484 Prof. E. Rutherford : Some 



plus recent**, il considere comme vraisemblable qu'il s'agit 

 (Pun gaz de la nature de ceux du groupe de l'argon. 



" Je pense qu'il n'y a pas actuellement de raisons suffisantes 

 pour admettre ^existence d'une emanation de matiere sous sa 

 forme atomique ordinaire. Nous avons anterieurement, M. 

 Debierne et moi, vainement cherche des raies nouvelles dans 

 les gaz radioactifs extraits du radium. Eirrm ^emanation 

 disparait spontanement en tube scelle. Je considere aussi 

 comme pen vraisemblable que les effets qui accompagnent 

 ^existence de Femanation aient leur origine dans une trans- 

 formation chimique. On ne connait en effet aucune reaction 

 chimique pour laquelle la vitesse de reaction soit independante 

 de la temperature entre —180° et +450°." 



Since the discovery of the thorium emanation, I have always 

 taken the view that the emanation consists of matter in the 

 radioactive state present in minute quantity in the surround- 

 ing gas. The experiments of Miss Brooks and myself 

 (' Nature,' p. 157, 1901) showed that the radium emanation 

 mixed with air diffused very slowly. By comparing the rate 

 of interdiffusion of the emanation into air with that of known 

 gases, it was deduced that the emanation particles behaved 

 like heavy gas molecules of molecular weight probably 

 lying between 40 and 100. I have long recognized that the 

 electrical and other effects produced by the emanations can 

 be manifested by an extremely minute quantity of radio- 

 active matter in the gaseous state. For this reason I am not 

 surprised that MM. Curie and Debierne have failed to obtain 

 evidence by the spectroscope or balance of the existence of 

 the emanation. At the same time I do not doubt that with 

 sufficient quantity of active material the presence of the 

 emanation will ultimately be detected by these means. I 

 do not consider that the emanations remain permanently in 

 the gaseous state, for it seems probable that the emanations 

 gradually change into the matter responsible for excited 

 activity, which is deposited on the walls of the containing' 

 vessel. Recent experiments by Mr. Soddy and myself show- 

 that the thorium emanation behaves chemically as an inert 

 gas. and in this respect resembles the gases of the argon 

 family. M. Curie has, apparently, not observed a recent 

 paper by us (Proc. Chem. Soc. p. 219, 1902) in which 

 it is shown that if the emanations of thorium or radium 

 mixed with air, oxygen, or hydrogen are passed slowly through 

 a spiral tube immersed in liquid air, the emanations are con- 

 densed in the tube, and the issuing gas is completely free 



* Eutherford and Soddy, Phil. Mag. Nov. 1902. 



