52 Mil. S. W. J. SMITH ON THE NATURE OF ELECTKOCAFILLAKY HIF.NnMKNA. 



in which the continuous depolarization current is written as a function of IT", because 

 of the assumption that if the area of the capillary electrode is kept constant, the 

 magnitude of the current will depend only on the potential fall at that electrode. 

 It is not to be expected that the depolarization current will remain constant for an 

 indefinite time. Owing to the variation of the concentration of the solution in the 

 neighbourhood of the electrode, which must necessarily accompany the passage of the 

 current through the electrolyte, the relation between IT" and the depolarization 

 current will alter ; but an effect of this kind will be gradual, and we may consider 

 the depolarization current to be constant for some time after the introduction of TT,. 

 In like manner, the accumulated effect of the continuous current upon the potential 

 fall at the large electrode will only be gradually perceptible. 



Adding the two above equations, and putting TT IT' = ir n , we get 



It therefore follows (as is otherwise obvious), that the effect of depolarization would 

 be to cause the potential difference at the small electrode to change less rapidly 

 than the applied E.M.'F. Hence, before one can proceed beyond the first hypothesis 

 to examine quantitatively whether the second hypothesis, concerning the relation 

 between the potential difference and the surface tension, is true, it is necessary to 

 determine whether the effect of the depolarization can under any circumstances 

 become appreciable. 



The magnitude of the effect will depend upon the value of (R + ft') /(""") The 

 internal resistance, R, will, of course, depend upon the nature of the electrolyte 

 employed, upon the internal cross-section of the capillary tube and upon the distance 

 between the mercury meniscus and the point of the capillary tube. Its value may 

 range from something like 50,000 or 100,000 ohms to a million ohms or more. So 

 that, under usual circumstances, the external resistance, R', can be neglected in 

 comparison with R. The value of / (IT") will depend upon the area of the mercury 

 meniscus. It will, therefore, be possible in a given electrometer to vary the value 

 of R/(TT") fora given solution, and (by comparison of the curves for two different 

 positions of the meniscus) to determine whether the form of the curve is appreciably 

 affected by the change. On the other hand, the effect may be rendered directly 

 evident and measurable by interposing a very high resistance in the external circuit, 

 so that, although /(ir"), and even R/(TT"), may be very small, R/(TT") will have an 

 easily observable magnitude. 



Experimental Determination of the Magnitude of the Depolarization Effect. 



I have used this latter method, and the following experiments may be given in 

 illustration of it. The high resistance consisted of graphite rulings upon ebonite, and 



