8 ROYAL SOCIETY OF CANADA 



between the plates without sparking, has to be obtained iji a very short 

 time after the active wire is introduced. 



We can, however, obtain an approximate estimate of the value of 



— and of V on the assumption that the beating effect of radium C 



is due entirely to the kinetic energy of the oc particles. From the 

 experimental results given by Rutherford and Barnes, it can be deduced 

 that about 31 per cent of the total heating efEect of radium is due to 

 the product radium C. Since one gram of radium emits heat at the 

 rate of about 100 gram calories per hour, the heating effect of radium 

 C present in one gram of radium is 31 gram calories per hour. 



Since radium C is a direct product of radium, the number of 

 particles expelled j^er second from radium C, present in one gram of 

 radium in radioactive equilibrium, is equal to the total number n of a 

 particles expelled per second from one gram of radium at its minimum 

 activity. I have recently determined this number by measuring the 

 charge carried by the a rays emitted from a thin film of radium 

 bromide at its minimum activity. Assuming that each a particle 

 carries the usual ionic charge of 1.13 X 10"^^ electromagnetic units, it 

 was deduced that 6.2 X 10^^ particles are expelled per second from 

 radium itself. 



Thus n = 6.2 X 10^'. 

 Now \ m n V^ = heating effect of a particles expelled per second 

 from radium C. 

 = 3.6 X 10^ ergs. 



Substituting again the value of the ionic charge e and the value of n, 



m ^ 



-Y = 1.03 X 10'". 



e 



In this result the value of e has not been assumed since w = L 



e 



where i was the measured current due to the charge carried by the a 



rays We have previously seen that 



'"-Y = 3.08 X 10\ 

 e 



From these two equations, it is seen that 



\ = 2.6 X 10^ cms. per second, 



and - = 6.5 X 10^ electromagnetic units 



7/1 



