OF ARTS AND SCIENCES. 



277 



heating to the highest temperatures whicli hiiril glass would bear. 

 On the other hand, copper reduced by hydrogen at the lowest possible 

 temperatures is well known to lose in weight on heating to bright 

 redness. Some of P^rdmaim and Marchand's experiments* show 

 that the exhaustion of the tube at the time of weighing makes very 

 little if any variation in the weight of the materials ; but from others,! 

 as well as from the fiftieth experiment below, it would appear that 

 exhaustion at the time of ignition introduces a somewhat more serious 

 correction. In this last case the apparatus was necessarily rather 

 complicated, to admit of the ignition and weighing of the copper and 

 its oxide in a Sprengel vacuum, but the full description of the con- 

 trivance would demand more space than it is worth. In the four pre- 

 ceding experiments Hampe's method was carefully followed. 



The mode of preparation of the cupric oxide was essentially that 

 recommended by Ilampe, and described in these Proceedings, Volume 

 XXV., page 199. In some cases the basic nitrate was not washed 

 with water before ignition, and in other cases it was thus washed. In 

 general, none but platinum vessels were used. Various slight unim- 

 portant modifications were introduced, which need not find a place here. 

 The essential conditions to be borne in mind are the invariable use of 

 the nitrate as the source of the oxide, and the variable temperatures 

 employed in the ignition. 



Analysis of Cl'pric Oxide. 



Weights reduced to Vacuum Standard. 



* Loc. cit. (see p. 241). 



t J. prakt. Chem , XXVI. 461. 



