406 Dr. G. von Hevesy on the 



(h) The diffusion velocity of Uranium X. 



The uranium X used was separated from uranyl nitrate 

 by precipitating it with iron as hydroxide in presence of 

 excess of ammonium carbonate. The iron itself was not 

 separated from the uranium X, and therefore constituted an 

 impurity. The amount of the uranium X in the layers was 

 obtained by comparing their /3-ray activities. Owing to the 

 presence of the impurity, the accuracy with which the 

 measurements were carried out was not so great as in most 

 of the other experiments. One c.c. of the solution used 

 contained 2 x 10" 

 results obtained : 



T) 1 — 



^le^ — 



ontained 2 x 10 -10 gm. uranium X. 



0-57 



D 



ii 



16°-9 : 



2-77x0-525 

 0-57 



The following were the 



0-392 



= 0-339. 



2*77x0-530 

 Therefore D i8 o = 0*400 sq. cm. per day. 

 The valency of uranium X is 4. 



The value of n is either 3 or 4. The latter value is pre- 

 ferred for reasons to be given later, and also because, in 

 accordance with the law of mass action, the 01 ions due to 

 the ferric chloride tend to prevent the dissociation of the 

 UrX Cl 4 . This, possibly gives rise to too low a value of the 

 charge carried. 



Table III. 



Diffusion constants of the radioelements at 18°, 

 . diffusion taking place in an excess of the anion. 



Substance. 



Diffusion Constant 

 (sq. cm. per day) 



UrX 



0-400 

 0-327 

 0667 

 0-651 

 0-646 

 0760 



0-329 



0-333 



0659 



1-21 



0625 



0-664 



Io 



Ea" 



EaD" 



EaE" 



EaF" 



Th 



Eadiothorium * ' ' * 



ThX" 



ThB ' (EaB ', ActB ') ... 



ThC ' * (EaC * \ ActC ' *) . 



ActX** 





