Dry cells

Another type of battery is the dry cell. Instead of a liquid, a dry cell contains a special paste of ammonium and zinc chloride. This makes it possible to carry the dry cell around with you without spilling any liquid. A dry cell is smaller than a wet cell and therefore is easier to carry. Inside the paste are two metal poles. One pole is made of zinc. This is the negative pole. The other pole, the positive one, is made of carbon. A dry cell works like a wet cell. Electrons are formed by the chemical action of the paste upon the zinc pole.

When wires are connected to the poles, the zinc sends the electrons through the wire to the carbon pole. This goes on until the zinc has been used up and holes have formed in it. The cell is then said to be worn out. Unlike the wet cell, a dry cell cannot be recharged. When it is worn out, it is thrown away and a new cell bought to replace it. Sometimes it is possible to use worn-out dry cells for a little while longer by punching holes in the sides of the cells. The cells are then placed in water, which soaks into the cell and mixes with the paste.

There is usually enough zinc left to form electrons and deliver electricity. Dry cells are used in flashlights and in bicycle lights. Usually two or three cells are used, with the top of one placed at the bottom of the other, making a series circuit. When a dry cell is used, it is better to keep the lights on for only a short period of time. The chemical action in the cell makes the battery grow weak if it is used for a long time without breaking the circuit. For this reason a flashlight should be turned on and off occasionally to give the dry cells a chance to rest.