310 Mr. H. A. M c Taggart on the 



The charge on a sphere o£ any size may be found by 

 multiplying this density by the surface area. The following 

 table compares with this the amount of electrification set 

 free (1) by a drop in a waterfall experiment, (2) by a drop 

 broken up in a current of air (Simpson, Phil. Trans. A. 209. 

 p. 379, 1909), and (3) by the breaking off of a drop from a 

 source (see Becker, loc. cit.) t 



Experiment. Diam. of Cnarg-e calc. 



sphere. in coulombs. 



Cataphoresis 7*8 mm. 7*6 . 10~ 5 



4-4 „ 2-4. 10" 5 



Waterfall exp 7*8 „ 2'8, 10^ 12 



4-4 „ 0-89. 10" 12 



Drops broken up by a 



current of air 7*8 „ 1"7 . 10 M2 



Breaking off of a drop... 4*4 „ 5'28 . 10~ u 



If the estimates made in these various cases are not too 

 wide of the mark, it is evident that only a very small fraction 

 of the charge is set free by such mechanical disturbances as 

 those mentioned. 



The difference of potential (V) between the surfaces of the 

 double layer may be calculated from 



fill _ __ KV . v _ 4:TTfJLU 



if the thickness of the layer be small in comparison with the 

 radius of the sphere. 

 In e.s. units 



4. 3'14. 0-0 1. 4. 1Q- 4 

 _ i 



300 



V =- -81 ' 



or in volts 



_ 4. 3-14, 0-01. 4. IP" 4 . 300 



300 * OJ - 



= 0-055. 



In a consideration of the electrical effects observed at 

 liquid-gas surfaces, differences must be noted between the 

 conditions of experiments like waterfall experiments, bubbling 

 of gas through water, or spraying experiments and cata- 

 phoresis experiments like those described in this paper. 

 The surface-density of electrification need not be the same in 

 the two cases. In solutions the concentration of the salt in the 

 surface does not reach an equilibrium value the moment the 

 surface is formed. For this reason, the electric density will 



