294 
about one day, this value being almost the minimum, and them 
increases slowly with the time. As we see from Fig. 1. the second 
part of eurve IT is parallel to eurve I which shows that the acti- 
vity of the first plate of crystal increases at the same rate as that. 
of the ether portion. 
The plate obtained from mother liquor (curve III), lost its ac- 
tivity during the first few days after erystallization. Its activity 
after reaching a minimum, and after a small increase remained 
practically constant. After two months it was observed to have 
decreased only 10°/. 
Disregarding for a moment the first rapid decrease of activity 
of both aqueous portions, which is exactly of the same nature as 
observed by Meyer and Schweidler, we see that we have the f 
activity in two cases increasing at the same rate 1. e. the increase 
of activity of the ether portion and of the plate of crystal first 
obtained. This points to the fact, that UrX was removed not only 
from the ether portion, but also in some degree from first obtained 
crystals. The mother liquor must contain then the greater excess 
of UrX. 
In connection with this, experiments were made with fresh ura- 
nium 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 fra- 
ctional erystallizations 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 treatment with ether. 
A large part of the UrX remained in the motherliquor 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 eurve II on Fig. 1.) 
In a similar way we can equally well explain the inerease of 
activity observed by Meyer and Schweidler !) in the erystals of 
uranium nitrate obtained from water solution. 
If in these experiments some part of motherliquor was poured 
1) Meyer and Schweidler Loe, cit. p. 1074, Figs. 6 and 7. 
