Actinium and Thorium Emanation. 



421 



along the rod and the ordinates the logarithm of the corre- 

 •sponding activity. 



Fio>. 4. 



r°~ ff * 



( &€snjT^rri&bsC4 



Tt will be seen from the last row of Table IV. that the 

 product pressure X diffusion coefficient (P x K) remains 

 sensibly constant, the mean value being 7*85. 



As in the case of actinium emanation no large deviation 

 from ordinary gas laws is observable when thorium emana- 

 tion diffuses into a monatomic gas of comparatively low 

 molecular weight like argon; the experimental value obtained 

 for the diffusion coefficient in this case being very nearly 

 that calculated by means of Graham's law. 



Comparison of Actinium and Thorium Emanation. 



A direct comparison may now be made between the 

 diffusion coefficients of these two emanations, which leads to 

 a ratio of their molecular weights. 



Taking the mean value of PxK for actinium emanation 

 in air as ( .)\34 , and for thorium as 7*85, and dividing each by 

 76 to reduce to atmospheric pressure, we have: — 



Diffusion coefficient of actinium emanation in air '123 _ 1 . 1Q 



Diffusion coefficient of thorium emanation in air "" '103 " 



which gives the ratio: — 



Molecular weight of thorium emanation 

 Molecular weight of actinium emanation 



= d'19) 2 = l-42. 



It is interesting to compare this ratio with that which is 

 obtained by taking the values of the diffusion coefficients of 



