Relative Activity of Radium and Cranium. 63 



Table VI. 



Element. Range at 20°. U\ 



Uranium I R,=2o4 1 \S7 



Uranium II R 2 =2'95 2'05 



Radium R 3 =3'36 2-24 



Radioactinium R 4 =4'29 2'64 



Actinium X R 5 = 4'34 2'66 



Actinium emanation R 6 =5'66 3*18 



Actinium A R 7 =6'37 344 



Actinium C R tf =5-24 3*01 



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 leading 

 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 a-rays 

 as compared with a single a-ray change in the case of 

 radium, and if equal numbers of atoms of each of the ele- 

 ments were disintegrating in unit time the ratio of the 

 activities would be* 



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



The observed ratio is, however, 0*28 : 0*40. 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 -.r) 2-24~~0-49' 



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

 out of every one hundred atoms of uranium II. disin- 

 tegrating, a total of eight atoms changed into actinium and 

 the remaining 92 changed into ionium (and ultimately 

 radium), the observed relations would exist between the 

 activity of the radium and the activity of the actinium pro- 

 ducts in a mineral. 



Based on considerations of this character a number of 

 attempts have been made to devise a scheme of transforma- 

 tion which will satisfactorily indicate the successive changes 

 undergone by the uranium atoms. The most plausible of 

 these have been proposed by Soddy and Cranston f and are 

 given on the following page. 



* Table VI. 



t Proc. Roy. Soc. A xciv. p. 384 (1918). 



