Chalk (carbonate of lime) is a soft white rock in a pulverent or only slightly consolidated state, being composed of minute fragments of shells, sponge spicules, etc., as may be seen on examination with a microscope. As far as is known, chalk in large quantities is to be obtained only in the South of England and in the North of France. Precipitated chalk is prepared thus. Add a solution of carbonate of soda to a solution of chloride of calcium until a precipitate ceases to fall; well wash the precipitate with pure water. To make prepared chalk, rub up pure chalk with sufficient water to form a smooth cream; stir into a large quantity of water, allow the coarser particles to settle, and decant the milky fluid; the prepared chalk will fall as a sediment in this, and must then be dried. To prepare camphorated chalk, reduce i lb. of camphor to a fine powder by triturating it in a mortar with a little alcohol; mix thoroughly with 1 lb. of precipitated carbonate of lime (chalk) and:-3 1/2 lb. of powdered orris root, and sift through finest bolting cloth.

Another process of preparing camphorated chalk is to mix together 1 oz. of camphor and 15 oz. either of precipitated or prepared chalk; the ingredients must be in the finest powder.