16 PROCEEDINGS OF THE AMERICAN ACADEMY 



The green precipitate was dried and analyzed, it gave, — 



Al^ALYSIS No. I. 



Per cents. Atomic Ratios. 



Copper oxide, 66.02 8.31 



Arsenic trioxide, 8.32 .42 



Carbon dioxide, 15.26 3.47 



Water, 10.33 5.74 



99.93 



This corresponds well with a mixture of dibasic carbonate and tribasic 

 arsenite. 



The brown basic carbonate produced by boiling the hydrocopper car- 

 bonate with water was then boiled with arsenic trioxide, but was not 

 changed in color. The filtrate from the green precipitate contained a 

 large amount of arsenic, but was free from copper ; and I failed to 

 obtain on evaporation the yellowish-green acid salt spoken of by Ber- 

 zelius. 



P'urther experiments on the carbonate were tried to see if it could 

 be completely decomposed by boiling with excess of arsenic trioxide, 

 but they all resulted in failure. 



It seems to me that Berzelius must have been misled by the produc- 

 tion of the brilliant green arsenio-carbonate, as he gives no analysis to 

 support his assertion. 



Arsenic trioxide seems to have a very strong influence in preventing 

 the blackening of copper carbonates and hydrates, a very small per- 

 centage preventing this well-known reaction. 



A series of expei-iments were then tried on the production of 

 Scheele's green, following the course laid down in the books and by 

 Scheele himself; viz., first, the production of a more or less basic, 

 sodium or potassium arsenite ; and, secondly, the addition of this to a 

 solution of copper sulphate. 



Experiment No. 1. 



Dissolved the potassium carbonate in water, boiled and added the 

 arsenic trioxide, filtered and added to the boiling solution of copper sul- 

 phate. The precipitate, when washed and dried, was of a yellowish 

 green; the filtrate was blue. 



