
Heating Ejject of the Radium Emanation. 207 
heat evolved, as we were directly concerned with the initial 
portions of the curves, for which relative values were all that 
were required. Asa check, however, we calibrated one pair 
of the differential thermometers, and founda very close.agree- 
ment for the heat emission of 30 milligrams of pure radium 
bromide, with the value obtained by the air-calorimeter. This 
amounted to a little over 100 gram-calories per hour for 
1 gram of pure radium, which agrees very closely with the 
values given by Curie and Laborde, and later by Runge and 
Precht*. : 
Measurements of Radioactivity. 
In the experiments, the emanation was driven off from the 
radium by heating it, and the emanation was then condensed 
ina small glass tube immersed in liquid air. It was im- 
portant to know how much of the emanation was removed by 
the heating, and how much of the emanation, which was driven 
off from the radium, was collected in the condensing-tube. 
This was done in the following way. 
The tube containing the radium was placed behind a lead 
screen 5 ems. thick, placed near a cylindrical metal electro- 
scope, in which the gold-leaf system was insulated by a 
sulphur bead, after the manner first employed by C. T. R. 
Wilson. The rate of. movement of the charged gold-leaf 
was observed by means of a microscope with a micrometer 
eyepiece. A rapid rate of movement of the gold-leaf was 
observed due to the y rays from the radium after passing 
through the lead screen 5 cms. thick. Preliminary ex- 
periments by one of us, showed that the y rays always 
accompanied the 8 rays from radium and were propor- 
tional in amount to them. If the radium was completely 
de-emanated, after sufficient time has elapsed for the excited 
activity to decay, the y rays, as well as the 8 rays, almost 
completely disappeared. If the radium, four or five hours 
after de-emanation, showed more than 1 or 2 per cent. of 
the original rate of discharge measured by the y rays, it 
was concluded that a portion of the emanation had not 
been removed. The proportion of the emanation left behind 
was in such a case directly proportional to the y rays, 
since the excited activity and consequently the rays left 
behind, after the lapse of four or five hours, is practically 
* Sitz. Akad. Wiss. Berlin, No. 38 (1903). 
+ In the first heating of the radium bromide to a temperature consider- 
ably below that of a red heat, the emanation was completely released. 
A second heating, after the radium had recovered its activity, only 
removed 75 per cent. of the occluded emanation. ‘ 
