﻿Thorium and Radium Emanations. 341 



the radium active deposit had come into equilibrium with 

 the condensed emanation and the thorium active deposit had 

 reached its maximum activity. The coil was then warmed, 

 and the radium emanation in it displaced by a stream of 

 fresh air. 7-ray measurements were immediately commenced 

 and continued for at least three hours, after which the 

 activity obtained is solely due to thorium active deposit. 

 By multiplying this quantity by the factor 1*119 the value 

 of the maximum activity of the thorium active deposit is 

 obtained. When this latter quantity is subtracted from the 

 initial activity, the remainder gives the effect due to radium 

 emanation alone. The experiment is repeated, of course, 

 for liquid air and room temperatures, and the fraction of 

 the emanation condensed, both in the case of radium as well 

 as of thorium, is obtained by substituting in expression (1). 

 The experiments for the points shown in the curves were 

 carried out in the course of a few hours, so that the radium 

 emanation had not materially decayed while they were in 

 progress. 



Curve B (figure 2) is that obtained for the condensation 

 of radium emanation, and curve C that for thorium 

 emanation. 



It is seen that the two curves are quite distinct, thorium 

 emanation being apparently more easily condensed than the 

 radium emanation. It has to be noticed, however, that the 

 form of the two curves is the same, while Rutherford and 

 Soddy found that when tested separately their shapes were 

 different. It has also to be observed that the speed of the 

 gas-stream influences the position of the condensation curve, 

 in the case of thorium the curve is displaced to the right by 

 increasing the amount of gas passing through the coil per 

 minute. It is thus evident that the exact temperature at 

 which the emanations condense depends to a large extent on 

 the physical conditions prevailing during the experiment. 



There must also be considered the effect of the vapour 

 pressures of the condensed emanations. It is well known 

 that even at the temperature of liquid air, radium emanation 

 has an appreciable vapour-pressure, and we can assume that 

 thorium emanation will likewise have that property. In 

 the case of radium emanation the vapour phase will be 

 continually swept away, while in the case of thorium the 

 condensed emanation quickly changes into the active deposit 

 which remains. Assuming for the moment that the two 

 emanations have the same condensing point, there would be 

 found relatively more thorium active deposit than radium 

 active deposit. Consequently the thorium emanation would 



