Characters. - Colourless, transparent, monoclinic prisms, efflorescent in dry air, odourless, having a cooling saline and sulphurous taste.

Reactions of Sodium Sulphite, Bisulphite, and Hyposulphite. - They all evolve sulphurous acid vapours, recognised by their giving the smell of burning sulphur on the addition of hydrochloric acid to an aqueous solution. The hyposulphite is distinguished from the sulphites by the acid causing sulphur to be deposited from the solution, and thus rendering it turbid, whilst solutions of the sulphites remain clear. The sulphites are distinguished from each other by the bisulphite having an acid and the sulphite a neutral or feebly alkaline reaction.

Dose. - 5 to 20 grains, or even up to 1 drachm (3.9 gm.).

Uses. - A solution of 1 part in 8 of water is used in cases of aphthae in the mouth; it has been given also to destroy sarcinae and torulae in cases of yeasty vomiting (vide Sulphurous Acid, p. 572). In some cases of boils the sulphite and hyposulphite in 15 to 20 grain doses every 2 or 3 hours are said to have effected a cure.