416 Dr. G. von Hevesey and L. von Putnoky on 



If uranium 1 diffuses at a different rate from that of 

 uranium 2, some of the layers will be more active, weight 

 for weight of uranium, than others, and the diffusion con- 

 stant obtained by the second way will be very different from 

 that obtained by the first. 



The diffusion apparatus employed in this experiment is 

 described in the preceding paper. 



The amount of uranium in a layer of the liquid was deter- 

 mined gravimetrically by evaporating the solution to dryness, 

 igniting first in air and then in hydrogen, and weighing as 

 U0 2 . The activity was determined by rubbing a small 

 quantity of the oxide in a finely powdered condition on a 

 ground-glass disk, and measuring it in an a-ray electroscope. 

 The amount of uranium oxide per sq. cm. exceeded in no 

 case more than 1/3. mg., as with thicker layers the absorption 

 of the rays by the material becomes of consequence. 



The uranyl nitrate used was purified by crystallization. 

 The urano salt was prepared by reducing a uranyl salt elec- 

 trolytically at a lead cathode surrounded by a diaphragm. 

 The current density employed was 0*15 amp. per sq. cm. 

 Reduction took place in an atmosphere of C0 2 . During the 

 diffusion of the urano salt also, the diffusion apparatus was 

 filled with C0 2 . 



The following are the results of the experiments made : — 



(1) Diffusion velocity of U0 2 (N0 3 ) 2 from a 1/5 molar 

 solution of uranyl nitrate and an 8 molar nitric acid solution 

 in 8 mol. HN0 3 . 



Diffusion constant at 18° calculated from the weight of 

 the material used 



0442 sq. cm. per day. 



Same calculated from the activity 



0-438 + 0*005 sq. cm. per day. 



In this experiment the diffusion of the U0 2 ion takes 

 place in an excess of the anion (N0 3 ) . In this case, as is 

 shown in the foregoing paper, differences in the nature of the 

 migrating cation are more pronounced than in the case when 

 it diffuses in water. The diffusion velocity of the cation in 

 water depends to the same extent on both ions. 



(2) Diffusion velocity of 1/5 molar U0 2 (N0 3 ) 2 in water. 

 Diffusion constant calculated from the weight of material, 



0*576 sq. cm. per day. 



Same calculated from the activity, 



0-581 ±0*006 sq. cm. per day. 



