Theory of Electrocapillarity . 367 



of n/1 Na a S0 4 saturated with paraldehyde (fig. 2, I.). The 

 middle part of the curve is here cut away and the maximum 

 is displaced to the left. Other organic suhstances, like pyro- 

 gallic acid, give curves with a maximum displaced to the right 

 ^fig. 2, II.). The potential difference solution / mercury 



Fiff. 2. 



lOOr 



I.— Na 2 S0 4 +paraldeliyde. 



II. — Na 2 S0 4 +pyrogallic acid- 



does not change when paraldehyde or pyrogallic acid is 

 added to the solution, no complex salts are therefore formed 

 and Krueger's supplementary term must vanish. Besides, 

 this term can cause ouly a displacement of the maximum 

 to the right and never one to the left, as we usually observe 

 in solutions of organic substances. 



We shall show that Paschen's relation still holds with 

 these solutions and that this relation can be deduced from 

 purely thermodynamical considerations without any special 

 assumptions as to the nature of the observed anomalies. 

 With this purpose let us consider the classical demonstration 

 of equation (1). 



Let us suppose that a drop of mercury and an electrode, 

 reversible for an anion, are immersed in a solution. We shall 

 assume the concentration of the corresponding anion to be 

 great as compared with the concentration of ions of mercury. 



