Fig. 2 represents an arrangement with blocks. The jar V, is provided with a cover of copper, E, screwing into the glass. This cover carries two vertical plates of sheet-iron, A, A', against which are fixed the prismatic blocks, B, B, by means of India rubber bands. The terminal, C, carried by the cover constitutes the positive pole. The zinc is formed of a single pencil, D, passing into a tube fixed to the center of the cover. The India rubber, G, is folded back upon this tube so as to make an air-tight joint. The cover carries, besides, another tube, H, covered by a split India-rubber tube, which forms a safety valve. The closing is made hermetical by means of an India rubber tube, K, which presses against the glass and the cover. The potash to charge the element is in pieces, and is contained either in the glass jar itself or in a separate box of sheet-iron. Applying the same arrangement, we form hermetically sealed elements with a single plate of a very small size. The employment of cells of iron, cast-iron, or copper, which are not attacked by the exciting liquid, allows us to easily construct elements exposing a large surface (Fig. 3). [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.