Theory of Elei'trocapillarity. 365 



the surface-tension independent of their electric charges and 

 not involved in equation (1). 



Freundlich * and Grouy f directed their attention to the 

 importance of adsorption phenomena in the study of electro- 

 capillarity. According to Gouy, e is zero at the maximum 

 of the electrocapillarv curve, but there may be a potential 

 difference between the solution and the mercury, caused by 

 adsorbed layers of ions. I shall try to show that this point 

 of view is the correct one and that it is incompatible with 

 Nernst's theory of ionic solution pressure. First, we must 

 consider the problem of the dropping electrode. 



With the object of explaining the mechanism of working 

 of a dropping electrode, the Lippman-Helmholtz theory 

 assumes a constant quantity of electricity to be on an insu- 

 lated mass of mercury ; therefore the charge on unit surface 

 and the potential difference between the solution and mercury 

 both decrease with increase of surface. But Palmaer's % 

 experimental investigations, in agreement with Nernst's 

 theory, have shown that the primary effect of a dropping 

 electrode is to change the concentration of ions of mercury 

 in the solution. If P >p, the potential difference between 

 mercury and solution and the charge of the mercury surface 

 are both negative ; when the mercury surface is increased 

 ions enter into the solution and the potential of mercury 

 therefore increases. If P <p } the potential difference and 

 the charge of the mercury are positive, by surface increase 

 ions of mercury are removed from the solution and the 

 potential of mercury decreases. Finally, if V=p — "null" 

 solution — the potential difference and the charge of the 

 mercury are zero, surface increase does not influence the 

 concentration of ions of mercury, and the potential of a 

 dropping electrode has the same value as the potential of a 

 still one. The potential of every dropping electrode is 

 bound to approach, independently of p, the same value, when 

 the rate of surface increase becomes infinite ; practically we 

 obtain the limit value, as Paschen § has shown, if the end of 

 the continuous part of the jet is in the surface of the 

 solution. 



Thus, if Nernst's " osmotic " theory were exact, Paschen's 

 dropping electrodes and Palmaer's null solutions would give 

 us a method of measuring absolute potentials not influenced 



* Kapillarchemte, p. 184. 



t C. R. cxlvi. p. 622 (1908) : cxxxi. p. 939 C1900). 

 % Zeit. phys. Chem. xxv. p. 265 (1898) ; xxviii. p. 257 (1899) ; xxxvi. 

 p. 664(1901); lix. p. 129 (1907). 



§ Wied. Ann. xli. p. 42 (1890) ; xliii. p. 585 (1891). 



