cted upon; but if touched in the solution by a plate of platina,
hydrogen is evolved on the surface of the latter metal, and the zinc is
oxidized exactly as when immersed in dilute sulphuric acid (863.). I
accordingly repeated the experiment before described with weighed plates of
zinc (864. &c.), using however solution of potassa instead of dilute
sulphuric acid. Although the time required was much longer than when acid
was used, amounting to three hours for the oxidizement of 7.55 grains of
zinc, still I found that the hydrogen evolved at the platina plate was the
equivalent of the metal oxidized at the surface of the zinc. Hence the
whole of the reasoning which was applicable in the former instance applies
also here, the current being in the same direction, and its decomposing
effect in the same degree, as if acid instead of alkali had been used
(868.).

933. The proof, therefore, appears to me complete, that the combination of
the acid with the oxide, in the former experiment, had nothing to do with
the production of the electric current; for the same current is here
produced when the action of the acid is absent, and the reverse action of
an alkali is present. I think it cannot be supposed for a moment, that the
alkali acted chemically as an acid to the oxide formed; on the contrary,
our general chemical knowledge leads to the conclusion, that the ordinary
metallic oxides act rather as acids to the alkalies; yet that kind of
action would tend to give a reverse current in the present case, if any
were due to the union of the oxide of the exciting metal with the body
which combines with it. But instead of any variation of this sort, the
direction of the electricity was constant, and its quantity also directly
proportional to the water decomposed, or the zinc oxidized. There are
reasons for believing that acids and alkalies, when in contact with metals
upon which they cannot act directly, still have a power of influencing
their attractions for oxygen (941.); but all the effects in these
experiments prove, I think, that it is the oxidation of the metal
necessarily dependent upon, and associated as it is with, the
electrolyzation of the water (921. 923.) that produces the current; and
that the acid or alkali merely acts as solvents, and by removing the
oxidized zinc, allows other portions to decompose fresh water, and so
continues the evolution or determination of the current.

934. The experiments were then varied by u