295 
off the surface of the plates of crystals, the uranium crystals would 
contain less of UrX than the uranium itself in a state of equili- 
brium. 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 the eurve corresponds to the constant of 22 days. 
The activity of the crystals obtained from the motherliquor at 
first decayed very rapidly and, after reaching a minimum, incre- 
ased a very small amount and finally remained almost constant 
falling only 10 per cent during two months. This is shown in 
eurve 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 the layer of erystals finally obtained from the mother 
liquor was about three times as thiek as in the previous fractions. 
In other experiments, where the thickness of the plate was relati- 
vely very small, the excess of activity diminished regularly and 
in a more marked degree. 
4. The effect of crystallization on the activity of uranium nitrate. 
We shall return now to the initial rapid decay of activity of 
uranium nitrate immediately after it was erystallized in the form 
of plates from the aqueous solution. 
A decay quite analogous to that shown in the first part of the 
curves Il and III was also obtained, when uranium nitrate had been 
obtained from the pure aqueous solutions, when no ether separation 
was applied. The following is one example. 25 grams of uranium 
nitrate were dissolved in a small amount of water; the solution was 
‚evaporated on a water bath till it lost all excess of water. This 
solution of uranium nitrate in its water of erystallization was kept 
for some minutes at the temperature of the room, where it ery- 
stallized forming a compact dry plate. The variation of activity 
with the time was then measured and one of the examples is gi- 
ven in the Table II, where T is time reckoned in hours from the 
moment of erystallization to the measurement. 
Table II. 
T (in hours) B Activity 
0 1310 
2:25 1130 
