Radium, Thorium, and Actinium in Electric Fields. 365- 



2 cm. in diameter in the centre of the plate. Plate (2) 

 having been placed on one side of ihe ebonite plate and 

 charged positively, (1) was placed in position opposite it 

 and charged negatively. The air was pumped out and the 

 gas under observation was admitted and pumped out five 

 times, and the pressure finally adjusted to about 15 cm.. 

 The field was then reversed and a stop-watch started. The 

 activation of plate (2) was continued for five minute*, at 

 the end of which time the field was again reversed so that 

 (2) ceased to receive RaB from (1). Piate (2) was quickly 

 removed and plate (3) substituted in its place, and the gas 

 pumped out and replaced by dry filtered air at about 15 cm. 

 pressure. This change could be made within one minute, 

 and when the stop-watch registered six minutes the field was 

 reversed and plate (3) activated for five minutes. When 

 exhausting the vessel, the pressure was not allowed to fall 

 below 1 cm., in order that EaB should not recoil directly 

 on to (2) or (3). The maximum alpha-ray activities of 

 plates (2) and (3) were compared. Since the amount 

 of RaA on CI) falls to one-quarter in six minutes, 



Percentage of RaB positively charged in the gas 

 Percentage of RaB positively charged in air 



maximum activity of (2) 

 4 X maximum activity of (3)' 



The results obtained for various gases are given in column 2 

 of Table II. No alteration in the results was found when air 

 was admitted in the first half of the experiment and the gas 

 in the second half, or when the activity of plate (1), and hence 

 the ionization between the plates, was increased by long ex- 

 posure to the emanation to ten times its usual amount. In 

 these experiments brass plates were used, except for ammonia, 

 acetylene, and hydrogen- sulphide, for which the plates were 

 of mild steel. Their surfaces were cleaned with fine emery 

 paper. 



In experiments on the distribution of tie active deposits 

 of radium and thorium emanations the transference from the 

 anode to the cathode of positively charged RaB or ThB atoms, 

 which were originally neutral RaA or ThA atoms, must be 

 considered. It was accordingly necessary to measure the 

 efficiency of recoil from surfaces similar to those used in 

 the experiments with radium emanation. These surfaces 

 had been cleaned with fine emery paper, except in the case 

 of the bell-jar apparatus, in which, as noted previously, thev 

 were highly polished. 



