
Heating Effect of the Radium Emanation. 203 
18 per cent., the _non-separable activity 25 per cent., and the 
excited activity 57 per cent. of the total activ ity of radium. 
The excited activity produced on bodies has been shown to 
be due to a deposit of radioactive matter on their surface. 
The term “ excited activity” refers only to the radiations 
from this active matter. It is convenient to have a definite 
name for the matter itself. It is suggested that the name 
“emanation X” be given to it, since fhe matter which causes 
excited activity is produced directly from the emanation. 
This name is given from analogy to the products UrX and 
and ThX, which are produced directly from uranium and 
thorium respectively. On this nomenclature, the radium 
produces the emanation at a constant rate, and this in turn is 
transformed into the emanation X. The matter of emanation X 
of radium itself undergoes at least three and probably four 
successive changes. The nature of these changes and their 
connexion with the radioactivity will be discussed later. 
On heating or dissolving a radium compound in an open 
vessel, the emanation is released and can be entirely removed 
bya current of air. The emanation X, which is non-volatile, 
is left behind with the radium, and it a once commences to 
lose its activity. In the course of a few hours the activity 
due to it has practically disappeared. The 8 and y rays 
which are produced only by emanation X disappear from 
the radium at the same time, and there then remains a 
non-separable activity of radium consisting entirely of a rays. 
At the same time that the emanation X, left behind in 
the radium, is undergoing change, fresh emanation X is 
being produced by the separated emanation, and at such a 
rate that the activity at any time due to the emanation X 
left in the radium, together with that due to the emanation X 
formed afresh by the emanation, is equal to the original 
activity of the emanation X nen up in the radium. 
Since fresh emanation is being continually produced by 
the radium and occluded in it, the activity of the radium after 
falling to its minimum gradually rises again, and in the 
course of about a month has nearly reached its original 
constant value. 
The experiments which will now be described were under- 
taken to see if the heat emission of radium varied in the 
same way as its activity when the emanation was removed. 
For this purpose, the heating effect of the radium was first 
determined. The emanation was then removed from it and 
collected by condensation in a small glass tube, and the dis- 
tribution of the heating effect between the emanation and 
emanation X and the radium was determined, and also the 
