', raised at one end and kept at a distance from the
oxide of copper and from the metal walls of the cell; three-quarters
of this is filled with a solution of potash. The terminals, C and M,
fixed respectively to the iron cell and to the zinc, serve to attach
the leading wires. To avoid the too rapid absorption of the carbonic
acid of the air by the large exposed surface, we cover it with a thin
layer of heavy petroleum (a substance uninflammable and without
smell), or better still, we furnish the battery with a cover. These
elements are easily packed so as to occupy little space.

We shall not discuss further the arrangements which may be varied
infinitely, but point out the principal properties of the oxide of
copper, zinc, and potash battery. As a battery with a solid
depolarizing element, the new battery presents the advantage of only
consuming its element, in proportion to its working; amalgamated zinc
and copper are, in fact, not attacked by the alkaline solution, it is,
therefore, durable.

Its electromotive force is very nearly one volt. Its internal
resistance is very low. We may estimate it at 1/3 or 1/4 of an ohm for
polar surfaces one decimeter square, separated by a distance of five
centimeters.

The rendering of these couples is considerable; the small cells shown
in Figs. 1 and 2 give about two amperes in short circuit; the large
one gives 16 to 20 amperes. Two of these elements can replace a large
Bunsen cell. They are remarkably constant. We may say that with a
depolarizing surface double that of the zinc the battery will work
without notable polarization, and almost until completely exhausted,
even under the most unfavorable conditions. The transformation of the
products, the change of the alkali into an alkaline salt of zinc, does
not perceptibly vary the internal resistance. This great constancy is
chiefly due to the progressive reduction of the depolarizing electrode
to the state of very conductive metal, which augments its conductivity
and its depolarizing power.

The peroxide of manganese, which forms the base of an excellent
battery for giving a small rendering, possesses at first better
conductivity than oxide of copper, but this property is lost by
reduction and transformation into lower oxides. It follows that the
copper battery will give a very large quantity of electricity working
through low resistances, while under these conditions manganese
batteries are rapidly polarized.

The ene