
Heating Effect of the Radium Emanation. 215 
Increase of Heat Emission after the Introduction of the 
Emanation into a Tube. 
If the total rate of heat emission is not altered by the 
transfer of the emanation from the radium to the emana- 
tion-tube, the curve showing the rise of heating effect of the 
emanation-tube should be complementary to the curve show- 
ing the decrease to a minimum of the heating effect of the 
radium after the removal of the emanation. This was found 
to be the case. The results are shown in fig. 6, curve A”. 
As the emanation-tube, during the condensation, was cooled 
to the temperature of liquid air, it was not feasible to take 
observations on its heating effect after such a short interval 
as in the case when the emanation was withdrawn without 
changing its temperature. The results, however, showed 
that the heating effect of the emanation-tube was about 75 
per cent. of its final value, after the emanation had been 
introduced into the tube 35 minutes. Over the range of 
observations, the curve of rise of the heating effect of the 
emanation-tube and curve of decrease of the heating effect 
of the emanation-tube, after withdrawal of the emanation, are 
complementary to one another. If the curves are plotted on 
the same scale the sum of the ordinates of the two curves, at 
any time, is constant. 
Discussion of Results. 
It has been shown in figs. 5 and 6 that there is a very 
sudden drop of the heating effect observed for both the 
emanation-tube and the radium after removal of the emanation. 
for the purpose of comparison, the decay curve of the activity 
of radium after removal of the emanation is plotted alongside 
the curve of decrease of the heating effect of radium (see 
fig. 5, curve A). It is seen that immediately after removal 
of the emanation there is a sudden drop of the activity to 82 
per cent. of the maximum value. This shows that the radia- 
tion from the emanation supplies about 18 per cent. of the 
total activity of radium, measured by the a rays. There then 
follows a fairly rapid decrease for 6 to 8 minutes, and then a 
more gradual decay to a minimum of 25 per cent. This 
rapid variation of the excited activity for the first few 
minutes is due to the fact that the first change in emanation 
X takes place very rapidly. The effect of this first change is 
clearly shown when a rod is exposed for a very short interval 
in the presence of the radium emanation. Onremoval of the 
* Three sets of curves were obtained, of the increase of the heating 
effect after introduction of the emanation, and of the decrease of the heating 
effect after removal of the ermanation. The curves in all cases were in 
good agreement. 
