OF ARTS AND SCIENCES. 21* 



XIII. 



CONTRIBUTIONS FROM THE CIIEIMICAL LABORATORY OF 

 HARVARD COLLEGE. 



ON CUPRIC OXYBROMIDE. 



By Theodore William IIiciiards. 



Presented by the Corresponding Secretary, October 8, 1890. 



A CAREFUL examination of the basic bromide of copper precipitated 

 by the solution of dried cupric bromide in water being an essential 

 consideration in the preceeding research upon the atomic weight of 

 copper, a quantity of the substance was gradually collected from 

 successive preparations for the purpose of analysis. 



The only mention of the preparation of a definite oxybromide of 

 copper in chemical literature is that by Et. Brun,* who obtained a 

 crystalline salt by the slow oxidation of a solution of cuprous bromide 

 in aqueous potassic bromide, as well as by the action of the latter 

 salt upon ammoniacal cupric sulphate. He describes his new prepa- 

 ration as consisting of very small dark green crystals totally insoluble 

 in water, and gives several analyses of different samples which agree 

 with the formula Cu2Br(OH)3, or 3 CuO . CuBr, . 3 HgO. It seemed 

 very probable that the substance under discussion was identical with 

 this body, although prepared in a very different manner. 



The oxybromide so often mentioned in the foregoing description of 

 the research upon the atomic weight of copper crystallizes in very 

 beautiful doubly terminated prisms, which undoubtedly belong to the 

 trimetric system and have the varying habit shown in the accompa- 

 nying sketch. When precipitated by the rapid addition of water to 

 solid slightly basic copper bromide, the prisms appear as extremely 

 thin plates (Fig. 1), often united in radiating groups ; but on more 

 gradual crystallization from stronger brown solutions, the crystals 

 develop nearly equally in all axial directions (Figs. 2 and 3). The 

 only angle even approximately measured with success by means of 

 the microscope was that of the two domes upon each other, giving an 



* Corapt. Rend., vol. cix. p. 66 (1889). Lowig and Berthemot describe an 

 indefinite substance. Liebig's Handw. Ch., iv. 714; Ann. de Chim. et de Phys., 

 [ii.] xliv. 385. 



