132 PROCEEDINGS OF THE AMERICAN ACADEMY. 



Some difficulty vvas experienced in obtaining the substance dry in a pure 

 state, as it begins to oxidize with the greatest readiness immediately upon 

 removal from the mother liquor. The best results were obtained by the 

 following method. The bell jar was so arranged that the mother liquor 

 could be siphoned off, and successive portions of alcohol and ether could 

 be introduced, the crystals all the time remaining in an atmosphere of 

 hydrogen. After thus washing with alcohol and ether, some of the 

 hj-drogen was pumped out, and the last drops of ether evaporated in 

 the partial vacuum. Prepared in this way, the substance was obtained 

 in perfectly colorless long flat prisms. When thoroughly dry, it is stable 

 and permanent at ordinary temperatures in the air. It is of course 

 readily soluble in amnionic hydrate and in nitric acid, but deposits 

 cuprous bromide upon treatment with other mineral acids, or with acetic 

 acid. On exposure to moist air, and when placed in water, the substance 

 oxidizes in a manner somewhat peculiar. The crystals first take on a 

 bluish green tint, then gradually turn to a bright yellow, and finally 

 change to a copper-red color. Owing to the fact that this change takes 

 place only on the surface, the crystal within being unchanged, it was 

 impossible to ascertain the nature of the yellow coating. 



Cuprosammonium bromide was repeatedly obtained under a great 

 variety of circumstances during many fruitless attempts to make the 

 double salt Cu2(NH3)2BrC2H302. Between —10" and 25° the simple 

 bromide appears to be by far the least soluble of the possible compounds 

 obtainable from mixtures of cuprous copper, ammonia, bromine, and 

 acetic acid. 



In the analyses the bromine was determined as argentic bromide after 

 dissolving the substance in ammonic hydrate, allowing the copper to 

 oxidize by exposure to the air, and acidifying with nitric acid. Copper 

 was determined electrolytically in a new portion after evaporating with 

 nitric and sulphuric acids. The ammonia was distilled over potash. 



Analyses of CuoBrj . 2 NH3. 



I. 0.2459 gram of substance gave, on electrolyzing, 0.0963 gram of 



copper. 

 II. 0.2059 gram of substance, distilled with caustic potash, required 

 13.04 cubic centimeters of decinorraal acid solution for neutrali- 

 zation. 

 III. 0.3537 gram of substance, distilled with caustic potash, required 

 22.00 cubic centimeters of decinormal acid solution for neutrali- 

 zation. 



