Ef`flo*resce" (?), v. i. [imp. & p. p. Effloresced (?); p. pr. & vb. n. Efflorescing (?).] [L. efflorescere to bloom, blossom; ex + florescere to begin to blossom, incho., fr. florere to blossom, fr. flos a flower. See Flower.] 1. To blossom forth. Carlyle.

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.