Sodii Carbonas, B.P. Sodium Carbonate.
Na2CO3, 10H2O = 286.16.
Sodium carbonate, Na2CO3, 10H2O, may be obtained by the interaction of sodium chloride and ammonium bicarbonate and subsequent ignition, or by the conversion of sodium chloride into sodium sulphate, and subsequent ignition of the latter with carbon and calcium carbonate. It occurs in translucent, colourless, efflorescent, rhombic crystals having a harsh and strongly alkaline taste. Its aqueous solution is alkaline to litmus, and gives a reddish-brown precipitate with solution of mercuric chloride. When heated to about 50° the crystals fuse, and above 80° lose the whole of their water of crystallisation. This loss amounts to 62.93 per cent. On exposure to air the crystals effloresce, the effloresced salt containing only five molecules of water of crystallisation. It should contain not less than 98.02 per cent. of pure crystalline sodium carbonate. For neutralisation, 20 parts of sodium carbonate require 9.8 of citric acid, or 10.5 of tartaric acid. Washing soda is a crude commercial form of this salt; for medicinal use it requires recrystallisation. Sodii Carbonas Monohydratus, U.S.P., contains one molecule of water of crystallisation (Na2CO3 + H2O = 124.016), and is known in commerce as "crystal soda"; it is largely employed as a water softener and bath salt.
Soluble in water (1 in 1.6); insoluble in alcohol.
Action and Uses.—Sodium carbonate is employed in the preparation of alkaline baths for use in scaly, skin diseases (see also Sodii Carbonas Exsiccatus), and an aqueous solution (0.5 per cent.) is used as a lotion, applied with a compress, to relieve irritation in eczema. The carbonate is also used to prepare "bath salts," being perfumed with oil of lavender for this purpose. It is 100 irritating for internal administration, except in very dilute solution or in effervescence with citric or tartaric acid.
Dose.—1/4 to 2 grammes (5 to 30 grains).
- Balneum Alkalinum, B.P.C.—ALKALINE BATH. 1 in 1000.
- For a full sized bath dissolve 280 grammes (5 ounces) of sodium carbonate in crystals in 140 litres (30 gallons) of water. This bath is used in skin diseases to remove scaly incrustations, also in gout and rheumatism.
- Solutio Sodii Carbonatis.—B.P. TEST SOLUTION OF SODIUM CARBONATE.
- Sodium carbonate, 10; distilled water, sufficient to produce 100.