To find out how the chemical action in batteries works, you might imagine that you can see electrons and what happens to them in a primary elec-tric cell. The basic source of electricity produced by chemical action is the electric cell and, when two or more cells are combined, they form a battery. Now if you could see the inner workings of one of these cells, what do you suppose you would see? First you would notice the parts of the cell and their relation to each other.
You would see a case or container in which two plates of different metals, separated from each other, are immersed in the liquid which fills the container. Watching the parts of the cell and the electrons in the cell you would see that the liquid which is called the electrolyte is pushing electrons onto one of the plates and taking them off the other plate. This action results in an excess of electrons or a negative charge on one of the plates so that a wire attached to that plate is called the negative terminal.
The other plate loses electrons and becomes positively charged so that a wire at- tached to it is called the positive terminal. The action of the electrolyte in carrying electrons from one plate to the other is actually a chemical reaction between the electrolyte and the two plates. This action changes chemical energy into electrical charges on the cell plates and terminals.
Chemical Action in a Primary Cell:-
With nothing connected to the cell terminals, you would see that electrons are pushed onto the negative plate until there is room for no more. The electrolyte would take from the positive plate enough electrons to make up for those it pushed onto the negative plate. Both plates would then be fully charged and no electrons would be moving between the plates. Now suppose you connected a wire between the negative and positive ter- minals of the cell.
You would see the electrons on the negative terminal leave the terminal and travel through the wire to the positive terminal. Since there would now be more room on the negative terminal, the electro-lyte would carry more electrons across from the positive plate to the neg- ative plate. As long as electrons leave the negative terminal and travel to the positive terminal outside the cell, the electrolyte will carry electrons from the positive plate to the negative plate inside the cell. While the electrolyte is carrying electrons, you would see that the nega-tive plate is being used up and you would notice bubbles of gas at the positive terminal.
Eventually the negative plate would be completely dissolved in the electrolyte by the chemical action, and the cell would be "dead," or unable to furnish a charge, until the negative plate is replaced. For that reason, this type of cell is called a primary cell - meaning that once it has completely discharged, it cannot be charged again except by using new materials. For plates in a primary cell, carbon and most metals can be used, while acids or salt compounds can be used for the electrolyte. Dry cells such as those used in flashlights and lanterns are primary cells.
Dry Cells and Batteries:-
Almost any metals, acids and salts can be used in primary cells. There are many types of primary cells used in laboratories and for special applications, but the one which you have used and will be using most often is the dry cell. You will use the dry cell in many different sizes, shapes and weights - from the cell used in a pencil-size flashlight to the extra large dry cell used in emergency lanterns.
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Regardless of size, you will find that the material used and the operation of all dry cells is the same. If you were to look inside a dry cell, you would find that it consists of a zinc case used as the negative plate, a carbon rod suspended in the center of the case for the positive plate, and a solution of ammonium chloride in paste form for the electrolyte. At the bottom of the zinc case you would see a tar paper washer used to keep the carbon rod from touching the zinc case. At the top, the casing would contain layers of sawdust, sand and pitch.
These layers hold the carbon rod in position and prevent electro- lyte leakage. When a dry cell supplies electricity, the zinc case and the electrolyte are gradually used up. After the usable zinc and electrolyte are gone, the cell cannot supply a charge and must be replaced. Cells of this type are sealed and can be stored for a limited time without causing damage. When several such cells are connected together, they are called a dry battery. You cannot use dry cells to furnish large amounts of power so you will find them only where infrequent and emergency use is intended.
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