Wellisch — Experiments on Active Deposit of Radium. 293 



tinued to pass during the exposure (1 minute) of the electrode 

 and were switched off when the electrode was removed. 

 These experiments were performed only when the original 

 batch of emanation had decayed considerably ; on this account 

 the extra ionization produced by the rays was relatively all the 

 stronger. It will be seen from the table given below that both 

 the positive and negative gas activity were considerably 

 increased as a result of the extra ionization. 



Date 



Duration of 



Potential 





1914 



exposure 



on case 



Activity 



2 June 



1 min. 



— 160 



•15 





1 min. 



— 160 



1-80 X-rays 





1 min. 



+ 160 



1*92 





1 min. 



+ 160 



3'05 X-rays 



In these measurements the activities were measured 25 

 minutes after removal of the electrodes ; the capacity of the 

 electrometer system was only 1/21 of its previous value. 



The second part of Table II is a continuation of the results 

 obtained as the emanation decayed still further. The activity 

 of the central electrode being relatively small is now deter- 

 mined by measurements made 25 minutes after its withdrawal 

 from the emanation, the capacity of the electrometer system 

 however remaining the same as before. The chief point of 

 interest in connection with this table is the rapidity with which 

 the charged gas activity falls off when the amount of emana- 

 tion decays beyond a certain value. In Table I the amount of 

 charged gas activity is approximately proportional to the 

 quantity of emanation in the vessel as measured by the satura- 

 tion current (cf. 2, 16 and 19). If in Table II we calculate the 

 ratio of the gas activity obtained with one minute exposure and 

 — 160 volts to the saturation current, we obtain for the five 

 successive days the following numbers : 



9*65, 9*74, 7-90, 2-62, -50 



A careful examination of all the results obtained indicates that 

 the proportion of charged deposit present in the gas contained 

 in the cylindrical vessel without a central electrode remains 

 approximately constant over a wide range ; but when the 

 emanation has decayed until the saturation current obtained 

 when a central electrode is introduced is about 5*0 X 10" 9 

 ampere this proportion suffers a sudden diminution in magni- 

 tude. A current of 5*0 X 10" 9 ampere implies the produc- 

 tion of 3*23 X 10 10 pairs of ions per second in the vessel and 

 as the volume of the vessel was 326 cc the number (q) of ions 



