654 . REPORT — 1895. 



was then led to suspect the existence of a heavier gas in the atmosphere. He set 

 to work to isolate this substance, and succeeded in doing so by the method of 

 Cavendish. In the meantime Prof. Ramsay, quite independently, isolated the gas 

 by removing the nitrogen by means of red-hot magnesium, and the two investi- 

 gators then combining their labours, followed up the subject, and have given us a 

 memoir which will go down to posterity among the greatest achievements of an age 

 renowned for its scientific activity. 



The case in favour of argon being an element seems ' to be now settled by the 

 discovery that the molecule of the gas is monatomic, as well as by the distinctness 

 of its electric spark spectrum. The suggestion put forward soon after the discovery 

 was announced, that the gas was an oxide of nitrogen, must have been made in 

 complete ignorance of the methods by wliich it was prepared. The possibility of 

 its being N^ has been considered by the discoverers and rejected on very good 

 grounds. Moreover, Peratoner and Oddo have been recently making some experi- 

 ments in the laboratory of the University of Palermo with the object of examining 

 the products of the electrolysis of hydrazoic acid and its salts. They obtained 

 only ordinary nitrogen, not argon, and have come to the conclusion that the anhy- 

 dride N3.N3 is incapable of existence, and that no allotropic form of nitrogen is 

 given oft'. It has been urged that the physical evidence in support of the mon- 

 atomic nature of the argon molecule, viz., the ratio of the specific heats, is capable 

 of another interpretation — that argon is in fact an element of such extraordinary 

 energy that its atoms cannot be separated, but are bound together as a rigid system 

 which transmits the vibrational energy of a sound-wave as motion of translation 

 only. If this be the state of affairs we must look to the physicists for more light. 

 So far as chemistry is concerned, this conception introduces an entirely new set of 

 ideas, and raises the question of the monatomic character of the mercury molecule 

 which is in the same category with respect to the physical evidence. It seems 

 unreasonable to invoke a special power of atomic linkage to explain the monatomic 

 character of argon, and to refuse such a power in the case of other monatomic 

 molecules, like mercury or cadmium. The chemical inertness of argon has been 

 referred also to this same power of self-combination of its atoms. If this explana- 

 tion be adopted it carries with it the admission that those elements of which the 

 atoms composing the molecule are the more easily dissociated should be the more 

 chemically active. The reverse appears to be the case if we bear in mind Victor 

 Meyer's researches on the dissociation of the halogens, which prove that under the 

 influence of heat the least active element, iodine, is the most easily dissociated. 

 On the whole, the attempts to make out that argon is polyatomic by such forced 

 hypotheses cannot at present be considered to have been successful, and the con- 

 tention of the discoverers that its molecule is monatomic must be accepted as 

 established. 



In searching for a natural source of combined argon Professor Ramsay was led 

 to examine the gases contained in certain uranium and other minerals, and by steps 

 which are now well known he has been able to isolate helium, a gas which was 

 discovered by means of the spectroscope in the solar chromosphere by Professor 

 Norman Lockyer in 1868. In his address to the British Association in 1872 ' the 

 late Dr. W. B. Carpenter said : — 



' But when Frankland and Lockyer, seeing in the spectrum of the yellow solar 

 prominences a certain bright line not identifiable with that of any known terrestrial 

 flame, attribute this to a hypothetical new substance which they propose to call 

 helium, it is obvious that their assumption rests on a far less secure foundation, 

 until it shall have received that verification which, in the case of Mr. Crookes' re- 

 searches on thallium, was afforded by the actual discovery of the new metal, whose 

 presence had been indicated to him by a line in the spectrum not attributable to 

 anj' substance then known.' 



It must be as gratifying to Professor Lockyer as it is to the chemical world 

 at large to know that helium may now be removed from the category of solar 

 myths and enrolled among the elements of terrestrial matter. The sources, mode 



' Reports, 1872, p. Ixxiv. 



