Chap. III. Alkalies and Alkaline Salts.

359

sake of other substances, as in the prepai'ation of muriate ofammonia, oxygenized muriatic acid, &c. It may be econo-mically obtained by making into a paste, with a sufficientquantity of water, eight parts of burnt gypsum, five of clay,and five of muriate of soda. This mixture is burnt in a kilnor oven, then ground to powder, diffused in a sufficient quan-tity of water, and, after being strained, is evaporated andcrystallized.

The primitive form appears to be a right rhomboid prismof about 72 and 108.

Sulphate of soda crystallizes in six-sided prisms, terminatedby dihedral summits. The crystals are often irregular, andtheir sides are usually channelled. Their taste is at first salt,and afterwards disagreeably bitter. They are soluble in 2.67parts of water at 60°, and in 0.8 at 212°. In the air theyeffloresce. They undergo the watery fusion, and, in a redhe;it, melt. They consist of 23.52 sulphuric acid, 18.48 so-da, and 58 water ; and when dried at 700°, of 56 acid, and44 soda. It is decomposed by baryta and potass, and saltscontaining these bases, and by the salts of silver, mercury,and lead.

Medical use. —Taken from half an ounce to an ounce, ormore, it proves a mild and useful purgative ; and in smallerdoses largely diluted, a serviceable aperient and diuretic. It iscommonly given in solution, but it may also be given in pow-der, after it has effloresced. In this form the dose must bereduced to one-half.

TaRTRIS POTASS.E ET SODiE ; olim, SAL RUPELLENSIS. Ed.

Tartritc of Potass and Soda, formerly Rochelle Salt.

It is prepared from the carbonate of soda and supertartrateof potass, in the same manner as the tartrate of potass.

Tartaras worn et kali. Dub.Tartrate of Soda and Kali.

Take of

Carbonate of soda, twenty ounces;

Crystals of tartar, in very fine powder, two pounds;

Distilled water, boiling, ten pints.

Dissolve the subcarbonate of soda in the water, and gradual-ly add the crystals of tartar; filter the liquor through pa-per; evaporate, and set it aside to crystallize by slowcooling.