90 PROCEEDINGS OP THE AMERICAN ACADEMY 



Experiment No. 3. 



The filtrate in Experiment No. 2 contained copper, arsenic trioxide, 

 and acetates. To this solution, in which no precipitate occurred on the 

 addition of more arsenic trioxide, sodium carbonate was added to 

 faint alkaline reaction. A yellow-green precipitate fell, which was 

 collected on a filter, washed until the filtrate was free from arsenic 

 trioxide. Dried, the composition was, — 



100.70 



This is copper arsenite of the following formula, CugAs^O,; 2H2O, 

 with about 4 per cent of hydroscopic water, and contained, as far as 

 could be ascertained by careful testing, no acetic acid. 



The question then arose. Does sodium arsenite precipitate pure cop- 

 per arsenite from copper acetate in all cases, or does it also carry down 

 some basic copper acetate with it ? This led to 



Experiment No. 4. 



Copper acetate, 33 grams. 



Sodium carbonate, 50 „ 



Arsenic trioxide, 18 „ 



The arsenic; trioxide was dissolved in the sodium carbonate, and the 

 solution mixed with the copper acetate solution, both being near the 

 boiling point. A 3'ellow-green precipitate fell, the supernatant liquid 

 contained acetates, arsenic trioxide, and carbonates, and was slightly 

 yellow. The precipitate was separated by a filter, and washed till no 

 arsenic trioxide was found in the wash-water. This was much like the 

 product obtained in Experiment No. 3, except that the color was a 

 little brighter and of a bluer shade, and when analyzed gave : — 



Analysis No. VI. 



100.78 



