Skction III., 1903 [ 37 ] Tbans. K. S. C. 



lY. — On the Radioactivity of Metals Generally. 

 By J. C. McLennan, Ph.D. 



Associate Professor of Physics, University of Toronto, 

 AND 



E. F. Burton, B.A. 



Fellow in Mathematics, University of Toronto. 

 (Comiiunicated by President Loudon, and read May 19th, 1903.) 



Introduction. In a former paper by the authors^ on the con- 

 ductivity of a mass of ordinary air confined within a large metallic 

 receiver it was shown that about 37 per cent of the conductivity wac> 

 due to an exceedingly penetrating radiation which, traversing the air 

 in the room, passed through the walls of the receiver. It was also 

 shown that the conductivity of fresh atmosplieric air, after being con- 

 fined in a metallic cylinder, rapidly fell to a minimum value, that a 

 gradual rise then took place, and that a steady state was reached after 

 some hours. 



On account of the known decay of the constituent in atmospheric 

 air responsible for excited radioactivity, the fall in the initial con- 

 ductivity was attributed to its presence in the cylinder, and the subse- 

 quent rise to an emanation of a similar character given off by the walls 

 of the containing vessel; the steady state representing a condition of 

 equilibrium, where the rate of decay of this emanation was equal to the 

 rate at which it was produced. 



It was also pointed out that the limiting value of the conductivity 

 thus reached varied with the metals forming the walls of the receiver. 

 In experiments with lead, tin and zinc the conductivity was highest 

 with lead and lowest with zinc. In view of these results, and on 

 account of the known complex character of the radiation from such 

 highly radioactive substances as radium and thorium, a series of experi- 

 ments was made to investigate still further the radioactivity of 

 ordinary metals. 



As a result of these experiments, we find that when a cylinder of 

 any metal is enclosed within a second of the same material, insulated 

 from it, and surrounded by air or other gases, it gradually acquires a 

 negative charge, and after a short time reaches a state of equilibrium 

 at a definite potential below that of the enclosing cylinder. 



' Phys. Review, Vol. XVI., No. 3, p. 184, 1903, and University of Toronto 

 Studies. Physical Science Series No. 2. 



