On the Active Battery	227
in part, known and understood; but as their importance,, and
that of certain other coincident results; will be more evident
by reference to the principles and experiments already stated
and described, I have thought it would be useful, in this investi-
gation of the voltaic pile, to notice them briefly here.

 771.	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 suffi-
cient 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.1
 772.	I have already referred to this consequence (739) 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. 63, 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 com-
plete, 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 com-
paratively 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.
773.	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 neutralised by the oxide formed;
1 Philosophical Transactions, 1826, p. 413.