Origin. - Prepared by saturating a solution of sodium carbonate or caustic soda' with sulphur-dioxide gas. It should contain in the uneffloresced and air-dried condition not less than 96 per cent. of pure sodium sulphite.

Description and. Properties. - Colorless, transparent, monoclinic prisms; odorless, and having a cooling, saline, sulphurous taste. In the air the salt effloresces and is slowly oxidized to sulphate. Soluble in 2 parts of water; sparingly soluble in alcohol. It should be kept in well-stoppered bottles, in a cool place.

Dose.- 5-60 grains (0.3-4.0 Gm.) [15 grains (1 Gm.), U. S. P.].

Sodii Bisulphis - Sodii Bisulphltis - Sodium Bisulphite. U. S. P.

Origin. - Prepared from sodium carbonate or bicarbonate and sulphur dioxide. It should contain not less than 90 per cent. of pure sodium bisulphite.

Description and. Properties. - Opaque, prismatic crystals, or a granular powder, exhaling an odor of sulphur dioxide, and having a disagreeable, sulphurous taste. Exposed to the air, the salt loses sulphur dioxide and is gradually oxidized to sulphate. Soluble in 3.5 parts of water and in 70 parts of alcohol. The drug should be kept in a cool place, in small, well-stoppered bottles, filled as full as possible. Dose. - 5-30 grains (0.3-2.0 Gm.) [7 1/2 grains (0.5 Gm.), U. S. P.].