The Preparation and some of the Properties of Pure Argon. 191 



the body possessing the high refractivity was not present in No. 6 in 

 greater proportion than in No. 2, otherwise the refractivity of No. 6 

 would have shown an increase over that of No. 2. 



The refractivity of pure argon differs somewhat from the value for 

 crude argon found by Lord Kayleigh, viz., O961,* and also from that 

 previously found by ourselves, 0-9596. The removal of neon, which 

 appears to have a very low refractivity, and of helium, of which the 

 refractivity is 0*1238, accounts for the increased refractivity of a sample 

 from which they are absent. The gases which we have recently found 

 in air and in crude argon will form the subject of a future communica- 

 tion. Suffice it to say that the amount of neon and helium is much 

 more considerable than that of the others, and that their effect on 

 crude argon is, therefore, much more marked on its density and 

 refractivity. 



To revert to the opening sentences of this communication, we may 

 point out that the remarks on the homogeneous nature of argon were 

 just at the time. The change in its physical constants, caused by the 

 mixture of more recently discovered gases which it has been shown to 

 contain, is exceedingly small, and does not call for any serious altera- 

 tion in the original paper on " Argon, a new Constituent of the 

 Atmosphere." 



The Density of Argon at the Boiling Point of Oxygen. 



In an addendum to the original paper on argon, f the expansion of 

 argon by rise of temperature to 250, as well as its contraction by fall 

 of temperature to - 88, was determined. There is a considerable 

 difference between the temperature at which nitrous oxide boils and 

 that at which oxygen boils, and it was thought worth while to ascertain 

 whether argon behaves as a normal gas down to the boiling point of 

 oxygen. OlszewskiJ gives the boiling point of argon as - 187, and 

 that of oxygen as - 182 7 ; at the latter temperature, therefore, argon 

 would not be far removed from its own condensing point. The 

 interesting question, of course, is the possible polymerisation of argon 

 at such a low temperature. 



No sign of any polymerisation has been observed, as is shown by the 

 following data : 



Hydrogen Thermometer. 



Temperature. Pressure. Volume. E. 



C. ram. 



99-7 1091-5 1-0026 2-9362 



0-0 803-2 1-0000 2-9421 



-182-7 269-6 0-9953 2-9715 



* ' Eoj. Soc. Proe.,' vol. 59, p. 205. 

 t < Phil. Trans.,' A, 1895, p. 239. 

 J Loc. cit., p. 257. 



