Sodae Sulphas. Lond. Sulphate of Soda

"Take of the salt which remains after the distillation of hydrochloric acid, two pounds; boiling water, two pints; carbonate of soda, a sufficient quantity. Dissolve the salt in the water; then add gradually as much of the carbonate of soda as will saturate the acid. Boil the solution until a pellicle appear, and after having filtered it set it apart to crystallize. Pour the water from off the crystals, and dry them."

Sulphas Sodae, Edin. Sulphate of Soda.

"Dissolve in water the acidulous salt which remains after the distillation of muriatic acid, and having mixed it with carbonate of lime (chalk) in powder to remove the superfluous acid, set it apart until the impurities subside; then, having poured off the liquor, filter it through paper, and reduce it by evaporation, that crystals may be formed."

Sodae Sulphas, Dub. Sulphate of Soda.

"Dissolve the salt which remains after the distillation of muriatic acid in a sufficient quantity of boiling water. Evaporate the filtered solution to a proper point, and set it apart, that, as it slowly cools, crystals may form."

Syn. Natron Vitriolatum, P. L. 1787. Sulphate de Soude (F.), Krystalisirtes Natrum (G.), Solfato di Soda (I.).

From the low price of the salt manufactured on a great scale (see Part ii.), it is preferable to saturate the acidulous salt remaining after the preparation of the hydrochloric acid with chalk, and reject the sulphate of lime. The salt obtained by the Dublin process has a slight acidulous taste, and contains a quantity of sulphuric acid, but so loosely combined as scarcely to entitle it to be regarded as a super-salt; nor do its crystals differ in form from those produced by the other two formulae.1

Qualities.-The taste of this salt is at first simply saline, but afterwards very disagreeably bitter. Its crystals are transparent, six-sided, irregular, channelled prisms, with dihedral summits; efflorescent, and rapidly falling to an opaque white powder, when exposed to the air. It is soluble in 2.86 parts of water at 60°, and 0.8 of boiling water; undergoes the watery fusion when heated2, and in a strong heat is partially formed by the solution of these powders is a tartrate of soda, and not a bicarbonate. The powders are packed in two distinct papers, the one blue and the other white; the blue containing 3 ss. of carbonate of soda, the white gr. xxv. of tartaric acid.

1 The crystals of the bisulphate formed by dissolving the sulphate in sulphuric acid, and crystallizing, are rhomboidal. The artificial salts, sold under the name of Cheltenham salts, owe their activity to this salt. For an account of them, see Dr. Paris's Pharmacologia; art. Sulphas sodae.

2 Mr. Faraday found that, when it is heated in a flask, one part dissolves in the water of crystallization, while the other is thrown down in an anhydrous decomposed. According to Berzelius, 100 parts contain 24.64 of acid, 19.36 of alkali, and 56 of water; and in the dried state, according to Bulcholz, 54 acid, and 46 of alkali1: but according to Mr. Phillips, 55.55 of acid, and 44.45 of soda in the anhydrous state2: or in its crystalline state, its constituents are, of soda 1 eq.=31.3 + 1 of acid = 40.1 + 10 of water =90; making the equivalent 161.4.

Medical properties and uses, - Sulphate of soda is a very common and useful purgative; but from its nauseous taste it is not very generally prescribed by the physician, although this may be readily disguised by a small quantity of lemon-juice, or of cream of tartar, added to the solution. It is incompatible in prescriptions with carbonate of potassa, chloride of calcium, nitrate of silver, and acetate of lead. The dose is from ss. to ij., but, in the effloresced state, half of these quantities is sufficient.