﻿emitted by Thorium and Actinium. 



185 



rays, after separation of actinium X, are shown in fig. 3*. 

 The period of actinium X deduced from the recovery curves 

 was about 10 days; a value closely agreeing with that originally 

 found by Godlewski, and later by Meyer and Schweidler. 



100 



80 



. 60 



" 40 



20 





A X 



^^> 







, — — — i 





I 1 















/ y ' 



< 



























f 















10 



20 



8(> 40 



Time in days. 



:»() 



60 



70 



From the small initial value of the /3-ray curve, it is seen 

 that actinium does not emit j3 rays. In other experiments 

 the initial /3 activity was between 3 and 5 per cent, of the 

 final maximum. 



There is, however, one marked point of difference between 

 my results and those obtained by Godlewski. We have seen 

 that the latter found that actinium freed from actinium X 

 showed very little a ray activity, while in my experiments 

 the a ray activity could not be reduced to less than about 

 2S per cent, of its maximum value. The cause of this dis- 

 crepancy was at first very puzzling, and an account of the 

 experiments may be given that have been made to clear up 



* The measurements of the activity were made twice a day at the 

 beginning of the recovery curve aud daily towards the end. Only a few 

 points are reproduced in the tig-are to show the general accuracy of the 

 measurements. There was, on several occasions, a sudden irregularity 

 in the activity of the preparation, which could not be accounted for by 

 supposing it to be due to errors of measurement, for the value found for 

 the activity of a standard preparation of uranium oxide tested under the 

 same conditions showed no variation. Similar alterations have been 

 noted bv Godlewski. 



