What is (a) The formation of the whitish powder or crust on the surface of efflorescing bodies, as salts, etc. (b) The powder or crust thus formed called?

efflorescence — (Chem.) (a) The formation of the whitish powder or crust on the surface of efflorescing bodies, as salts, etc. (b) The powder or crust thus formed. (Webster's 1913.)

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