OF ARTS AND SCIENCES. 283 



Subsequently, more dilute boiled sulphuric acid was used ; and the 

 apparatus was sealed by fusion after exhausting, but before mix- 

 ing the acid and base. The mixture was digested upon the water 

 bath until the action was nearly or (juite completed. It was found 

 that this com2)k'tiou was greatly facilitated by violent shaking at the 

 moment when the acid was poured upon the cupric oxide, for other- 

 wise the materials inevitably formed a hard cake which dissolved very 

 slowly. In one or two cases a small amount of unchanged cupric 

 oxide was weighed, and subtracted from the original amount. 



The apparent evolution of gas was at first very violent; but this 

 violence might have been partly due to ebullition caused by the heat 

 of the chemical action. The tubes were opened under boiled water or 

 mercury, and the gas was analyzed by means of liempel's apparatus, 

 somewhat modified for accurate use with very small quantities of mate- 

 rial. The portion of the gas which was not absorbed by caustic potash, 

 but was absorbed by pyrogallol, is tabulated below as oxygen. The 

 remainder refused to support combustion, suffered no diminution of 

 volume upon the addition of oxygen, and appeared perfectly inert ; 

 hence it was undoubtedly nitrogen. In order to test the solution of 

 pyrogallol, analyses of air were made from time to time, with satis- 

 factory results. The volumes were of course corrected for tempera- 

 ture and pressure, as well as for the tension of aqueous vapor, before 

 the weights of gas were calculated. The conditions varied so little 

 from the mean, 24° C. and 760 mm., that a statement of these data 

 seems inessential. 



The occlusion of an inert gas by cupric oxide was so peculiar a 

 phenomenon that many experiments were needed to carry conviction. 

 Several blank experiments were tried, in order to test the freedom of 

 the acid from dissolved air. Tlie fact that only a very small amount 

 of gas was evolved in the second experiment is also valuable evidence 

 upon this point. 



The material used in Experiments 58, 63, and 64 was four years 

 old, while that used in Experiments 59, 65, 66, and 67 had been 

 recently prepared. Both of these samples were made from cupric 

 oxynitrate, whereas the one used in Experiment 61 was precipitated 

 by caustic alkali. The tubes of Nos. 64 and 67 were opened under 

 mercury. In No. 64 the cupric oxide was cooled for forty-eight 

 hours after igniting, while in No. 66 the oxide was still very hot 

 when introduced into the tube. 



