6 ARGON, A NEW CONSTITUENT OF THE ATMOSPHERE. 



2. Reasons for Susi'ectinu a llriiii;i;ni Uxdiscovkhki) CoxsTrrrENT in Aih. 



When the tliscrepaiiey <>f weights was first encountered, attempts were natu- 

 rally made to explain it by contamination with known inip\irities. Of these the 

 most likely appeared to be hydrogen, present in the lightei- gas in spite of the pas- 

 sage over led-hot cujiric oxide. But inasmuch as the intentional introduction of 

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

 oxide, had no etl'eet upon its weight, this explanation had to be aljandoned, and 

 finally it became clear that the difference could not be accounted for l>y the pres- 

 ence of any known impurity. At this stage it seemed not improbable that the 

 lightness of the gas exti'acted fiom chemical comj)ounds was to be explained by 

 pai'tial dissociation of nitiogen molecules N^ 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 experiment pointed still more markedly in the 

 negative direction. The chemical behavioi' of nitrogen is such as to sugtiest tiiat 

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

 they might be formed in the fiist instance their life would probably be short. On 

 standing they might be expected to disappeai-, in partial analogy with the known 

 behavior of ozone. With this idea in view a sample of clicmically prepared niti'o- 

 gen was stored for eight mouths. iJut at the end of this time tiie ilensity showed 

 no sign of increase, lemaining exactly as at first.' 



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

 ture, containing as the case might be an ingredient nuich heavier or much lighter 

 than ordinary nitrogen, we had to consider the relative proi)abilities of the various 

 })ossible interpretation.s. Kxcejit upon the already discredited hypothesis of dis- 

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

 To .su})pose this would be to atlniit two kinds of nitric acid, hardly reconcilable 

 with the work of Stas ami others upon the at<iMiic weight of lliat substance. The 

 simplest exi>Ianation in many respects was to admit the existence of a second in- 

 gredient in air from which oxygen, nu)isture, and carbonic anhydride had already 

 been removed. The proportional amount recpiired was not great. If the density 

 of the supposed gas were double that of nitrogen, one-half per cent only by volume 

 would be needed ; or if the density were but half as nuich again as that of nitro- 

 gen, then one per cent would still suffice. But in accepting this explanation, even 

 provisionally, we had to face the improbability that a gas surrounding us on all 

 sides and present in enoi'mous (ju.uititirs could have remained so long unsuspected. 



' FrocceJiiigs of the Koyal Society, \'ol. LV, ]>. 344, 1894. 



