416 PROCEEDINGS OF THE AMERICAN ACADEMY. 



(83) 0.43 c.c. gas from 1 gr. CuO heated for 10 min. contained 19 per cent oxygen. 



(84) 0.45 " " " " 16 



Average 17.5 per cent oxygen. 



(85) 0.46 c.c. gas from 1 gr. CuO heated for 8 hours contained 6 per cent oxygen. 



(86) 0.45 " " " " 4 " 



Average 5 per cent oxygen. 



It is clear that we are dealing here with a phenomenon precisely simi- 

 lar to that observed in the case of zinc. Tlie decomposition of the 

 remaining traces of nitric anhydride takes place much more slowly at 

 low temperatures than at high ones, aud the oxygen formed by this 

 decomposition is liberated far more rapidly during the hotter ignitions. 



A single series of experiments,* made some years ago with magnesic 

 oxide, showed that this substance too acted in the same way, and it 

 is probable that all the other oxides retaining traces of occluded gases 

 would give similar results. The data obtained from maguesic oxide 

 are repeated below, in order that all the facts may be at hand for 

 the following consideration of the causes of the anomaly. 



Gas Evolved from Magnesic Oxide. 



(^Temperature of Ignition was about 700°-800°.) 



1 gram MgO after ignition 30 minutes gave 3.60 c.c. nitrogen and 7.2 c.c. oxygen. 



6.3 

 " 4.4 " 



3.6 

 2.8 " 



Hypothetical Explanation. 



The facts are now perfectly clear, and it remains only to account for 

 them by means of a plausible theory. In the first place, there can 

 be no question that the gases proceed from a residue of basic nitrate 

 imprisoned in the oxides in question ; the fact that oxides prepared from 

 the carbonates contain little or no gas would alone be sufficient support 

 for this point of view. The first matter to be considered is, then, the 

 dissociation of this residual nitrate, which is probably wholly analogous 

 to that of calcic carbonate as studied by Le Chatelier.f AVe may 

 express this reaction, perhaps, in the following fashion, which indicates 

 tliat the proceeding is supposed to take place in the gaseous phase, 

 while the solids enter into the reaction solely by their vapor tension. 



* These Proceedings, XXVIII. 209. 



t Compt. Rend., CII. 1243 (1886). Nernst, Tliepret. Chem., p. 377 (1894). 



