[BOYLE] ABSORPTION OF THORIUM EMANATION BY CHARCOAL 147 



The heating was carried out in a specially constructed oven, the 

 greatest variation of temperature being not more than three or four 

 degrees. 



The air current, after passing thrnueh the charcoal, circulated 

 through a short coil of copper tubing immersed in water, in order to 

 cool the air entering the testing vessel to ordinary temperature. Corres- 

 ponding curves of non-absorption were determined. 



By using a large quantity of cnarcoal it was found that tliere was 

 appreciable absorption up to a temperature of about 300° C, but here 

 the ionization current in the testing vessel began to increase and soon gave 

 the same value as in the case of non-absorption. It was found that 

 the charcoal began to give off carbon dioxide at 211° C, so that the 

 increase of ionization current just mentioned can be explained by the 

 loss of absorbing charcoal bv oxidation, and by the presence of carbon 

 dioxide in the testing vessel. (For a ray ionization the conductivity 

 of carbon dioxide is 1.5 times that of air.) 



TABLE II. (Fig. 4). 

 Multiply current by 616 x 10"^'^ for amperes. 



Sec. III., 1908. 10. 



