x] RADIO-ACTIVE PROCESSES 307 
This result is confirmed by observations on the increase of 
activity of Th X after removal. It has been shown in section 
190 that the activity due to the emanation X, produced from 
the Th X, is equal to ‘44 when the activity of the Th X, together 
with the emanation it produces, is taken as unity. Now the 
activity of the separated Th X and the emanation is equal to 54 
of the total. The proportion of the total activity due to emana- 
tion X is thus 24 per cent., a result which is not very different 
from the value of 21 per cent. obtained previously. It is difficult 
to make an accurate estimate of the activity of the emanation, 
compared with that due to the emanation X. An approximate 
estimate was however made in the following way. 
Some thorium hydroxide enclosed in a paper envelope was 
placed inside a closed cylinder with an insulated central electrode 
kept charged negatively. After an interval of several days, a state 
of radio-active equilibrium was reached, and the ionization was 
measured : 
(1) with the thorium inside the cylinder, and 
(2) with the thorium removed. 
(1) gave the ionization current due to the emanation and the 
emanation X on the central electrode, and (2) gave the current due 
to the emanation X. Taking into consideration that half of the 
radiation from the emanation X was absorbed in the central elec- 
trode, it was deduced that the amount of ionization produced by the 
emanation in the gas was not very different from that produced by 
the emanation X. This result pomts to the conclusion that the 
emanation and emanation X in a thorium compound supply about 
an equal proportion of the total activity. The relative activities 
of the different products are shown in the following table. The 
numbers must only be considered as approximate. 
Residual activity of thorium ... aes es bide 25) fe 
Activity of Th X alone a Ms C00 Bee PAL Ife 
ss » emanation alone ... 48 ae ue 24 °/, 
ss due to first change emanation X ... oe OGis 
” ” second ” ” y= 000 eee 24 us 
Leaving out of account the first change in emanation X, which 
is of a character quite distinct from the others, it is seen that the 
activity is approximately equally divided amongst the products. 
20—2 
