376 Prof. J, C. McLennan on Diffusion of Actinium 



of the emanation, varies inversely as the square of the pressure 

 of the gas into which it is diffusing;, i. e., that 



K 1= A'//, 



then we have ^ a - P v a l x 



r = —.1=. pe a x . 



and with the condition of maximum deposit -=— =0 applied 

 we have **p 



<\/±*=i, 



or _ /Ail 



^=Vxr,> ( 2 ) 



which is the law observed by Kennedy. 



There seems no sufficient reason, however, for assuming 

 the inverse square law for the coefficient of diffusion of the 

 emanation, and it would seem, therefore, that we must look 

 elsewhere for an explanation of the discrepancy. 



In the argument presented above we have tacitly assumed 

 (1) that g, the rate at which the emanation leaves the salt, 

 is the same for all pressures, and (2) that a direct propor- 

 tionality exists between the concentration of the positively 

 charged active deposit particles and the concentration of the 

 emanation, for all pressures of the gas in which the emanation 

 is diffusing. 



If the active deposit particles became positively charged 

 directly in the process of their creation from the emanation, 

 then such an assumption as the latter might be warrantable. 

 If, however, these deposit particles gain their charge from 

 the ions produced in the gas by the radiation emitted by the 

 emanation in the process of transformation (as would seem 

 to be true from the results of Schmidt*), then a factor de- 

 pending on the pressure of the gas should be introduced into 

 the relation connecting the concentration of the emanation 

 and that of the positively charged active deposit particles at 

 any point. For the concentration of the emanation at a 

 distance x from the salt, assuming K 1 =A 1 /p, we have, as 

 shown above, 



P 



_ gy^ ~ V£ P .. 



~e 



\AiAi 



Let now D be the concentration at the same point of the 

 * Phys. Zeit. 9 Jahr. No. 6, p. 184, 1908. 



