﻿Electricity on Insulators and Metals. 



271 



Pt 



Sn 

 AgJ 



Bi j 



Pb \ 

 Tl j 



Negatively charged 

 when rubbed 

 with silk. 



Positively charged 

 when rubbed 

 with silk. 



Sb^ Positively charged if 

 Zn I polished, negatively 

 Cu Y charged if rough, 

 Fe | when rubbed with 

 A1J silk. 



The sign and magnitude of the charge produced by the 

 friction of the metals do not appear to be a well-defined 

 physical property of the metals. A possible relation between 

 the maximum charges for different elements would thus be 

 difficult to obtain, since, except with metals of high atomic 

 weight, the sign of the charge seems to be largely deter- 

 mined by the physical state of the surface, and not merely 

 by the nature of the material rubbed. Iu fig. 5 the maximum 



Fiff. 5. 





i / 



Arc vie. Weight. 



I / 



( 



-i- 



'¥ 



V 



charge obtained by the friction of the surfaces of the metal, 

 polished when possible, is plotted against the atomic weight. 

 An examination of the curve shows that there appears to be 

 here some evidence of a periodicity in property with increase 

 of atomic weight, and that, like some other physical pro- 

 perties of the elements, this property possibly conforms to 

 the Periodic Law. 



