[KENNEDY] ACTIVE DEPOSIT FROM ACTINIUM 55 



II. Apparatus. 



The apparatus consisted of a metallic cylinder about 5.5 cms. in 

 diameter which was supported horizontally in an air-tight chamber. 

 Into this cylinder (as shown in Fig. 1) there were fitted two electrodes 

 provided with guard plates. The salt was carried in a small tray which 

 could move freely up and down in a vertical tube (1.5 cms. in diameter) 

 which led into the cylinder. The tray could be clamped in position at 

 any desired distance from the electrodes, and the latter, which were 

 capable of easy motion, could readily be placed in the exposing cylinder 

 at any selected distance apart. The air-tight chamber was also provided 

 with tubes for the admission and removal of the different gases used, 

 and through its base, wires suitably secured were led for the purpose of 

 charging the electrodes. The electrodes, which were circular, were 2.5 

 cms. in diameter and the guard-plates which surrounded them were each 

 .5 cms. in width. 



III. Measurements. 



In the various experiments which are to be described later, the 

 sample of aitinium used was obtained from the Chininfabrik, Braun- 

 schweig. In making the exposures the electrodes were exposed in every 

 case to the action of the emanation for two hours before being removed 

 from the exposing vessel for measurement. The activities of the elec- 

 trodes were tested by an ordinary alpha ray gold leaf electroscope, and 

 all the values which are quoted in the paper represent the activities of 

 the electrodes 10 minutes after the exposures ceased. In making the 

 measurements of the activities of the two electrodes, observations were 

 continued for a period of forty or fifty minutes. From these observa- 

 tions, of which Fig. X is illustrative, the rates of decay of the deposits 

 on both anode and cathode were found to be the same, and to be ap- 

 proximately about 39 minutes. In making all the exposures the elec- 

 trodes were charged to a potential of approximately 250 volts. 



IV. Active Deposits and Distance Between the Electrodes. 



In commencing the study of the active deposits from actinium, a 

 set of measurements was made on the active deposits obtained on the two 

 ^electrodes when the salt was placed in the vertical tube at a constant 

 distance from the cylinder and the electrodes were gradually separated. 

 In a particular set of observations the plates were placed vertically 1 mm. 

 apart, and the salt was brought as close to them as the construction of 

 the apparatus would permit. With this arrangement, the salt which was 

 always covered with a layer of thin filter paper, was at a distance of 11 

 mms. from the lower edge of the plate electrode. 



