Wellisch — Experiments on Active Deposit of Radium. 303 



of the vessel. The values of this fraction are for air,* hydro- 

 gen and carbon dioxide respectively 88*2, 88'2 and 78*9. 

 When the emanation is mixed with ethyl ether practically all 

 the deposit particles are neutral. 



In a previous paper the view was put forward that the dis- 

 tribution of charge among the deposit particles had its origin 

 in the motion of recoil of these particles when expelled from 

 the atoms of emanation. The recoil atom during its motion 

 produces a large number of ions and in all probability is 

 ionized itself so that it acquires a positive charge ; however 

 it is always liable to lose its positive charge by collision with an 

 electron and all the more readily in the case of those gases or 

 vapors such as carbon dioxide and ether where the electrons 

 do not quickly leave the columns.f The general effect to be 

 expected from such a process is that when the deposit particles 

 are brought to relative rest among the gas molecules there will 

 be a definite fraction positively charged, the remainder being 

 neutral. 



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 connection 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 



*It is of interest to record here that Lucian has found the number 94'9 

 for the fraction of the deposit particles of actinium -which are formed 

 with a positive charge in air. 



fCf. Wellisch and Woodrow, this Journal, xxxvi, p. 214, Sept., 1913. 



