Agriculture. a whitish layer of mineral salts, especially sodium sulfate, sodium chloride, and magnesium sulfate, often occurring on top of soils where rainfall is low.
refined soda ash.
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British Dictionary definitions for white alkali
refined sodium carbonate
any of several mineral salts, esp sodium sulphate, sodium chloride, and magnesium sulphate, that often appear on the surface of soils as a whitish layer in dry conditions
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