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XL. The Valency of the Radioelements.- By G. YON 

 Hevesy, Rh.U,, Hon. Research Fellow in Physics, Man- 

 chester University *. 



§ 1. Introduction. 



HpHEKE is at present no recognized intimate relation 

 JL between the processes that occur inside an atom and the 

 processes that take place outside it, that is to say, between 

 the radioactive and the chemical properties of an atom. It- 

 may be said, however, that there is some connexion between 

 atomic weight and radioactive phenomena, for only elements- 

 of atomic weight greater than 200 disintegrate with evolution 

 of helium. Rubidium and potassium, elements of low atomic 

 weight, however, appear to be radioactive, emitting /3-rays. 



In the search for a relation between radioactive and 

 chemical properties, the most likely line of attack seemed to 

 be to investigate the connexion between the nature of the 

 radiation accompanying the disintegration of an element,, 

 and the difference in valency between the resultant and the 

 parent product. Since the discovery of Faraday's law of 

 electrolysis, valency has become more and more to be con- 

 sidered from an electrochemical point of view. When an 

 a- particle is expelled from an atom, the atom loses positive 

 electricity, and when a /3-particle is expelled, it loses negative 

 electricity. It is therefore to be expected that this loss of 

 positive and negative electricity, as the case may be, would 

 have a definite influence on the valency of the resultant 

 atom. To investigate this point, the valency of a great many 

 radioelements has been determined. Apart altogether from 

 the interest of this problem, it is important to know what 

 are the valencies of the various radioelements, as very little 

 is known of the chemical properties of many of these bodies, 

 especially of those which follow the emanations in the 

 disintegration series. 



The two chief methods of determining the valency of an 

 element are the stoichiometrical and the electrochemical. 

 In the former method, the valency is obtained from an 

 analysis of various compounds of the element under con- 

 sideration; in the latter method, it is obtained from the ratio 

 of the number of coulombs passing during electrolysis and 

 the quantity of metal deposited from, or passing into solution. 

 The amount of radioactive bodies at one's disposal, however, 

 is so small that neither of these methods can be applied to 



* Communicated by Prof. E. Entherford, F.R.S. 



