PAKT III.

Alkalies and Neutral Salts.

617

" Take of the salt which remains after the distillation ofmuriatic acid, two pounds; boiling water, two pints and a half. 'Dissolve the salt in the water: then add gradually as muchsubcarbonate of soda as will saturate the acid. Boil the solu-tion until a pellicle appears, and after having filtered it set itapart to crystallize. Pour the water from off the crystals, anddry them on bibulous paper."

Sulphas Sodje, Edin. Sulphate of Soda." Dissolve in water the acidulous salt which remains afterthe distillation of muriatic acid, and having mixed with it car-bonate of lime {chalk) in powder to remove the superfluousacid, set it apart until the impurities subside; then, havingpoured off the liquor, filter it through paper, and reduce it byevaporation, that crystals may be formed."

Dublin." Dissolve the salt which remains after the distillation ofmuriatic acid in a sufficient quantity of boiling water. Evapo-rate 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.), KrystalisirtesNatrum (G.), Solfato di Soda (I.).

The theory of the London process for preparing this salt isanalogous to that of the process for preparing the sulphate ofpotass; but, from the low price of the salt, manufactured on agreat scale (see Part ii.) it is preferable to saturate the super-abundant acid with chalk, and reject the sulphate of lime. Thesalt obtained by the Dublin process has a slight acidulous taste,and contains a quantity of sulphuric acid, but so loosely com-bined as scarcely to entitle it to be regarded as a supersalt; nordo its crystals differ in form from those produced by the othertwo formulae. 1

Qualities. — The taste of this salt is at first simply saline, butafterwards very disagreeably bitter. Its crystals are transparent,six-sided, irregular, channelled prisms, with dihedral summits ;efflorescent and rapidly falling to a white powder when exposedto the air. It is soluble in 2'86 parts of water at 60°, and 0 - 8 ofboiling water ; undergoes the watery fusion when heated, andin a strong heat is partially decomposed. According to Berze-lius, 100 parts contain 2.4-64 of acid, 19"36 of alkali, and 56 ofwater; and in the dried state, according to Bulcholz, 54' acid,and 46 of alkali. -

Medical properties and uses. — Sulphate of soda is a verycommon and useful purgative ; but from its nauseous taste it is

1 The crystals of the supersulpbate formed by dissolving the sulphate in sul-phuric acid, and crystallizing, are rhomboidal. The artificial salts, sold under thename of Cheltenham Sails, owe their activity to this salt For an account of them,see Dr. Paris's Pharmacologia ; art. Sulphas soda?,

" Nicholson s Journal, 4to. iii. 215.