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. 2.--Requires little or no looking after. 3.--It may be kept ready for action in store without in any way deteriorating. 4.--It is comparatively very cheap. These advantages combine to make a Leclanché battery the most suitable of any other form of electrical battery for use as the exploding agent for electrical submarine mines, and it is now universally used for such purposes. _Signalling Battery._--The signalling battery should be so constituted as to be capable of working the electro magnet of the shutter apparatus effectually when the circuit is closed direct to earth, and yet not so powerful as by the continuous passage of the current generated by it to fire the fuze in the mine. In the case of a platinum wire fuze being in the circuit, plenty of power may be given to the battery without fear of a premature explosion from this cause, but in the case of a high tension fuze it is necessary to be very careful in order to guard against such a contingency. As in the case of a signalling or shutter battery, the electric current will be continually flowing, it is necessary to employ a constant battery, or one that requires least trouble and expense to maintain it in working order, and it is for this reason that a modified form of Daniell battery has been adopted to work the shutter apparatus.