24 PROCEEDINGS OP THE AMERICAN ACADEMY 



more or less basic copper arsenite, which may or may not contain basic 

 copper sulphate and carbonate ; the composition of it seeming to de- 

 pend to a considerable extent upon the degree of concentration of the 

 liquid from which it is precipitated. Its basicity also seems to depend 

 to a considerable extent upon the same fact, the more dilute the solu- 

 tion the more basic tlie salt. 



The composition also depends, to some extent, on the amount of 

 wash-water used in washing it. 



The normal pi<fment which is represented by Analysis XVIII. may 

 be described as follows : — 



It is of a yellowish green color, soluble in dilute acids and in caustic 

 alkalies. It dissolves in alkalies with a blue color, and is decomposed 

 by excess of soda or potassa, or their carbonates, but is not decom- 

 posed by ammonia, even upon boiling. It does not blacken upon 

 boiling with distilled water. When dissolved in ammonia, if a solu- 

 tion of soda or potash is added, the solution is bleached, from the 

 reduction of the copper salt to a cuprous salt. 



Its average composition, as generally prepared, omitting the sulphur 

 trioxide which is generally found in it, is about as follows : — 



This approximates closely to the formula, 



Cu3As20,2Il20. 



This formula would give the following percentages : — 



Taking this view of the subject, Scheele's green is the normal tri- 

 cupric arsenite, and corresponds to the triargentic arsenite described 

 by Bloxam. 



It is almost impossible, however, to obtain a perfectly constant prod- 

 uct, from the strong tendency to form basic sulphates and basic 

 arsenites. 



As a matter of economy in the preparation, it will be found more 

 advantageous to take the following proportions rather than those given 

 by Scheele : - 



