438 Experiments on the Active Deposit of Radium. 



Let us now consider what happens after formation of the* 

 deposit atoms, and let us, for convenience in exposition, 

 assume that the emanation is situated in a cylindrical vessel 

 with a central electrode. 



If we wish to bring over to the cathode all the positively 

 charged deposit particles, an electric field must be established 

 of sufficient strength to prevent both the columnar and 

 volume recombination with negative ions to which the 

 particles are subject. In this connexion it should be pointed 

 out that the recombination between these particles and the 

 negative ions is more intense than that between positive and 

 negative ions. As long as the electric field is large enough 

 to prevent volume recombination, the fraction of the total 

 deposit which settles on the cathode is independent of the 

 amount of emanation in the vessel, because if there is now 

 any loss after formation, it is due to columnar recombination, 

 which is conditioned by the value of the electric field. 



With large values of the electric field the neutral deposit 

 particles reach the electrodes by the process of diffusion ; let 

 us now consider the process at work when there is no electric 

 field present or when the electric field is so small that there 

 is considerable volume recombination present in the gas. 

 What happens in these cases depends on the amount of 

 emanation in the vessel. With fairly large quantities of 

 emanation, the active particles which exist in the gas form 

 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 increasing 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 diminution 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 ionization, 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 



