VIII] RADIO-ACTIVE EMANATIONS 241 
compound, and the temperature was observed at the instant an 
appreciable movement of the electrometer was observed. This 
gave the temperature at which a small fraction of the thorium 
emanation escaped condensation, and not the value 7; observed 
for the radium emanation, which gave the temperature for which 
a small fraction of the previously condensed emanation was 
volatilized. 
The following table illustrates the results obtained. 





Current of Gas Temperature | 
Hydrogen _.... “71 G.c. per sec. — 155°C. | 
5 ISHS) eg Ae —159°C. | 
Oxygen a ato ep is TCE | 

On comparing these results with the values obtained for the 
radium emanation, it will be observed that with equal gas streams 
the temperatures are nearly the same. 
A closer examination of the thorium emanation showed, how- 
ever, that this apparent agreement was only accidental, and that 
there was, in reality, a very marked difference in the effect of tem- 
perature in the two emanations. It was found experimentally that 
the radium emanation was condensed very near the temperature 
at which volatilization commenced, and that the points of conden- 
sation and volatilization were fairly sharply defined. 
On the other hand, the thorium emanation required a range 
of over 30°C. after condensation had started in order to ensure 
complete condensation. Fig. 46 is an example of the results 
obtained with a steady gas stream of 1°38 cc. per sec. of oxygen. 
The ordinates represent the percentage proportion of the emana- 
tion uncondensed at different temperatures. It will be observed 
that condensation commences about — 120°, and very little of the 
emanation escapes condensation at — 155° C. 
To investigate this difference of behaviour in the two emana- 
tions, a static method was employed, which allowed determinations 
of the two emanations to be made under comparable conditions. 
The emanation, mixed with a small amount of the gas to be used, 
was introduced into the cool spiral, which had previously been 
R. B.-A. 16 
