"Take of the salt which remains after the distillation of nitric acid, two pounds; boiling water, two gallons. Ignite the salt in a crucible until the excess of sulphuric acid is entirely expelled, then boil it in the two gallons of water till a pellicle floats, and after filtering the liquor set it aside to crystallize. Pour off the water, and dry the crystals."

Sulphas Potassa, Edin. Sulphate of Potassa.

"Dissolve the acidulous salt, which remains after the distillation of nitrous acid, in hot water, and add as much carbonate of lime in powder as will saturate the superfluous acid, and leave the whole at rest, until the faeces subside. Having poured off the fluid, filter it through paper, and evaporate until crystals form."

Sulphas Potassae, Dub. Sulphate of Potassa. "Dissolve the salt which remains after the distillation of nitric acid in a sufficient quantity of warm water. Add as much common carbonate of potassa as will saturate the superfluous acid. Let the filtered solution be evaporated with heat, that crystals may be formed."

1 This name was imposed by the French chymists in 1787. The following are some of its old names: nitrum flxum, arcanum duplicatum, sal de duobus, sal polychrestus, tartarum vitriolatum, kali vilriolatwn.

Syn. Sulphate de Potasse (F.), Schwefelsaures Kali Vitriolweinstein (G.), Zwavelzuures Kali (Dutch), Solfato di Potassa (I.).

The London College has much improved the process for making this salt, as far as refers to economy. In the Edinburgh process, the carbonate of lime, which is added to the solution of the salt, combines with the superfluous sulphuric acid, while the carbonic acid is expelled; and the residue is thus converted into sulphate of potassa. The Dublin formula is objectionable on the score of expense; the value of the salt, at the price of the pure salt made on the large scale, being to its cost very nearly as 5 to 10.l The greater part of the sulphate of commerce is prepared from the residue of the distillation of nitrous acid from nitre and sulphate of iron. This is a mixture of sulphate of potassa and red oxide of iron, from which the sulphate is easily separated by boiling water, while the oxide remains undissolved.2

Qualities. - Sulphate of potassa has a naseous, bitterish taste. It is usually procured in small, grouped, transparent crystals, of which the form is a pyramidal dodecahedron with isoceles triangular faces; but this form is subject to various modifications, according to the mode of conducting the evaporation.3 Their specific gravity is 2.4073.4 The crystals are not efflorescent; they decrepitate when heated; and are soluble in 17 parts of water at 60° and 5 parts of boiling water. The salt is decomposed by tartaric acid, by chloride of barium, chloride of calcium, bichloride of mercury, nitrate of silver, and acetate and diacetate of lead, which therefore cannot enter into formulae with it. Charcoal also decomposes it at a high temperature. Its constituents, according to the analyses of Mr. Phillips 5, are 45.45 of acid, 54.55 of alkali; that of Berzelius, 47.1 of acid, and 52.9 of alkali; and that of Berard, 42.76 of acid, and 57.24 of alkali6, or of 1 eq. of potassa = 47.15 + 1 of sulphuric acid = 40.1, making the equivalent 87.25.

1 Vide London Medical Review, April, 1810, p. 135.

2 This oxide, when dried, is of a deep red colour, and is the colcothar of commerce.

3 When a tepid solution of sulphate of potassa is in the act of crystallizing, light is evolved.

4 Hassenfratz, Amu de Chimie, xxviii. 12.

5 System of Chymistry, 4th edit. ii. 660. 6 Annales de Chimie, lxxi. 47.

Medical properties and uses. - This salt is deobstruent and cathartic. It is given with great advantage in the visceral obstructions to which children are liable; and, in combination with rhubarb or with aloes, I have found it more useful than any of the other saline purgatives, in jaundice and dyspeptic affections. On account of its sparing solubility, it is generally given in the form of powder, in doses of from grs. x. to 3j. according as it is intended to act as a deobstruent or a purgative.

Officinal preparation. - Pulvis Ipecacuanhae compositus, L. E. D.