[Illustration: FIG. 3.]

The cell, A, forming the positive pole of the battery is of iron plate
brazed upon vertical supports; it is 40 centimeters long by 20
centimeters wide, and about 10 centimeters high.

We cover the bottom with a layer of oxide of copper, and place in the
four corners porcelain insulators, L, which support a horizontal plate
of zinc, D, D', 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.