﻿340 



Mr. A. Fleck on the Condensation of 



standard time. The small activity obtained by this last 

 measurement was deducted from all measurements taken at 

 low temperatures. The fraction / of the emanation con- 

 densed is therefore given by the expression 



/= 



A T -A B 



A L -A R ' 



(1) 



where A T , A L , and A E are respectively the activities obtained 

 for immersions of a coil at some low temperature T, liquid 

 air, and room temperatures. The curve obtained by plotting 

 the fraction condensed against the temperature is shown 

 (figure 2, Curve A), and from it, it is evident that the 









Fig. 2. 







S 

 Jo-6 



<3 



sr 

 ■e 







/ 









r 



\ 













o 

 J->- 



*u>^ 











*— S - 



•g — —- 



J J 







-iMf -iso" -ibo" -rjo 



Curve A. Thorium emanation alone. 



-rto° -/90 

 Curves B and C. Mixed emanations : B, radium ; C, thorium. 



thorium emanation is gradually condensed until about 

 — 154° C, at which temperature it becomes completely 

 condensed. 



Mixed Thorium and Radium Emanations. — The object 

 of this preliminary experiment having been attained, the 

 experiment with the mixed radium and thorium emanations 

 was proceeded with. The iron cylinder was exhausted and 

 14 millicuries of radium emanation introduced, after which 

 the pressure was again raised to 10 atmospheres. The 

 cylinder was allowed to stand over night to ensure complete 

 diffusion of the emanation, and the experiment carried out 

 the following day. In this experiment, the current of air 

 carrying emanation was 100 c.c. per minute, and the time of 

 exposure was again 40 minutes at the given temperature. 

 After the exposure, the temperature of the coil was lowered 

 to that of liquid air and kept there for 3J hours, 1. e. until 



