Valency of the Radioelements. 413 



Similarly, the properties o£ thorium C given in this paper 

 refer to the product called thorium C by Marsden and Darwin. 

 This is the parent substance o£ thorium C 2 , a quick changing 

 product o£ unknown valency. In both these cases, therefore, it 

 Is obvious that the connexion between change of valency and 

 expulsion of an a-particle must remain at present unsettled. 



/3 in the fourth column of the table means that the parent 

 substance of the element is a /3-ray body. The electro- 

 chemical behaviour of radium A renders it very probable 

 that radium A, and therefore very probably thorium A and 

 actinium A, are divalent. It would be extremely difficult 

 to settle this point with certainty. 



It is seen from the above table that expulsion of a 

 /3-particle seems to affect the valency in a direction opposite 

 to that affected by the a-ray change. In the case of expulsion 

 of an a-particle, the relation is much more obvious. There 

 are nine cases in which the valency of the resultant atom is 

 two units different from that of the parent atom after the 

 latter has expelled an a-particle. These are the trans- 

 formations of ionium into radium, radium into emanation, 

 thorium into mesothorium 1, radiothorium into thorium X, 

 thorium X into emanation, radioactinium into actinium X, 

 and actinium X into emanation. The case of uranium 1 

 and 2 is rather a complex one, and will be dealt with in 

 the paper that follows. In ten further cases it is impossible 

 to say whether or not this rule holds, owing to want of 

 ^complete data, but there is at present no reason to assume 

 that it is not fulfilled. Whether the rule be shown to 

 hold strictly or not by subsequent research, there can be 

 no doubt that the change of valency with expulsion of an 

 a-particle is not simply fortuitous. 



After the present work was finished the author's attention 

 was directed to a view, practically the same as that given 

 above, put forward by F. Soddy in his recent book *. It is 

 there pointed out that all long-lived radioelements are elements 

 of even valency, and that the valency suffers a change of 

 two units when an a-particle is expelled. In addition to the 

 nine cases cited above, the change of radium D into radium 

 F, and of the latter into lead, are cited as obeying the rule. 

 Each of these three bodies has a valency of 2. Radium D 

 and lead, however, belong to group IV. of the periodic 

 system, and radium F very probably to group VL In the 

 present state of our knowledge, therefore, the rule holds 

 better, if instead of saying that the valency of an element 

 suffers a change of two units, we say that the number of the 



* ' Chemistry of the Radioelements,' p. 29. 

 Phil. Mag. S. 6. Yol. 25. Xo. 147. March 1913. 2 F 



