(From levis, light). The pharmaceutical operation, by which hard substances are reduced to an impalpable powder; but unless the instrument is very hard, as much of the stone as of the medicine may be discovered in it. In many instances the substances are levigated with water, and suffered to dry on chalk; sometimes the fine powder is separated, after levigation, by washing. If the whole is agitated in water, the coarser parts will subside, while the finer ones may be poured off with the fluid, and will subside after a longer rest. Thus the powder may be obtained of any degree of fineness, according to the time suffered to elapse before the water is first poured off. We observe, however, in the Encyclopedia Britannica, a very convenient instrument called a fanner, which separates the finer powder by a blast of air, on the same principle as the machine for winnowing corn acts, but know not how it really succeeds in practice, so that we shall not fill our page with the description.