Resistance to Electrolysis

219

the whole of any plate; and occasionally small glass rods were
put into the cups, between the plates, to prevent their contact.
Single plates were used to terminate the series and
complete the connection with a galvanometer, or with
a decomposing apparatus (634, 703, etc.), or both.
Now if fig. 50 be examined and compared with fig. 51,
the latter may be admitted as representing the former
in its simplest condition; for the cups, i, 11, and in of

the former, with their contents, are represented by___

the cells i, n, and in of the latter, and the metal Fig< 49.
plates Z and P of the former by the similar plates
represented Z and P in the latter. The only difference, in fact,
between the apparatus, fig. 50, and the trough represented
fig. 51, is that twice the quantity of surface of contact between
the metal and acid is allowed in the first to what would occur
in the second.

745. When the extreme plates of the arrangement just de-
scribed,, fig. 50, are connected metalli-
cally through the galvanometer g, then
the whole represents a battery con-
sisting of two pairs of zinc and platina
plates urging a current forward, which
has, however, to decompose water
unassisted by any direct chemical
affinity before it can be transmitted
across the cell in, and therefore before
itTcan circulate. This decomposition
of water, which is opposed to the
passage of the current, may, as a
Fi matter of convenience, be considered

as taking place either against the

surfaces of the two platina plates which constitute the electrodes
in the cell in, or against the two surfaces of that platina plate
which separates the cells 11 and iir, fig. 51, from each other.
It is evident that if that plate were away,
the battery would consist of two pairs of plates
and two cells, arranged in the most favourable
position for the production of a current. The
platina plate therefore, which being introduced
as at x, has oxygen evolved at one surface
and hydrogen at the other (that is, if the
decomposing current passes), may be considered as the cause
of any obstruction arising from the decomposition of water by

latina