30 Journal of the Mitchell Society \^July 



of years Rutherford's announcement of his theory of suc- 

 cessive transformation or the disintegration of the atom. It 

 is a question whether the fact that an atom is undergoing 

 disintegration is to be regarded as a property in the same 

 sense as the mass, valence, etc., but so long as this change can 

 not be induced, changed or stopped and is known to take 

 place only in the case of a fraction of the elements it is 

 certainly distinctive and may be called a property for lack 

 of a better name. There is, however, undoubtedly a cause 

 for this disintegration and this instability may be due to 

 some inherent property of the atom. 



At present there are some thirty-seven radio-active bodies 

 known, with the possibility of still others being identified. 

 Each has distinctive radio-active properties. For a number 

 of these the chemical and physical properties are known. 

 Each is an atom hitherto unknown and must be considered a 

 new element. Of course, the present accepted arrangement of 

 the periodic system does not provide for so many additional 

 elements and indeed is rather hopeless for even the sixteen 

 rare earth elements. What is to be done with this embar- 

 rassment of riches ? 



Soddy's study of the grouping in well-known families of 

 a number of the l)etter known radio-active elements according 

 to their chemical properties, combined with a consideration 

 of the kind of disintegration by which it was produced led 

 him to a generalization which would enable one to place cor- 

 rectly any radio-active element whose source was known, and 

 at the same time give an approximation as to its atomic 

 weight. 



Fajans arrived at the same generalization independently 

 from an examination of the electro-chemical evidence, find- 

 ing that the product of an a ray change was more electro- 

 positive, while that oi n (3 ray change was more electro-nega- 

 tive. Similar conclusions from various evidence were reached 

 by Fleck and Russell. 



The generalization is as follows : 

 When an a particle is expelled it carries with it two atomic charges 



