Prep. By heating in a clay crucible, to dull redness, one pound of nitrate of soda, with an ounce and a quarter of recently burned charcoal in fine powder. In this process the nitrate is partially deoxidized by means of the charcoal.
Prop. & Comp. The nitrate is a fusible salt, occurring in white fragments, opaque, soluble in water and rectified spirit. The watery solution gives a precipitate with nitrate of silver (nitrite of silver), which dissolves when the solution is heated. When a fragment is moistened with a solution of sulphate of copper it acquires a fine emerald green colour from the formation of the green nitrite of copper. Tartaric acid, added to a strong solution, developes ruddy fumes, by setting free the nitrous acid, but gives no precipitate, showing that no potash is present. Composition (Na O, No3).
Use. It is used in the formation of Spiritus AEtheris Nitrosi. Sodoe Phosphas. Phosphate of Soda; Tasteless Purging Salts.
Prop. So Comp. Phosphate of soda forms large, transparent, oblique, rhombic prisms, with a mild saline taste, efflorescing in the air. It imparts a yellow colour to flame, is alkaline in reaction, very soluble in water, and is precipitated white by chloride of barium, the precipitate (phosphate of baryta) being soluble without effervescence in dilute nitric acid; with nitrate of silver it throws down the yellow phosphate, also soluble in nitric acid; it loses 63 per cent. of water at a dull red heat, and the remaining salt dissolved in water gives with chloride of barium a precipitate entirely soluble in dilute nitric acid, and with nitrate of silver a precipitate of a white colour, owing to the change of the tribasic acid into pyrophosphoric acid, by the action of heat. Composition (2NaO, HO,Po5+24HO).
Therapeutics. In large doses it acts as a mild saline purgative; in smaller ones as a diuretic, altering also the condition of the urine, rendering it alkaline, and increasing its solvent power for uric acid; sometimes employed as a pleasant purgative for children and delicate persons, and frequently in the uric acid diathesis.
Dose. As a purgative, 1/2 oz. to 1 oz.; as a diuretic, 30 gr. to 120 gr. - given in mutton broth it is almost tasteless.
Adulteration. It frequently contains a little phosphate of lime, which renders the solution milky.