378 Mr. A. Frumkin on the 



On substituting the values of ^~, ~^~^> ~^> and^-^ 

 from (3) and (4) in (2) we obtain ° s ° s ° G ° c 



^f§J = -(r^ a +r cl ), .... (5) 



i. e. Gibbs's equation. 



Let us now suppose that the valency of the anion is n A 

 and the valency of the cation n K ; instead of (3) we must 



dc ~n K cF' ~dc ' n A c -^' 

 If we express the quantities F in gr. eq. per cm. 2 equation 

 (4) will keep its form, hence 



££"©.-(&■ ■ ■ • < 5 "> 



Let us compare (5 a) with the equation of the electro- 

 capillary curve 



1 J*Z-r — r 



Fof A K * 



I. Descending branch. 



The mercury is charged negatively. In the surface-layer 

 there is an excess of cations and a deficiency of anions, so 

 that T A has a negative value ; the absolute value of Y A is at 

 any rate less than cB, where 8 is the thickness of the surface- 

 layer and may be neglected if the solution is a dilute one *. 

 This agrees very well with experiment, as the form of the 

 descending branch, at a certain distance from the maximum, 

 does not depend on the nature of the anion. In consequence 

 we may put r A = 0, whence 



a-f RT 3 logo" 



The integral of this equation is 



7=/(^+^logc) (6) 



Ifyi=?2> rt rx 



whence -om 



^_ tl=n _ log _; (7) 



In consequence, the horizontal distance between the descending 

 * In fact, if c = w/100, cS will be of the order 10~ 12 gr. eq./cm. 2 , 

 whereas the quantity — ; ^Z i s f the order 10 ~ 10 gr. eq./cm. 2 . 



