Page:Electrical Engineering Volume 1.djvu/309

Rh contained in the cell, It follows that there is enough peroxide in the porous cup to last while four zincs are being consumed, while the ammonium chloride will not last longer than $1 1⁄2$ zincs. As the zincs are usually replaced when eaten away to about $1⁄8$ in, or $1⁄16$ in. diameter, the solution need not be replaced until two zincs have been consumed, and the contents of the porous cup will last as long as five or six zincs. The consumption of zinc in the Leclanche cell is about 23 ampere-hours per ounce of zinc, and as about $1 3⁄4$ ounces of each zinc rod may be consumed, the life of each zinc is then about 40 ampere-hours. The E. M. F. of this type of cell is about 1.48 volts, and its internal resistance about 4 ohms.

2677. It is usual to seal the carbon and depolarizer into the porous cup by some compound, such as sealing-wax, leaving small tubes or holes, by which whatever gas not absorbed by the depolarizer may escape. This sealing necessitates the entire renewal of the porous cup, with contents, when the depolarizer is exhausted; to obviate this expense, some makers use a carbon porous cup and place the zinc inside, at the center, the space between the zinc and carbon being filled with peroxide.

2678. A form of Leclanche cell, made by the Law Battery Co., also replaces the clay porous cup by one made of carbon, but in this case the zinc is outside the carbon, as in the regular form. The carbon cup is made with a screw cover, also of carbon, which renders the replacing of the depolarizer a simple matter. This construction reduces the cost of maintenance of the cell, but increases the first cost.

2679. Another widely used form of Leclanche cell is the Gonda Leclanche, which uses no porous cup whatever; the manganic oxide is mixed with granulated carbon and some gummy substance, and compressed into cakes under great pressure. These cakes are attached to the sides of the carbon plate, and act in the same manner as the depolarizer in the regular form.