

Radium, Thorium, and Actinium in Electric Fields. 369 



It is readily found from the boundary condition, viz. 

 )i — when r— +1, that 



- cosb &) 



ai = ana a 2 = * 



Q 



Let 5 be the fraction of the neutral A-atoms produced 

 in the gas that reaches the central electrodes before trans- 

 forming into B-atoms. Then 



ql 



= ai tanh lr)»> 



Wellish * found 0'045 for the coefficient of diffusion of 

 the neutral deposit atoms of radium emanation in air at 

 atmospheric pressure. He neglected, however, ihe effect 

 of the recoil of RaB during his experiments. On taking 

 this into account, the writer has found that Wellish's results 

 lead to the value O056. Using this value, for RaA in air at 

 atmospheric and at 20 cm. pressure, in the vessel shown in 

 fig. 1, s — 0*978 and 994 respectively. The corresponding- 

 values for ThA are 0'107 and 0'207, and for AcA 0*018 

 and 0"025. At the latter pressure the amount of RaA trans- 

 forming before reaching the electrodes may be neglected. 



VI. Radium A. 



The percentage of RaA initially positively charged in 



c — d 

 a gas may be deduced from the value of 7 found in an 



° J c + d 



experiment in which the gas is mixed with radium emanation, 



and from the percentage of RaB initially positively charged 



at the end of a recoil path in that gas. 



Let a = the fraction of RaA atoms initially positively 



charged. 



b = the fraction of RaB atoms initially positively 



charged. (Column 3, Table II.) 



r = the efficiency of recoil of RaB from the electrodes. 



This number includes both the positive and 



neutral atoms. 



c — d 

 ^!= c and d being the cathode and anode 



activities in an exposure in which the gas is 

 mixed with radium emanation. 

 * Loc. cit. 



