GLAD BER'S SALT (so called from Glauber, who discovered it in 1658) is the popular name of the neutral sulphate of soda, whose chemical composition is represented by the formula 10aq. It occurs in long four-sided translucent prisms, terminated by dihedral summits, and containing 10 atoms of water. On exposure to the air, the crystals lose all their water, and become resolved into a white powder. When heated, they readily melt in their water of crystallization; and if the heat is sufficiently con tinued, the whole of the water is expelled, and the anhydrous salt remains. Glauber's salt has a cooling, bitter, and saltish taste; it is readily soluble in water; its solubility (iu the ordinary crystalline form) increasing up to 92°, when it appears to undergo a molecular change, and to be converted into the anhydrous salt, which at this tempera ture is less soluble than the hydrated compound, and separates in minute crystals. This and other anomolies which occur in the solubility of this salt have been carefully studied by Lowel (Ana. de Monte, 3d ser. vol. ix. p. 50).
Glauber's salt is a constituent of many mineral waters, and occurs in small quantity in the blood and other animal fluids. It occurs, under the name of thenardite, near Madrid, iu the form of anhydrous octahedra deposited at the bottom of some saline lakes; and is found combined with sulphate of lime, as Glauberite in the valley of the.Ebro.
The anhydrous salt is prepared in enormous quantity from common salt and 'Oil of ,vitriol, with the view of being afterwards converted into carbonate of soda. See SODA.
For medical use a purer form is required. The salt which remains after the distilla tion of hydrochloric acid—this salt being sulphate of soda contaminated with free Sill phuric acid—is dissolved in water, to which is added powdered white marble (carbonate of lime), to neutralize the free acid, and to precipitate it as an insoluble sulphate; the solution is boiled down till a pellicle appears, is strained, and set aside to crystallize.
It is used as a common purgative, and is especially applicable in fevers and inflam matory affections, when it is necessary to evacuate the bowels without increasing or exciting febrile disturbance. The usual dose is from half an ounce to an ounce; but if it is previously dried, so as to expel the water of crystallization, it becomes doubly effi cient as a purgative. It is now much less frequently used in domestic medicine than formerly, having given place to milder aperients.