Sodii Carbonas Exsiccatus, B.P. Exsiccated Sodium.
Na2CO3 = 106.0.
Exsiccated or nearly anhydrous sodium carbonate may be obtained by heating any of the crystallised forms of sodium carbonate until the water of crystallisation is expelled, or by heating the bicarbonate precipitated in the ammonia-soda process. It occurs as a white, amorphous, odourless, loose powder, which does not cake on pressure, and absorbs moisture from the air without becoming moist. For analytical use this salt is required to be free from sulphate and chloride, a condition which can only be realised by heating the purest bicarbonate, or by repeated recrystallisation of the carbonate. Each 53 grains of exsiccated sodium carbonate is equivalent to 142 grains of the crystalline salt.
Freely, but somewhat slowly soluble in water, the solution having the same properties as those of the crystalline salt.
Action and Uses.—Exsiccated sodium carbonate is largely used as a bath powder and water softener, to precipitate lime and magnesia salts from hard water. It is also the basis of anti-uric bath salts for use in gout and rheumatism.
Dose.—2 to 6 decigrams (3 to 10 grains).