404 Dr. G. von Hevesy on the 



(d) The diffusion constants of RaD, RaE, and RaF. 



A solution of these substances was obtained by dissolving 

 in acid the active deposit formed in a glass tube in which a 

 large quantity of radium emanation had disintegrated. 

 One c.c. of the solution used contained 2 x 10" 7 gm. RaD 

 and 2 x 10~ 10 gm. RaF. The same experiment serves to 

 determine the diffusion constants of both RaD and RaE. 

 The /3-ray activities of the layers were compared immediately 

 after the experiment had been stopped, and from these results, 

 the diffusion constant of RaE was obtained. After an interval 

 of forty days the /3-ray activities of the same layers were 

 compared, and from these results the diffusion constant of 

 RaD was obtained. It was found that the constants of both 

 bodies were very similar. 



The following results were obtained : — 



RaD. 



(1) D 1 I 5 o-6 = 0-654 

 DL I o. 6 = 0-648 



(2) D[ 5 o. 6 =0'651 



D^o. 6 = 0-646. 



Mean value Di 8 o = 0'651 sq. cm. per day. 

 The valency of RaD is therefore 2. 



RaE. 

 The value of Di S o = 0*646 sq. cm. per day. 

 The valency of RaE is therefore 2. 



RaF. 



(1) D[ 5 o. 8 = 0-700 

 Dgo. 8 = 0-712 



(2) Df 5 o. 6 =0-702 



D&, 6 = 0-711. 



Mean value Di 8 o = 0*760 sq. cm. per day. 

 The valency of radium F is therefore 2. 



(e) The diffusion velocity of Radiotliorium. 



From comparison of the activities of the different layers 

 immediately after the experiment had been stopped, a dif- 

 fusion constant of about 0*7 was deduced. In the course of 

 a month the ratio of the activities fell to a value correspond- 

 ing to the diffusion constant given below. One gram of the 

 solution used contained 4 x 10" 10 gm. radiotliorium. 



