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Page 298

| Figure 15-7 Lead-acid storage battery. |

| Containers. Containers are usually made of glass, hard rubber, plastic, or asphaltic composition. For stationary cells, glass is almost universally used because of its durability, transparency, and low cost. Hard rubber or plastic is used where there is danger of breakage; they are not transparent and also cost more. For small and less expensive portable batteries, asphaltic compositions are used as well as hard rubber. A cross section of a lead battery and its container is shown in Fig. 15-7. |

| Although sealed, containers provide openings for venting of accumulated gases and to permit water to be added to the cell. A removable vent plug designed to allow for the escape of gas may also serve as a removable stopper to allow filling. |

| Alkaline Battery.. |

| Plates. The positive plate consists of a nickel-plated steel frame or grid fitted with pockets made of perforated nickel-plated steel ribbon. The pockets are filled with alternating layers of nickel hydroxide and flakes of pure metallic nickel. In the so-called nickel-cadmium battery, purified graphite is used in place of the nickel flakes. The negative plate is similarly constructed, but its pockets are filled with finely divided iron oxide mixed with a small amount of an oxide of mercury as a catalyst. |

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