•_>(!»; Duane — Heat Generated by Radio-active Substances. 



ing the salt from the calorimeter found that the phosphorescent 

 light had disappeared. It is impossible to affirm, therefore, 

 that the heat effect is directly related to the emission of visible 

 phosphorescent light. It may be due to the emission of visi- 

 ble and invisible rays together, or it may be caused by some 

 reaction of a secondary nature. 



These researches, however, have suggested to me the follow- 

 ing question : if a quantity of radium is mixed with a phos- 

 phorescent salt, causing it to phosphoresce brilliantly, does the 

 mixture generate the same quantity of heat as the radium 

 would generate alone ? There appear to be three possibilities : 

 (a) the energy of the rays is absorbed (at least in part) in pro- 

 ducing chemical reactions in the phosphorescent salt. In this 

 case the heat effect of the mixture should be less than that of 

 the radium alone, at least at first, (b) the radium rays acting 

 on the atoms and molecules of the salt liberate a part of their 

 chemical or subatomic energy. In this case the heat produced 

 by the mixture should be larger than that produced by the 

 radium alone. (<?) the energy of the radium rays is rapidly 

 transformed (in part) into the energy of the phosphorescent 

 light without producing other reactions, and in this case, if all 

 the light is absorbed in the vessel containing the mixture, the 

 heat produced should be the same as that due to the radium 

 alone. 



In order to investigate this question I made the following 

 experiments. On December 3d, 1909, a certain quantity of 

 a salt containing finely pulverized radium chloride and barium 

 chloride was divided into two parts. One part, A, weighed 

 ■0314 gram and was sealed into a small glass tube. The other 

 part, B, weighing "0206 gram, was thoroughly mixed with 

 •267 gram of phosphorescent zinc sulphide, and then sealed in 

 a second glass tube similar to the first. 



Several times during the five weeks following the sealing 

 of the tubes I measured the heat effects of each of them, and 

 I also compared the intensity of the 7-radiation emitted by 

 them with that due to a standard tube containing 26"5 grams 

 of radium chloride. The following table (3) contains the 

 results of these experiments : 







Table 3. 









Date of 



Quantity of EaCl" 2 



Production of 



Eatio 



of 



that produces the 



heat calories 



A. 



experiment 



same 



7-rays 



per hour 



* 



B 





A 



B 



A 



B 





December 7 



1-66 



1-07 











1-55 



December 7 











•152 



•098 



T55 



December 21 



2-37 . 



1-57 







_ 



1-51 



December 21 











•199 



•129 



1-54 



January 5.. 



2-39 



1-56 











1-53 



January 6 . . 











•201 



•127 



1-58 



