242 RADIO-ACTIVE EMANATIONS fer: 
exhausted by means of a mercury pump. The amount of emana- 
tion remaining uncondensed after definite intervals was rapidly 
removed by means of the pump, and was carried with a constant 
auxiliary stream of gas into the testing vessel. 





Condensation Curve 
Thorium Emanation 


0 
-100 -110 -120 -130 -140 -150 -160 
Temperature Centigrade 
Fig. 46. 
Tested in this way, it was found that the volatilization poimt 
of the radium emanation was very nearly the same as that ob- 
tained by the blowing method, viz. — 150°C. With thorium, on | 
the other hand, the condensation started at about — 120° C., and, 
as in the blowing method, continued over a range of about 30° C. 
The proportion of the emanation condensed at any temperature 
was found to depend on a variety of conditions, although the point 
at which condensation commenced, viz. — 120° C., was about the 
same in each case. It depended on the pressure and nature of the 
gas, on the concentration of the emanation, and on the time for 
which it was left in the spiral. For a given temperature a greater 
proportion of the emanation was condensed, the lower the pressure 
and the longer the time it was left in the spiral. Under the 
same conditions, the emanation was more rapidly condensed in 
hydrogen than in oxygen. 
