414 On the Valency of the JRadioelements. 



group in the periodic system to which it belongs is changed 

 by two units, after an a-parfcicle has been expelled. Of 

 course when Soddy put forward this view, the valencies of 

 most of" the radioelements had not been directly determined, 

 but had been simply assumed to be those of the common 

 elements, to which they are chemically most akin. 



Summary. 



From the velocity with which a cation diffuses in great 

 excess of its anion, it is shown that it is possible to determine 

 the number of charges borne by the cation, and therefore its 

 valency. The diffusion constants of radium, thorium X, 

 actinium X, uranium X, radiothorium, thorium B, thorium 

 C, radium D, radium B, radium F, ionium, and thorium have 

 been determined, and from these results the valencies of these 

 bodies have been obtained. 



By measuring the mobilities and the diffusion constants of 

 radioactive bodies their valencies can also be obtained. This 

 second method may therefore be used to check the results 

 obtained by the first. The mobilities of radium, thorium X, 

 actinium X, thorium B, thorium C, radium C, radium D, 

 radium E, and radium F have been determined, and from 

 these results the valencies of these bodies have been calcu- 

 lated. The values obtained by the second method are in 

 good agreement with those obtained by the first. 



Nernst's theory of the diffusion of electrolytes, which was 

 derived and proved to hold for monovalent electrolytes, is 

 shown to be applicable for electrolytes of any valency. 



From the relation between the mobilities of ions and their 

 position in the periodic system, light has been thrown on 

 the chemical nature of thorium B. 'The three B bodies are 

 monovalent, but do not belong to the alkaline metal group 

 of bodies. Their chemical properties lie most probably 

 between those of thallium and lead. 



In nine cases after the expulsion of an a-particle by a 

 parent substance, the valency of the resultant product differs 

 from that of its parent by two units. It is at present im- 

 possible to say if this rule holds strictly in all cases owing 

 to absence of complete data. The relation is certainly more 

 than a mere fortuitous one. 



I wish to thank Professor Rutherford very much not only 



for the continued interest he has taken in the research, but 



also lor the valuable radioactive preparations he has placed 



at my disposal. 



Physical Laboratories, 



Manchester University, 



November 1912. 



