L 51 1 



v. 



THE ELECTEICAL CONDUCTIVITY OF POWDERS IN THIN 



LAYERS. 



By PROFESSOR J. A. McCLELLAND, D. So., F.R.S., 



AND 



J. J. DOWLING, M.A., 

 University College, Dublin. 



Kead February 22. Published May 17, 1915. 



1. The experiments described in this paper refer to thin layers of 

 powders so formed that they can be charged and discharged as one plate of a 

 condenser. 



The layers were formed in the following manner. A metal plate P (fig. 1, 

 plan and elevation) was covered with a thin coating of paraffin wax W, one 

 or two millimetres thick, and a small quantity of the conducting powder was 

 spread on the smooth surface of the wax and lightly rubbed with a pad of 

 cotton wool. Tinfoil terminals T t and T 2 were fixed so as to make good 

 connexion with the powder. 



Shunt 



l\ey l. 



B, 



HHIililh 



T T 



icra. 



Fig. 1. 



/W 



P/ 



Key Z. 



II 



Ea.rtk Wm 



Fig. 2. 



Powdered graphite was used for the earlier experiments, but later we 

 used a bronze metal powder, and all the curves given in the paper refer to 

 experiments in which this powder was employed. 



The conductivity of the layer was measured between the terminals 1\ and 

 1\, the battery 2?, (fig. 2) being employed for this purpose, and either the 



K.I. A. PROC, VOL. XXXII, SECT. A. 



[8] 



