A section of one of these cells is shown at [Fig. 72]. It consists of a glass vessel a, to contain the diluted sulphuric acid, within which is suspended a plate b of platinised lead, which is bent round into a cylindrical form to fit close around the inner surface of the glass vessel. In the centre of this latter is hung a porcelain perforated cup c, containing some cut-up zinc and mercury to keep it (the zinc) amalgamated. The top of each cell is furnished with a porcelain cover, through which the wires attached to the positive and negative poles of the cell project.
Due to the large quantity of liquid contained in the cell, the tendency to alter its internal resistance is retarded; also by the arrangement of the porcelain cup, above detailed, the consumption of zinc and mercury, which in an ordinary Voltaic battery is very considerable, is materially diminished.
Chromic Acid or Bichromate Battery.—This form of battery is very similar to Grove's, the difference being that, in the place of the nitric acid as the exciting liquid, either chromic acid, or a solution of bichromate of potash, sulphuric acid and water is substituted.
A form of this battery, as designed by Dr. Hertz, is used in connection with the German system of torpedo defence.
Leclanché Voltaic Battery.—This form of Voltaic battery was invented by M. Leclanché, some twelve years ago. At [Fig. 73] is shown a cell of this battery in its original form. The positive pole a consists of a plate of graphite in a porous pot b, and surrounded by a mixture of peroxide of manganese and graphite. The negative pole c is a rod or pencil of amalgamated zinc. The whole is enclosed in an outer vessel of glass d containing a solution of sal ammoniac.
A modified form of the Leclanché cell as used in a firing battery is shown at [Fig. 74]. It consists of an ebonite trough or outer vessel a about 16" long, 9" deep, and 2-3/4" wide. The negative pole or zinc plate b is of similar shape to the trough a, but with its base removed, and does not fit the trough exactly, the space between it and the trough being left to ensure the former being completely surrounded by the sal ammoniac solution; the positive pole, or carbon element, consists of four gas carbon plates c attached together at their head by means of lead, and enclosed in a flannel bag, in which they are firmly embedded in the peroxide of manganese mixture; the positive element is of such a shape that it fits loosely between the sides, and is nearly of the same height as the zinc plate.
The object of such a form of cell was to obtain an electric current of large quantity, with as few cells as possible, by which means the loss of power which might occur from the employment of a great number of small cells is avoided.
Advantages of a Leclanché Firing Battery.—The advantages of the Leclanché firing battery are:—
1.—The absence of chemical action when the battery circuit is not complete, and consequently there is no waste of material.