Radioactive Properties of Uranium. 51 



The mother liquor must contain then the greater excess 

 of UrX. 



In connexion with this, experiments were made with 

 fresh uranium nitrate, and they showed that by even one 

 crystallization it is possible to separate the uranium nitrate 

 into two parts, namely the crystals and the mother liquor ; 

 the latter part containing seven times as much of UrX as 

 the former. By means of several fractional crystallizations 

 we can deprive uranium almost completely of the substance 

 UrX, which is so readily soluble in water. 



This at once explains the radioactive behaviour of the 

 crystals first obtained from the aqueous solution after treat- 

 ment with ether. A large part of the UrX remained in the 

 mother liquor, and the crystals themselves contained even 

 less than the equilibrium amount of UrX. In consequence, 

 the activity of the crystals must increase according to a 

 recovery curve of UrX. The experiments show that this is 

 really the case. (See curve II on fig 1.) 



In a similar way we can equally well explain the 

 increase of activity observed by Meyer and Schweidler* 

 in the crystals of uranium nitrate obtained from water 

 solution. 



If in these experiments some part of mother liquor was 

 poured off the surface of the plates of crystals, the uranium 

 crystals would contain less of UrX than the uranium itself 

 in a state of equilibrium. The increase of activity would 

 thus be due to the recovery of the separated UrX. And in 

 fact the authors state that this part of curve corresponds to 

 the constant of 22 days. 



The activity of the crystals obtained from the mother 

 liquor at first decayed very rapidly and, after reaching a 

 minimum, increased a very small amount and finally 

 remained almost constant, falling only 10 per cent during two 

 months. This is shown in curve III. 



The percentage decrease observed in this experiment is 

 smaller than the percentage rise observed in curves I and II. 

 This is due to the fact that the layer of crystals finally obtained 

 from the mother liquor was about three times as thick as in 

 the previous fractions. 



In other experiments, where the thickness of the plate was 

 relatively very small, the excess of ft activity diminished 

 regularly and in a more marked degree. 



* Meyer and Schweidler, loc. cit. p. 1074, figs, d & 7. 



E 2 



