1 4 POPULAR SCIENCE MONTHLY. 



rate of evolution of heat from radium was unaltered by plunging the 

 radium into liquid air or liquid hydrogen. 



It seemed probable that the evolution of heat by radium was 

 directly connected with its radioactivity and the experiments of 

 Eutherford and Barnes proved this to be the case. The heating effect 

 of a quantity of radium bromide was first determined. The emana- 

 tion was then completely driven off by heating the radium, and con- 

 densed in a small glass tube by means of liquid air. After removal 

 of the emanation, the heat evolution of the radium in the course of 

 about three hours fell to a minimum corresponding to one quarter of 

 its original value, and then slowly increased again, reaching its original 

 value after an interval of about one month. The heat emission from 

 the emanation tube at first increased with the time, rising to a maxi- 

 mum value about three hours after its introduction. It then slowly 

 decreased according to an exponential law with the time, falling to 

 half value in about four days. 



The curve expressing the recovery from its minimum of the heating 

 effect of radium is complementary to the curve expressing the diminu- 

 tion of the heating effect of the emanation tube with time. The curves 

 of decay and recovery agree within the limit of experimental error 

 with the corresponding curves of decay and recovery of the activity of 

 radium when measured by the a rays. Since the minimum 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 y rays, since the (3 or y 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 suc- 

 cessive 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 re- 

 sults show that the matter deposited by the emanation breaks up in three 

 successive and well marked stages. For convenience, these successive 

 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: 



