beate water. And this induces me to passan eulogium upon the artificial waters madeat Brighton, where the greatest care istaken, as I have had an opportunity of see-ing, to produce, under the superintendanceof adequate chemists, and by means ofappropriate machinery, the most correctimitation of the native waters. And I cansee no reason why the imitation of thechemical nature of the native mineralwaters, should not produce exactly thesame effects on the constitution, as thenative water itself; especially if their useshould be combined with the respiration of

good air, and the enjoyment of exercise andother amusements usually practised, in whatare called watering places. 1 omitted to

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mention, that the crystals of the proto- Icarbonate of iron are rhomboidal. ’

Now I have gone through the principalsalts of iron, and I have nothing further toremark upon, than the application of thetheory of proportions to the salts of iron,the theory tallying exactly in its applicationto the proto salts, but not with the per salts.

There remains for our consideration, a

curious compound of iron and cyanogencalled Prussian blue, the varieties of ironand steel, and some general remarks on thebest tests for detecting the presence of themetal.

LECTURE XXXIV.

On the Salts of Iron; and on the Manufactureof Iron and Steel.

IF you act upon the salts of iron by thehydrocyanate of potash, you produce from thesalts containing the protoxide, a white pre-cipitate, and from those containing the

peroxide, a deep blue precipitate, which is aferrocyanate, containing the peroxide of iron,and which has been called Prussian blue,from the circumstance of its having been ac-cidentally discovered by a dyer in Berlin ;a substance, which is extensively used inthe arts and in the laboratory. The modeof obtaining Prussian blue, is usually as

follows:&mdash; subcarbonate of potash and someanimal substance, such as hoofs, horn shav-ings, or dried blood, are mixed together inabout equal quantities, heated red hot, andkept in that state for some hours ; andwhen quite cold, six or eight parts of waterare poured upon the mixture. The filteredsolution is found to contain hydrocyanate ufpotash along with carbonate of potash, andsome other products. It is then mixed witha solution of one part of sulphate of iron,and two of alum, when a green precipitatefalls down, which, by frequent washingswith diluted muriatic acid, acquires a fineblue tint, which is the Prussian blue. Thealuminous earth contained in the alum givesa body to the precipitate, which improves itas a pigment. The black matter remainingafter the combustion of these materials, is a

cyanuret of potassium, which, by beingacted upon by water, is converted into a hy-drocyanate of potassa; a little carbonic acidand ammonia are also formed, the latter ofwhich is expelled by heat, and we thereforehave a carbonate and hydrocyanateofpotassa,which, when added to a solution of the sul-phate of iron, form a precipitate of oxideand ferrocyanate of iron; tLe oxide may beremoved by the dilute muriatic acid. A

variety of opinions have been entertainedrespecting the nature and composition of.Prussian blue, but this appears to me to bethe simplest and most correct view of it. i

Now, when Prussian blue is acted uponby boiling it with potash, the oxide of ironis separated, it loses its blue colour, and onevaporating the solution, a triple salt isformed, containing hydrocyanic acid, pot.ash, and oxide of iron, which has beencalled ferroprussiate tij’ potash, and j’errocya.nate of potash. This salt forms yellow cubicand tabular crystals, which are insoluble inalcohol, more soluble in hot than in coldwater, permanent, and of a peculiar taste.Here is a very fine specimen of the crystal-lized salt, which was presented to me bythe late Mr. Parkes. The proportions inwhich the elements forming this salt aremixed, I shall not endeavour to lay beforeyou, since chemists have very much differedin their opinions respecting it; but that thisis the nature of its composition, those whoare best acquainted with the salt, are agreed.A very few years ago, this salt was madeonly in small quantities, as a matter of

curiosity in the laboratory, but it is nowmanufactured very largely in Glasgow as amordant for the calico printers, which weshall have to consider hereafter.

If you digest Prussian blue with strontia,and baryta, and magnesia, ammonia, soda, andlime, in water, you obtain ferrocyanates ofthese alkalies and earths.The ferrocyanate of potash is used as a

test for the presence of many of the metals,by the colour of the precipitates thrown down,and a very valuable test it is. You have,therefore, in the elementary works on che.mistry, tables giving you the different co-lours of the precipitates ; but I must cautionyou against too much confidence in thesetables, because the colour of the precipitatewill very much depend upon the salt havingan excess of acid, or an excess of base, onits being a proto, or a persalt. Here is atable showing you the colours of some of theprecipitates obtained by this salt. Manga-nese affords a white precipitate ; iron, theprotoxide, a pale blue ; the peroxide, Prus-sian blue ; zinc, a yellowish white ; tin, theprotoxide, white ; the peroxide, white,which becomes yellow, and then bluish;copper, a deep brown, and so on; and itwas at one time proposed to give it thename of calorific acid, from the number oftints which it produces in combination withthe oxides of the different metals. So much,then, for Prussian blue, and the fenocy-anates generally.With respect to the general characters of

the salts of iron, they are soluble in water,and are, for the most part, of a green co-

lour, becoming brown on exposure to air;they furnish a blue precipitate with ferro.cyanate of potash, and a black precipitate onthe addition of galls, or any other vegetableastringent. They will be distinguished bytheir styptic, austere, inky taste, and by the

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great facility with which they blacken a

Igreat many vegetable bodies. The sulphu-retted hydrogen gas, and the pure sulphu-rets, give no precipitation to the salts of

iron ; nor do the iodides.In this Lecture, in connexion with the

action of vegetable astringents on the saltsof iron, I am in the habit of showing theclass the composition of writing-ink, and Ihave found the following proportions of thematerials the best for its manufacture :

Galls................ 8 oz.Logwood ............ 4 !

Gum..... 3

Sulphate of iron ...... 4Sulphate of copper .... 1

Cloves’.............. &frac14;The galls, logwood, gum, and sulphate ofiron, powdered, should be boiled in twelvepints of water to six ; and toward the end ofthe boiling, the sulphate of copper andcloves should be added. The mixture shouldbe allowed to stand twenty-four hours, andthen decanted and bottled for use. The

copper gives the ink a bright black appear-ance, and the cloves a pleasant odour, andprevent it from getting mildewed on itssurface.Few of the nllmas of iron are of any im-

portance. We shall mention the alloy ofiron nud tin to form tin-plate on anotheroccasion ; some few other alloys have beenused, but few are of any importance. Thevarieties of iron met v-itli in t!ie arts is a mat-ter of considerable importance, which willlead us to speak very briefly of the matut-facture of iron. With regard to tin-plate, Imav just say, that it consists of thin platesof iron, which are dipped into melted tin, soas to give them the appearance of tin. Be-fore considering the varieties of iron, I maycall your attention a little more in detail tosteel, which is a carburet of iron, containingfive per cent of carbon, and 95 of iron ; andthere are generally present minute portionsof other substances.The manner of making steel, is this : a bar

of iron is heated in a vessel containing char-coal, and it is kept exposed for a long timeto the heat ; it is ultimately found, that thebar of iron has been penetrated, or per-meated, as it were, with the vapour of car-bon, which has combined with it through-out, and formed carburet of iron. Whenwithdrawn from the furnace, it is foundto be blistered; its fracture and generalappearance are altered, and it is thenknown under the name of blistered steel. Thebars of this first manufacture are heatedagain, and drawn down into smaller barsby powerful machinery and beaten, andit is then called ti/ted steel; which, whenbroken up and welded, and drawn into bars,forms shear steel; and this, when melted along

with some vitrifying flux, and cast into bars,forms what is called cast steel or English steel.The properties of steel are exceedinglysingular, its texture varies in differentspecimens ; sometimes it presents more orless of a crystalline fracture, and silky inothers ; and the appearance of the fractureleads the artist to apply it to particular pur-poses. You must see, in the selection ofsteel for any particular use, that the frac-ture is regular; and if you see a spot in itmore white than another, wipe it over withnitric acid; and if the spots become darker,the specimen is not good steel. It meltsmore readily than iron, and it admits ofwelding, or uniting with iron, at high tempe-ratures. It has a great variety of curiousproperties, on which its value in the arts,in a great measure, depends. Here is apiece of steel which is pliable ; and if I heatit, and allow it to become cold again slowly,I anneal it, as it is called, and it is still moreflexible than before ; but, by rapidly coolingit, it becomes so brittle, that you may breakit like glass. Now steel, in this excessivelyhard state, is a very intractable substance ;but if it be gradually heated up to a certainpoint, it again acquires a degree of softness ;and if you heat it red hot, it becomes assoft as before. I find that, at a temperatureof about 430&deg;, it begins to soften; and that,at 6 or 700, it becomes very soft, and,therefore, by proper management, the artistcan give it any degree of hardness he mayrequire, and this process is called the tem-pering of steel. The manufacturer of a razor,for example, forges out the blade in the softstate of the metal; he would then finish it,and render it hard by quenching it in water;after which it is heated, until he sees by thecolour of the blade, that it is brought downto the degree of hardness required. A razor,and a dinner knife, maybe made of exactlythe same kind of steel ; but the differencein their hardness depends upon their tem-pering. Experience has taught us, thatdifferences of temperature give to steel

peculiar degrees of hardness, fitting it forparticular purposes; and, in the common

way, the process of tempering consists in

heating oil or mercury, or fusible metal, upto a certain point, in which a thermometeris placed, and the best manufacturers arenow guided entirely by the thermometer inthe process of tempering ; whereas, for.

merly, the instruments were heated withoutany thermometer, the workmen being guidedonly by the change in the colour of thesteel, which is a very slovenly, and oftenfallacious test. Polished steel at 430,

: begins to acquire a pale straw coloured tint,. and from that to 465, it becomes so fartempered, as to be tit for razor blades, andinstruments of that kind, requiring delicate

edges. From 480 to 500&deg;, it acquires a

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buff tinge, and becomes softer; it is nowsoft enough for pen-knives, and certain sur-gical instruments, and other purposes; at

500&deg;, or from 515 to 530&deg;, it becomes yellow,and begins to acquire a purple tint ; from530 to 5500, it becomes decidedly purple,and is then fit for common knives, and otherinstruments, requiring great toughness. At t

550, or from that to 580&deg;, the steel beginsto acquire a blue colour; and it is softenough in that state for a number of pur-poses, especially fpr thin blades intendedto have great elasticity, and little hardness ;and, at 590&deg;, it becomes so soft, as to bebent without any risk of breaking, as is thecase in watch-springs. This is the historyof the tempering of steel ; and you see, thatby these differences of temperature, it

acquires various degrees of density andcolour ; but what the nature of this changeis, we do not know ; you see, however, howvaluable it becomes, in consequence. Thereis not much difficulty in tempering a bar,or thin plate of steel ; because, when youheat it red hot, and plunge it into coldwater, you obtain an uniform degree of hard-ness throughout ; but when you have to

deal with a mass of steel, as with a die,for example, it is a long time before thewhole of the heat escapes, and you have ahard crust of steel outside, whilst the in-terior is soft ; you have it only case-hard-ened ; and it sometimes happens, thatthese are broken by violence, like the coatsof an onion, into layers,-layer after layer,showing a soft nucleus in the midst of thedie. I have now given you the outline ofthe formation of steel, of the modes of ac-quiring different degrees of induration, at

different temperatures. A very curiousprocess, for making steel, has been latelyadopted by Mr. Mushet, of Glasgow, bypassing coal gas through, vessels, when redhot bars of iron are exposed to its action,and it may be a preferable mode, in somecases, to the other.Now then we arrive at the different kinds

af iron found in the arts, and to the modesof obtaining them.

Iron seems to have been known at remote

periods, for we find, in holy writ, furnacesand modes of reducing the metal, spoken of.There can be no difficulty in obtaining ironfrom the pure oxides of the metal, by mixingthe oxide with charcoal, and submitting themixture to heat. The oxygen will be carried

off, and the globules of the metal collected ;and in this way it was, for a long time, ex-clusively obtained in this country and else-where, until our manufacturers were broughtto a stand still for want of charcoal, and wewere, for a long time, dependent on Swedenfor a supply, especially for the purpose ofmaking steel. About seventy or eightyyears ago, the attention of several iron ma-

nufacturers, in this country, was called tothe subject of manufacturing iron with com-mon pit coal; they used the poor ores ofiron ; they converted coal into coke, dis.pelling great quantities of sulphur and otherimpurities, and they obtained a tolerableiron, but still inferior to that imported fromabroad. At length it was ascertained thatthe iron ore, poor as it was, if used withcoal, might be used conveniently for mak.ing iron ; experiments were made, the re-sult of which was, that the inventor of theexperiment lost much money. Then it wasfound, that with the coal in the adjoining strata there was a great quantity of nodulesof clay iron stone, which is, as you recol-lect, a very impure oxide of iron, and thiswas tried, but the experiment failed also;the metal was found diffused in globulesthrough a very intractable mass, which pre-vented it from running down in the furnace,and this difficulty was not overcome for along time, until it was discovered, that thelime stone found in the neighbourhood ofthe ore combined with iron stone in thefurnace, and melted it down, which was avery valuable discovery. The process nowemployed is this : the ore is first roasted,by which process it crumbles down into areddish substance ; this is mixed with acertain quantity of lime stone, by weight,and also with a certain quantity, by weight,of coke, when the mixture is thrown intoa large furnace, and exposed, as rapidly aspossible, to an intense heat. The conse-

quence is, that when the coke, lime, andiron stone are exposed to a high tempera-ture, the lime and clay combine to form akind of glassy compound, and the coke actsupon the iron and deoxidises it; and theglobule of metal, falling through the mix-ture, is collected in a basin in the bottomof the furnace, which is now and then tap-ped, and the metal, collected in moulds, isthen called cast iron. The height of a fur.nace for this purpose is about sixty feet,and when the fire is once lighted it is neverallowed to go out, and it continues fit foruse for six or seven years, if well built.The substance produced by the union ofthe limestone and clay of the iron ore iscalled the slag, and the due admixture ofthe coke, lime stone, and ore is a matter ofgreat nicety, and one upon which the suc-cess of the process depends. The workmen

generally know, by the appearance of theslag, what addition or alteration to make inthe charge of the furnace. The furnace is

tapped once in six or eight hours ; and ofthis cast iron there are two principal va-rieties, the grey pig and white iron. The

grey pig contains oxide of iron with themetallic iron, and some other metals, as

silicium and calcium, and other substances,differing considerably in their relative pro-

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portions, By carefully testing, and by at-tending to the matrices in the furnace, theiron thus obtained is fit for a great varietyof purposes in the arts. It is not very brittle, and is opposed to white cast iron, whichis merely used for its weight, and is there-fore a comparatively useless metal. The

grey iron requires to be submitted to otherprocesses, in order to convert it into a moreuseful form of metal , and this purificationconsists in submitting it to intense heat in

a reverberatory furnace, called a refining ftir-nace, where it is stirred whilst in a state of fusion, so that every part may be exposedto the air and flame, and this operation is i’called puddling. This process is continueduntil the mass becomes tenacious, and it isthen submitted to the rolling mills, wherea large quantity of extraneous matter isforced out, and the metal is rolled out intomalleable bars. These bars are afterwardsbroken up, fagoted, as it is called, and again’submitted to the refining furnace, where itundergoes another puddling, and being thenagain submitted to the rolling mills, it forms.the best bar iron.The discovery of this process of obtain-

ing iron must be considered an importantone for that branch of manufactures in thiscountry, and, in its details, is very interest-ing and curious ; but what I have given youis of course only a bare outline of the sub-ject.

In the next lecture we shall begin thedescription of the properties and salts oizinc, tin, and cadmium.

FOREIGN DEPARTMENT.

REPRODUCTION OF BONE.

THE substance from which new bone isformed; the changes which it undergoes;its relation to the periosteum ; the coiidi.tions which retard or promote its formation,are the circumstances deserving of our mostattentive consideration.The first appearance which presents itself,after a fracture, is an extravasation of blood,extending along the whole limb, and cover-ing the muscle and the fracture. The bloodthus extravasated has been supposed, bysome, to have some part in the reproductionof the bone, and the formation of the callus.Macdonald has treated the subject in

this way, and examined the changes withconsiderable minuteness. The blood appearsto come principally from the medullary struc-ture of the bone, .not from the vessels of theosseous substance itself; because the blood is

not found on the edges of the bone. Exudedblood is thus supposed to be the basis ofunion ; the red part becomes absorbed,and the remaining portion converted intogelatine. The periosteum inflames and be-comes thickened ; and in the gelatine ef-fused beneath it, the first points of ossi-fication may be observed, not close to thefracture, but at some distance from it ; onthe surface of the periosteum, and not onthat of the bone. The central portion ofthe callus, between the fractured extremi-ties, becomes ossified last, and not until thenew periosteum, as it appears, has formedfrom the cellular membrane of the circum-

jacent muscles. The new periosteum is atfirst thick and loose, but connected with thecallus. The points of bone appear at firstrather externally than in the middle of thegelatine.

It appears then that the ossification of thecallus stands in close connexion with theformation of the periosteum, and that thedevelopment of the latter precedes that ofthe former. The result of observations, op-posed t) these, may be probably explainedby the part which the old undestroyedperiosteum may have had in the formationof the callus. The regenerated bone runsthrough the same stages as the originalbone. The gelatinous substance at first be-comes hardened. It appears a proper ques-tion, whether callus, prior to its conversioninto bone/become cartilage or not ?&mdash;Meckel’sArchiv.

RUSSIAN MEDICAL SERVICE.

INVITATION TO ENGLISH SURGEONS.

Official Notification.1. FqREIGN medical men, and especially

those of Sclavonian extraction, are invitedto enter the Russian service, either in the

regiments of the army, in the military hos-pitals, or in the navy. During the ist yearthey will be attached to some hospital inorder to enable them to acquire the Russianlanguage, so as to understand their patients,and be understood by them.

2. The candidates are required to producecertificates of good conduct, as well as satis-factory testimonials, from the Universitiesor schools where they have been educated.

3. The candidates will be divided into twoclasses, according to the degree of know-ledge required. Those who have studied

every branch of medical science, may beappointed to the superior functions of themedical departments of the land or navalforces, and will belong to the 1st class.

They are to be examined in natural history,natural philosophy,. chemistry, pharmacy,botany, anatomy, physiology, pathology andtherapeutics, in materia medica. surgery,