_ ne 
= ‘ 
162 RATE OF EMISSION OF ENERGY [CH. 
The emanation from the 30 milligrams of radium bromide was 
then removed by heating the radium (section 141). By passing the 
emanation through a small glass tube immersed in liquid air, the 
emanation was condensed. The tube was sealed off while the 
emanation was still condensed in the tube. In this way the 
emanation was concentrated in a small glass tube about 4 cms. 
long. The heating effects of the “de-emanated” radium and of the 
emanation tube were then determined at intervals. It was found 
that, after removal of the emanation, the heating effect of the 
radium decayed in the course of a few hours to a minimum, 
corresponding to about 30 per cent. of the original heat emission, 
and then gradually increased again, reaching its original value after 
about a month’s interval. The heating effect of the emanation 
tube was found to increase for the first few hours after separation 
to a maximum, and then to decay regularly with the time according 
to an exponential law, falling to half its maximum value in about 
four days. The actual heat emission of the emanation tube was 
determined by sending a current through a coil of wire occupying 
the same length and position as the emanation tube. 
The variation with time of the heating effect from 30 milli- 
grams of radium and the emanation from it is shown in Fig. 32. 
Heat Emissions in Gram Calories per Hour 




Hours 
Fig. 32. 
