﻿at the Boundary between a Liquid and a Gas. i^89 



The zero point was reached at a concentration o£ about 

 7 x 10~ 8 , a result rather higher than that given in a former 

 [>aper. The salt was an entirely different sample, and may 

 not have contained the same proportion of water of crystal- 

 lization. (See Abegg and Auerbach, ' Inorganic Chemistry.') 



A series of readings was then taken for spheres of air of 

 different sizes, one object being to observe the charge on 

 very small spheres. It is very difficult, by the use of any 

 kind of pipette, to introduce into the rotating cell bubbles 

 smaller than 1/5 mm. in diameter. To avoid this difficulty 

 the following mode of working was adopted. The solution 

 was first placed in a partial vacuum to remove as much 

 dissolved air as possible, and afterwards poured into the cell. 

 A bubble into this gas-free solution slowly decreased in size 

 by absorption until it vanished, while the electric charge 

 could be observed at any stage. 



Under these circumstances it was found that for a suitable 

 concentration of solution a sphere of air which began with a 

 small negative charge almost invariably and in a regular 

 way reduced its charge to zero, and gradually took on a 

 positive charge. 



The following readings illustrate this point — 



No. 1. 



Concentration. 



Equivalents 



per c.c. 



~ 9 Xo-7 



Diameter of 

 sphere 

 in mm. 



0-26 



0-17 



Sign 

 chare 





- 





0-14 



- 





0-10 









0-08 



+ 



No. 2, 



10- 



Concentration. 



Equivalents 



per c.c. 



X5*7 



Diameter of 

 sphere 

 in mm. 



0-44 



0-35 



0-26 



0-17 



0-14 



Sign of 

 charge. 



