In order to generate electricity it is necessary to employ cells, batteries, or dynamos. Since the construction and operation of a dynamo is somewhat intricate, it will be better to start with the simpler methods of electric generation, and so work up to the more complicated forms. For small apparatus, such as electric bells and light magnets and motors, the zinc-carbon-sal-ammoniac cell will answer very well; but for larger machinery, where more current is required, the bluestone and the bi-chromate batteries will be found necessary.
A simple and inexpensive cell may be made from electric-light carbons, with the copper coating removed, and pencils of zinc, such as are used for electric-bell batteries and which can be purchased for five cents each. Copper wire is to be bound around the top of each pencil of carbon and zinc, and firmly fastened with the pliers, so that it will not pull off or become detached. It will be well to cut a groove with a file around the top of both the carbon and zinc, into which the wire will fit. The elements should then be clamped between two pieces of wood and held with screws, as shown in Fig. 1. A more efficient carbon pole is made by strapping six or more short carbon pencils around one long one, as shown in Fig. 3. The short pieces of electric-light carbons are bound to the longest carbon with heavy elastic bands, or cotton string dipped in paraffine or wax, to make the cotton impervious to water and the sal-ammoniac solution.
Another arrangement of elements is shown in Fig. 2, where a zinc rod is suspended between two carbons, the carbons being connected by a wire that must not touch the zinc.
A fruit-jar, or a wide-necked pickle-bottle, may be employed for a cell, but before the solution is poured in, the upper edge of the glass should be coated with paraffine. This should be melted and applied with a brush, or the edge of the glass dipped in the paraffine.
The solution is made by dissolving four ounces of sal-ammoniac in a pint of water, and the jar should be filled three-fourths full. In this solution the carbons and zinc may be suspended, as shown in the illustration (Fig. 4) of the sal-ammoniac cell. The wood clamps keep the carbon and zinc together, and the extending ends rest on the top of the jar and hold the poles in suspension. Plates of zinc and carbon may be clamped on either side of a square stick and suspended in the sal-ammoniac solution, as shown in Fig. 5, taking care, however, that the screws used for clamping do not touch each other.