12 PROCEEDINGS OP THE AMERICAN ACADEMY 



The older writers give the formula CuOAs^Og, this would give the 

 percentages of copper oxide and arsenic trioxide, as follows : — 



Copper oxide, 29.50 



Arsenic trioxide, 70.50 



100.00 



(The atomic weights used through this paper are: oxygen, 16; 

 copper, 63.4 ; the old formulas being changed to correspond to these 

 weights. As a matter of convenience, I have made all statements of 

 composition in terms of copper oxide and arsenic trioxide, but in so 

 doing I have no wish to be understood as asserting that they exist as 

 copper oxide and arsenic trioxide in the compound.) 



Berzelius * gives the formula, Cu2:S.s ; this, in modern notation, would 

 be Cu^As^Og ; or in percentages. 



Copper oxide, 44.50 



Arsenic trioxide, 55.50 



100.00 



He describes the methods by which it may be obtained as either, by 

 digesting carbonate of copper with water and arsenious acid, or by 

 Scheele's method, giving for the latter almost exactly Sclieele's receipt. 

 Ure t gives Scheele's receipt, and then says it consists of oxide of 

 copper, 28.51, arsenious acid, 71.46. This corresponds to the first 

 formula given above, CuAs^O^. 



Miller t gives the formula CuHAsOg. This in percentages would 

 be: 



Copper oxide, 42.37 



Arsenic trioxide, 52.83 



Water, 4.80 



This formula seems to be the favorite one at present, and may be 

 found in most of the text-books. 



Bloxam,§ in the course of his long and elaborate investigations of 

 the arsenites, made some experiments upon copper arsenite, but 

 failed to obtain a definite compound. The first salt made, he says, 

 contained : — 



« Ure's Diet., New York, 1847, p. 1100. 



t Traite ile Cliemie, Tome 4, p. 182. Paris, 1847. 



t Miller's Elements of Chemistry. London, 1864, p. 292. 



§ Bloxam, C. L., Jour. Chem. Soc, 1862, p. 292. 



