vul] RADIO-ACTIVE EMANATIONS 221 
does not at first possess appreciable emanating power. This loss 
of emanating power 1s not due, as in the case of the de-emanated 
oxide, to a retardation in the rate of escape of the emanation 
produced; for the hydroxide, when dissolved in acid, still gives 
off no emanation. On the other hand, the solution, containing 
the Th X, possesses emanating power to a marked degree. 
On leaving the precipitated hydroxide and the Th X for some 
time, it is found that the Th X decreases in emanating power, 
while the hydroxide gradually regains its emanating power. After 
about a month’s interval, the emanating power of the hydroxide 
has nearly reached a maximum, while the emanating power of 
the Th X has almost disappeared. 
The curves of decay and recovery of emanating power with 
time are found to be exactly the same as the curves of decay 
and recovery of activity of Th X and the precipitated hydroxide 
respectively, shown in Fig. 35. The emanating power of Th X, 
as well as its activity, falls to half value in four days, while the 
hydroxide regains half its final emanating power as well as half its 
lost activity in the same interval. 
It follows from these results that the emanating power of Th X 
is directly proportional to its activity, ve. that the rate of produc- 
tion of emanating particles is always proportional to the number 
of a particles, projected from the Th X per second. The radiation 
from Th X thus accompanies the change of the Th X into the 
emanation. Since the emanation has chemical properties distinct 
from those of the Th X, and also a distinctive rate of decay, it 
cannot be regarded as a vapour of Th X, but it is a distinct 
chemical substance, produced by the changes occurring in Th X. 
On the view advanced in section 127, the atom of the emanation 
consists of the part of the atom of Th X left behind after the 
expulsion of one or more a particles. The atoms of the emana- 
tion are unstable, and in turn expel a particles. This projection 
of a particles constitutes the radiation from the emanation, which 
serves aS a measure of the amount of emanation present. Since 
the activity of the emanation falls to half value m one minute 
while that of Th X falls to half value in four days, the emanation 
consists of atoms, which disintegrate at intervals nearly 6000 times 
shorter than do the atoms of Th X. 
