Deposit of Radium in an Electric Field*. 437 



vessel was considered to be sufficiently constant in successive 

 experiments. The measurements were made by means of a 

 Wilson tilted electroscope mentioned above, or a /3 and <y ray 

 electroscope of ordinary type when the activities were too 

 large to be measured by a rays. 



Experiments were first carried out without the additional 

 source of ionization inside the vessel. As was to be expected 

 from the experimental data previously known, in the case of 

 small quantities of emanation the activities deposited on the 

 anode and the cathode were found to be as 1 to 10 approxi- 

 mately, while when large quantities of emanation of the 

 order of several millicuries were introduced into the vessel, 

 the anode activity increased to 60 per cent, ol that concen- 

 trated on the cathode. 



Now, if the anode activity is really due to the uncharged 

 carriers of active matter carried to the anode by the electric 

 wind, we must expect it to increase with the rate of recom- 

 bination of the recoil atoms. For this purpose the additional 

 source of ionization was introduced into the vessel and placed 

 in the middle of the tube A, at equal distances from the 

 electrodes, in which case the electric wind is directed from 

 the middle of the vessel towards both of the electrodes. 

 Under these conditions the anode activity was found to be 

 equal to the cathode activity and the ratio to be independent 

 of the quantity of emanation introduced into the vessel. It 

 has been found also that the sum of the activities deposited 

 on both electrodes is the same with or without the source 

 of ionization in the vessel, which shows the efficiency of the 

 electric wind in carrying the uncharged recoil atoms towards 

 the electrodes *. 



Experiments were also made with the source of ionization 

 placed at one of the electrodes. For this purpose one of the 

 plates P was made active in Wertenstein's exposure vessel, 

 and 30 minutes after was covered with two sheets of thin 

 aluminium foil, the lower sheet protecting the upper from 

 contamination by direct contact with the active surface of the 

 plate. Since the activity deposited on a plate may in some 

 way depend upon the physical conditions of its surface, the 

 other plate was also covered with aluminium foil. The elec- 

 trodes were then introduced into the vessel and exposed to 

 the emanation, the active plate serving as the anode or the 



* In a vessel where large quantities of emanation have been constantly 

 kept for a long- time, the walls are covered with a layer of polonium 

 serving as a strong source of ionization. In such a vessel the anode 

 activity is always equal to the cathode activity. This phenomenon, occa- 

 sionally observed, has led to the present investigation (see sec. 1). 



