480 A Contribution to the Theory of El ectro capillar it ij. 



of electricity which passes from K to A during the formation 

 of unit surface be — q. It changes in potential by an 

 amount — V, and therefore the work performed is qV. 

 Let the negative charge on the chlorine ions removed from 

 the solution during the formation -of unit surface be — q. 

 This charge also passes to the mercury surface, and an amount 

 of work q'Y is performed. The electrical energy required 

 to introduce the small excess of mercury ions can be neglected. 

 The total electrical work performed is (q + q')Y or QV, 

 Q being the charge on unit surface of the mercury. An 

 amount of work equal to T v , the surface tension corresponding 

 to a difference of potential Y, is also performed. 



III. Mercurous chloride is introduced into the solution 

 until the difference of potential between the mercury and 

 the solution is zero. This work is opposite in sign and 

 almost equal to that performed in operation I. During the 

 destruction of the double layer the excess of potassium ions 

 re-enter the potassium alloy, whilst the deficiency of chlorine 

 ions is supplied by the chlorine which entered the chlorine 

 alloy during the formation of the surface. It is easy to see 

 that the electrical work performed by the engine in order to 

 effect this change will be 



Tv.rfQ. 



IV. The surface is reduced by unity, and the work per- 

 formed by the engine is T , the maximum surface tension. 



If we sum the work performed on the engine in the cvcle 

 of ^operations and equate it to zero we obtain 



T -T„ = QV- Cyo!Q= CQdV. 



Jo Jo 



Now it has generally been assumed that the capacity of 

 the condenser formed by the double layer is constant. This 

 assumption would obviously make T — T» proportional to Y 2 : 

 but the first part of this investigation shows that the assump- 

 tion is not justified. 



Substituting in the above equation the value of Q from 

 equation (D), we find that 



eV gV 



i - T -=j;v i &("-«""> 



fr'V e\- 



2R /K» / as ~au\* 

 6 V 2tt V J 



