Deposit of Radium in an Electric Held. 433 



As the air in the cube is ionized by the active matter present, 

 it may be supposed that the recoil atoms are carried to the 

 electrode by the electric wind, which in this case o£ uniform 

 density o£ ionization throughout the vessel is directed partly 

 to the plate and partly to the walls of the vessel. On the other 

 hand, the large activity on the electrode P could be explained, 

 if we suppose that neutral atoms of radium B may acquire a 

 positive or negative charge from the ions present in the 

 vessel. The experiments to be described prove conclusively 

 that the first supposition is true. 



A strong source of ionization, such as a small disk Q 

 coated with polonium or radium (B + C)* is introduced into 

 the vessel with the object of producing an electric wind, 

 strong compared with that produced by the active matter in 

 the cube K, and of a desired direction. When the disk Q is 

 placed in a position opposite to the plate P, as shown in the 

 figure, the electric wind is directed mainly towards the plate. 

 In this case the amount of activity deposited on the electrode 

 P was found to become exceedingly large, in some expe- 

 riments 150 times larger than the value without the appli- 

 cation of an electric field, while the walls of the vessel under 

 these conditions acquired only small traces of active matter. 

 When the source of ionization is placed in the centre of the 

 plate P, so as to produce a wind in the direction from the 

 plate to the walls of the cube K, almost the whole activity 

 is deposited on the walls of the cube, the activity of the 

 electrode P remaining very small. It was found that the 

 sign of the charge on the plate P had no influence whatever 

 on the distribution of the active matter in the vessel. The 

 activity of the inner surface of the vessel has been inves- 

 tigated in these experiments by measuring the activity 

 per square unit of small pieces of aluminium foil placed at 

 different parts of the vessel. 



Table I. gives the results of three series of experiments as 

 described above. In column I. the activity of the plate P is 

 given in the absence of an electric field, with or without the 

 additional source of ionization Q in the vessel K; column II. 

 shows the activity of the electrode P, positively or negativel v 

 charged, without the source of ionization Q ; column III. 



* In the case when a disk coated with active deposit of radium is 

 used, sufficient time must he given to radium A to decay before 

 introduction. It was also found necessary to cover the disk with 

 aluminium foil in order to prevent any spreading of the active 

 matter. 



Phil. Mag. S. 6. Vol. 34. No. 203. Nov. 1917. 2 H 



