a particles from 1 honum and Actinium Products. 649 



ground-glass ring SS ; the latter fitted air-tight over a ground- 

 glass plate FF, thus forming a shallow circular box FSSF 

 (see fig. 1), just large enough to hold the active film. A 

 small hole was drilled through the centre o£ the glass plate 

 FF to allow the gas to escape from the box when the pres- 

 sure in the bell-jar BB was reduced. Since the glass plate 

 on which the active matter was deposited and the plate 

 forming the base of the box were in close contact no 

 measurable amount of emanation could escape while measure- 

 ments were taken, On account of the very slow escape of the 

 gas from the box it was necessary to exhaust, and readmit 

 the air, very slowly to prevent breakage of the mica. 



Fte. 2. 











































\J 



A 

















1^ 



/ 



A 

















1/ 



/ \ 



\ V 



% 















S\ 



v 



\ 















A 



>\ 



1 



*<>"> 



s*\ 



\ 











\ 



it 







\ 



3 4 5 6 



Range of <x particles /a/cms. 



Curve I. = o particles from Th X, Th Em., Th A, Th C 15 Th C 2 . 

 II. „ „ Th X, Th Em., Th A. 



III. „ „ ThX,ThEm. 



IV. „ „ ThX. 



V. 



Th C\, Th C 2 



The thorium X was obtained from radiothorium, and a 

 very thin film of high activity was prepared. Two days 

 were allowed to elapse before measurements were taken, so 

 that the active deposit might attain equilibrium with the 

 thorium X. The ionization curve was then determined as 

 described above, and is shown by Curve I. of fig. 2. To 

 deduce the ranges of the products composing Curve I., 



