^^4 ■^'■'"l if 2"/'«, and Anatyifis of its Orel, 



the number of f.i(?ts for which the moft fruitful imagination could not afford a probable fo- 

 lutloii. This dilRculty has vanifhed fince it has been difcovered that the metals are capa- 

 ble of being converted into acids by a fufiicicnt quantity of oxygene. Tin is one of the 

 metals which mud have nioftcfFfclually contributed to fix the attention of chemifts upon 

 this combination. In this manner it is feen that the precipitation of gold by tin in the form 

 of a purple oxide is fimply, as I have announced in the Elements of Chemiftry of the Aca- 

 demy of Dijon, the rcfult of the aflion of the (lannic acid upon gold. This oxigenation 

 of tin is much more evidently feen in the operation which I have dcfcribed in the firft vo- 

 lume of the Chemical Diclionary of the Encyclopedia, p. 632 ; an operation which feeniS 

 well calculated to exhibit at the fame inftant every fundamental principle of the pneumatic 

 chemiftry. For when the diluted nitric acid and tin are treated fimply in the retort, the 

 rcfult is oxide of tin and nitrate of ammoniac, the latter of which is formed by the azote or 

 bafis of the acid, and the hydrogene of the water, without the appearance of nitrous gas at 

 any period of the operation. 



Ko further difficulty remained therefore with refpeft to the oxidation of tin by the nitric 

 ncid, as it is evidently effeftcd by the decompofition of the acid and the affinity of the tin 

 for oxygene. But no account has yet been given of the (late in which this metal exills in 

 its ores, particularly in the cryftals of tin (zinn-graupen, zinnfteln, of the Germans), nor 

 cfthe caufcs which oppofe their folution in acids. 



This queftion prefented itfelf to my confideratlon on reading the publication of Mr. 

 Klaproth on the ores of tin in the fecond volume of Analyfes with which he has enriched 

 chemiftry and mineralogy. 



He Ijegins by comparing the produfls of the fame ore treated with alkaline reducing 

 fluxes, and with charcoal alone. The difference convinced him, that in the firft proccfs the 

 alkali retains a confiderable portion of the metal in the ftate of oxide. He afterwards en- 

 deavoured to complete the analyfis in the humid way. For this purpofehe followed Berg- 

 man's procefs, which confifts in digefting the powdered ore in concentrated fulphuric acid ; 

 adding muriatic acid after the cooling, and precipitating the folution by foda. By this treat- 

 ment 13! parts of precipitate ought to be afforded for every 100 parts of metal contained 

 in the ore. Mr. Klaproth, in fa£l, obtained a folution of about 0,19 of that rather fcarce 

 tin ore which the Englifh call wood-tin ; but he could not fucceed in charging the muri- 

 atic acid with any perceptible quantity of tin, by fubje£ling the other more common va- 

 rieties to the fame treatment. 



Reflc£ling on the nature of the obftacle which might probably oppofe the a<Slion of the 

 muriatic acid on a fubftance which he eftimated to contain 0,99 of oxide of tin, he ima- 

 gined that it could be nothing but an excefs of oxygene. 



To remove this excefs, he firft attempted to treat the ore in the retort with a mixture of 

 fulphur. Moft of the fulphur wasfublimed, and the refidue, flightly agglutinated, had ftill 

 the fame grey whitiffi appearance as after the pulverization, excepting that fome brilliant 

 gold-coloured fpecks were feen ; namely, fulphate of tin, or aurum-mufivum. The mi- 

 neral, however, was not more folublc in the muriatic acid than before. 



After many other trials equally unfuccefsful, the celebrated chemift of Berlin had re- 

 eourfc to tliat fubftance which in Jiis hands has become fo powerful an inftrumcnt of ana- 

 lyfis. 



