1895.] on Argon. 525 



puzzled me very much, aud which, at that time, I regarded only with 

 disgust and impatience, I published a letter in ' Nature ' inviting 

 criticisms from chemists who might be interested in such questions. 

 I obtained various useful suggestions, but none going to the root of 

 the matter. Several persons who wrote to me privately were inclined 

 to think that the explanation was to be sought in a partial dissocia- 

 tion of the nitrogen derived from ammonia. For, before going 

 further, I ought to explain that, in the nitrogen obtained by the 

 ammonia method, some — about a seventh part — is derived from the 

 ammonia, the larger part, however, being derived as usual from the 

 atmosphere. If the chemically-derived nitrogen were partly dis- 

 sociated into its component atoms, then the lightness of the gas so 

 prepared would be explained. 



The next step in the enquiry was, if possible, to exaggerate the 

 discrepancy. One's instinct at first is to try to get rid of a dis- 

 crepancy, but I believe that experience shows such an endeavour to 

 be a mistake. What one ought to do is to magnify a small 

 discrepancy with a view to finding out the explanation ; and, as it 

 appeared in the present case that the root of the discrepancy lay in 

 the fact that part of the nitrogen prepared by the ammonia method 

 was nitrogen out of ammonia, although the greater part remained of 

 common origin in both cases, the application of the principle sug- 

 gested a trial of the weight of nitrogen obtained wholly from 

 ammonia. This could easily be done by substituting pure oxygen for 

 atmospheric air in the ammonia method, so that the w r hole, instead 

 of only a part, of the nitrogen collected should be derived from the 

 ammonia itself. The discrepancy was at once magnified some five 

 times. The nitrogen so obtained from ammonia proved to be about 

 one-half per cent, lighter than nitrogen obtained in the ordinary 

 way from the atmosphere, and which I may call for brevity " atmo- 

 spheric " nitrogen. 



That result stood out pretty sharply from the first ; but it was 

 necessary to confirm it by comparison with nitrogen chemically 

 derived in other ways. The Table before you gives a summary of 

 such results, the numbers being the weights in grams actually con- 

 tained under standard conditions in the globe employed. 



Atmospheric Nitrogen. 



By hot copper (1892) 2-3103 



By hot iron (1893) 2'3100 



By ferrous hydrate (1894) 2 "3102 



Mean 2-3102 

 Chemical Nitrogen. 



From nitric oxide 2-3001 



From nitrous oxide 2 • 2990 



From ammonium nitrite purified at a red heat 2-2987 



From urea 2 • 2935 



From ammonium nitrite purified in the cold 2*2987 



Mean 2 ■ 2990 



