tlie Active Deposit of Radium. 



4,27 



of charged aggregates of active deposit *. Experiments 16 

 and 17 or 20 and 21 show that the amount of positively 

 charged gas activity is slightly greater than the amount 

 which is negatively charged ; the ratio is roughly the same 

 as that o£ the mobilities o£ the negative and positive gas 

 ions ; in other words, the amounts of positive and negative 

 activity are roughly in the same proportion as the numbers 

 of positive and negative ions present in the gas. 



More direct evidence that the aggregates acquire their 

 charge from the ions present in the gas is furnished by 

 investigating the effect produced by causing Rontgen rays 

 to pass through the gas. A beam of fairly intense Rontgen 

 rays passed through the aluminium bottom of the vessel for 

 about 15 minutes before the introduction of the electrode ; 

 the rays continued 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 

 onization. 



Date 

 1914. 



Duration of 

 Exposure. 



Potential 

 on case. 



Activity. 



2 June... 



1 in in. 



-160 



•15 





1 min. 



-lfiO 



1-80 Xrays 





1 min. 



+160 



1-92 





1 min. 



+ 160 



305 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 connexion with this table is the rapidity with 

 which the charged gas activity falls off when the amount of 



* Of course the charged aggregates also suffer recombination, but they 

 acquire a fresh charge from the ions present in the gas. 



