Active Deposit of Actinium in an Electric Field. 760" 



consistent direction, as one would be led to expect from 

 the consideration of the different shapes of the bottoms. 

 Evidently the high velocity of the air stream helped to 

 smooth out the irregularities that would be expected at 

 lower pressures. Finally the curved gauze, shown in the 

 diagram, was adopted in order to match up with the curva- 

 ture of the corners. It will be noticed that the distance of 

 the electrode from the gauze is adjusted so that the average 

 electric intensity at the bottom of the vessel would not by 

 any chance be smaller than in the body of the vessel. 



III. Experimental Results. 



Before giving the experimental results of this investigation 

 it may be useful to recapitulate the transformations which a 

 quantity of emanation undergoes, according to our present 

 state of knowledge. 



The complete scheme of transformation, after Marsden and 

 Perkins*, is as follows: — 



fl 



«(57cm 3 .) a (6.5) /3 



All the products after the emanation compose what is known 

 as the active deposit. 



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

 tribution 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 reaches 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, 



2Yk 



Xlog — (b- — a-) 

 a a 



1 ^ J-- c 2V* 



(7> 2 -a 2 )Xlog 



a 



} 



* E. Marsden and Dr. P. B. Perkins, Phil. Mag. vol. xxvii., April 

 1914. 



