Crude chalk is prepared for use by the processes of levigation and elutriation, by which it is reduced to the state of an impalpable powder. in the pasty state in which it is deposited by the water, in elutriation,.

It is made to assume the form of little cones, in which it is usually kept in the shops. Prepared chalk is of a grayish-white colour, a soft feel, pulverulent, inodorous, and of a very slight peculiar taste. it is insoluble in water when quite pure, but is taken up by it in small proportion when containing carbonic acid; and, as water ordinarily contains a little of this acid, it is capable of dissolving the calcareous carbonate. Thus limestone water is formed, in which it is probable that the lime is in the state of a bicarbonate. Chalk effervesces with acids. it always contains impurity, but not sufficient, or of such a character as to impair its efficiency.