Transformations in the Active Deposit of Actinium. 695 



a particles were present. It is obvious, moreover, that the 

 difference between the curves is much more than could be 

 accounted for by such a small fraction of long-range 

 a. particles as found above ; indeed these particles would 



Fiff. 3. 



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have no detectable influence on the ionization curve as 

 ordinarily determined. Consequently we have repeated the 

 experiments and determined the ionization curves for polo- 

 nium, actinium C, radium C, and thorium C. Our expe- 

 riments do not confirm her results, yet they have brought to 

 light some interesting points in connexion with ionization 

 curves, and they will therefore be described at length. 



The apparatus used is shown in fig. 4, and is essentially the 

 same as the well-known Bragg apparatus, except that the 

 source was moved by a ground-glass joint J instead of through 

 a stuffing-box. The source S was placed in a narrow brass 

 tube T which could be moved vertically inside the wide glass 

 tube. Consequently a narrow pencil of a. particles was 

 directed normally through two wire gauzes Qx l and Gr 2 on to 

 the electrode. G^ was connected to the brass cylinder C 

 which was also connected to earth. Gr 2 was insulated from 

 C by a ring of mica, and was connected to a battery of 

 320 volts, the other terminal of which was earthed. The 

 electrode D was connected to a sensitive Wilson-Rave 



