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id with difficulty, for tha narrowing ofthe brim remains, and by endeavouring toeittact the cranium in this manner, youmav detach the head from the body.-Turning, therefore, I cannot approve. In

narrowings at the brim, it is better, as ageneral practice, either to suffer the womanto be delivered by the natural efforts, or tohave recourse to the instruments alreadyenumerated-the tractor, forceps, orperfo-ntor.

Again, it may be asked, granting thatthese two modes of delivery are to be pre-ferred, how are we to decide whether weought to commit the delivery to the naturalefforts, or have recourse to the embryospas-tic instruments ? Why, to this, as to manyother emergencies, the general rule will ap-ply; and, if the woman have not been inlabour for twenty-four hours, and if no dan-gerous symptoms are appearing, it is betternot to interfere ; but if, on the other hand,the woman have been in labour for twenty-four hours, or, if dangerous symptoms aremanifesting themselves-the pulse rising,the bladder closing, inflammation of the ab-domen appearing—then we may, properly,have recourse to the lever or the forceps ;and further, if these instruments fail, or if

dangerous symptoms appear, or, indepen-dently of any dangerous symptoms, if thewoman have been six-and-thirty, or, at anynte, eight-and forty hours in labour, weare again justified, though unwillingly, inhaving recourse to the perforator.What I stated to yon in a former lecture

is well worth remarking here, namely, thatin those instances where you have laboriouslabour, from a narrowing of the brim, thehead will sometimes mould itself, and thuscome away. In the morning you apply yourforceps, but cannot extiact the cranium.Well! no dangerous symptoms manifestingthemselves, you wait till evening, and thentry the forceps again ; and now the headmoulded by compression and the pains, soas to adapt it to the passage, on this secondapplication of the forceps, a living foatus isabstracted. Thus much, then, with respectto those laborious labours which arise fromthe second cause, namely, a want of roomamong the bones of the pelvis. Of the la-bours with rigidity, we will treat at our nextmeehng.

.

LECTURES ON CHEMISTRY,

BY

PROFESSOR BRANDE.

Delivered at the Royal Institution of GreatBritain.

LECTURE XLI.

On Silver and its Compounds, and Gold.

WITH the general properties of silver,and its numerous applications in the arts, 1have no doubt you are already acquainted.It is found native in a variety of combina-tions, sometimes massive, and sometimescrystallised, in cubes and ocioedra. Thenative silver, however, is seldom pure ; and,therefore, for chemical purposes, it is neces-sary to dissolve it in pure nitric acid dilutedwith its weight of water, and then precipi-tate it upon clean copper dipped into thesolution ; or it may he obtained, by adding asolution of common salt to the solution ofthe nitrate, made as I have just described,the precipitate being first washed and dried,and then fused with its own weight of car-bonate of potash.The specific gravity of silver Is 60.5, and

it is so ductile, that it may be drawn intowire finer than the human hair, and maybe extended into leaves not exceeding theten thousandth part of an inch in thickness.This is a specimen of the silver leaf; which,as you see, on exposure to the voltaic bat-

tery, burns readily with a green light, andthrows off abundant fumes, which are theoxide of silver. It melts at a bright redheat, and appears very brilliant when infusion ; if the heat be pushed to great in-tensity, it boils and evaporates. It crystal-lises, if suddenly cooled. It is procured inconsiderable quantities from the native sul-phurets, which are reduced by amalgama-tion ; and, in this country, it is most gene,rally found combined with galena, the sul-phuret of lead.

Silver unites with oxygen, and forms anoxide, which consists of one proportional ofmetal, and one of oxygen ; but, from someexperiments of Mr. Faraday, it would seemthat there is another combination of silverand oxygen; containing a smaller proportionof oxygen, but which is not capable ofuniting with the acids. The oxide may beeasily obtained, by adding lime-water to thesolution of the nitrate of silver, and washingthe precipitate. It is insoluble in water, ofa dark-green colour, and when heated, theoxygen is driven off, and metallic silver isobtained. The composition of the oxide

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has been a matter of some dispute ; but thatwhich I have mentioned, is pretty nearlycorrect. Bv dissolving it in ammonia, a

fulminating powder is obtained, and thebest mode of making it, is to pour a smallquantity of liquid ammonia upon the oxide,by which means a portion of the oxide isdissolved, and a black powder remains,which is the powder in question. It ex-

plodes when gently heated ; nitrogen andwater are given out, and the silver is reduced.It should be. handled with- great caution,and made in very small quantities at a time,as it sometimes explodes while wet.

Chlorine and silver combine to form achloride of silver, and the combination iseasily effected by adding a solution ofchlorine, or common salt, to a solution of (nitrate of silver ; a heavy white powder is I

precipitated, which, on exposure to light,becomes brown, and ultimately black. lfheated to redness in a crucible, it melts ;and, on cooling, concretes into a semi-

trausparent grey substance, which has beencalled lzczzd corllca. or horn silver; but ifheated to a white heat in an open vessel, itis volatilised. It is vt*:y soluble in ammo-nia, by which circumstance it may be dis-

tinguished from the other chlorides; but youshould be cautious how you apply heat tothis solution, as a precipitate of fulminatingsilver is sometimes formed. If the fused!chloride be exposed to ammoniacal gas, itabsorbs a considerable portion of it; and ifthis substance be thrown into chlorine, theammonia spontaneously inflames. Fromseveral experiments, which have been madeon its composition, we may state, that it isa compound of one proportional of silver,and of one of chlorine. If you digest oxideof silver in chloric acid, you obtain smallrhomboid crystals, which are chlorate of sil-ver. If you attach a slip of silver to one ofzinc, and put them into muriatic acid, the Isilver instantly acquires a crust of chloride I,in consequence of the negative energy im-parted to it by the zinc, and the zinc be-comes rapidly dissolved ; a fact which seemsto illustrate the influence of electricity onchemical action in a very beautiful way.. * ,The iodide Iff silver is of a greenish yellow

colour, insoluble, and decomposed whenheated with potash ; it may he obtained inthe form of a precipitate, by adding hy-driodic acid to a solution of nitrate of silver.

The nitrate of silver is formed by dissolvingsilver in nitric acid, diluted with three partsof water ; and there is, at the same time,an evolution of nitric oxide gas. Thesolution should be perfectly clear andcolourless ; but if any copper be mixed withthe silver, it will always have a greenishtint; and if any muriatic acid should be

present, the solutiou will be turbid, and

will deposit a white powder. It is highlycaustic, tinging animal substances of a yellowcolour, which, by exposure to light, become=.purple, and ultimately’black. It is solublein about its own weight of water at 60‘, bavthe solution blackens on exposure to light,and is then no longerperfectly soluble in ra.ter, owing to the separation of a portion ofmetallic silver. When fused, and cast intosmall cylinders, it is called the lunai’ caustic,or the ar,,,reziti ncitras, of the present Phar.macopoeia. If a few grains of the nitrate bemixed with a little sulphur, and struck

smartly with a hammer, a detonation takesplace ; or if a small bit of phosphorus hemixed with a bit of the nitrate, and struckin the same way, it produces a very rioleatexplosion. A stick of phosphorus intro.duced into a solution of the nitrate, soon

becomes beautifully incrusted with themetal. A plate of copper occasions a bril.liant precipitation of silver, and the copperis dissolved in the acid. If you make an

amalgam of one part of silver, and seven ofmercury, then introduce a portion of thisinto a solution, composed of six drachms ofa saturated solution of nitrate of silver, andfour drachms of a saturated solution of mer.

cury, diluted with five ounces of distilledwater, and the vessel in which it is made be

kept perfectly at rest, you will find that 111 afew minutes small filaments of silver darkenthe surface of the amalgam, and, in forty.eight hours, the whole will have separatedin an arborescent form.The solution of the nitrate of silver is

sometimes used as an ink, with which to

mark linen ; the mark is produced by a pre-cipitation of the oxide of silver upon thefibre of the linen. The solution of thenitrate of silver is generally thickened witha little gum, and coloured with a little sapgreen, or Indian ink ; and then, by way ofprecaution, the linen is previously prepared,by wetting the place, on which you intendto write, with a weak solution of subcarbo-nate of soda, and a little gum; the alkaliyevents the acid, if there be any in excess,from acting upon the linen, and the oxideof silver is precipitated, giving, when Cry,a dark-coloured cipher on the part. 1 hissalt is ridiculously enough resorted to for

the manufacture of those compounds em-ployed to change the colour of the ha.r’black, and when applied recently to greyhair, certainly does render it black; buttheglory only lasts for a day or two, the greyroots of the hair again appear, giving tLeperson the odd appearance of having liairhalf grey and half black ; and sometimes

you see it all become purple; at othertimes there are patches of purple and grey,giving such victims of vanity a very whim-sical appearance.’ The sulpfwte of silver is usually obtained

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articially, although it exists native, of which .Bthis is a specimen. - There is another beau-6iol ore of silver, which I can merely men-tion to you, namely, a compound of anti-menv and silver; it is a triple sulphuret ofantimony and stlver; it is called the red, orruby silver ore. The sulphur is with difficul-ty soluble, and therefore is easily obtainedby precipitation; the salt dissolves in boil-m water, and deposits, on cooling, fila-mentous crystals; it requires 90 parts ofwater for its solution, at common tempera-tares, and is composed of one proportional ofoxide of silver and one of sulphuret of anti-mooc. It is occasionally employed in the ’,laboratory as a test for muriatic acid.

Phosphorus combines with silver, and

produces a phosphuret of silver, a brittle me-tal1ic compound of no use or importance ;and the same may be said of the borateand carbonate.

I need say nothing to you of the modesof Mstinguishing the salts of silver, as fromwhat has been shown you, you must bealready acquainted with their properties,namely, their affording a white precipitate,with mmiatic acid, which becomes blackon exposure to air, and the precipitation ofmetallic silver upon a plate of cepper..imong the alloys of silver there are some

of considerable importance. The standardsilver of this country is a metal too soft tobe used in its pure state tor general pur-poses, and therefore it is customary to addto it a small proportion of copper, by whicha hardness is much increased, and its co-lour not materially impaired. What is calledsilver plate, the silver used for the manu-facture of plate, and that used for coin, is

composed of 11 2/20 parts of pure silver andand 18/20 of copper. Eleven ounces and two

pennyweights of pure silver, and eighteenpennyweights of copper, form a pound troyof standard silver; and this is coined into

sixty-six shillings. Other alloys, but notof much importance, are formed withlead, antimony, cobalt, and bismuth, bywhich the metal is rendered brittle, and itmay be made so brittle as to be entirelyuseless, It enters into combination readilywith mercury, and forms an amalgam usedfor plating. The amalgam being heated ona sheet of clean copper, the quicksilver isdriven off by heat, and the silver is left; bulthis is a very imperfect moda. The best wayis to roll out the two metals together, whiclU1l3wers all the purposes of silver at a lessF3:pense. The manufacture of plated goodihas been brought to great perfection in thiicouttrv, especially in Birmingham and Sheffield; the edges should be made of standardsilver, especraily when worked or orna

and goods thus manufactured answer exceedingly well.

As silver is a very important article u

the commercial world, it becomes necessaryto be in possession of some mode of deter-mining its purity, and this process, whichis a very important one, is almost constantlyperformed by the refiners of silver, and byassayers, for the purpose of ascertainingthe real standard nature of the coin ; and,as you know probably, every piece of silvermanufactured into plate must be subjectedto analysis, at the Mint, in order to ascer-tain whether it is standard silver. It might’be done in a very simple way, by thehumid process, as it is called, or solution ;supposing that you have a button of silver,containing a certain weight of copper, youweigh the button and dissolve it in nitricacid, and then precipitate the silver bymeans of muriatic acid or chlorine ; the sil-ver falls down in combination with the

chlorine, and the copper is left in solution ;the chlorine, you know, combines with thesilver in a definite proportion, and therefore,by taking the weight of the chloride preci-pitated, you obtain the quantity of fine silvercontained in the solution. This process,however, takes up too much time, and theshortest and best mode is that of cupellation,a mode of assaying which I shall endeavourbriefly to describe to you ; and here I mustobserve, that I have frequently endeavouredto show it within the limits of a lecture,but never with much success.

In the first place, you employ a m’!ifJledfurnace, so contrived that a crucible can beintroduced into it, heated red hot, leavingconvenient access to the mouth of the cru-cible. Having a strong red heat in themuflie, we take the silver which we are to

analyse, and weigh a portion of it very care-fully, about 20 grains, we will say ; and thishaving been done, you then roll it up inabout two or three times its weight of lead,which must also be carefully weighed, andthe lead must be very pure for this purpose.Well, you roll the silver up in the lead, andput it upon what is called a cupel, a littlecrucible made of bone earth. As soon as. the lead begins to feel the heat, it melts,the silver melts also, and you get an

alloy of the two metals. You then intro-duce the alloy further into the muSie, wherethe heat is greater, and where the lead isconverted into an oxide, which, during its

L oxidisation, oxidises also the coppfr, whichr was previously in combination with the sil-ver. At a red heat, the lead and copper are; readily oxidised, an;l the oxides are burnedaway in the cupel, which being done, ulti-

niately the globule of silver becomes appa-rent, and when no longer any oxide is visi-1 ble upon its surface, and the motion of the

: globule ceases and it assumes a brilliant ap-

- pearanee, you withdraw it and weigh it ;the loss of weight gives you the quantity of

i copper burnt out of it by the lead. Know-

202

ing that silver is not oxidisable in the com-mon furnace, and that copper is so, youmight think that it would only be necessaryto expose it to a white heat to get rid ofthe copper ; but the oxide of copper is not

very fusible, and the lead is, so that leadis usually selected for the purpose. This

process was called, formerly, the balneummetallorum, or bath of the noble metals.Now, you may have fifty or sixty little

cupels in a munte at once, and you may,therefore, be trying as many bars of silverat the same time. In the process of coin-

age, this operation is conducted with greatcaution ; the first experiment is made uponthe bars as they are imported ; they arethen melted into smaller bars, to fit the

machinery of coinage, and are again assayed,and then subjected to the operation of rol-ling and coinage. After coinage, a sampleis taken from the bulk of coiu and assayeda third time, and if the two last assaysagree, there is evidence that the true stand-ard has been adhered to. There is then athird operation, namely, the examination ofthe picks, which is this : a piece of coin ispicked out of every seven hundred, both ofgold and silver coin, and put into a box andlocked up, which, in due time, is examined

by a committee, composed of the great offi-cers of the state, the principal officers of theMint and of the Goldsmiths’ Company.

In the process of cupellation upon a largescale, when the object is to act upon large I,quantities of silver, exactly the same opera- I,tion is resorted to; instead of using a furnaceof this kind, they employ a large reverbera-tory furnace, by which they can refine severalhundred weight of the metal. The oxide oflead, which is necessarily formed in large I,quantities, is raked off as it forms, and thesilver gradually makes its appearance ; theoxide of lead or litharge thus collected, isafterwards reduced, and thus the lead is ’,saved.

Among the other alleys of silver, there arenone, perhaps, deserving notice, if we ex-

cept those with steel, which the experimentsof Messrs. Faraday and Stodart have taughtus to be very valuable in the manufacture ofsome cutting instruments. The quantity ofsilver mixed with the steel was very minute,only one part of silver to 500 of steel, andyet this small quantity materially alteredthe quality of the steel ; it seems to give thesteel a very peculiar toughness, and if youonce get a razor made of this alloy whichcuts well, it will retain its sharpness for along time.

Gold.—Gold, like silver, is found in themetallic state, and it will be worth while togive you a short account of the manner inwhich it is collected. It is found in minesassociated with other metals, and sometimesin the metallic state, occasionally in such

quantities that it may be scraped off a umasses ; but generally the gold is fdiffused through the stone, and is separatedby various processes, but principally by amma-gamatioa, triturating the rock with mercuryand then washing away the earthy matter anddistilling the mercury. There have been con-sidcrable quantities of gold found masme italluvial deposits ; many of the great riversof Asia and America are celebrated for thi

quantities of gold they have produced. Thisgold is brought into the market under t1-name of alluvial, river, or grain gold, Issome alluvial soils, masses of gold havebet:found of considerable size, as large as ,

man’s fist; and some of the first visitor 0’America who followed Columbus, discoveredmasses of gold, of large dimensions. ande:great purity, and in such quantities, tba:

they thought they had discovered an ian.haustible source of the metal. Here ar-

some specimens of gold found in Cornwallin the tin-stream works, the product of

some alluvial rock. When gold is found in

rivers and torrents pretty near to the sourcesor falls, we may, in such cases, arenerally coii.elude, that it is derived from the adjaceathills or mountains, and that it has bee4washed down in consequence of its greatspecific gravity towards the valleys. Bo:

occasionally it seems to have been deposit-ed in the -soil in which it is found in ano.

therway, as seems to be the case with thegold found in the Rhine at Strasbureh; theriver had perhaps penetrated some vel!l8

containing gold, or it had, perhaps, setthrough a stream containing gold, and thismav account for the finding of gold in theplains and on the banks of the river.Gold is remarkable for its immntabiiitl

on exposure to air, for its fine rich yellowcolour, and for its exceeding ductility andmalleability. You may easily extend goldwire infinitely finer than a human hair, soas not to be visible without a magnifier; anda piece of gold leaf shows you to what aaextreme tenuity it may be reduced. It maybe made so light as to float in the air. laDr. Lewis’s Philosophical Commerce of the Arts,there is a very interesting account of wiredrawing and gold beating. Now the ex-

ceeding extensibility of gold is seen in whatis called gilt wire, which is silver wire gilded,A single grain of gold may be extended npoemore than 30,000 feet of silver wire, andthis will seem to give you a notion of theextensibility of gold, and the divisibility ofmatter.

If you were to take a piece of gold wireand heat it by the voltaic pile, the effectwould be the melting of the gold, and itwould put on the appearance of boiling, ardby holding a piece of coin iuediatel,vabove it, you would obtain a film of metalshowing yon that it is sibraitted to tL-

203

highest temperature ; but it does not ap-pear to he oxidised by this process. Fromwhat has been said, you are conversant within chemical properties, and you are alsoaware, that it is applied to a great variety ofimportant purposes, useful and ornamental.

fhe salts ot gold will not detain us long ;see shall proceed to the consideration of themm the next Lecture, and the combinationsof p:aunum.

FOREIGN DEPARTMENT.

EXPERIMENTS OS THIt RE-UNION OR CICA-

TRIZATION OF WOUNDS OF THE SPINAL

MARROW AKD THE NERVES.

BY M. P. FLOURENS.*

IB my former experiments it has beenseen, that different parts of the nervous

system may be completely separated fromthe rest of the body, and still present acertain degree of life or action, so that theyare susceptible of being united to parts fromwhich they have been separated, and reco-fer m certain cases the full exercise of theirfunctions. One of the hemispheres of thebrain, for instance, on being divided, in-stautly loses its functions; after the lapseof a certain time the incision cicatrizes, andthe functions of the part return. This, in-deed, is the case with all the parts of thebrain and spinal marrow.The experiments of Fortana on the re-

union of the nerves are well known ; theyhave been repeated by a great number ofphysiologists and by myself also. f dividedthe eighth pair on a cock. Two months after-vrards, the wound being cicatrized, I againexposed the nerve on which I had operated,and found it a little enlarged, but the endscompletely united. J thought it importantto ascertain whether the inferior extremityhad acquired, by its union with the superior;the power of again uniting if divided, whichI found, by a repetition of the experiment,that it had.The following are the results of my expe-

riment, which contain some points that dcnot appear hitherto to have been noticed :-The ends of a nerve that has been com-

pletely divided, can again unite.A nerve that has been divided unites, and

re-union also takes place if the nerve beagain divided below the points at which thetiperiment was originally tried.Two different nerves may be crossed so,

* Annales des Sciences Nat. Feb. 1828,

that the inferior extremity of the one maycorrespond to the inferior of the other, andvice versa, and in this case also union takesplace.

Lastly, if the divided extremity of theeighth pair be brought in contact with a cer-vical nerve, union takes place.As to the return of the functions, I have

not been able accurately to determine thisI point in some of my experiments ; the func-tions have, in others, not been restored.

SPONTANEOUS COMBUSTION.

In the Journal de Pharmacie, there is acase. recorded by Professor Rudolphi, of aman who suddenly felt a pain in the arm,similar to that produced by the blow of astick, and immediately perceived in thesame spot a small flame, which burnt hisshirt. There is also the case of a girl men-tioned, seventeen years of age, in whom akind of blueish sulphureous name appearedaround the finger ; the flame could not beextinguished by water; it burnt the cloth-ing brought in contact with it, but couldonly be distinguished in the dark. Thebest electrometers placed in contact withthe patient, presented no sign of electricity.

CONGENITAL DISLOCATION OF THE FEMURS.

A man, seventy years of age, was affectedwith retention of urine, for which he wasadmitted into the Hotel Dieu ; the waterwas withdrawn, but the patient soon ex-

pired. He also appeared to have congenitaldislocation of the femurs, on which accountM. Dupuytren wished to examine the bodywith great care. -

The thighs could not be separated fromthe body, without describing with the feet asegment of a circle ; the trochanters weremore closely approximated to the ilia, andmuch more elevated than in the natural

, state ; the heads of the ossa femorum weresituated higher, the knees carried more in-wards, and the thigh shorter than usual ; iu

fine, there was a total change of relations, and, a marked difference in direction and length.From this change of the relations of thebone, it results, says M. Dupuytren, that

. the cavity destined by nature for the bone,, either does not exist, or is more or less ob*. literated. From the change in length and di-rection, the points of insertion of some of themuscles are also changed. Some of the mus*

cles being relaxed, others put on the stretch.The superior part oftlie thighs was enlarged,the trunk bent backwards, and the abdomencarried forwards ; the pelvis, instead of

being oblique, was nearly transverse ; thebuttocks soft and flabby, which must have

been owing to the approximation of the in-, sertion of the glutæi magni. Passing then