s and experiments already stated and described, I
have thought it would be useful, in this investigation of the voltaic pile,
to notice them briefly here.

1035. When the battery is in action, it causes such substances to be formed
and arranged in contact with the plates as very much weaken its power, or
even tend to produce a counter current. They are considered by Sir Humphry
Davy as sufficient to account for the phenomena of Ritter's secondary
piles, and also for the effects observed by M.A. De la Rive with interposed
platina plates[A].

[A] Philosophical Transactions, 1826, p. 113.

1036. I have already referred to this consequence (1003.), as capable, in
some cases, of lowering the force of the current to one-eighth or one-tenth
of what it was at the first moment, and have met with instances in which
its interference was very great. In an experiment in which one voltaic pair
and one interposed platina plate were used with dilute sulphuric acid in
the cells fig. 103, the wires of communication were so arranged, that the
end of that marked 3 could be placed at pleasure upon paper moistened in
the solution of iodide of potassium at _x_, or directly upon the platina
plate there. If, after an interval during which the circuit had not been
complete, the wire 3 were placed upon the paper, there was evidence of a
current, decomposition ensued, and the galvanometer was affected. If the
wire 3 were made to touch the metal of _p_, a comparatively strong sudden
current was produced, affecting the galvanometer, but lasting only for a
moment; the effect at the galvanometer ceased, and if the wire 3 were
placed on the paper at _x_, no signs of decomposition occurred. On raising
the wire 3, and breaking the circuit altogether for a while, the apparatus
resumed its first power, requiring, however, from five to ten minutes for
this purpose; and then, as before, on making contact between 3 and _p_,
there was again a momentary current, and immediately all the effects
apparently ceased.

1037. This effect I was ultimately able to refer to the state of the film
of fluid in contact with the zinc plate in cell i. The acid of that film is
instantly neutralized by the oxide formed; the oxidation of the zinc
cannot, of course, go on with the same facility as before; and the chemical
action being thus interrupted, the voltaic action diminishes with it. The
time of the rest was required for the diffusion of the liquid, and its
replacement