04 PROCEEDINGS OF THE AMERICAN ACADEMY 



100.00 



This salt is in color the most brilliant of all the samples in my pos- 

 session, and of a decidedly different shade from thei samples of the 

 formulae, — 



(CuOC,H,.0,) 3(CuOAs20,) and 

 2(CuOC,H,63) 3(CuOAsA), 



being more grass-green, having less blue in it. It comports itself 

 with acids and alkalies in a similar manner to the last-mentioned salt, 

 but is a little more dense ; it holds to its five molecules of water 

 strongly, it not being decomposed at 120° C. When heated for a long 

 time at this temperature, it oxidizes slowly and gains steadily in 

 weight. Tliis is probably the salt existing in the commercial samples 

 examined minus tlie water, and is the nearest approach to them I 

 have been able to make, the exact formula for their production being 

 a trade secret. 



"* Wagner states that the formula given by Ehrmann is only 

 empirical, because a portion of the copper is present as the suboxide, 

 and a portion of the arsenic as arsenic acid." 



To test this statement, I examined my samples of Schweinfurt green 

 in the following maimer: In each case a weighed amount of the green 

 was dissolved in pure hydrochloric acid, made alkaline with ammonia 

 water and " magnesia mixture " added, and in each case a precipitate 

 occurred. After allowing this to stand over night, it was filtered off 

 and washed with aqua ammonia dissolved in hydrochloric acid, and 

 neutralized with ammonia, then acidulated with acetic acid, and acetate 

 of uranium solution of known strength added, testing in the usual way 

 for an excess, with ferrocyanide of potash. The first drop of uranium 

 solution gave a brown coloration when tested with the ferrocyanide, 

 and an excess gave no precipitate, proving beyond a doubt the absence 

 of arsenic pentoxide. 



The precipitate obtained by the " magnesia mixture " was doubtless 

 basic magnesium sulphate and magnesia itself. 



* Handbook Chemiual Technology, Rudolf Wagner, Ph. D. Translated by 

 W. Crooks, F.R.S. Appletou & Co., N. Y., 1872. Page 58. 



