Prepared by saturating a solution of carbonate of soda with sulphurous acid gas, and crystallizing. It occurs in white efflorescent prisms which have a slight alkaline reaction, and the odor and taste of sulphurous acid; soluble in cold water (1 part in 4), and in less than 1 part boiling water.

Sodoe Hyposulphis - Hyposulphite of Soda (Appendix B. P.). - Prepared by gently warming a solution of sulphite of sodium with finely-powdered sulphur, or by passing sulphurous acid gas through it. Occurs in colorless crystals (oblique rhombic prisms); bitter, slightly alkaline, and sulphurous in taste, less unpleasant than the sulphite. Very soluble in water, not in alcohol; decolorises iodine solutions, and dissolves salts of silver which are commonly insoluble, e.g., the chloride. A solution of hyposulphite is distinguished from one of sulphite by the precipitation of sulphur on adding sulphuric acid. Hyposulphites do not act on iodide of potassium.