0^ Copfcr and of Iroti. 223 



ticularly the province of cvyliallography ; yet he who would 

 expc6l that it fhoiild declare the nature of thoi'c fubftances 

 which it beholds for the Hvll time, would exad; more than it 

 ever has promifed;, or ever could perform. Among foflils, it 

 may clafs, and find new i'pecies; but chemical analyfis is the 

 bafis of all arrangement among metallic ores. In them, to 

 fcparate, is the talk of the one ; to affign a place, is the bu- 

 fiaefs of the other. 



Cupreotis Arfen'tate of Ir07i *. 



One hundred parts of this arfeuiate, expofed to a low red 

 heat, loft 12, which were pure water. Nitric acid was poured 

 upon the refiduum ; and, finding that it was dilVolvcd with 

 difficulty, the ebullition was continued during ievcral hours. 

 The liciuor was then filtered. Sixty parts, which Ihall pre- 

 fently be examined, remained undiilolved. Into this filtered 

 liquor, nitrate of lead was poured, which occafioned a preci- 

 pitate, as ufual ; but the operation was difcontinued until I 

 fliould obtain all the aifeniate of copper which I imagined 

 to be contained in the ore. For this purpofe, I had re- 

 courfe to the 60 parts mentioned above. They were in the 

 form of a greenifh gray powder, very hard and gritty, which 

 had every appearance of filica, contaminated by a fmall por- 

 tion of copper interpofed between the molecules of that earth. 

 I refolved to treat it in the fame manner as all filiceous ftones, 

 and proceeded to boil it with potafh. 



In lefs than three minutes it became of a very red brown, 

 from the greeniOi gray which it originally was ; and feemed 

 confiderably attenuated in its particles. The liquor \vas de- 

 tanled, and examined. It was found to contain arfenic acid ; 

 and the precipitate, which had refilled the a6lion of the pot- 

 afti, was proved to be a mixture of iron and copper. 



Thefe jirelimiuarv experiments were fuflicient to indicate a 

 ready method of analyfis. 100 parts, boiled with potafh, 

 immediately became of a deep reddifh brown. The liquor 

 was feparatcd from the refiduum by filtration ; and, after the 

 ufual neutralization, evaporation, and afiiifion of nitrate of 

 lead, (all of which operations were detailed in the firll part 

 of this paper,) ga\c a piecipitato eorr<.fponding to 35,5 of 



"* This fpccics had been mentioned by Mr. Prouft, but in a manner 

 which, as it was 3 new iubftancc, ;ind demanded particular attention, dots 

 not give all the fatisfailion which that cheniilt generally atVords. No 

 doubt the -Ccarcity ot the ore prevented his making every ni.cefl'ary re- 

 fcarch; and I may deem mvfeif fortunate in having been fo near the Ipot 

 in which it is found. My friend Mr. Hatcliett very obligingly f^.ive me 

 a fptcimen of liiis ore, which he had received from Ur. I'allas, who had 

 brought it with him from Siberin, where it liad been found. 



arfenic 



