THE GASES OF THE ATMOSPHERE 129 



on the " Gases present in the Atmosphere," but the 

 progress of his work can be traced by the aid of passages 

 in letters to Lord Rayleigh and to his wife, which have 

 been preserved. Thus he wrote to the latter on 23rd 

 April, 1894 : 



" By the way curiously I am at work on nitrogen, but not 

 from the commercial point of view, or rather Williams is. Nitro- 

 gen of air is heavier than nitrogen from ammonia in the ratio of 

 251 to 250. That would correspond with the addition of some 

 light gas to the heavy one, or of some heavy gas to the light one. 

 If the light gas were hydrogen, it would need 7 parts in 2000 to 

 make it so much lighter. Now no one has ever taken all the 

 nitrogen out of the air, or rather, after all oxygen has been 

 removed from air, no one has combined all the nitrogen. It 

 is quite possible that there is some inert gas in nitrogen which 

 has escaped notice. So Williams is at it now combining the 

 nitrogen of the air with magnesium, and seeing if there is any- 

 thing over, anything not nitrogen. We may discover a new 

 element." 



After several previous letters to Lord Rayleigh he 

 wrote as follows on 24th May, 1894 : 



" I intended to ask you to-day, what is probably quite un- 

 necessary, not to say anything about the gas which I think I 

 have got. It may turn out a mare's nest and it would be well 

 that no one should know of its existence. Another thing occurs 

 to me. I have got a large amount of nitride of magnesium, 

 which when treated with water gives ammonia. I can easily 

 get the nitrogen out of this ammonia, and I shall be glad to give 

 you it, if it can be conveyed to you by any way ; or what might 

 perhaps be better, I could give you the ammonia as chloride of 

 ammonium and you could liberate the ammonia and pass it, 

 mixed with oxygen, over red-hot copper. I find on making a 



