﻿at the Boundary between a Liquid and a Gas. 387 



of air when a particular electrolyte, Thorium Nitrate 

 [Th(N0 3 )J, was dissolved in water. This salt was selected 

 tor special study because it had been found to be unusually 

 active in charging these surface layers. 



The apparatus used was similar to that referred to in a 

 former paper, one or two changes being made in it for 

 greater convenience. The arrangement is shown in fig. 1. 



Fig. 1. 



K 



- T BT 



J OlD 



A is a small cylindrical glass cell rotating about its axis 

 on pivots and driven by a belt of thread from a pulley F on 

 a Rayleigh motor. This motor was made in the laboratory 

 workshop, and has, instead of the usual fly-wheel with a 

 hollow rim filled with water, a solid brass wheel H — a modi- 

 fication suggested by Professor Wilberforce of Liverpool. 

 The wheel, although loose on the shaft, has enough friction, 

 when a heavy oil is used for lubricant, to keep the shaft in 

 steady motion after synchronism with the tuning-fork is 

 attained. 



D is a timing device consisting of a vertical post carrying 

 a pointer and made to rotate by a toothed wheel working in 



9 Q v 



