June 28, 1895.] 



SCIENCE. 



703 



purities, especially against the presence of 

 hydrogen, which might seriously lighten any 

 gas in which it was contained. I believe, 

 however, that the precautious taken were 

 sutflcient to exclude all questions of that 

 sort, and the result, which I published 

 about this time last year, stood sharply out, 

 that the nitrogen obtained from chemical 

 sources was diSerent from the nitrogen ob- 

 tained from the air. 



"Well, that difference, admitting it to be 

 established, was sufficient to show that 

 some hitherto unknown gas is involved in 

 the matter. It might be that the new gas 

 was dissociated nitrogen, contained in that 

 which was too light, the chemical nitrogen 

 — and at first that was the explanation to 

 which I leaned: but certain experiments 

 went a long way to discourage such a sup- 

 position. In the first place, chemical evi- 

 dence — and in this matter I am greatly de- 

 pendent upon the kindness of chemical 

 friends — tends to show that, even if ordi- 

 narj- nitrogen could be dissociated at all 

 into its component atoms, such atoms would 

 not be likely to enjoy any verj- long contin- 

 ued existence. Even ozone goes slowly 

 back to the more normal state of oxygen; 

 and it was thought that dissociated nitrogen 

 would have even a greater tendency to re- 

 vert to the normal condition. The experi- 

 ment suggested by that remark was as fol- 

 lows — to keep chemical nitrogen — the too 

 light nitrogen which might be supposed to 

 contain dissociated molecules — for a good 

 while, and to examine whether it changed 

 in density. Of course it would be useless 

 to shut up gas in a globe and weigh it, and 

 then, after an interval, to weigh it again, 

 for there would be no opportunity for any 

 change of weight to occur, even although 

 the gas within the globe had undergone 

 some chemical alteration. It is necessaiy 

 to re-establish the standard conditions of 

 temperatiu'C and pressure which are always 

 understood when we speak of filling a glol)p 



with gas, for I need hardly say that fill- 

 ing a globe with gas is but a figure of 

 speech. Everything depends upon the 

 temperature and pressure at which you 

 work. However, that obvious point being 

 borne in mind, it was proved bj- experiment 

 that the gas did not change in weight 

 by standing for eight months — a result 

 tending to show that the abnormal light- 

 ness was not the consequence of dissocia- 

 tion . 



Further experiments were tried upon the 

 action of the silent electric discharge — both 

 upon the atmospheric nitrogen and upon 

 the chemically derived nitrogen — but neither 

 of them seemed to be sensibly affected by 

 such treatment; so that, altogether, the 

 balance of evidence seemed to incline 

 against the hypothesis of abnormal light- 

 ness in the chemically derived nitrogen be- 

 ing due to dissociation, and to suggest 

 stronglj-, as almost the only possible alter- 

 native, that there must be in atmospheric 

 nitrogen some constituent heavier than true 

 nitrogen. 



At that point the question arose. What 

 was the evidence that all the so-called ni- 

 trogen of the atmosphere was of one qual- 

 ity? And I remember — I think it was 

 about this time last year, or a little earlier 

 — putting the question to my colleague, 

 Professor Dewar. His answer was that he 

 doubted whether anything material had 

 been done upon the matter since the time 

 of Cavendish, and that I had better refer 

 to Cavendish's original paper. The advice 

 I quickly followed, and I was rather sur- 

 prised to find that Cavendish had himself 

 put this question quite as sharplj- as I could 

 put it. Translated from the old-fashioned 

 phraseologj- connected with the theory of 

 phlogiston, his question was whether the 

 inert ingredient of the air is i-eally all 

 of one kind, whether all the nitrogen of 

 the air is really the same as the nitro- 

 gen of nitre. Cavendisli not only asked 



