the Arseniates of Copper, and of Iron. 207 
Oxide of copper 49,51 . , . r 
Water - - 12 J formln S hydrate, of copper 
Phosphoric acid - - 
Water of crystallization - 
61 ,5 
35 
3,5 
100,0 
And this is the order which should be adopted, in the statement 
of all analyses of salts of copper. 
I could easily produce, by the same method, a pale green, 
or a brown arseniate ; and, in nature also, the colour of the 
ore accurately corresponds with the proportion of water, as 
may be seen by comparing together any of the foregoing 
analyses. 
Having thus convinced myself, by analysis, that copper is 
found in nature united with arsenic acid in different propor- 
tions, I next wished to ascertain, whether art could effect 
similar combinations. For this purpose, I poured into arseniate 
of ammonia, a solution of nitrate of copper. The metallic arse- 
niate was immediately precipitated in crystalline grains, of a 
blue colour, rather more intense than the phosphate already 
mentioned ; and the liquor, which remained blue, was decanted. 
The colour which this latter retained, I imagined,- was due to 
the presence of a greater quantity of nitrate of copper than was 
necessary to precipitate, from its alkaline basis, the arsenic 
acid combined with the copper. After a partial evaporation, I 
poured in alcohol ; and found, to my surprise, that the conse- 
quence was another precipitation, which was much increased by 
allowing the liquor to remain. Crystals, still more rich in colour 
than the former, and very evidently rhomboidal, even to the 
naked eye, were gradually formed. Imagining there must be 
