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Black and white photograph showing the "chance" flotation process at a coal cleaning plant.

This photograph shows the top of the cone (looks like a circular tank). The cone contains a mixture of sand and water, which, being kept in motion by an upward current, forms a dense mixture on which coal floats, while the heavier shale sinks to the bottom of the cone. When the plant is in operation, the small coal from the screens is fed into the cone from the inclined shute, and the clean coal, with sand and water, flows into the trough on the left, and thence onto the perforated screenplates.