126 SIR WILLIAM RAMSAY 



The ammonia method of preparation had been sug- 

 gested to him by Professor Ramsay. 



A paper on the subject, under the title " An Anomaly 

 encountered in the Determinations of the Density of 

 Nitrogen Gas," by Lord Rayleigh, was published in the 

 Proceedings of the Royal Society in April 1894. In this 

 paper the author discussed the difficult question as to 

 the possible impurities in atmospheric nitrogen which 

 would account for its apparent greater density, and, on 

 the other hand, the impurities lighter than nitrogen 

 which conceivably might be present in the gas derived 

 from chemical sources. 



As to the gas obtained from air it was shown con- 

 clusively that the superior density could not be attri- 

 buted to the presence of unabsorbed oxygen. 



Of the gases lighter than nitrogen the presence of 

 water vapour or ammonia could be dismissed from 

 consideration at once, in view of the conditions under 

 which the experiments were conducted. The only gas 

 which required special attention was hydrogen, but this 

 and such light hydrocarbons as marsh gas would be 

 removed by the hot copper oxide over which the gas is 

 made to travel. An experiment in which hydrogen was 

 purposely introduced proved in fact that it was com- 

 pletely burnt out by this treatment. 



Other experiments followed in which nitrogen obtained 

 by removing oxygen from the oxides of nitrogen by 

 means of heated iron was compared with nitrogen 

 derived from air by the absorption of oxygen by means 



