290 Wellisch — Experiments on Active Deposit of Radium. 



withdrawn. The definite period chosen was 4 hours 40 

 minutes. The measurements of the activity were made at a 

 sufficiently long time after removal, so that thenceforth the 

 activity decayed with the period of RaB. 



These experiments were designed to furnish information 

 with regard to the activity accumulating in the gas ; by 

 repeating them from day to day we could ascertain how this 

 gas activity varied as the amount of emanation decreased 

 through disintegration. In addition to these experiments 

 electrodes were often introduced with various potentials 

 applied to the case and allowed to remain for several hours 

 before removal ; their activity was estimated in the same 

 manner as before. Moreover advantage was taken of these 

 long exposure experiments to determine the relative amount 

 of emanation in the vessel. This was accomplished by measur- 

 ing the ionization current by means of a sensitive Siemens 

 Halske galvanometer (4*5 X 10" 9 ampere per cm. when un- 

 shunted) ; in measuring the current a potential of 1000 volts was 

 applied because with potentials of only a few hundred volts 

 there was evidence of abundant recombination, so that with 

 these small potentials the currents would not be proportional 

 to the amount of emanation. 



Two distinct series of experiments were made in this 

 connection ; in each instance about 2J millicuries of emanation 

 were introduced and each series occupied a little over one 

 month. Several hundred measurements of the activity were 

 made under various conditions, but for the sake of brevity only 

 a few results which are most typical are here given (Table II). 

 These, however, are sufficient to illustrate the interpretation 

 which is given later. 



The column headed ' accumulation ' gives the time during 

 which the deposit particles were allowed to accumulate in the 

 gas before the insertion of a central electrode. This time is 

 reckoned from the time of withdrawal of the electrode which 

 had been previously inserted. Exposures referred to as ' long ' 

 were for periods of over twelve hours. 



The point of chief interest in connection with the results 

 of this table is the large amount of deposit which goes to the 

 central electrode with negative potentials applied to the case. 



The results are readily explained on the view that there are 

 present in the gas charged aggregates of active deposit. These 

 aggregates diffuse very slowly and therefore accumulate in the 

 gas so that in the steady state there is a large amount of gas 

 activity. Experiments 15, 16 and 17 in conjunction show that 

 the amount of charged activity in the gas constitutes alone 

 approximately half the total amount of active deposit in radio- 

 active equilibrium with the emanation. The slow rate with 



