300 
when the hot solution was stirred during crystallization, no in- 
crease of activity at the end of the crystallization was observed. 
It must now be noted that in this case we did not get any decay 
after crystallization. 
We see then that the first rapid decay is the decay of the ex- 
cess of activity produced artificially by erystallization, when the 
latter caused the uneven distribution of UrX throughout the plate. 
This suggests the probability that the decay of 8 activity in 
the first days after crystallization is produced by the diffusion of 
UrX from the upper layers of the plate, where it was in greater 
concentration, to the lower, where its concentration is smaller. Thus 
if we cbserve the decay of activity when the upper surface is turned 
to the electroscope we should expect to see the analogous increase 
when the bottom of the plate faces the electroscope. Experiment 
showed this to be the case. Some of the experimental results are 
shown in Table IV where T gives the time reckoned in hours from 
the moment of erystallization to the eorresponding measurements. 
Table IV. 
8 Activity of the plate B Activity of the plate 
when turned with the when turned with the 
Ah upper surface to the 12 lower surface to the 
electroscope. ”  electroscope. 
0 1840 01 538 
16 1310 16 747 
42 1030 42 731 
68 1010 68 950 
The same experiment made with a very thin plate 
0 760 01 570 
1 740 1 600 
2 730 2 620 
37 720 3:6 630 
45 700 45 650 
23 690 23 680 
In order to completely establish that we here have to do with 
the diffusion of UrX through the plate from the layers of higher 
to lower concentration. the following experiment was made. 
