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



It can be seen that the curve o£ fig. 3 conforms to these 

 conditions. 



The relation deduced in (1) shows us that the ionization- 

 current depends not only on q, the speed o£ the air-current, 

 and on W, the volume of the testing-vessel, but also on V y 

 the free volume of the space through which the emanation 

 has to pass before it reaches the testing-vessel. When V is 

 increased, i is decreased ; and, following from the condition 

 for a maximum (2), q must be increased to give the maximum 

 ionization-current. Hence it follows, that in experimenting 

 to compare the absorption by different substances, or by 

 different quantities of the same substance, the free volume 

 between the thorium hydroxide and the testing-vessel should 

 be constant. In the experiments described later, where it 

 was desired to compare the absorption, care was taken to have 

 this condition fulfilled, 



When an absorbing material is inserted between the 

 thorium hydroxide and the testing-vessel, there is less 

 emanation available for ionization and the i-q curve is much 

 altered *. In the case of charcoal, in granulated form, it has 

 been found that the amount of absorption depends on 



(a) The nature of the charcoal, 



(h) The speed of the air-current through the absorbent* 



(<?) The amount of charcoal surface exposed to the* 

 emanation, 



(d) The temperature of the charcoal. 

 In the experiments on these points, the results of which 

 are given later, the i-q curves in the cases of non-absorption 

 were obtained by substituting for the tube containing the 

 charcoal a similar tube containing a non-absorbing sand of 

 the same volume and of the same size grain as the charcoal 

 used. This precaution was necessary in order to have the 

 same volume between the thorium hydroxide and the testing- 

 vessel in the case of non-absorption as in the case of absorption. 

 In all experiments with a given sample of sand or charcoal, an 

 attempt was made to have the grains of uniform size by sifting 

 through a set of sieves and collecting separately the residues 

 caught in the meshes of each sieve. 



(a) Nature of the absorbent. 

 Fig. 5 (Table II.) shows the i-q curves, taken under the 

 same experimental conditions, for the cases of absorption by 

 ordinary wood, animal, and coconut charcoal, all of the 



* The Effect of Temperature and of Velocity of Gas-Current on the 

 Absorption of Radioactive Emanations by Charcoal." R. W. Bovle, 

 Trans. Royal Soc. Canada, May 1907. 



