put into the alkali becomes positive, that in the acid being negative. Whichsoever is in the alkali is oxidised, whilst that in the acid remains in the metallic state, as far as the electric current is concerned.
678. When sulphuretted solutions are used (665) in illustration of the assertion that it is the chemical action of the metal and one of the ions of the associated electrolyte that produces all the electricity of the voltaic circuit, the proofs are still the same. Thus, as Sir Humphry Davy[1] has shown, if iron and copper be plunged into dilute acid, the current is from the iron through the liquid to the copper; in solution of potassa it is in the same direction, but in solution of sulphuret of potassa it is reversed. In the two first cases it is oxygen which combines with the iron, in the latter sulphur which combines with the copper, that produces the electric current; but both of these are ions, existing as such in the electrolyte, which is at the same moment suffering decomposition; and, what is more, both of these are anions, for they leave the electrolytes at their anodes, and act just as chlorine, iodine, or any other anion would act which might have been previously chosen as that which should be used to throw the voltaic circle into activity.
679. The following experiments complete the series of proofs of the origin of the electricity in the voltaic pile. A fluid amalgam of potassium, containing not more than a hundredth of that metal, was put into pure water, and connected through the galvanometer with a plate of platina in the same water. There was immediately an electric current from the amalgam through the electrolyte to the platina. This must have been due to the oxidation only of the metal, for there was neither acid nor alkali to combine with, or in any way act on, the body produced.
680. Again, a plate of clean lead and a plate of platina were put into pure water. There was immediately a powerful current produced from the lead through the fluid to the platina: it was even intense enough to decompose solution of the iodide of potassium when introduced into the circuit in the form of apparatus already described (615), fig. 33. Here no action of acid or alkali on the oxide formed from the lead could supply the electricity: it was due solely to the oxidation of the metal.
681. There is no point in electrical science which seems to
- ↑ Elements of Chemical Philosophy, p. 148.
