304: Wellitsch — Experiments on Active Deposit of Radiu 



m. 



large aggregates which acquire positive and negative charges 

 from the ions present in the gas ; the aggregates become then 

 of course liable to lose their charge by recombination, but they 

 can then regain it as before, so that on this account a moderately 

 small field is able to bring over to' the central electrode either 

 as anode or as cathode a considerable amount of active deposit. 

 In fact with negative potentials applied to the vessel, the active 

 deposit on the central electrode (anode) increases with increas- 

 ing potential because over a wide range the number of ions 

 present in the gas remains approximately constant ; but when 

 the applied potential becomes large enough to effect a diminu- 

 tion in the number of ions present in the gas the anode activity 

 diminishes. In the circumstances now under review the 

 number of charged deposit particles in the gas is in general 

 greatly increased by the production in the gas of extra ioniza- 

 tion, e. g. by means of Rontgen rays. 



The formation of large aggregates appears to cease abruptly 

 when the concentration of the emanation and the density of 

 ionization sink below certain values ; the deposit particles 

 remaining in the gas may still carry electric charges, but as the 

 emanation decays still further the deposit atoms in the gas are 

 practically all neutral and reach the electrodes through dif- 

 fusion. On this account the general process becomes again 

 the relatively simple one of electric convection and diffusion 

 to which reference has previously been made. 



Under conditions which are such that the deposit atoms in 

 the gas no longer form aggregates nor are charged by means 

 of gas ions their coefficient of diffusion through dry air at one 

 atmosphere pressure and at ordinary room temperature (about 

 20° C.) is approximately -045 ctn2 sec" 1 . 



Sloane Laboratory, 



Yale University, 



June 17, 1914. 



