It is thus possible to reduce ferric chloride in one vessel by hydrogen sulphide poured into another vessel,[517] and an electric current may be obtained from the simultaneous discharge of the sulphide and ferric ions in the action.
Effects of Ion Concentrations on the Current.
Further Illustrations.
It would appear possible, in fact, to obtain an electrical current from any oxidation-reduction reaction, if the oxidizing and reducing agents can be, experimentally, properly arranged for this purpose.
Summary.
Need of the Study of the Quantitative Relations.
The mere possibility of a transfer of charges, or electrons, is therefore apparently[521] not sufficient to induce an oxidation and reduction reaction—much in the same way as, for instance, the mere presence, simultaneously, of the barium-ion and the carbonate-ion, in itself, does not necessarily lead to the precipitation of barium carbonate (p. [90]), although the latter is difficultly soluble. In order to understand the problem of precipitation or nonprecipitation of salts, it was found necessary to examine the question from its quantitative side (p. [91]), and, similarly, the solution of the difficulty concerning the occurrence or nonoccurrence of oxidation and reduction reactions, where the possibility of a transfer of electrons is given, will be found in a study of the problem from its quantitative side.
Oxidation and Reduction Reactions as Reversible Reactions.
Cu2+ + SO42− + Zn ↓ → Zn2+ + SO42− + Cu ↓,
or, since the sulphate-ion is not directly concerned in the action, we have more simply: