OF ARTS AND SCIENCES. 



289 



Occluded Gas in Cdpric Oxide. — Third Series. 



The cupric oxide of the last determination was ignited for three 

 hours in a stream of air, and for twenty minutes in a stream of oxygen, 

 at a medium red heat. It was impossible to determine whether the 

 material had reached constant weight, for the hard glass tube in which 

 the ignition was conducted was very much altered by the heat. 



As might have been expected, the very pure cupric oxide employed 

 in these experiments contained a slightly greater amount of occluded 

 gas than the less carefully prepared material of the earlier experiments. 

 Since the latest samples of material were precisely similar to those 

 used in the quantitative analysis of cupric oxide, it is fitting that the 

 latest correction should be applied to those quantitative results. The 

 2.97909 grams of cupric oxide used in Experiments 48 and 49 (page 

 277) must have contained 0.00276 gram of occluded gas. That is to 

 say, 2.97633 grams of pure cupric oxide correspond to 2.37811 grams 

 of metallic copper. The difference between these weights now really 

 represents the weight of combined oxygen present. The atomic 

 weight of copper upon this basis is easily found to be 63.605. 



Correcting the indirect results from the synthesis of cupric sulphate 

 in the same way (see page 276) the number 63.603 is obtained. 

 Averaging this result with that immediately above, the value 63.604 

 is found as a mean of five determinations including two wholly distinct 

 methods. 



Since it is impossible to learn exactly the amount of gas occluded 

 by Hampe's cupric oxide, the correction of his results will not be 

 attempted. The residue left after the ignition of cupric sulphate can 

 hardly contain any nitrogen ; and this supposition more than accounts 

 for the difference between the results of Baubigny's analysis and the 

 present syntheses of cupric sulphate (see page 275). 



VOL. XXVI. (N. 8. XVIII.) 19 



