386 



Mr. R. W. Boyle on the .Absorption of 



The same law holds for the radioactive emanations when 

 absorbed by any kind of charcoal. To examine this point, 

 experiments were carried out at different temperatures with 

 samples of wood, animal, and coconut charcoal. The weight 

 of the coconut charcoal used was about 1*8 gm. 



Temperatures were measured by a Callendar platinum 

 resistance thermometer, the bulb of which was surrounded 

 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. 

 Ear. 8. 



PLRTirvutvi 



GLASS WOOL 



The lowest temperatures mentioned were obtained from a 

 mixture of solid carbon dioxide and ether ; those next above 

 were the temperatures of the room. The remaining were 

 obtained by heating in a specially constructed oven, so that 

 the temperature variation was not any more than three or 

 four degrees. 



The air-current, after passing through the charcoal, was 

 circulated through a short coil of copper tubing immersed in 

 water, in order to ensure that it should not be above ordinary 

 temperature in the testing-vessel. 



For coconut, charcoal curves were taken at five tempe- 

 ratures, viz. 185, 124, 69*5, 17*6, and —75*5 degrees centi- 

 grade. (See fig. 9, Table IV.) 



