G OL

G O L

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however minute is fufficient to impair both itscolour and du&ility. If befides lead the mix-ture contains copper to the amount of onetwenty-fourth of the gold, the whole of the leadwill be feparated but hardly any of the copper.If in addition to the above ingredients the alloycontains a fomewhat greater proportion of filverthan it does of copper, this latter is feparated bycupellation and a little of the lead remains: butif the amount of filver is equal to or exceedsthat of the gold, both the copper and lead maybe compleatly worked off, the gold and filverremaining behind. Hence it is that the refinersin feparating the bafe metals from gold by cu-pellation, always add to the mixture a confider-a-ble proportion of filver.

Cupellation with lead alone does not fucceedwhen gold is alloyed with tin: in this cafe thetin with part of the lead forms a very fpungyand refractory oxyd, which floats upon the fur-face of the melted metal and retains a part ofthe gold. This difficulty however is ingeniouflyobviated by the addition of fome iron filings,which combine with the tin into an alloy thatmay be fcorihed by lead without any greattrouble.

Separation of Gold from Antimony .

If the proportion of antimony exceeds that ofthe gold, the alloy, which will be very brittle,mult be reduced to fmall pieces and mixed withabout a fourth of its weight of fulphur andfufed in a covered earthen crucible. When thefufion is compleat it mull be poured into amelting cone previoufly heated and greafed, andwhen cool will be found to confift of two partsreadily feparable from each other; the upperwill be fulphuret of antimony holding a verylittle gold; the lower will be the reft of thegold ftill combined with regulus of antimony.The greater part of the antimony being thusfeparated, the reft may be got rid of by meltingthe alloy at a high heat and directing a ftreamof air from a pair of bellows into a cruciblecontaining it, by which the antimony is oxy-dated and volatilized in the form of a whitevapour. Shortly after this appearance hasceafed and the gold has acquired a clear brightgreen colour, it is to be poured out, and beingthen remelted in a fmaller crucible, togetherwith fome nitre, the laft portions of antimony,if any fhould happen to remain, will be com-pleatly oxydated and feparated from the gold.The fmall quantity of gold detained in the ful-phuret of antimony may be procured by bring-ing it into thin fufion and then precipitatingpart of the antimony by the addition of about

a fifth of its weight of iron filings: the goldwill fall down together with the antimony, andmay be feparated in the way juft defcribed.

Separation of Gold from Silver and the imperfeBmetals by Sulphuret of Antimony.

By this method all the common imperfeftmetals except zinc may be feparated from gold :for in the firft place gold is incapable of com-bining with fulphur, and in the next place moftof the other metals have a ftronger affinity forfulphur than antimony has. It is obvious there-fore that if to an alloy of gold and copper, forexample, be added fome fulphuret of antimony,the copper will become fulphuretted at theexpence of the antimony, which in its turn willcombine with the gold.

Earthenware crucibles are the only ones thatcan be employed where fulphuretted metals areconcerned, but if thefe are ufed without anypreparation they are extremely liable to crackand be corroded. The black-lead crucibles arefitter for this purpofe than the common kind,but thefe laft when prepared according to themethod recommended by Scheffer are moredurable and convenient than thofe of black-lead..The preparation is very Ample: take a well-burnt crucible and foak it for two or three daysin linfeed oil, then clear away the oil to fuch adegree as that fome finely pulverized glafs ofborax being dufted over the inner furface mayjuft adhere, let it then be fet by in a dry placefor two or three weeks and it is ready for ufe.In fuch a crucible above two hundred fufions,according to Scheffer,maybe performed in fafety.

The gold alloy being melted in the crucible,there is thrown in at two or three differenttimes, about twice its weight of coarfely pul-verized fulphuret of antimony : at each additionthe mixture froths and fwells up fo that thecrucible muft be large in proportion to thequantity contained; and efpecial care muft betaken to prevent any pieces of charcoal fromfalling in, as this would infallibly caufe themelted matter to run over. If the purity ofthe gold as previoufly found by the alfay is lefsthan 16 carats, the crude antimony before it isadded fhould be melted with about' a fourth ofits weight of common fulphur, by which toolarge an addition of antimony to the gold isavoided. As foon as the mixture fparkles onthe furface and is perfectly fluid, it muft bepoured into a melting cone previoufly heatedand greafed, and a tremulous motion by con-tinued flight blows muft be communicated tothe mould to promote the fettling of the precious