146 



ROYAL SOCIETY OF CANADA 



The experiment shows tliat it is not the mass of the absorbent on 

 which the amount of absorption depends, ])ut rather the amount of sur- 

 face which the mass of charcoal exposes to the emanation. Of course, 

 by increasing the quantity of charcoal of a given size grain the amount 

 of absorbing surface is also increased and consequently there is increased 

 absorption. 



(b) Temperature of the Charcoal. 



Tlie paper referred to before showed that the absorption of thorium 

 emanation gradually decreased as the temperature of the cocoanut char- 



/JSBCS roS AND 



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CHflftCO/iL 



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coal was raised, and indicated tliat there was a possibility of the charcoal 

 not absorbing at all at 310° C. 



To test the latter point an experiment was performed in which obser- 

 vations of the ionization current in the testing vessel were taken as the 

 temperature of the charcoal was gradually raised, the velocity of the 

 air current being kept constant. The temperatures were measured by a 

 Oallondar platinum-resistance thermometer, the bulb of which was sur- 

 rounded by the charcoal. The stem of the thermometer was sealed 

 into the tube containing the charcoal by an asbestos and plaster of 

 Paris packing, so that the joint was perfectly air-tight. The diagram 

 shows the arrangement (Fig. 3). 



