Boy Mechanic

The following is copied from The Boy Mechanic

The high cost of dry cells has encouraged many to make and use homemade cells of various kinds, and the one described has the merit of cheapness and efficiency, as well as long life. For the battery jar, an old can about 6 in. high and 4 in. in diameter, is used. A porous cup is required, and this is made by rolling a strip of blotting paper around a stick, 1 1/2 in. in diameter, and securing the ends with melted paraffin. The bottom of the cup is made by standing it on a smooth surface which has been greased with Vaseline, and pouring in plaster of Paris, or melted paraffin, to a depth of about 1/2 in. When completed, the porous cup is stood in the center of the can, the outside space is filled with chips, borings, and turnings of iron, and a strip of zinc is placed inside the cup, as shown in the drawing.

The battery solution is made by dissolving caustic soda (powdered lye) in water in water until it will take no more; a saturated solution, in other words. The cell is filled with this solution to within an inch of the top, and connection is made with the zinc strip and the can by means of the binding posts, as shown. Owing to the caustic character of the battery solution it should not be allowed to come into contact with the skin or clothing. Such a cell has a voltage of about 1.2, and will deliver approximately two amperes on short circuit, depending on the purity of the chemicals and the fineness of the borings and turnings. The internal resistance of these cells is high, and best results are obtained by connecting a battery of them in parallel, if a large amount of current is required. However, one or two such cells will give good results for light service, such as a doorbell circuit.