Deposit of Radium in an Electric Field. 435 



motion o£ radium in an electric field observed by Joly* is a 

 particular case of this phenomenon. 



4. It is clear from the results given in the previous 

 section, that the activity diffusing to the inner surface of the 

 vessel K in the absence of an electric field is exceedingly 

 small compared with the quantity of active matter contained 

 in the vessel and circulating with the electric wind. This 

 may be illustrated by the following experiments. The plate 

 P is exposed to the active atoms in the cube K, the disk Q 

 being placed in a position opposite to it. During the first 

 15 minutes of exposure the plate P is earthed and then 

 raised to a negative or positive potential for a few minutes. 

 The experiments show that the activity acquired by the plate 

 is almost as large as in the case when it is charged during 

 the whole time of exposure. Since during the first 15 minutes 

 the quantity of radium A present on the disk R has decayed 

 to a very small value, it must be supposed that the recoil 

 atoms of radium B were circulating along the apparatus 

 during 15 minutes without diffusing to the walls of the 

 vessel. This is in full agreement with the results of 

 Debierne's experiments on the active deposit of radium f. 

 Experiments on the active matter suspended in a vessel con- 

 taining emanations (see sec. 10) lead to the same conclusion. 

 It must be supposed that neutral carriers of active matter 

 l>ecome readily attached to dust particles or tend to aggregate 

 together, forming thus large particles with a slow rate of 

 diffusion. The formation of large radioactive particles whose 

 distribution is affected by gravity has been observed in a 

 more direct way by Mine. Curie J. 



Mole of the Electric Wind in the Pi % ocess of Distribution of the 

 Active Deposit of Radium in an Electric Field. 



5. It has been shown in the previous chapter that uncharged 

 radioactive atoms are carried by the electric wind to the 

 electrodes independently of the sign of the electric field. 

 A question immediately arises whether the origin of the 

 anode activity may be traced to the same phenomenon. In 

 a vessel containing emanation the density of ionization is 

 large enough to account both for the neutralization of a con- 

 siderable part of the recoil atoms and for the production of 

 an effective electric wind. The fact that the anode activity 



* Joly, Phil. Mag. vii. p. 303 (1904). 



t A. Debierne, Le Radium, vi. p. 97 (1909). 



% Mme. Curie, C. It. cxlv. p. 477 (1907). 



2H2 



