Characters. - White, opaque, deliquescent, crystalline masses having the odour of hydrocyanic acid, like which it is intensely poisonous (p. 586).

.B.P. Preparation for which it is used. Bismuthum Purificatum. Potassii Bromidum, B. and U.S.P. - Vide p. 553. Potassii Iodidum, B. and U.S.P. - Vide p. 559. Sodium. Na; 23. Sources of Sodium Salts

The chief source of sodium is common salt obtained by the evaporation of sea-water, or from salt mines. Two subsidiary sources are the nitrate of sodium and borax, both of which are found native.

General Reactions of Sodium Salts. - They are not precipitated by any of the ordinary reagents. The special test for them is the yellow colour which they give to flame. The mere appearance of the yellow colour is the test adopted by the British Pharmacopoeia, but it is improved upon in the American Pharmacopoeia, which directs that the flame should not appear more than transiently red when observed through a blue glass. In this way sodium salts are both more readily distinguished from those of potassium, and the presence of the slightest impurity is easily observed; for sodium salts are so widely distributed in nature, and the yellow colour which they give to the flame is so bright, that minute quantities of sodium mixed with potassium may disguise the violet colour which the potassium gives, although it should be present in much greater quantity than the sodium. To distinguish between potassium salts and sodium salts, it is therefore necessary to look at the flame through a blue glass, which cuts off the yellow rays emitted by the sodium of the flame, and thus allows the violet ones of the potassium to be seen.

Preparation Of Sodium Salts

Prepared from

By

Sodium chloride . .

Sea-water. . . .

Evaporation. Or found native.

Sodium sulphate . .

Sodium chloride .

Heating with sulphuric acid in the preparation of hydrochloric acid.

Sodium carbonate .

Sodium sulphate . .

Roasting with calcium carbonate and coal.

Sodium . . . .

Sodium carbonate .

Igniting with charcoal.

Sodium ethylate (Liquor)

Sodium . . .

Dissolving in ethylic alcohol.

Dried sodium carbonate

Sodium carbonate .

Heating.

Sodium bicarbonate .

Ditto .

Mixing with dry carbonate and saturating with carbonic acid.

Caustic soda . .

Ditto .

Decomposing by lime.

Sodium acetate . .

Ditto .

Neutralising with acetic acid.

Effervescent citro-tartrate

Ditto .

Heating dry carbonate with tartaric and citric acids.

Tartrate of soda and potash (soda tar-tarata)

Ditto .

Neutralising solution with acid tartrate of potassium, evaporating and crystallising.

Sodium benzoate, U.S.P.

Ditto .

Neutralising a hot solution with benzoic acid and crystallising.

Sodium phosphate .

Ditto .

Decomposing bone-ash with sulphuric acid, and saturating the acid phosphate of calcium thus obtained with sodium carbonate.

Sodium hypophos-phite

Ditto .

Decomposing hypophosphite of lime with sodium carbonate.

Liquor sodae chlori-natae

Ditto .

Passing chlorine through its solution.

Sodium valerianate .

Ditto .

Neutralising by valerianic acid.

Sodium salicylate, B. and U.S.P.

Ditto .

Neutralising solution by salicylic acid with slight excess of acid and evaporating.

Sodium sulphocarbo-late, B. and U.S.P.

Ditto .

Decomposing by barium sulpho-carbolate. The barium sulpho-carbolate is prepared by mixing equal parts of carbolic and strong sulphuric acid, allowing them to stand for some days, diluting and neutralising with barium carbonate.

Sodium bisulphite, U.S.P.

Sodium carbonate .

Saturating its solution with sulphurous acid.

Sulphite, B. and U.S.P.

Sodium bisulphite .

Adding an equal weight of sodium carbonate to the bisulphite prepared as above.

Hyposulphite, U.S.P. and B.P., App.

Sulphite . . .

Heating with sulphur.

Borax . . .

-

Found native.

Nitrate . . .

-

Found native.

Arseniate . . .

Carbonate and nitrate

Fusing with arsenious acid.

General Impurities of Sodium Salts. - As sodium carbonate is prepared from sodium sulphate, and the latter from sodium chloride, sulphates and chlorides may be present as impurities in it. As the other sodium salts are chiefly obtained from the carbonate, chlorides and sulphates also come to be present as impurities in them. They also occur even in the nitrate of sodium found native.

General Tests for Impurities in Sodium Salts. - In order to distinguish between salts of potassium and sodium, as well as to prove the absence of potassium as an impurity, the B.P. directs that the solutions of sodium salts, when acidulated, should not give a precipitate with perchloride of platinum. The U.S.P. directs that the yellow colour which sodium salts give to the flame should not appear more than transiently red when seen through a blue glass. The absence of chlorides and sulphates is ascertained by the usual tests (pp. 594, 595), and the absence of metals by the want of any colour or precipitate on the addition of hydrosulphuric acid or ammonium sulphide.

General Action of Sodium Salts. - Salts of sodium diffuse more slowly than those of potassium. They are neither absorbed nor excreted so readily, and have not a marked diuretic action. When locally applied to muscle and nerve in large doses they paralyse both, but not so powerfully as salts of potassium, nor have they such a paralysing action upon the involuntary muscle, either of the heart or the intestine. In large doses they lengthen the muscular curve, and increase the length of the curves produced by calcium and strontium instead of shortening them, like potassium (p. 142).

Urate of sodium is less soluble than urate of potassium or lithium. It is therefore less readily excreted, and forms the nodules known by the name of chalk-stones in gouty patients.