1909] 



071 Problems of Helium and Radium. 



729 



but at very high temperatures, by the collocation of certain dis- 

 sociated constituents and with the simultaneous absorption of heat." 

 This suggestion of endothermic elements was made fifteen years 

 before the isolation of radium, and the proof of its continual thermal 

 emission by the Curies. Rutherford has shown that the de-electrified 

 particle of the <r<-rays of radium turns into ordinary helium, and 

 radium itself has been traced to uranium as its parent. As far as 

 our knowledge of the emanations of radio-active bodies goes, it would 

 seem that they are substances a little more volatile than carbon dioxide. 

 The annexed tables show the relative atomic weights and volatilities 

 of the Series of Rare gases. 



New Constituents op the Atmosphere. 



Helium 

 Neon (new) 

 Argon (inactive) 

 Crypton (hidden) 

 Xenon (stranger) 



X\ 



£C, Radium emanation 



Atomic AVeight 



4 



20 



40 



82 



128 



172 



222 



Boiling Point abs. 



40 



32 



87 

 121 

 164 



211 



Log P. 



Log P.\ 

 Xenon / 



A. 

 = 7-626 



= 7-332 



= 6-950 



= 6-963 



Radium Emanation. 

 Vapour Pressure. 

 B. 



- 1020/T I ~ ^^o ) Rutherford 



- 941/t(-^^o6) Ramsay 



- «^^/T(boiltgpdnt)^--y 



- 669/T 



The volatilites of the rare gases and that of the emanation of 

 radium are here expressed by the well-known Rankin equation — 



B 

 T 



Log P = A 



where P and T are the pressure in mm. of Hg and the absolute tem- 

 perature respectively, and A and B are constants ; B is here propor- 

 tional to the molecular latent heat. The tables thus show that not 

 only does the emanation fit into a series with the rare gases when 

 classified chemically, but that also in its chief physical properties it 

 allows of such a grouping. It seems probable, therefore, that x^ and x^^ 

 of which the latter is the radium emanation, together with that from 

 thorium and actinium, would suitably find a place in this series of 

 gases. It may be added that the B constant for liquid carbonic 

 acid is 869 ; that for sulphuretted hydrogen is a little lower. The 

 radium emanation, therefore, is of the same order of volatility as 

 these substances. 



