TIN

TIN

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ration in the metallic form, whilll tlie remain-der of the tin, which is the greateft portion,undergoes a greater degree of calcination (I. e.oxygenation) and hence too the folution after itsutmoft aftion on copper ftill retains a quantityof tin. In other words, the difi'olved tin di-vides itfelf into two portions, one of which re-turns to the metallic ftate, and adheres to thecopper, whilft the whole of the oxygen con-denfes in the other portion, which remains dif-folved.

To fliew that a correfpondihg folution of theprecipitant (I e. the copper) is not neceflary tothe feparation of the precipitate , M. Gadolinboiled forne fine gold with tin and tartar, andafter a fliort time the gold was compleatly co-vered with a coating of reduced tin, and itcannot be fuppofed that any of the gold fnouldhave been diffolved by the tartar. This experi-ment would have been more compleat if the tinhad been again feparated from the gold by mu-riatic acid, and the gold had been weighed be-fore and after the operation, but if this ftate-ment is accurate (which there is no apparentreai'on to doubt) it is a curious fa£f, and onefor which in addition to M. Gadolin’s explana-tion, we muft probably refer to the late difeo-vered experiments in Galvanifm. This is con-firmed by the circumllance that in every one ofthe experiments on tinning above related, theprefence of two diffimiiar metals in the regulineftate is required, fo that the moment the me-tallic tin is withdrawn from the tartareous folu-tion the precipitation of tin upon copper ceafes,though we can hardly fuppofe that any imme-diate change in the ftate of oxygenation of tliefolution takes place.

With refpedt to the circumftance of no cop-per being found in the folution of tartar aftercommon tinning, we may obferve however thatthe failure of the ufual teft of the volatile alkaliis no certain proof of the abfence of this metalin this inftance, as the later difeoveries ofProuft on this fubjecl (which are detailed un-der the article Copper) fhew that when copperis in folution with tin in a low ftate of oxyda-tion, it is fo far deprived of oxygen by the tin,as not to turn blue with ammonia.

The experiments in which iron, copper, andtin were immerfed into a Solution of tin, arecomplicated, and the exa£I operation of all theaffinities between the refpective fubftances isnot eafily made out. The order of precipi-tation with a Angle metal, and a fingle me-tallic folution, is copper, tin, iron; that is to

fay, iron immerfed into a folution of tin dis-places the tin, and precipitates it moftly in tne'metallic form; and tin immerfed into a folutionof copper precipitates the latter metal. But inthe above complicated cafe both the iron andcopper become tinned, fo that the tinning orthe iron may be effected by fimple and direcStaffinity, but that of the copper requires a com-plicated adxion, to which probably the metallictin prefent contributes.

When cream of tartar has been long boiledwith tin till it can diflblve no more, the folu-tion ftill remains acidulous, and when evapor-ated and cryftallized a triple fait is obtained,,compofed of tartareous acid, potafli, and oxydof tin,, which may be termed a fuper-tartrite ofpotajh %vitb iitii.

The fixed alkalies have fome aftion uponmetallic tin, tarr.ifhing its furface and drflblvinga final! portion though with difficulty. But onthe oxyds of this metal alkali adds with greatenergy, diffolving them copioufly and with cafe.The circumftances of folution and precipitationof the oxyd from the add falts By potafli, have-been already mentioned. Potafli appears tohave a ftronger affinity for the perfect oxydthan the fub-oxyd, fo that in a mixture ofthe two it diflblves the former in prefer-ence. This folution does not readily depofitits oxyd bv keeping, or by expofure to air, asthe folutions of the fame oxyd in acids do, but.may be cryftallized by gradual evaporation.

The effedt of alkalies in breaking the aggre-gation of the native oxyd, and thus renderingit foluble in acids, has been mentioned in theanalyfis of the ores.

Muriat of ammonia ads upon tin by theaffiftance of heat. When this fait and tin filingsare heated in a retort, a fmall quantity of hy-drogen gas is firft given out, r and if the heatbe continued, for a time, below rednefs, a falinemafs is formed, compofed of muriated ammo-nia, muriat of tin, and fome tin filings un-changed. The muriat of tin contains the metalin the ftate of fub-oxyd, as it gives a purple,precipitate with folution of gold, and a black,one with hydro-fulphuretted water.

Tin unites readi y with fulphur by fufion,.For this purpofe ■ melt lonie tin in a crucible,heat it fhort of rednefs,. throw upon it about athird or.a fourth of its weight of fulphur, andftir them together when melted... The mixture :inflames when heated to a certain degree, andfhould then be covered. When this has fub-fided remove the crucible, and. black brittle ful,

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