OUTLINE OF RADIOACTIVITY 119 



only Lord Ea3'leigh's collaborator in the discovery of argon, but by him- 

 self identified terrestrial helium, and, with Mr Travers as collaborator, 

 discovered neon, krypton, and xenon. With Mr Soddy, he was also the 

 first to demonstrate that radium emits helium. By the methods which 

 he developed the detection of neon and argon is not a matter of serious 

 difficulty, and when he tells us that from water treated with radium ema- 

 nation he got an imcondensable gas which gave a brilliant neon spectrum 

 in which every line was identified by comparison with a vacuum tube 

 containing atmospheric neon, there seems to be no room for doubt.^* 

 These chemists confirm once more the fact that radium emanation in an 

 otherwise vacuous vessel, or when mixed with oxygen and hydrogen 

 gases, yields helium as one of its products. 



If argon and neon are produced under the conditions just mentioned, 

 it would appear either that the a particles are of various kinds, according 

 to circumstances, or that they are something different from molecules of 

 the gaseous products. Messrs Cameron and Eamsay incline to the latter 

 hypothesis, and suggest that the degradation of molecules of emanation 

 is due to their bombardment by a particles, the disintegration being 

 most complete and yielding helium under the simplest conditions, but 

 less complete in the presence of water or copper salts, so that then heavier 

 inert gases, argon and neon, result. This would leave the true nature of 

 the o. particles an open question. From its density and its probable 

 position in the periodic series. Sir William thinks that radium emana- 

 tion should be assigned an atomic weight of approximately 316.5.^® 



Another surprising feature of their investigation is a redetermination 

 of the average life of radium from three experiments on the volume of 

 emanation set free by radium bromide and radium sulphate. Their 

 result is 236 years,^* while Mr Eutherford, by a less direct method, 

 obtained no less than 1,800 years. 



It appears then that much remains to be done before even so brief a 

 sketch of radioactivity as is here presented can be drawn without includ- 

 ing uncertain features. Thus, for the present purpose, it must be con- 

 sidered how far facts of radioactivity which are undoubted bear upon 

 geology. No one questions the enormous energy of radioactive transfor- 

 mations, which is also readily explained by the electronic theory of the 

 atom, while the dissemination of radioactive substances in nature makes 



" In this connection It Is interesting to remember that the gases of the hot springs 

 of Bath contain neon, the proportion of this gas being much greater than in the atmos- 

 phere. 



1= Journal of the Chemical Society, vol. 91, 1907, p. 931. 



10 Journal of the Chemical Society, vol. 91, 1907, p. 1282. 



