Radium, Thorium, and Actinium in Electric Fields. 373 



of AcB. 0£ the original 82 '4 positive A-atoms, 86 per 

 cent, at 600 volts break up before reaching the cathode, 

 and therefore 82'4 x 0*86 x 0'07 or 4'96 become neutral 

 B-atoms. The total number of neutral B-atoms is then 6'19, 

 and since the half-transformation period of AcB is 36 minutes, 

 they all diffuse to the walls and remain there at the ^-trans- 

 formation to AcO. Lucia n found, for the smallest quantity 

 of emanation used, 6*3 per cent, neutral, volume recombination 

 being apparently not entirely absent. At 980 he found 

 values ranging from 5*3 to 5*0, while the value calculated as 

 above is 5*9 ; at 1700 he found 5*1 per cent, neutral, while 

 the calculated value is 5*8. It is to be noted that the neutral 

 B-atoms resulting from the disintegration of positive A-atoms 

 have been carried some distance towards the cathode, and 

 hence the cathode receives a greater percentage of the neutral 

 atoms while the field is on than when there is no field. The 

 values found by Lucian are calculated on the assumption that 

 the cathode receives the same percentage of neutral atoms in 

 both cases, and hence they are too small. Lueian's results 

 are therefore consistent with the general explanation advanced 

 for the distribution of the active deposits. 



IX. Discussion of the Results, 



These experiments confirm Wellish's conclusion that there 

 is a definite limiting value to the percentage of the active 

 deposit initially positively charged in a gas, and that the 

 anode activity is due to the diffusion of neutral uncharged 

 deposit. The latter conclusion is at variance with that of 

 Ratner *, who maintained that the anode activity is due to 

 the carriage to it by an electric ivind of deposit particles which 

 have lost their charge. It is difficult, however, to see how 

 there can be any wind involving the motion of neutral gas 

 molecules or neutral deposit atoms in an enclosed parallel 

 plate vessel such as used in the present experiments. The 

 gas-pressure acting on the two plates is certainly increased 

 as a result of the electric force acting on the positive and 

 negative ions ; but there will be no wind unless these forces 

 are unbalanced, as, for example, if the plates were perforated, 

 or as in the case of discharge from a point. While there is 

 no doubt that many of Ratner's experimental results were due 

 to an electric wind, quite a different explanation is suggested 

 for those made in the glass tube with disk electrodes, and 

 which have most bearing on the present subject. It is possible 

 that the Jarge amount of emanation used per e.c, which was 



* Ratner, Phil. Mag. xxxiv. p. 429 (1917). 

 Phil. Mag. S. 6. Vol. 41. No. 243. March 1921. 2 C 



