equivalent of ion.[1] Thus mE (u + v) = total current = k = mλ, or λ = E (u + v). The determination of v/u by the method of Hittorf, and of (u + v) by the method of Kohlrausch, made it possible to calculate the absolute velocities of drift of the ions from experimental data.
Meanwhile, important advances in voltaic theory were being effected in connexion with a different class of investigations.
Suppose that two mercury electrodes are placed in a solution of acidulated water, and that a difference of potential, insufficient to produce continuous decomposition of the water, is set up between the electrodes by an external agency. Initially a slight electric current—the polarizing current,[2] as it is called—is observed; but after a short time it ceases; and after its cessation the state of the system is one of electrical equilibrium. It is evident that the polarizing current must in some way have set up in the cell an electromotive force equal and opposite to the external difference of potential; and it is also evident that the seat of this electromotive force must be at the electrodes, which are now said to be polarized.
An abrupt fall of electric potential at an interface between two media, such as the mercury and the solution in the present case, requires that there should be a field of electric force, of considerable intensity, within a thin stratum at the interface: and this must owe its existence to the presence of electric charges. Since there is no electric field outside the thin stratum, there must be as much vitreous as resinous electricity present; but the vitreous charges must preponderate on one side of the stratum, and the resinous charges on the other side; so that the system as a whole resembles the two coatings of a condenser with the intervening dielectric. In the case of the
- ↑ i.e. E is 96580 coulombs.
- ↑ The phenomenal of voltaic polarization was discovered by Ritter in 1803. Ritter explained it by comparing the action of the polarizing current to that of a current which is used to charge a condenser. Volta in 1805 put forward the alternative explanation, that the products of decomposition set up a reverse electromotive force.
