166 PHYSICS OF THE ELECTRON 



The curve expressing the recovery with time of the heating effect 

 of radium from its minimum is complementary to the curve express- 

 ing the diminution of the heating effect of the emanation tube with- 

 time. The curves of decay and recovery agree within the limit of ex- 

 perimental error with the corresponding curves of decay and recovery 

 of the activity of radium when measured by the a rays. Since the 

 minimum, or non-separable activity of radium, measured by the a 

 rays, after the emanation has been removed, is only one quarter of 

 the maximum activity, these results indicate that the heating effect 

 of radium is proportional to its activity measured by the a rays. It 

 is not proportional to the activity measured by the /? or f rays, since 

 the /? or f ray activity of radium almost completely disappears 

 some hours after removal of the emanation. 



These results have been confirmed by further observations of the 

 distribution of the heat emission between the emanation and the 

 successive products which arise from it. If the emanation is left for 

 several hours in a closed tube, its activity measured by the electric 

 method increases to about twice its initial value. This is due to the 

 "excited activity," or in other words to the radiations from the active 

 matter deposited on the walls of the tube by the emanation. The 

 activity of this deposit has been very carefully analyzed, and the 

 results show that the matter deposited by the emanation breaks up in 

 three successive and well-marked stages. For convenience, these suc- 

 cessive products of the emanation will be termed radium A , radium B, 

 and radium C. The time T taken for each of these products to be half 

 transformed, and the radiations from each product, are shown in the 

 following table: 



Product T Radiations 



Radium a rays 



I 

 Emanation 4 days 



I 

 Radium A 3 mins. 



1 

 Radium B 21 mins. 



i 

 Radium C 28 mins. 



When the emanation has been left in a closed vessel for several 

 hours, the emanation and its successive products reach a stage of 

 approximate radioactive equilibrium, and the heating effect is then 

 a maximum. If the emanation is suddenly removed from the tube by 

 a current of air, the heating effect is then due to radium A, B, and C 

 together. On account, however, of the rapidity of the change of 

 radium A (half value in three minutes), it is experimentally very diffi- 



