Harper's Electricity Book for Boys

by Joseph H. Adams

A porous cup is an unglazed earthen receptacle, similar to a flower-pot, through which moisture will pass slowly. The porous cup contains an amalgamated plate of zinc immersed in a solution of diluted sulphuric acid—one ounce to one pint of water. The outer cell contains a saturated solution of sulphate of copper in which a cylindrical piece of thin sheet-copper is held by a thin copper strap, bent over the edge of the outer cell. A few lumps or crystals of the copper sulphate, or bluestone, should be dropped to the bottom of the jar to keep the copper solution saturated at all times. When not in use, the zinc should be removed from the inner cell and washed off; and if the battery is not to be employed for several days, it would be well to pour the solutions back into bottles and wash the several parts of the battery, so that it may be fresh and strong when next required. When in action, the solutions in both cups should be at the same level, and be careful never to allow the solutions to get mixed or the copper solution to touch the zinc. Coat the top of the porous cell with paraffine to prevent crystallization, and also to keep it clean. Take great care, in handling the acid solutions, to wear old clothes, and do not let the liquids spatter, for they are strong enough to eat holes in almost anything, and even to char wood. The two-fluid cells are much stronger than the one-solution cells, and connected up in series they will develop considerable power.

For telegraph-sounders, large electric bells, and as accumulators for charging storage-batteries, the gravity-cell will give the most satisfactory results. The one shown in [Fig. 8] consists of a deep glass jar, three strips of thin copper riveted together, and a zinc crow-foot that is caught on the upper edge of the glass jar. These parts will have to be purchased at a supply-house, together with a pound or two of sulphate of copper (bluestone).

To set up the cell, place the copper at the bottom and drop in enough of the crystals to generously cover the bottom, but do not try to imbed the metallic copper in the crystals; then fill the jar half full of clear water. In another jar dissolve two ounces of sulphate of zinc in enough water to complete the filling of the jar to within two inches of the top; then hang the zinc crow-foot on the edge of the jar so that it is immersed in the liquid and is suspended about three inches above the top of the copper strip. The wire that leads up from the copper should be insulated with a water-proof coating and well covered with paraffine. A number of these cells may be connected in series to increase the power of the current, and for a working-battery this will show a high efficiency. Note that at first the solutions will mingle. To separate them, join the two wires and start the action; then, in a few hours, a dividing line will be seen between the white, or clear, and the blue solutions, and the action of the cell will be stronger. After long-continued use it may be necessary to draw off some of the clear zinc sulphate, or top solution, and replace it with pure water. The action of the acids reduces the metallic zinc to zinc sulphate and deposits metallic copper on the thin copper strips, and in this process an electrical current is generated.

A Plunge-battery

When two or more cells (in which sulphuric acid, bi-chromate of potash, or other strong electropoions are employed) are coupled in series, it would be well to arrange the copper and zinc, or the zinc and carbon, poles on a board, so that all of them may be lowered together into the solutions contained in the several jars. A simple arrangement of this kind is shown in [Fig. 9], where a rack is built for the jars and at the top of the end boards a projecting piece of wood, supported by a bracket, is made fast. A narrow piece of board nearly the length of the jar-rack is fitted with the battery-poles, as shown at [Fig. 9] A. The carbon and zinc, or copper and zinc, poles are attached to small blocks of wood (as described for [Fig. 5]), and this block in turn is fastened to the under side of the board with brass screws. The poles of the cells are to be connected (as explained in [Fig. 6]), and when the battery is in use the poles are immersed in the solution contained in the jars. When the battery is at rest the narrow board should be lifted up and placed on the projecting arms of the rack, so that the liquid on the poles may drain into the jars directly underneath. One or more of these battery-racks may be constructed, but they cannot be made to hold conveniently more than four or six cells each; if more cells are required, those contained in each rack must be coupled up in series.

A simpler plunge-battery is shown in [Fig. 10]. A cell-rack is made of wood and given two or three coats of shellac. The narrow board (to the under side of which the battery-poles are attached, as explained in [Fig. 9]) is hung on chains or flexible wires, which in turn are made fast to an iron shaft running the entire length of the cell-rack. This shaft is of half-inch round iron, and is held in place, at one end, by a pin and washer; while at the other the end is filed with a square shoulder, and a handle and crank is fitted to it, so that the shaft may be turned. A small hole, made at the side of the crank when it is hanging down, will receive a hard-wood peg, or a steel nail, and this will prevent the crank from slipping when the board holding the poles is raised. If a gear-wheel and tongue can be had to fit on the shaft, it will then be possible to check the shaft securely at any part of a turn of the crank. The battery-poles are to be connected in series along the top of the portable board, as explained for [Fig. 6]. When two or more of these plunge-batteries are used at one time, the wire from the carbon of one is to be connected with the zinc pole of the next, and so on. The wire from the zinc of the first battery, and the wire from the carbon of the last battery, will be the ones available for use.

A Storage-battery

When more current is desired than the simple batteries will give, a storage-battery should be employed as an accumulator. This result can be secured by coupling primary cells in series, so that they will be constantly generating and feeding the battery. Storage-batteries are too heavy to be shifted about, like single cells or small plunge-batteries; they should be placed in a cellar, where the charging or primary cells can be located close by, and, unless positively necessary, the battery of cells and the accumulator should not be moved.

With sufficiently large insulated wires (Nos. 12, 14, or 16 copper), the current may be carried to any part of the house for use in various ways—such as running a light motor or a fan, lighting a lamp-circuit, or fusing metals and chemicals for experimental purposes. While the battery to be described is not a light one in weight, nor as economical as the improved new Edison storage-battery, it is a good and constant one, and, if not overcharged or abused, will last for several years.