OF ARTS AND SCIENCES. 



13 



Copper oxide, 

 Arsenic trioxide, 

 "Water, 



The second contained : — 



Copper oxide, 

 Arsenic trioxide. 

 Water, 



The third product gave : — 



Copper oxide. 

 Arsenic trioxide, 

 Water, 



The fourth gave : — 



Copper oxide. 

 Arsenic trioxide, 

 Water, 



From this last analysis he deduces the formula CuIIAsO.. In a 

 foot-note he says : " Scheele's prescription for the commercial green 

 arsenite of copper involves 2.3 equivalents of oxide of copper for one 

 equivalent of arsenious acid, so that Scheele's green dried at 212° F., 

 appears to be essentially a mixture of CuHAsO^, with an excess of 

 oxide of cojiper." 



This observation is perfectly correct if nothing is taken into the ac- 

 count except the quantities taken by Scheele ; but Sclieele himself says, 

 in a foot-note:* "Tlie water with which the color is lixiviated con- 

 tains a little arsenic, and must not be thrown out in a place to which 

 cattle have access." The evident tendency of this loss of arsenic 

 would be to make the salt more basic than the formula (CuO)2.32As„03 

 (H.,0)g2 calls for, this being the formula which Bloxam supposes to 

 represent Scheele's green. 



In Watts's Dictionary,! under the head of arsenite of copper, this 

 sentence occurs : " It is a light green precipitate, which dissolves in an 

 excess of ammonia, without color, yielding a solution of arsenic acid 

 and cuprous oxide." 



Berzelius's formula is given, and the sentence just quoted is evi- 



* Scheele's Essays. London, 1786, p. 254. 

 t Vol. I., p. 376. 



