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Page 301

| Figure 15-9 Hydrometer battery tester. |

| will float higher out of the liquid. This is the principle of the hydrometer (Fig. 15-9). |

| Now since the acid in a lead battery becomes more dilute on discharge, it becomes possible to determine the approximate condition of the cell at any time by a simple hydrometer reading of the specific gravity of the electrolyte. When a lead battery is fully charged, the density of the acid is about 1.220, which means that it is 22 percent heavier or denser than water. When the battery is fully discharged, the density is about 1.150. |

| In an alkaline battery, the electrolyte remains essentially unchanged throughout its operating cycle, and the measurement of its specific gravity is thus of less importance than for the lead battery. Nevertheless, occasional measurements are made because the weakening of the electrolyte decreases |

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