IX | EXCITED RADIO-ACTIVITY 279 
for the first few hours after removal, is due to the excited activity 
produced by the emanation on the walls of the containing vessel. 
Some experiments were recently made by H. T. Barnes and 
the writer! on the division of the heating effect of radium between 
the successive products of radium. For measurement of the 
heating effects, a pair of differential platinum thermometers, 
wound spirally in the inside of a glass tube, were used. The 
radium or its emanation, enclosed in a fine glass tube, was 
placed inside the platinum spiral and the rise of temperature 
observed. 
The heating effect of 30 milligrams of radium bromide was 
first determined. The emanation was then removed from it by 
heating, and condensed in a small glass tube. The heating effect 
of the de-emanated radium was determined ten minutes after the 
removal of the emanation, and was found to have diminished to 
59 per cent. of its original value. It then diminished more slowly 
with time to a minimum corresponding to 25 per cent. of its 
original value (see section 106). 
The curve of diminution with time of the heating effect of 
radium to the minimum of 25 per cent. should be identical with 
the corresponding curve of diminution with time of the heating 
effect of the emanation tube to zero after removal of the emanation. 
This was found to be the case. The emanation was allowed to 
remain for several hours in a small glass tube in order that the 
excited activity should reach a maximum value. The emanation 
was then rapidly withdrawn from the tube, and the heating effect 
of the tube determined at regular intervals. ‘There was a similar 
initial drop within the first 10 minutes, then a slower variation, 
and finally a decrease to zero according to an exponential law with 
the time, falling to half value in about 30 minutes. 
The curve of increase of the heating effect of the emanation 
tube to a maximum after the introduction of the emanation was 
found to be complementary to the curve of decrease of the heating 
effect to zero after withdrawal of the emanation. It was not found 
possible to separate the heating effect of the emanation itself 
from the first rapid change in emanation X, since temperature 
1 Phil, Mag. Feb. 1904. 
