310 Mr. J. Frenkel on the Surface Electric 



A more modern and efficient method of liberating free 

 electrons would consist in the ionization of the layers 

 adjacent to the contact surface by means of Rontgen ravs. 

 According to this theory, the free electrons would be driven 

 by the electric field in the residual double-layer from the 

 body with the smaller intrinsic potential to that with the 

 larger, until the electromotive force is completely annihilated 

 owing to the formation of the condenser above referred to. 

 One of the dielectrics may be, of course, replaced by a metal. 

 I am not, however, aware of any experiments having been 

 made in this direction. 



The electrolytes, again, differ from the metals not by the 

 absence of intrinsic potentials, but by the absence of free 

 electrons which are replaced by ions. These ions cannot 

 penetrate in the metal, but must form electric double-layers 

 near its surface, along with the ions of the metal itself. 

 A complete equalization of internal potentials seems, however, 

 impossible in this case, since besides the mere electrostatic 

 forces there are other forces — especially the osmotic pressure 

 of the ions — which now come into play. 



Part II. — Surface Tension. 



§ 6. When mercury is in contact with an electrolyte, its 

 surface-tension is diminished, as compared with its value 

 in vacuo, by about one-third of the latter. This value may 

 be restored by the application of an external electromotive 

 force, balancing the contact potential difference, and is again 

 diminished when the balance is destroyed. The phenomena 

 of electro-capillarity disclose, thus, an intimate relation 

 between the contact electromotive forces and surface-tension. 

 On this theory, both are due to the same cause — the atomic 

 (or molecular) electric layer enveloping the surface of solid 

 and liquid bodies — the former depending upon its intrinsic 

 potential, and the latter upon its energy. 



That a certain portion of the surface-tension must be due 

 to this energy immediately follows from the fact that the 

 latter is proportional to the surface of the body. The con- 

 siderable effect produced upon the surface-tension of mercury 

 by the secondary electric layers which are formed when it is 

 in contact with an electrolyte, shows that this portion may 

 be very large. In order to make an estimate of it, we shall 

 compare tlie surface-tension cr, numerically equal to the 

 (free) energy of unit surface of the liquid, with the electro- 

 static energy W, enclosed per sq. cm. in its surface electric 

 layer. Let us, as before, begin with metals. 



