On the Arfeniates of Copper a7id of Iron. 3T3 



Gray vitreous copper ore, when obtained in its greateft 

 purity, is by many degrees the richcd cupreous pyrites known 

 in nature ; and, in the large way, the metal may be cxtratltd 

 by the eafiert procelles. 100 parts of this ore, in dilute ni- 

 tric acid, left 12, which were fulphur. Ammonia, poured 

 in excefs into the nitric folution, rediffolved, with the ex- 

 ception of 4, the whole of the precipitate which it had 

 formed ; the 4 were iron; and, from the ammoniacal liquor, 

 105 of black oxide of copper, equal to 84 of metallic copper," 

 were obtained by evaporation, and then boiling with potafli. 

 Sulphur - - - I a 

 Copper - - - 84 



Iron - - - - 4 



100 

 Although I have mentioned, in the preceding ftatements, 

 only a fingle analyfis of each fpecimen, it is by no means to 

 be uiiagined, that fo fmail a number would be iufficient to 

 fatisfy inquiry. None of the above refults have been taken 

 into account, unlefs confirmed by frequent repetition ; and 

 tlie probationary experiments have been diverfiHed, as mucH 

 as lay in my power, by many different tfclis, and various che- 

 mical reagents. ' ' 

 With regard to the colour of fomc fpecimens of arfeniate 

 of copper, itiscafily to be accounted for upon chemical prin- 

 ciples. The millake under which we have long laboured, 

 that the green is the real oxide of copper, has hajipily been 

 rectified by M. Prouft*. He has proved it to be a particular 

 lubftancc, (to which he has given the very imj)roper name of 

 hydrate of copper \,) endowed with peculiar properties, and 

 compofed of the brown oxide, and of water, in a (late of 

 combination. From his experinuuts, and from what I my- 

 fclf have fecn, I am inclined to draw the ouclufion, that we 

 have never yet obtained bv art any real fait of oxide oi copper. 

 In examining, for inftance, fulpiiate of copper, we lind it to 

 afford blue cryftals : and to contain a known quantity of 

 water of cryftallizatiun, and of what we iinncrly '•died the 

 oxide. But that oxide (till retains a quanuty of water, of 

 which when it is deprived it pafles to a very dark brown, and 

 '•lianges its chemical nature and properties. 



'* Annates de Chiiiiie, vol. xxxii. p. id. 



+ Copptn is not tlie only metal capable of a fimilar combination. Co- 



ilt, nicKcl, and uraniimi, cnjcv the fame property. This miy, in f'>me 

 .' afnrc, explain tbc cliange ot col<>ur whicli the liquid muriates of fome 



it ilicfc metals un<ler}»o by gentle iioat} it may likcwilt throw Ibini; lijiht 

 ijon tile rympatliciic ink of cobalt. 



O 3 If, 



