of Copper and of Iron, 22^ 



under that denomination. Heating it on charcoal, before 

 ihe blowpipe, he perceived a fniell of arfeuic, and, at length, 

 ohtained a metallic button, which was found to be copper. 

 That there is copper in this ore, is evident from analyfis. But 

 tlic mere arfenical fnicll was not a fufficienf ground to afl'ert 

 that it contained arfenic acid; for this metal might, with as- 

 much probability, have been in any other Hate. If, indeed, 

 that verv accurate and al)le analvft had, upon trying the ore 

 with the blowpipe in a platina Ipoon, perceived no fumes, 

 he might then have concluded that the arfenic muft be in 

 the (late of acid, and ihtt charcoal was ncceflary to operate 

 a partial reduction, to which the arfenic owed its volatility 

 and its fuiell. But no fuch experiment is reported, 



It is alio rather extraordinary that Mr. Gmelin flunild 

 have taken this ore out of the clafs of arlenical ores, and left 

 it as an unknown fpecies of copper; when, in fa£t, it is an 

 arfenical ore, but not an arfenical ore of copper. 



I examined fome cryftals which are commonly attached Ux 

 the fpecimcns of this ore. They were thofe which, according 

 to M. de Bournon, are in a ftate of decompofnion. By tliis 

 fpontaneous decay, they become of a deep brounith red, not 

 unlike the fubftance called colcothar ; but they ilill retain 

 their cubic form. They contain a little acid and water, 

 owing, ])erbaps, to their having efcnped from total decompo- 

 fition. The fame theory that accounts for the dithculty of 

 afcertriiuing the quantity of water will account for the red 

 colour tliey thus allume. 



When green iulphate of iron is cxpofcd in a crucible to a 

 red heat, it is well known that lulphureous acid is dH'cn2:a(.';cd 

 in great quantities ; and that, it the operation is contniued 

 long cnouab, there remains a red powder, (u this cafe, the 

 green oxide of iron has taken up oxygen from the acid ; and 

 this latter has been partly decompofed, and ahnoll totally 

 volatilized. Now, in the fpecies liere fpokcn of, the iron, a.s 

 in the green fidphalc, is in the (lale of green oxide; therefore 

 capable (jf receiving an additional portion of oxvgcn. Puit 

 arfenic acid will, at a high temperature, lofe a part of its 

 -oxygen, and, retrograding to the Itate of white oxide, wiil 

 be volatilized; and ftdl more eaiily will thofe changes lake 

 place, when oxide of iron, ready to receive, and arienic acid, 

 ready to yield oxyoen, arc in contaft. A lefs degree of heal, 

 therefore, will fuftice to drive oH* this acid, from green arfe- 

 MJaie of iron, than from arfeniale of copiK-f. Hut we mull 

 not from this conclude, that the atlinity of Me latter metal 

 for arlenie acid is fupenor to that of the firmer; for, the at- 

 Irat'-.tion of arei-n oxide of iron for oxygen, and of caloric for 



Vol. Xli. No, 47. P wluic 



