Akgox. 99 



and careful series of experiments extending over a period of several 

 years conducted and repeated on thoroughly scientific lines, by means 

 of physical and chemical methods, the outcome of the combined labours 

 and knowledge of physicists and chemists of the age, which I think we 

 may safely say is the most brilliant, and withal the most accurate that 

 science has ever known 



Lord Rayleigh had previously proved that nitrogen extracted from 

 chemical compounds was about one-half per cent, lighter than " atmos- 

 pheric nitrogen." Thus, the [mean] result for the weights of nitrogen 

 gas in the globe, prepared from the following compounds : Nitric oxide, 

 nitrous oxide, ammonia nitrite, urea was 2.2990, while that for "atmos- 

 pheric nitrogen " prepared and purified by the best hitherto known 

 methods was 2.3102. Reduced to standard conditions, their figures 

 give 1 2505 grms of "chemical" nitrogen and 1.2572 grms of "atmos- 

 pheric " nitrogen per litre. This difference, though small, was quite 

 sufficient to arouse in the mind of Lord Rayleigh the suspicion that 

 " atmospheric nitrogen " was not pure nitrogen. 



We may very briefly at this stage consider the details of one 

 method for the preparation of nitrogen, used in these investigations of 

 Lord Rayleigh and Prof. Ramsay: By the ignition of the metal 

 magnesium in nitrogen, a compound of the two is formed, (magnesium 

 nitride) which on subsequent treatment with water yields ammonia ; 

 from the latter by many methods the combined nitrogen may be 

 determined. 



As magnesium nitride, nitrogen was extracted from the air, then 

 liberated with water and carefully estimated. The result obtained 

 proved that, prepared in this way, nitrogen which in the first stages of 

 the method of preparation was part of the atmosphere was practically 

 identical in physical cdnstants with nitrogen from chemical compounds. 



It was, therefore, conjectured that nitrogen separated from the 

 atmosphere by all the methods save the one just quoted, was not pure 

 nitrogen. What then was its impurity? In other words, is there not 

 another gaseous constituent in the atmosphere unknown? 



We have now stated briefly the grounds for suspecting a hitherto 

 undiscovered constituent in the air. In a review of this character it is 



