OF ARTS AND SCIENCES. 



199 



Gooch perforated crucible with all possible care. The crucible with 

 its coutents was dried at 130° to constant weight, and showed no loss 

 in any case on additional heating to 180°. 



Syntheses of Argentic Bromide. 



The above variation is not greater than a possible error in the oper- 

 ations concerned, and the testimony which these results give to the 

 purity of the materials is sufficient for the present purpose. Other 

 experimenters in this Laboratory have obtained values ranging from 

 57.442 to 57.450. 



Preparation of Cupric Bromide. 



The salt used in the preliminary series of experiments upon the 

 atomic weight of copper was formed by the solution of the purest 

 obtainable cupric oxide in the hydrobromic acid which has been 

 described above. For the preparation of the" oxide of copper pure 

 electrolytic metal (of the quality used in the experiments published 

 three years ago) was converted into sulphate by means of pure nitric 

 and sulphuric acids, and the resulting salt was purified by six frac- 

 tional recrystallizations after the expulsion of the remaining nitric 

 acid by heat. From a dilute solution of the purest cupric sulphate 

 acidified with nitric and sulphuric acids, about half the metal was 

 deposited upon the interior of a large platinum dish. The remaining 

 liquid being decanted, the film was washed, redissolved, and partially 

 redeposited through the agency of two Bunsen cells. It was hoped 

 that this fractionation would rid the copper of that jjrobable impurity 

 which almost invariably manifests itself as minute dark spots upon 

 the surface of the film of a completed electrolysis, but the hope proved 

 to be a vain one, and no method of purification was devised which 



