of Radium and Uranium. 15 



Table VI. 



Element Kangeat20° E 2 A 



Uranium I Ri = 254 1-87 



Uranium II R 2 = 2-95 205 



Eadium R 3 = 3-36 2-24 



Badioactinium R 4 = 4-29 2-b4 



Actinium X - . . .R 5 = 434 *66 



Actinium emanation R 6 = 5-66 o-lo 



Actinium A R 7 = 6-37 3-44 



Actinium C R s = 524 301 



Applying the data available we may calculate what 

 proportion of the total number of atoms of uranium II 

 would have to be assumed to disintegrate in a mode lead- 

 ing to the production of actinium in order that the ratio 

 of the activity of the actinium products to the activity 

 of the radium would have the value 0-28/0-49 indicated 

 in table V. There are five actinium products emitting 

 <x-rays as compared with a single a-ray change in the 

 case of radium, and if equal numbers of atoms of each 

 of the elements were disintegrating in unit time the ratio 

 of the activities would be 20 



(2-64 + 2-66 + 3-18 + 3-44 + 3-01) : 2-24 = 66 : 1. 



The observed ratio is, however, 0-28: 0-49. If 100^ atoms 

 of uranium II are assumed to disintegrate in unit time 

 of which x disintegrate to form actinium, we have the 

 relation 



14-9 x __ 0-28 



(100 - x) 2-24 ~ 0-49 



which gives a value for x of approximately 8. So that, 

 if, out of every one hundred atoms of uranium II dis- 

 integrating, a total of eight atoms changed into actinium 

 and the remaining 92 changed into ionium (and ulti- 

 mately radium) the observed relations would exist 

 between the activity of the radium and the activity of 

 the actinium products in a mineral. 



Based on considerations of this character a number of 

 attempts have been made to devise a scheme of transfor- 

 mation which will satisfactorily indicate the successive 

 changes undergone by the uranium atoms. The most 

 plausible of these have been proposed by Soddy and 

 Cranston 21 and are given on the following page. 



20 Table VI. 



21 Proc. Boy. Soc, A 94, 384, 1918. 



