[BOYLE] ABSORPTION OF THORIUM EMANATION BY CHARCOAL 143 



there is no absorbing material between the thorium hydroxide and the 

 testing vessel the equation of this ionization current is 





Li-e ^ J, 



where i = the ionization current, 



N = the number of free emanation atoms given off by the thorium 



hydroxide per second, 

 q = the flow of the air current in c.c. per second, 

 V = the total free volume of the conducting tubes between the 



thorium hydroxide and the testing vessel, 

 W = the volume of the testing vessel, 

 K ^ a constant of proportionality. 



This equation shows that the curve with values of i as ordinates, 

 and of q as abscissas, must have such a shape as that of curve I, Fig. 2, 

 or, in other words, the ordinate must rise from zero to a maximum, and 

 ,then fall off to nothipg as the speed of the air current increases in 

 infinity. 



The equation also shows that, in comparing cases of absorption 

 with those of non-absorption, it is necessary to have the free volmne 

 between the thorium hydroxide and the testing vessel a constant in all 

 cases. In the experiments this condition was always, as nearly as 

 possible, fulfilled. 



When the absorbing material is inserted between the thorium 

 hydroxide and the testing vessel, there is less emanation available for 

 ionization, and the ordinates of the i-q curve are considerably reduced.^ 



In the results following the i-q curves, for 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 

 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 for non-absorption as for absorption. 



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

 attempt was made to have the grains of unifonn size by sifting through 

 a set of sieves and collecting separately the residues caught in the meshes 

 of each sieve. 



' Paper already referred to. 



; . 



.r<^\ 



