172 ESSAYS BIOGRAPHICAL AND CHEMICAL 



further investigation. It may be added that the deter- 

 mination by Gray of the density of nitric oxide, a com- 

 pound containing one atom of nitrogen in combination 

 with one atom of oxygen, entirely corroborates the results 

 of Lord Rayleigh and Leduc. Experiments are now in 

 progress to combine a weighed quantity of nitric oxide 

 with oxygen, so as to cause it to take up one other atom 

 of oxygen, and to find the increase in weight ; and also 

 to remove from it the atom of oxygen, and to find the 

 weight of the oxygen removed ; we may, therefore, hope 

 for some explanation of the above discrepancy at no dis- 

 tant date. 1 



The writer of this article was so much impressed by the 

 consideration of this discrepancy, that some years ago, in 

 conjunction with Miss Aston, an attempt was made to 

 find whether the fact of a compound having been formed 

 with absorption, instead of, as is commoner, with evolu- 

 tion of heat, had any influence on the proportions of the 

 elements which it contained. For this purpose the salts 

 of a curious acid derivative of nitrogen named hydrazoic 

 acid, HN 3 , were analysed ; but there is reason to distrust 

 the results, for it is possible that decomposition occurred 

 during the preparation to some small extent, and so may 

 not have led to trustworthy conclusions. But such as 

 they were, they were in favour of the supposition that the 

 atomic weight of nitrogen in such compounds is less than 

 in those formed with evolution of heat, like the nitre 

 analysed by Stas and by Richards. 



An entirely new light has been thrown on the numerical 

 relations of the atoms by the remarkable discovery of 

 radium by the Curies, and by the discovery by Rutherford 

 and Soddy, that what are termed the ' rays ' from its salts, 



1 Such investigations have since been carried out by Dr. R. Gray and 

 by Professor Philippe Guye, with the result that the true atomic weight 

 of nitrogen has been fixed as 14*01. 



