Sand is known as "argillaceous," "siliceous," or "calcareous," according to composition. It is procured from pits, river-shores, sea-shores, or by grinding sand-ones; and is chiefly used for mortar concrete and plaster. Pit sand has an angular ain, and a porous, rough surface, winch makes it good for mortar, but it often contains and similar impurities. River sand is not so sharp or angular in its grit, the stains having been rounded and polished by attrition; it is fine and white, and therefore suited for plastering. Sea sand also is deficient in sharpness and grit from the me cause; it contains alkaline salts, which attract moisture. When sand contains or stones it should be "screened," or, if required of great fineness, passed rough a sieve. Sand found to contain impurities, such as clay, loam, etc, which unfit for almost every purpose, should be washed by being well stirred in a wooden trough. having a current of water flowing through it, which carries off the impurities. It is sometimes washed by machinery, such as an Archimedean screw revolving and carrying > the sand, while a stream of water flows down through it. Clean sand should leave stain when rubbed between the moist hands.

Salts can be detected by the taste, and size and sharpness of the grains can be judged of by the eye.