Glauber's Salt sulphate of soda, found native, and produced artificially. The artificial salt was named from its discoverer (see above), who obtained it in making muriatic acid. The natural salt is usually met with as an efflorescence, sometimes deposited around hot springs, as at Carlsbad and Cheltenham, or about saline ponds, as in the country between the head waters of the Arkansas and Santa Fe, on the route to the Rocky mountains. It also occurs in a cavern near a volcano on the island of Hawaii, where it is produced by the action of the volcanic heat and gases upon the sea water. It is found as an efflorescence on the limestone rocks below the Genesee falls, Rochester, N. Y. It crystallizes in forms derived from an oblique rhombic prism. The crystals effloresce in the air, and lose their water of crystallization. It is most soluble in water at the temperature of 93.2° F., when, according to the experiments of Lowel, 412.22 parts of the hydrated salt are dissolved by 100 of water; at 77° only 98.48 parts are taken up, and at 68°, 58.35 parts. The salt has a taste cool at first, then saline and bitter.

It is white, transparent to opaque, of vitreous lustre, of hardness from 1.5 to 2, and specific gravity 1.481. Its composition is represented by the formula NaO, SO3 + 10IIO, making its equivalent 161, and the percentage of water 55.76. It is artificially prepared by decomposing common salt by sulphuric acid (as in the preparation of hydrochloric acid, of which process it is the residue), with an excess of acid, which is taken up by the addition of carbonate of lime. It is very largely manufactured in England and France in order to prepare from it carbonate of soda and soda ash; to avoid the production of muriatic acid, a process has been introduced of making the salt by the reaction of common salt and sulphate of iron upon each other. It is also obtained as a residuum in the manufacture of bleaching salts, muriate of ammonia, etc, and from sea water, by exposing the \vater to intense cold, when this, the least soluble salt, separates by crystallizing. - Sulphate of soda is principally of value as a medium for obtaining the other salts of soda. Formerly it was much used in medicine as an aperient and diuretic; but sulphate of magnesia has taken its place, though it is still sometimes used in small doses in combination with other drugs.

By dissolving it in hydrochloric or dilute sulphuric acid, cold is produced, by which water may be frozen in summer; and wine coolers have been made designed for its use, in which, with 12 lbs. of the salt and 10 lbs. of acid, 10 to 12 lbs. of ice have been formed in an hour. The salt is an ingredient in some kinds of glass.