Faraday's Researches

190

of the base in conformity with the current and according to
the general principles already so fully laid down.

665. This view of the oxidation of the metal, or other direct
chemical action upon it, being the sole cause of the production
of the electric current in the ordinary voltaic pile, is supported
by the effects which take place when alkaline or sulphuretted
solutions (666, 678) are used for the electrolytic conductor
instead of dilute sulphuric acid. It was in elucidation of this
point that the experiments without metallic contact, and with
solution of alkali as the exciting fluid, already referred to (619),
were made.

666. Advantage was then taken of the more favourable con-
dition offered, when, metallic contact is allowed (630), and the
experiments upon the decomposition of bodies by a single pair
of plates (634) were repeated, solution of caustic potassa being
employed in the vessel v, fig. 37, in place of dilute sulphuric
acid. All the effects occurred as before: the galvanometer
was deflected; the decompositions of the solutions of iodide of
potassium, nitrate of silver, muriatic acid, and sulphate of soda
ensued at x; and the places where the evolved principles ap-
peared, as well as the deflection of the galvanometer, indicated
a current in the same direction as when acid was in the vessel v ;
i.e. from the zinc through the solution to the platina, and back
by the galvanometer and substance suffering decomposition to
the zinc.

667. The similarity in the action of either dilute sulphuric
acid or potassa goes indeed far beyond this, even to the proof
of identity in quantity as well as in direction of the electricity
produced. If a plate of amalgamated zinc be put into a solu-
tion of potassa, it is not sensibly acted 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 oxidised exactly as
when immersed in dilute sulphuric acid (598). I accordingly
repeated the experiment before described with weighed plates
of zinc (599, etc.), 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 oxidisement of 7.55 grains of zinc, still I found that the
hydrogen evolved at the platina plate was the equivalent of the
metal oxidised 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pported the opinion that acids and alkalies in combining