Active Deposit of Radium in Electric Fields. 549 x 



apparatus o£ the same dimensions using actinium emanation 

 is also given *. The anode activity being due to uncharged 

 deposit, it consequently follows that the loss of: charge of the 

 active deposit of radium for small values of time is directly 

 proportional to the time taken for the active deposit to get 

 on to the wire. In other words, the positively charged 

 radium A atoms are subjected to recombination, and at 

 exactly the same rate as the atoms of actinium A under 

 similar conditions. In conjunction with the observations of 

 Schmidt f and others, this indicates that a positively charged 

 atom of radium A behaves exactly like any other positive 

 ion produced in the same enclosure. It has exactly the 

 same chance of recombination and the same mobility. 



The anode activity in the case of radium consists there- 

 fore of two parts, a constant proportion of uncharged deposit 

 which varies only with the dimensions of the apparatus, and 

 is unaffected by changing the strength of the electric fields, 

 and a portion which is due to the diffusion of those atoms of 

 active deposit which have recombined before renching the 

 cathode under the influence of the electric field. The latter 

 is a variable quantity depending only on the strength of the 

 field employed. The behaviour of radium and actinium 

 active deposits in electric fields only differ therefore in the 

 initial activity which is found in the case of radium. There 

 is some evidence which seems to show that this has been 

 derived from an initially uniform distribution of uncharged 

 radium A. 



It has been shown that the chemical and physical properties 

 of the emanations and of the B and C products of radium, 

 thorium, and actinium are very similar. One might there- 

 fore expect the same similarity to hold in the case of the A 

 products. On these grounds the anomalous behaviour of 

 radium would be attributed to a secondary effect, some in- 

 trinsic property of radium A, which is not manifested in the 

 case of actinium A on account of its short life. Thorium A 

 also has a very short period, so that the effect would not be 

 noticeable at all in the case of thorium active deposit, or only 

 to a slight extent. The evidence available supports this 

 view. 



To explain the constancy of the anode activity, Wellisch % 

 employs the well-known fact that recoil atoms produce an 

 intense ionization throughout their range §, where their 



* Walmsley, Phil. Mag. xxvi. p. 388 (1910). 

 f Schmidt,' Phys. Zeit. ix. p. 184 (1908). 

 t Loc. cit. 

 § Wertenstein, Le Radium, p. 6, Jan. 1912. 



