328 Prof. E. Rutherford and Mr. H. Robinson on the 



The results obtained for the heating effect of one curie of 

 emanation under various conditions are tabulated below. 





Heat emission of one curie of ema- 

 nation in gram calories per hour. 







Screen. 



a rays. 



99-2 

 99-2 

 99-2 

 99-2 



(3 rays. 



y rays. 



Total. 



Equivalent to l'3mm. of aluminium 



4-2 



4-8 

 4-8 

 4-8 



0-1 

 1-5 



3-0 

 4-7 



103-5 

 1055 

 1070 



108-7 



+4 - 4 mm. of mercury ... 

 -J-14G mm. of mercury . . 



imnir 



These results are expressed in terms of the Vienna Radium 

 Standard. 



§ 3. Calculation of Heating Effect of Radium and its 



Emanation. 



The energy of the a particles and recoil atoms liberated 

 from one o-ram of radium or of any of its products in equi- 

 librium with it can readily be calculated. This energy is 



equal to 



/ m\ 1 mir /., , m\ 



for each of the a-ray products concerned. The value 



"—. was directly determined by Rutherford for the a. particle 

 2e 



from radium C by measurement of the electrostatic deflexion 

 of the rays, and found to be 4'21 X 10 u . Taking the velocity 

 of an a particle to be proportional to the cube root of its 



mw 

 rano-e the corresponding values of *=- for radium, emana- 

 tion, and radium A, are 2*56, 2-95, 3'13 x 10 14 respectively. 

 The' masses of the recoil atoms from radium, emanation, 

 radium A, and radium 0, are 222, 218, 214, and 210 respec- 

 tively. The value of 1 + ifj is consequently slightly less 



than 1*02 for each product. ^ 



The value of ne, the total charge carried by the a particles 

 from one gram of radium itself, has been found by Rutherford 

 and Geiger to be 1*054 x 10~ 9 e.m. unit. Substituting these 

 values, the emission of energy is for one gram of radium in 

 equilibrium 1*38 x 10° ergs per second, and for the emanation 

 in equilibrium with it 1'10 x 10 6 ergs. 



The corresponding heating effect of one gram of radium 



