A plate-negative is a molten metal element containing active mass (spongy lead).
The negative plate in a lead acid cell consists of a lead alloy lattice or grid in which the spaces of the grid are filled with chemically-active lead sponge. If a fully charged negative plate is removed from the acid and exposed to the air it will heat up rapidly, produce steam from the water on the surface and quickly form a deposit on the surface. During this chemical reaction, oxygen from the air reacts with the lead to produce lead oxide (PbO) and heat.
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