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Look at the circuit diagram. When the lamp is operating, the zinc slowly dissolves in the electrolyte. As the dissolving goes on, an excess of electrons builds up in the zinc. Since electrons have the same electrical charge, they repel one another along the circuit. They thus force their way into the bulb filament, pass through the carbon rod, and enter the black mixture, where other reactions occur. It is this continuing movement of electrons along the circuit that we call current and that causes the high resistance filament to become white hot.

Things You Need

Carbon Electrode: a worn-out #6 dry cell (if you plan to build the cigar-box microphone later in this booklet, try to get two dry cells while you're at it). Zink Electode: zinc sheet about 5” by 10” (use whatever zinc you can salvage from the dry cell; or try galvanized sheet metal, which is zinc coated). Electrolyte: ammonium chloride (get a small block of sal ammoniac from the hardware store; it's used for cleaning soldering irons and is quite inexpensive). Container: a wide-mouthed quart jar, including lid and waxed cardboard liner. Lamp Base: wood disk about 4” in diameter. Light Source: a 1-cell penlight bulb with socket. Socket Support: tin-can strip, 1” by 2”. Switch: tin-can strip, 1/4” by 2”. Minor Items: hook-up wire, aluminum foil, napkin, old nylon stocking, small nails, small screw, wax (optional).

How to Prepare the Parts

THE CARBON ELECTRODE. Let’s begin by opening up the old dry cell. We should try to do it in a way that won’t dis turb the caked mixture around the carbon rod. Measure up ward 1/2” from the bottom of the cell and draw a line around the outside. With a metal saw, make a series of cuts through the zinc casing, turning the cell slightly after each cut. When you have finished, you will be able to pull the bottom off. Then do the same thing at the top of the cell, only this time measure downward about 1-1/4”. After you have cut through the casing at the top, run the saw into the mixture till you reach the carbon rod. A little twisting will now enable you to remove the top.