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| Figure 15-6 Iron-clad plate construction: (A) Positive plate, (B) detail of positive plate, and (C) negative plate. |

| Separators. The separators inserted between adjacent positive and negative plates have three functions: |

| 1. They serve as mechanical spacers to prevent actual contact. |

| 2. They serve as electrolytic channels or diaphragms that permit current to pass but prevent small particles of lead sediment from lodging on the negative plate and eventually bridging across the plates and causing a short circuit. |

| 3. They act to retain the active material in the slots, preventing it from being dislodged. |

| Separators are usually made of treated wood, such as cypress, cedar, or redwood, but they are also made of mats of felted glass wool, diaphragms of microporous rubber, or sheets of perforated hard rubber. In the iron clad type of plates, the slotted rubber cylinders act as the separators. |

| Electrolyte. For lead batteries, the electrolyte consists of diluted sulphuric acid. The ratio of water to sulphuric acid for a specific gravity of about 1.2 is approximately 2.4 to 1 by weight or 4.5 to 1 by volume. The ratios will change with a change in specific gravity. |

| When a storage battery is discharging, sulphuric acid is replaced by water. The electrolyte not only becomes weaker, it also becomes lighter because sulphuric acid is heavier than water. On the other hand, when the battery is charging, sulphuric acid replaces water and the electrolyte becomes correspondingly heavier. |

| Impurities in an electrolyte may attack the grids of the positive plates, attack the separators, or cause small local actions in the plates that will decrease the output of the batteries. |

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