﻿184 Dr. M. Levin on the Origin of the ft Rays 



which is finally reached. In this case, the time required to 

 reach the maximum is only three to four hours, and in this 

 short time actinium X has not lost 1 per cent. o£ its initial 

 activity. When actinium X is in equilibrium with its pro- 

 ducts three a products are present, namely, actinium X, the 

 emanation, and actinium B. No product analogous to thorium 

 C exists in actinium. This point has been examined by Dr. 

 Hahn working in the same laboratory as the writer. Assuming 

 that each of these products supplies an equal fraction of the 

 total activity, the initial value of the a. activity would be 

 about two-thirds of the maximum, whilst no lower value tiian 

 72 per cent, has been experimentally observed. 



From the measurements of the ft ray activity we must 

 conclude that actinium X does not emit ft rays, but only 

 a, rays, and in this respect is quite analogous to thorium X. 



Since the actinium emanation is in equilibrium with acti- 

 nium X from the beginning of these observations, this ex- 

 periment also shows clearly that the emanation does not emit 

 ft rays. 



Grodlewski concluded that actinium X emitted ft rays, 

 since he was unable to reduce the ft activity to less than half 

 its maximum value by heating to a high temperature. It 

 appears probable that the residues present with his actinium 

 X prevented the escape of the active deposit. Under more 

 favourable conditions, we have seen that all but a few per 

 cent, of the ft rays can be got rid of. 



Since the active deposit of actinium consists of the ray less 

 product actinium A of period of about 36 minutes, and of 

 actinium B period 2*15 minutes, it is to be expected that the 

 ft ray recovery curve should be complementary to the decay 

 curve of the active deposit corresponding to a long exposure 

 to the emanation. This was found to be the case. From an 

 examination of a number of recovery curves, the mean value 

 of the period of actinium A was found to be 36'0 minutes — 

 a value agreeing closely with that found by Bronson, and by 

 Meyer and Schweidler, and by Hahn and Sackur. 



Actinium. 



By means of successive precipitations of actinium by 

 ammonia in order to remove actinium X, Godlewski was 

 able to obtain actinium which was almost free from a and /3 

 rays, and consequently concluded that actinium was a rayless 

 substance. In the course of this research, the experiments of 

 Godlewski were repeated in the manner described by him. 

 The recovery curves of actinium measured by the a, and ft 



