2. (Chem.) To change on the surface, or throughout, to a
whitish, mealy, or crystalline powder, from a gradual
decomposition, esp. from the loss of water, on simple
exposure to the air; as, Glauber's salts, and many others,
effloresce.
3. To become covered with a whitish crust or light
crystallization, from a slow chemical change between some
of the ingredients of the matter covered and an acid
proceeding commonly from an external source; as, the walls
of limestone caverns sometimes effloresce with nitrate of
calcium in consequence of the action in consequence of
nitric acid formed in the atmosphere.