Valency of the Radio-elements. 593 



The valency of actinium is therefore 3, and this gives 

 more evidence in favour of the view that actinium is the 

 absent homologue of lanthanum. This determination is 

 further of interest as there is no known element that 

 should be non-separable from actinium, and therefore the 

 methods which Fleck and others have used for the exami- 

 nation of the chemical nature of the radio-elements here 

 fail. 



In addition to the radio-elements the valency of which 

 the author has determined from diffusion data, there are still 

 mesothorium 1 and radio thorium, and also perhaps actinium 

 B and radium C l5 to which the diffusion method might be 

 applied. The diffusion velocities of three elements non- 

 separable from mesothorium 1, and of four non-separable 

 from radiothorium, have, however, been determined, so that 

 these investigations offer little interest. The determination 

 of the diffusion constants of a member of the thallium type, 

 as for example that of radium C 2 , thorium D, or actinium D, 

 would, however, be of importance. Likewise of great interest 

 would be the measurement of the velocity of diffusion of 

 uranium X 2 *, which is a new type of element. It is un- 

 fortunate that the half-value period of the latter element 

 is only of the order of one minute, and thus is far too short 

 for measurements of its diffusion constant. In the case of 

 all the other elements, it can be shown by the measurement 

 of the velocities of diffusion of the respective ions that the 

 change of valency that an atom experiences by disintegra- 

 tion is determined by the number and sign of the charges 

 which that atom gives out in its transformation. 



The diffusion constants and the corresponding valencies 

 are given in the Table. It is not always that a perfect 

 dissociation becomes manifest, for example, not in the 

 case of uranium X, but nevertheless the valency can be 

 determined with certainty in every case from the diffusion 

 constant. 



Since radium F and also radium A send double charged 

 ions into solution, it cannot be determined from diffusion 

 experiments alone whether the transition from the emanation 

 takes place into the second or eighth group of the periodic 

 system. I have previously put forward the suggestion that 

 the former takes place, but this view has been shown to be 

 erroneous. 



* Fajans & Gohring, Die Naturwissenschaften, i. p. 399 (1913) : Phys. 

 Zeit. xiv. p. 877 (1913). Ilalin & Meitiier, Phys. Zeit. xiv. p. 758 (1913); 

 Fleck, Phil. Mag. xxvi. p. 528 (1913). 



