OF ARTS AND SCIENCES. 217 



The salt is decomposed by continued boiling with water into the 

 normal bromide and a dark insoluble compound of uncertain compo- 

 sition. Brun has already pointed out the fact that the crystals are 

 quite decomposed when heated to 250°. 



On account of the very small amount of substance at hand, the 

 analysis was undertaken with all possible care. 



I. 0.20003 gram of copper oxybromide yielded, on evaporation with 

 nitric and sulphuric acids and subsequent electrolysis, 0.09823 

 gram of metallic copper. 

 II. 0.0828 gram of copper oxybromide yielded, on solution in am- 

 monia, acidification with nitric acid, and precipitation by silver 

 nitrate 0.0606 gram of argentic bromide. 



Analysis of Cupric Oxybromide. 



The results agree with the theoretical as well as could be expected, 

 considering the small quantities of substance used. 



By the very slow oxidation of cuprous bromide, kept under water 

 in the dark for six months, groups of emerald green radiating prisms 

 over a tenth of a millimeter in length were obtained (Fig. 4), which 

 by their terminal angles, color, and general appearance showed them- 

 selves to be identical with the compound whose analysis has just been 

 given. The amount of these crystals was so small that it was im- 

 possible to determine their percentage composition, but there can be 

 no doubt of its agreement with that given above. The crystalline salt 

 was also obtained by the long continued action of cupric oxide upon 

 a strong solution of cupric bromide. 



It will be seen that the formula 



Cu2(OH)3Br (or, 3 CuO . CuBr^ . 3 H,0) 



does not exactly correspond to that of any one of the known oxy- 

 chlorides, containing only three fourths as much water as atacamite 

 (3 CuO . CuCU. 4 H2O). It is a noteworthy fact, however, that 

 many of the more definite basic salts of copper contain, as these do, 

 three molecules of copper oxide to every single molecule of the 

 normal compound. 



