Mi;. S. W. ,T. SMITH ON THE NATURE OF ELECTKOCAPILLAKY Till N '\||.N.\ 57 



not only upon the chemical nature of the ions, but also ii]x>n their concentration in 

 the solution. This can be readily rendered obvious by the above method. 



Fig. 4. 



For the above solution of potash it is clear that within the range of the experiment 

 the effect of depolarization upon the direct curve can be considered negligible. The 

 same can be said of most of the solutions considered later. 



The Second Hypothesis of the Lippmann-Hclmholtz Theory. 



The second hypothesis in the Helmholtz explanation of electro-capillary curves is 

 that the electrical effect upon the surface tension is a purely electrostatic effect 

 d'|H-!idmg at a given potential difference upon the capacity of the electrode per unit 

 area. It supposes that, in general, the capacity per unit area is independent of the 

 chemical nature of the solution employed in the electrometer. From the approxi- 

 mately parabolic nature of some of the curves through a considerable portion of their 

 course, the Helmholtz theory leads not only to the view that through the range 

 considered the capacity per unit area is constant, but also makes it possible for the 

 value of this capacity to be calculated. Assuming the inductive capacity of the 

 dielectric of the double layer to be unity, the theory further allows an estimate to be 

 formed of the dist:m<v between the parallel charges forming the double layer. That 

 the distance so calculated is of the same order of magnitude as molecular distances 

 calculated in other ways is, however, no proof of the validity of the Helmholtz view. 

 For the distance let\veen the layers, as so calculated, might have amounted to some- 

 thing very much larger without standing in opposition to other known data concerning 

 molecular distances. In other words, there is no <i priori objection to a view which 

 supposes that the rapacity per unit area of the common surface may really be much 



VOL. c \< III. A. 1 



