the Active Deposit of Radium. 

 Table I. 



419 



Pressure. 



Potential. 



Percentage deposit 



mm. 



volts. 



on central rod. 



82 



• +750 



91 



87 



-750 



9-2 



82 



-160 



96 



88 



- 20 



9-2 



89 



+ 20 



100 



89 



-160 



92 



93 



+ 4 



10-4 



80 



- 2 



101 



87 







103 



above series ; however, the assumption was there made that 

 the neutral particles were distributed on the central rod 

 and the case in the proportion of the areas exposed. This 

 assumption is not justifiable ; it is in fact easy to obtain a 

 theoretical expression which will give approximately the 

 relative distribution on rod and case which results from the 

 process of diffusion. 



Let us consider a cylindrical condenser of infinite length, 

 the radius of the inner electrode being a, and that of the 

 outer b. 



Let q be the number of deposit particles that are produced 

 per c.c. per second in the gas as a result of the disintegration 

 of the emanation. 



Let n be the number of deposit particles present per c.c. in 

 the gas at a region distant r from the axis. 



Let D be the coefficient of diffusion of the deposit 

 particles. 



Then, if there be no applied electric field, we will have, 

 using cylindrical coordinates, as the equation for the steady 

 state 



T./d 2 n 1 dn\ 



D -J-V+ — — )=— q 



\a?" r ar ] ± 



The solution of (1) is given by 



w=«-^r 2 +C 1 logr + C Sl 



(1) 



(?) 



where (Ji and C 2 have yet to be determined. 



Inasmuch as the deposit particles adhere to the exposed 

 solid surfaces, the concentration in the gas will be zero in the 

 vicinity of the metal, i. t. n = for r = a and r = b. 



2E 2 



