92 



PROCEEDINGS OF THE AMERICAN ACADEMY 



Experiment No. 6. 



To Ihe filtrate from the pigment obtained in Expt. No. 5, 50 grams 

 of arsenic trioxide were added and some free acetic acid : a new forma- 

 tion of the well-known color of Schweinfurt green occurred after a 

 prolonged boiling ; this was allowed to stand over night in contact with 

 the solution from which it was precipitated ; it was tiien tiltered off and 

 washed free from the excess of arsenic trioxide. The filtrate was blue, 

 and acid, containing copper, arsenic trioxide, and acetates ; on the addi- 

 tion of more arsenic trioxide, no precipitate fell, but, on neutralizing, 

 one was produced having the color of the one in Expt. No. 3, and 

 it was probably of similar composition, but was in too small an amount 

 for analysis. The composition of the pigment obtained was : — 



Analysis No. VIII. 



100.00 

 This is very near the formula, — 



2(CuOCJI,03) 5(CuOAs,03)-}-2II,0, 

 which when calculated in percentages is : — 



Copper oxide. 

 Arsenic trioxide. 

 Acetic anhydride, 

 Water, 



Per cents. 



31.12 

 55.43 

 11.43 



2.02 



100.00 



Atomic Ratios. 

 7.00 

 5.00 

 2.00 

 2.00 



This was the first hydrated copper aceto-arsenite obtained, excepting 

 the resulting pigments from Expts. Nos. 5 and 6, whicli may be consid- 

 ered as mixtures; for, although there was a small amount of water in 

 nearly all samples, it was hydroscopic water, and was entirely driven 

 oflf by heating to 105° C. 



This experiment was repeated, giving : — 



