Valency of the Radio elements. 411 



electronegative, its most probable position is between thallium 

 and lead . This conclusion is supported by the electrochemical 

 and the chemical behaviour of the substance, as shown by 

 the recent work of the author *, and by Fleck f respectively. 



Table V. 

 Mobility of the cations. 



Rubidium 



Caesium 



3344 

 4355 

 64-67 

 67-60 

 68-20 



Silver 



54-02 



'. 155-4 



f Radium B 

 < Thorium B .. 

 [ Actinium B . . 



Magnesium .. 

 Calcium 



. 490 

 530 

 540 

 573 

 57-6 

 . 58-0 

 . 56-1 



Copper 



475 

 49-0 



Strontium 



Barium 



f Radium 



■1 Thorium X .. 

 [ Actinium X .. 



§ 9. Expulsion of an a-particle or a ^-particle from a dis- 

 integrating atom, and the difference in valency between 

 the parent and the resultant atom. 



The valencies of no less than 22 radioelements are now 

 known. They are given in Table VI. (p. 412) . It now remains 

 to discuss with these data how far the difference in valency 

 between the parent and the resultant atom is due to the 

 expulsion of an a- or a /3-particle. For two reasons, however, 

 it is necessary to be cautious in drawing conclusions. The 

 first is that the valency of an element is not an invariable 

 quantity like its atomic weight, but depends on various 

 factors such as, for instance, the nature of the element with 

 which the element is combined. In all our experiments, the 

 radioelements were present as chlorides in a weakly acid 

 solution, and there is no reason therefore for believing that 

 the valencies found are not the chief valencies. The second 

 reason is that all the elements in a disintegration series may 

 not yet be discovered, and the discovery of new elements 

 intermediate between known elements in the series may 

 profoundly modify our conclusions. In this connexion the 

 recent work of Marsden and Darwin J on the complexity of 

 thorium C, and of Fajans § on radium C, is of considerable 



* Phil. Mag. vol. xxiii. p. 628 (1912). 



t British Assoc. Reports, Dundee, 1912. 



X Marsden & Darwin, Proc. Roy. Soc. A. vol. lxxxvii. p. 17 (1912). 



§ Fajans, Phys. Zeit. vol. xiii. p. 699 (1912). 



