Actinium in an Electric Field. 547 



All the products after the emanation compose what is known 

 as the active deposit. 



It will be noticed that the determining factor in the distri- 

 bution of the active deposit of actinium is Act. B. Act. A 

 being a short-lived product decays rapidly before any appre- 

 ciable amount of it readies the central electrode, for smaller 

 potentials. In fact it may be shown by calculation, using the 

 following expression for the fraction of the Act. A particles 

 that reach the central electrode, 



A log ^(6 2 - a*)] 

 \ 1 _ e 2Vk 



v ' & a 



where, 



V= applied potential, 



, cm 2 .... . . ... , 



k =1*54- r , mobility of the positive ion, assumed to 



sec. volt' J r ' 



represent approximately the mobility of the deposit particle also. 

 a = '01 5 cm., the radius of the central electrode. 

 b = 2*45 cms., the inner radius of the vessel. 

 A = 350 sec -1 , transformation const, of Act. A. 



that with 600 volts about 25 per cent of the deposit reaches 

 the wire as actinium A, with 1000 volts less than 40 per 

 cent, and with the highest potential used (1700 volts) less than 

 55 per cent. Since, as will be shown later, no increase of 

 potential difference above 1000 volts appreciably alters the 

 percentage of the cathode deposit, it may be assumed that 

 with increasing potentials the increased amount of actinium 

 A on the central electrode has no effect on the distribution of 

 the deposit ; at least, in so far as the final result is concerned. 

 It seems probable, therefore, that actinium A and actinium 

 B are born with the same physical characteristics and exhibit 

 the same peculiarities in an electric held. 



The following experimental results were obtained in connec- 

 tion with the three special objects of investigation mentioned 

 in the introduction. 



First of all, the dependence of the distribution of activity 

 on the amount of emanation employed claimed attention and 

 was made the subject of investigation. It was found that the 

 cathode percentage, which we shall call A v (activity at poten- 

 tial v, referring to the cathode), depended to a great extent on 



