

1895.] Argon, a new Constituent of the Atmosphere. 269 



" atmospheric nitrogen " no substance other than nitrogen capable of 

 forming a basic compound with hydrogen. 



II. Reasons for suspecting a hitherto Undiscovered Constituent in Air. 



When the discrepancy of weights was first encountered, attempts 

 were naturally made to explain it by contamination with known 

 impurities. Of these the most likely appeared to be hydrogen, 

 present in the lighter gas in spite of the passage over red-hot cupric 

 oxide. But inasmuch as the intentional introduction of hydrogen 

 into the heavier gas, afterwards treated in the same way with, cupric 

 oxide, had no effect upon its weight, this explanation had to be 

 abandoned, and finally it became clear that the difference could not 

 be accounted for by the presence of any known impurity. At this 

 stage it seemed not improbable that the lightness of the gas ex- 

 tracted from chemical compounds was to be explained by partial 

 dissociation of nitrogen molecules N 2 into detached atoms. In order 

 to test this suggestion both kinds of gas were submitted to the action 

 of the silent electric discharge, with the result that both retained 

 their weights unaltered. This was discouraging, and a further ex- 

 periment pointed still more markedly in the negative direction. The 

 chemical behaviour of nitrogen is such as to suggest that dissociated 

 atoms would possess a high degree of activity, and that even though 

 they might be formed in the first instance their life would probably 

 be short. On standing they might be expected to disappear, in 

 partial analogy with the known behaviour of ozone. With this idea 

 in view, a sample of chemically prepared nitrogen was stored for 

 eight months. But at the end of this time the density showed no 

 sign of increase, remaining exactly as at first.* 



Regarding it as established that one or other of the gases must be 

 a mixture, containing, as the case might be, an ingredient much 

 heavier or much lighter than ordinary nitrogen, we had to consider 

 the relative probabilities of the various possible interpretations. 

 Except upon the already discredited hypothesis of dissociation, it 

 was difficult to see how the gas of chemical origin could be a mixture. 

 To suppose this would be to admit two kinds of nitric acid, hardly 

 reconcilable with the work of Stas and others upon the atomic 

 weight of that substance. The simplest explanation in many respects 

 was to admit the existence of a second ingredient in air from which 

 oxygen, moisture, and carbonic anhydride had already been removed. 

 The proportional amount required was not great. If the density of 

 the supposed gas were double that of nitrogen, ^ per cent, only by 

 volume would be needed ; or if the density were but half as much 

 again as that of nitrogen, then 1 per cent, would still suffice. But in 



* ' Roy. Soc. Proc.,' vol. 55, p. 344, 1894. 



