nt,
are generally divided into two portions; one of these is exerted locally,
whilst the other is transferred round the circle (947. 996.); the latter
constitutes the electric current of the instrument, whilst the former is
altogether lost or wasted. The ratio of these two portions of power may be
varied to a great extent by the influence of circumstances: thus, in a
battery not closed, _all_ the action is local; in one of the ordinary
construction, _much_ is in circulation when the extremities are in
communication: and in the perfect one, which I have described (1001.),
_all_ the chemical power circulates and becomes electricity. By referring
to the quantity of zinc dissolved from the plates (865. 1120.), and the
quantity of decomposition effected in the volta-electrometer (711. 1126,)
or elsewhere, the proportions of the local and transferred actions under
any particular circumstances can be ascertained, and the efficacy of the
voltaic arrangement, or the waste of chemical power at its zinc plates, be
accurately determined.

1121. If a voltaic battery were constructed of zinc and platina, the latter
metal surrounding the former, as in the double copper arrangement, and the
whole being excited by dilute sulphuric acid, then no insulating divisions
of glass, porcelain or air would be required between the contiguous platina
surfaces; and, provided these did not touch metallically, the same acid
which, being between the zinc and platina, would excite the battery into
powerful action, would, between the two surfaces of platina, produce no
discharge of the electricity, nor cause any diminution of the power of the
trough. This is a necessary consequence of the resistance to the passage of
the current which I have shown occurs at the place of decomposition (1007.
1011.); for that resistance is fully able to stop the current, and
therefore acts as insulation to the electricity of the contiguous plates,
inasmuch as the current which tends to pass between them never has a higher
intensity than that due to the action of a single pair.

1122. If the metal surrounding the zinc be copper (1045.), and if the acid
be nitro-sulphuric acid (1020.), then a slight discharge between the two
contiguous coppers does take place, provided there be no other channel open
by which the forces may circulate; but when such a channel is permitted,
the return or back discharge of which I speak is exceedingly diminished, in
accordance with the principl