vill] RADIO-ACTIVE EMANATIONS 239 
0° and —192°C., cutting the temperature axis if produced nearly 
at the absolute zero. The resistance of the spiral, deduced from 
Millivoltmeter Ammeter 
To Earth 

readings on an accurately calibrated Weston millivoltmeter, with 
a constant current through the spiral, was thus very approximately 
proportional to the absolute temperature. The liquid ethylene was 
kept vigorously stirred by an electric motor, and was cooled to any 
desirable temperature by surrounding the vessel with liquid air. 
The general method employed for the radium emanation was 
to pass a suitable amount of emanation, mixed with the gas to be 
employed, from the gas holder B into the spiral, cooled below the 
temperature of condensation. After the emanation was condensed 
in the spiral, a current of electrolytic hydrogen or oxygen was 
passed through the spiral. The temperature was allowed to 
rise gradually, and was noted at the instant when a deflection of 
the electrometer, due to the presence of emanation in the testing 
vessel 7, was observed. The resistance, subject to a slight correc- 
tion due to the time taken for the emanation to be carried into 
the testing vessel, gave the temperature at which some of the 
emanation commenced to volatilize. The ionization current in 
the testing vessel rose rapidly to a maximum value, showing that, 
for a small increase of temperature, the whole of the radium 
emanation was volatilized. The following table gives an illustration 
