362 Mr. Briggs on Distribution of Active Deposits of 



where brush discharge occurred a deposit of smoke was 

 observed. 



Further confirmation of Wellish's conclusion that there is 

 a definite limiting value to the percentage of radium active 

 deposit positively charged was given by the results found f or 

 ethylene. At 720 volts and 20 cm. pressure, using the vessel 

 shown in fig. 1, the value for ethylene was 23'4. Higher 

 values were not obtained at voltages as high as 12,000, using 

 the vessel shown in fig. 2. 



III. The Diffusion of the Neutral Deposit Atoms. 



The experiments were then continued, using the ebonite 

 ring type of vessel, in an endeavour to discover how r the per- 

 centage depended on the nature of the gas. The positively 

 charged atoms which reach the central disks EF or GH 

 'fig. 3) are drawn from gas in the cylindrical volume 

 EFHG. A portion, however, of the neutral atoms produced 

 in this volume will diffuse out of it towards the walls AG 

 and BD. Unless the number that so diffuse is negligible, 

 this type of vessel wall yield values for the percentage 



Fig. 3. 



positively charged that are too high. Wellish * showed 

 that the number of neutral deposit atoms at any point in a 

 cylinder is given by the following equation : 



n=^V>> 



o 



°-q 



1 x z , ■ 



a 1 e n + e 



\nZ 



Jo(^) 



6D n=l X»» e x n l +e- VJi(A.„&) 



where r and z are cylindrical co-ordinates, the origin being at 

 the centre of the cylinder and z being measured along its 

 axis. 



b is the radius of the cylinder, and 21 its length, q is the 

 number of neutral atoms produced per c.c. by the decay of 

 the emanation, and D their diffusion coefficient. 



* Loc. o't. 



