Travees. — Presidential Address. 127 



assumption that some of the supposed simple bodies were 

 in reahty compound. These discrepancies were especially 

 obvious in the case of atmospheric nitrogen, for when ob- 

 tained from that source by any of the methods usually em- 

 ployed for the purpose, it was invariably found to be heavier 

 in an appreciable degree than when obtained from any other 

 compound of which it formed a part. This would doubtless 

 have been noticed by Berzelius, or Davy, or Faraday, who 

 had also experimented on atmospheric nitrogen, had any of 

 them compared its relative densities when obtained from that 

 and other sources, such, for example, as ammonia, and yet 

 the fact that nitrogen entered into the composition of am- 

 monia was one of those which led some of the older chemists 

 to infer its compound character. It would certainly be strange 

 if Lord Eayleigh was unacquainted with these older specula- 

 tions, although, so far as my reading goes, I have seen no 

 reference to them in the published accounts of his experi- 

 ments. The difference actually found by him between the 

 weight of atmospheric nitrogen and that chemically obtained 

 from its compounds was that its average weight in the 

 former was 1-2572 grammes, whilst in the latter it was 

 only 1-2505, a difference of -0067 grammes. Many sug- 

 gestions were offered to explain this discrepancy, all of which, 

 however, were based upon the supposition that atmospheric 

 nitrogen was the purer of the two, and that the nitrogen chemi- 

 cally prepared must still contain some lighter gas. But upon 

 proper test experiments being applied in connection with 

 these suggestions they were found to be untenable, and it 

 soon became clear that the supposed position must be re- 

 versed, and that atmospheric nitrogen must have in combina- 

 tion some heavier gas previously unknown. For some time 

 after this discovery the test of separating argon from the 

 atmospheric compound proved to be a very difficult one. 

 Nitrogen, chemically speaking, is an inert substance, by 

 which is understood that it is very difficult to force it into 

 combination with other substances, and it soon became 

 obvious that argon could only be obtained as a residue after 

 removing from any given quantity of atmospheric air all its 

 other constituents. This was effected in several ways, all of 

 which were slow and wearisome. It has, however, been 

 justly remarked that " chemical bodies must be taken as we 

 find them, and that those amongst them which, even in the 

 hands of the best experimentalists, yield only to methods 

 outside of ordinary chemical routine are precisely those whose 

 investigation leads most to the extension of chemical know- 

 ledge." 



The chemical nature and properties of the new substance 

 have as yet been only partially ascertained, the chief obstacle 



