CHARGE OF A CONDENSER AND POLARIZATION OF ELECTRODES. 495 



Jiquid ; it is the extension to a solid surface in contact with mercury 

 of the law mentioned above (651) for mercury. The curve of 

 Fig. 232 for water acidulated by sulphuric acid, agrees for any 

 electrolyte which gives oxygen and hydrogen. Each electrolyte 

 has on this curve its own origin corresponding to the normal electro- 

 motive force between it and the electrode. 



In order to demonstrate this law, M. Blondlot places the two 

 electrodes in different liquids separated by a porous diaphragm. As 

 the electromotive forces of contact are unequal, the system forms a 

 couple ; but if this is closed until there is no current, the exact effect 

 of polarization is to reduce the falls of potential on either side to 

 equality. If one of the electrodes is very large, and remains without 

 appreciable change, it is found that the initial capacity of the small 

 one is then the same as when it is immersed in the same liquid as 

 the large one. If the electrodes are equal, M. Blondlot shows from 

 the following considerations that the capacities are equal. 



Let e at a given instant be the difference of potential between the 

 electrode and the liquid in contact; in the time dt this difference 

 undergoes a total variation 



(1) de = dt-\ dq ) 



the first term representing the spontaneous depolarization by dif- 

 fusion, the second the passage of a quantity of electricity dq across 



the electrode. If it be observed that the ratio represents the 



da 4 



inverse of the capacity, and the intensity of the current * which 



traverses the electrode, we may write 



(2) de 



When the couple is short-circuited a very feeble current is pro- 

 duced, which ultimately becomes constant; we have in that case 

 de=Q, and for each electrode we may write 



V 



