﻿Thorium and Radium Emanations. 347 



The tube was kept at room temperature until the active 

 deposit had come into equilibrium, and the 7 activity of the 

 exposed end was then determined as accurately as possible by 

 repeated measurements. Limb A was suddenly plunged into 

 liquid air, and 7-ray measurements were continuously made 

 until the activity became very small, when alternate 7 and /3 

 measurements were made for a time, after which the latter 

 alone were continued. The /3-ray measurements continued 

 to decrease until the activity due to the tube was 6'9 d.p.m. 

 Calculated from the factor obtained when alternate readings 

 were made, it was found that the' tube had an initial /3-activity 

 of 7550 d.p.m., so that taking the ratio of these two values, 

 there is 0*0915 per cent, of the emanation uncondensed in a 

 good vacuum at liquid-air temperature. 



The determination of the condensation curve for the 

 emanation in this tube was then proceeded with. The method 

 was to regulate approximately the temperature registered on 

 the voltmeter by surrounding the wide tube with a cylin- 

 drical flask of liquid air, a stream of air being kept con- 

 tinuously going through the tube. When the temperature 

 was satisfactorily adjusted and the activity ol the experi- 

 mental end had been determined, the liquid-air vessel keeping 

 the emanation condensed in limb A was quickly removed and 

 continuous readings were made with the J3 electroscope for 10 

 to 15 minutes. The temperature was kept constant by altering 

 the volume of air going through the wide tube. Limb A was 

 replaced in liquid air exactly at the end of five minutes, and 

 the increase of activity which had resulted during this time 

 was read off from the curve and then a correction made, as 

 previously explained, to eliminate the effect of the decay of 

 emanation. 



In these experiments, what was actually observed was the 

 quantity of emanation volatilized, in distinction to the earlier 

 ones which gave the amount of emanation condensed. The 

 fraction of emanation volatilized is, therefore, B T /B B where 

 B T is the increase, after correcting for decay, obtained by 

 exposing limb A to room temperature for the standard time 

 when limb B is at the temperature T, and where B R is the 

 increase of activity similarly obtained when both limbs are 

 exposed to room temperature. The fraction of emanation 

 condensed / is therefore given by 



Bt 

 /=1 "B- 



