536 Researches on the Elementary Law of Ilydrodiffusion. 



nnpolarizability exists only approximately 'with extremely feeble 

 polarizing currents, and entirely disappears as the intensity 

 of the current is increased, since that time the false opinion 

 has prevailed in the literature of galvanism that amalgamated 

 zinc electrodes in zinc-sulphate solution are unpolarizable. 



The second of the methods of diffusion employed by me 

 exhibits in the most striking manner the considerable pola- 

 rizability of the combination in question. Not only does a 

 demonstrable polarizability exist, but upon it the most rigorous 

 and most convenient method of measurement of the course of 

 diffusion can be based. At the same time this method reveals, 

 with all the clearness that can be wished for, the genesis of 

 this polarization. The polarizing is not a consequence of the 

 electrolysis that goes on at the electrodes (the separation of 

 the gases), but the result of the alterations of the concentra- 

 tions in the layers of the zinc-sulphate solution in contact with 

 the electrodes, conditioned by the migration of the ions. 



The correctness of these assertions I have already, about six 

 years ago, in an altogether different way demonstrated, in the 

 Berlin Laboratory, by the following simple experiment : — Two 

 amalgamated zinc electrodes are placed in a solution of 

 sulphate of zinc, not vertical and opposite to one another, but 

 horizontal and one above the other. A polarizing current is 

 passed during a short time through the combination, which is 

 then inserted in the circuit of a sensitive galvanometer. In 

 the first place, with all, even the weakest intensities of the 

 polarizing current, and with any, even the shortest time 

 during which the current passes through it, the combination 

 constantly shows itself to be so polarized that the polarization- 

 current generated possesses the opposite direction to that of the 

 polarizing one. Further, the quantity of polarization produced 

 is very different according to the direction of the polarizing 

 current : if the polarizing current passes through the combina- 

 tion during a certain time in the direction from below upwards, 

 the produced electromotive force of the polarization (measured 

 by the galvanometer-deflection) proves to be from 5 to 7 times 

 as great as in the case where the same polarizing current 

 during the same time passes through the combination in the 

 opposite direction. In the first case the alterations of concen- 

 tration produced at the electrodes (at the lower an increase, 

 ut the upper a decrease) by the polarizing current are but 

 extremely little diminished by the diffusion ; in the latter case, 

 on the contrary, the action of gravity almost completely 

 destroys the alterations of concentration of the zinc-sulphate 

 solution produced at the electrodes by the passage of the 

 current through it. 



