Mag*ne"si*a (?; 277), n. [L.
Magnesia, fem. of Magnesius of the country Magnesia,
Gr. h` Magnhsi`a li`qos a magnet. Cf. Magnet.]
(Chem.) A light earthy white substance, consisting of
magnesium oxide, and obtained by heating magnesium hydrate or
carbonate, or by burning magnesium. It has a slightly alkaline
reaction, and is used in medicine as a mild antacid laxative. See
Magnesium.
Magnesia alba [L.] (Med. Chem.), a
bulky white amorphous substance, consisting of a hydrous basic
carbonate of magnesium, and used as a mild cathartic.