154 THE ROYAL SOCIETY OF CANADA 



pains were taken to see that the collecting bottles were clean. In 

 collection two methods were adopted. In most cases five gallon water 

 bottles were used and the gas collected by water displacement. When 

 full the bottle was securely sealed by an indiarubber stopper and 

 efiicient metal clasp. In some cases where the gas pressure was 

 considerable and where a large quantity of gas was wanted large steel 

 cylinders were employed. These were filled up to rock pressure 

 and blown off several times in succession depending on the value of 

 the pressure. The remaining air would not be more than one in ten 

 thousand of the whole gas. The date and time of collection of the 

 gas were noted as in some cases days elapsed between collection in 

 the field and testing in the laboratory. 



All the radioactive measurements and calculations were made 

 by Dr. Satterly in the Physics Building of the University of Toronto. 

 The methods used were very similar to those used by him in his 

 earlier work* on the radioactivity of gases and in his Canadian work 

 with Mr. R. T. Elworthy*on the radioactivity of the mineral waters 

 of this country 



At the same time the gases were subjected to a brief further 

 examination. Fractional condensation was carried out with liquid 

 air to see how much of the gas was uncondensed at about — 185°C. 

 This residue is chiefly nitrogen. It was, however, further treated 

 to find the percentage of helium in the original gas. The details of 

 this work will be found in a larger paper. 



Principles of the Methods Used for the Measurement of the Radio- 

 activity of a Gas. The gas issuing from the ground will usually con- 

 tain both radium and thorium emanations, but the latter has such a 

 short average life (about a minute and a half) that it quickly decays 

 into insignificance. The average life of radium emanation is much 

 longer. In four days it has dropped to half its initial value and after 

 twenty-five days there is still one per cent left. Unless, therefore, 

 the gas is tested as it issues the radioactivity measured is due solely 

 to radium emanation and it is the amount of this emanation per litre 

 of the gas that is the subject of» discussion in this paper. 



The amount of emanation is usually deduced from the increased 

 conductivity of the gas containing it over the conductivity of normal 

 air. This conductivity is measured in a ionisation vessel fitted 

 with a gold leaf electroscope. The details of almost the identical 

 apparatus will be found in the paper by Satterly and Elworthy men- 

 tioned above. The gold leaf is charged and its rate of fall over a 

 definite part of a microscope scale observed. This rate of fall or 



*See references at end of paper. 



