80 MR. S. W. J. SMITH ON THE NATURE OF ELECTROCAPILLARY PHENOMENA. 



From these results we see that, assuming the potential difference between the liquids 

 is as calculated, the respective effects of Na and K on the electro-capillary curves are 

 practically identical. To examine the effect when hydrogen is the kation, I have 

 also performed similar experiments with hydrochloric acid of different strengths. The 

 curves are practically the same as those for Nad and KC1, with the exception that 

 the hydrochloric acid curves eventually flatten out in a similar way to the sulphuric 

 acid curve described earlier, and doubtless for a similar reason. Subsequently I hope 

 to describe how the surface tension for a given potential difference depends upon the 

 nature and concentration of the kation in the general case. 



RELATION BETWEEN THE SURFACE TENSION FOR A GIVEN POTENTIAL DIFFERENCE 

 AND THE CONCENTRATION OF THE SOLUTION EMPLOYED IN THE ELECTROMETER. 



Following the same hypotheses as have been adopted above, it is easy to see, 

 from the curves just given, the nature of the effect of the kation upon the surface 

 tension. The surface tension for a given potential difference would seem to increase 

 as the concentration of the solution diminishes, or conversely, for a given surface 

 tension the potential fall from the solution to the electrode would seem to increase 

 with diminishing concentration. Thus, to take the potassium chloride curves, suppose 

 ir ". """M' an ^ "'M a ' re the natural potential differences between the large electrode and 



the solution (reckoned from the electrode to the solution) in the , , and ;- solu- 



2i 10 ^U 



tions respectively. Considering the parallel portions of the curves, let tr v 7r, 10 , and 

 IT,,, be the E.M.F.s required to be applied between the terminals in the respective 

 cases, in order to produce a given surface tension. If the surface tension depends 

 only on the electrostatic effect we should have 



assuming, as in the previous cases, that there are no appreciable potential falls within 

 the solutions, or that, if present, they are the same for all. 

 Suppose, now, that we measure the E.M.F.s of the cells 



