592 Dr. G. Hevesy on the Diffusion and 



since it is well known that actinium itself emits no a-rays. 

 The diffusion constant, which is obtained by a comparison of 

 the activities of the layers immediately after the interrup- 

 tion of the experiment, is not that of actinium but that of 

 actinium X, or, to speak more correctly, the resultant of the 

 diffusion constants of actinium X and radioactinium. The 

 former predominates since the short lived products are 

 present in equilibrium with actinium X. 



Diffusion velocities measured by comparison of the activities 



immediately 



II. 



fter the interruption of the experiment :- 



D150. Dl8°. 



0-60 0-65 



0-807x3-10 



0-57 

 0-280x3-12 



0-65 



0-70 



IL 0TO02- °' 6 « ' 73 



Mean value for Di 8 o is 0*69 sq. cm. per day. 



This gives a valency or 2, which corresponds to that of 

 actinium X. 



The above measurements were made between the 9th and 

 13th November 1912, immediately after stopping the dif- 

 fusion experiment, and the valency obtained is that 

 corresponding to actinium X. The activities of the layers 

 were taken about 200 days later, on the 5th of June 1913, 

 after the radioactinium, actinium X, and the short lived 

 products had come into equilibrium with actinium. The 

 numbers obtained at that later date are as follows : — 



Measured by comparison of the activities of the layers 

 six months later. 



-D150. Dl8°« 



L 0TO10 °- 41 <> 44 



IL 5TOT2 °' 43 ' 46 



I. 9^L 0-42 0*45 



' 0-452x3-00 u v *° 



II — 0-44 0*47 



±J - 0-424x302 U V 



Mean value for Di 8 ° is 0'46 sq. cm. per day, corresponding 



to the valency 3. 



