Electrodes in Water free from Air. 147 



It is not true that it requires any definite electromotive 

 force to begin to polarize electrodes in air-free water ; any elec- 

 tromotive force, however small, will do it. Its detection is only 

 a question of a sufficiently delicate galvanometer ; and we may 

 therefore say that any electromotive force, however feeble, act- 

 ing on platinum electrodes, builds up a corresponding amount 

 of polarization equally in air-free as in aerated water. But no 

 liberation of free gas is possible under these circumstances, 

 until the external electromotive force just exceeds the counter- 

 electromotive force of the electrodes when polarized to their 

 fullest extent. 



With regard to the second question, whether polarization, 

 however small, means literal chemical decomposition, I am not 

 aware that it has ever been called into questiom. There is 

 abundant evidence to show that it is not a mere physical state 

 of the chemically unaltered electrolyte, but that there is some- 

 thing deposited on the electrodes which can only be the pro- 

 ducts, primary or secondary, of electrolysis. Although a vol- 

 tameter charged by a weak electromotive force resembles very 

 closely a condenser, yet there is something very different be- 

 tween the state of strain or electrical displacement in a con- 

 denser's dielectric and the electrolyte after having had a current 

 passed through it. 



That even very feeble polarization does really in every case 

 consist in the deposition of products of an unseen electrolysis 

 in or on the electrodes receives support, in addition to many 

 other facts, from the following : — Platinum plates were placed 

 in the inside of a vertical glass tube, and made to communicate 

 with the outside by wires sealed through the glass. The tube 

 was so arranged that dilute acid could be made to flow down 

 through the tube from a reservoir, without the plates being ever 

 exposed to air. The tube being full of acid, the platinum 

 plates were now polarized feebly. If the acid was allowed to 

 flow out slowly, so as to gradually replace the liquid which was 

 between the plates when polarized by other fresh acid, the 

 plates gave, on discharge, a nearly equal current to that which 

 they would have given if no replacement had been made ; but 

 if the liquid was made to rush down violently and then stopped, 

 little or no polarization was found, provided the plates had been 

 only slightly polarized. If the plates were defended by strips 

 of cloth laid over them, no such removal was effected by the 

 liquid rushing down. This all seems to indicate that there is 

 something on the plates which can be iciped off mechanically. 

 This can only be the products of electrolysis. This experiment 

 has no analogy in a condenser. These and many other facts 

 seem to point out that polarization is in all cases only unseen 

 electrolysis. 



