CONTRIBUTIONS FROM THE CHEMICAL LABORATORY OF 

 HARVARD COLLEGE. 



ON THE CAUSE OF THE RETENTION AND RELEASE 



OF GASES OCCLUDED BY THE OXIDES 



OF METALS. 



By Theodore William Richards. 



Presented March 9, 1898. 



In a recent critical discussion of Stas's work upon the atomic weight 

 of carbon, Dr. Alexander Scott* of London had occasion to repeat some 

 observations made at Harvard several years ago.t According to these 

 observations, cupric oxide made from cupric nitrate had been found 

 usually to contain several times its volume of occluded gases, chiefly 

 nitrogen, and moreover it was shown that this gas resulted from the 

 decomposition of minute traces of residual nitrate confined in the 

 inmost recesses of the masses of oxide. Dr. Scott, however, could not 

 find as much as one tenth of this amount of gas in his material. Since 

 he was unable to explain the apparent discrepancy, it is one of the 

 objects of the present paper to shed a clearer light upon the subject. 



The essential point whicli escaped Dr. Scott's notice is this : the 

 temperature of ignition is the most important condition determining the 

 amount of the occluded gases. When the temperature is very high, 

 nearly all of the imprisoned impurity is set free. To quote Dr. Scott's 

 words, his oxide was exposed " for varying times to a full red heat in a 

 muffle lieated with gas." It is well known that at a temperature of 

 about 1000° cupric oxide melts, with a very considerable loss of oxygen. 

 It is obvious, then, that temperatures in this neighborhood are quite out 

 of the question when the atomic weight of copper is concerned ; hence, 

 among the many experiments made by me in 1891, only three dealt with 

 material which had been heated above 700°. The evidence of these 

 three experiments (Nos. 59, 81, and 95), is unanimous in showing that 



* Journ. Chem. Soc. Trans., LXXI. 559. (1897.) 



t These Proceedings, XXVI. 281 ; Z. Anorg. Chem , L 196. 



