﻿Thorium and Radium Emanations, 



339 



atmosphere, while the other was connected to a copper spiral 

 made of tube of an internal diameter of 2 millimetres. The 

 end of the spiral was also connected to the outer atmosphere. 



Fig. 1. 



| 0«xt«r 

 Atmosphere 



J s 



A 



In the hollow of the spiral there was a vertical stirrer 

 driven by an electric motor, and the whole was enclosed by 

 a wide test-tube which contained pentane, cooled externally 

 by liquid air. The temperature was measured by a 

 previously calibrated iron-eureka couple, the hot junction 

 being kept at the temperature of melting ice. 



Thorium Emanation alone. — The first experiments that were 

 made were with thorium emanation alone. Air was pumped 

 into A with the help of the liquid air machine until the 

 pressure was equivalent to that of 10 atmospheres. A constant 

 air-stream of 60 c.c. per minute was maintained across the 

 radio-thorium, the gas being sent direct to the atmosphere, 

 while the temperature of the pentane was adjusted to some 

 constant value. When the temperature had been fixed, the 

 air containing thorium emanation was then diverted through 

 the copper spiral and allowed to flow for 40 minutes. The 

 gas-stream was then stopped, the coil removed from the bath 

 and its <y activity measured until the thorium active deposit 

 had attained its maximum after, approximately, three and a 

 half hours. The experiment was repeated, using a fresh 

 coil, for an immersion at liquid air temperature, and, again, 

 with the coil maintained at room temperature for the 



Z2 



