Prep. Generally made, at the present time, from dolomite, a magnesian lime-stone (consisting of the carbonates of lime and magnesia), by treating it with sulphuric acid, which dissolves out the magnesia, and leaves the lime in the form of an insoluble sulphate of lime. Formerly it was prepared from bittern, the residual liquor left after the crystallization of common salt from sea water.

Prop. & Comp. In 4 or 6-sided colourless prisms, with from 2 to 6 terminal planes; as generally sold it is in small acicular crystals; they should not deliquesce in the air, but have a tendency to effloresce; sulphate of magnesia is soluble in water; and the solution gives copious white precipitates with chloride of barium (sulphate of baryta), and with a mixed solution of ammonia, hydrochlorate of ammonia, and phosphate of soda (ammonio-mag-nesian phosphate). The salt should not give off hydrochloric acid fumes when treated with sulphuric acid. Its aqueous solution at ordinary temperatures is not precipitated by oxalate of ammonia, showing that no lime is present. The precipitate given by carbonate of soda, when obtained from a boiling solution of 100 grains of the salt, should, when washed, dried, and heated to redness, weigh 16.26 grains. Composition (Mg. O, So3 + 7 HO).

Off. Prep. Enema Magnesiae Sulphatis. Enema of Sulphate of Magnesia. [Not officinal in U. S. P.]

Synonym. Enema Catharticum. Edin. Dub. (Sulphate of magnesia, one ounce; olive oil, one fluid ounce; mucilage of starch, fifteen fluid ounces.)

Therapeutics. In ordinary doses it acts as a saline purgative, causing a pretty free secretion of watery fluid from the canal. In small doses, and freely diluted, it causes diuresis. Epsom salts are employed very frequently, either alone or in combination with other purgatives; and are especially adapted to the treatment of febrile affections, and also where the portal system is congested: with the infusion of senna, sulphate of magnesia forms the ordinary black draught. The enema is used as a purgative.

Dose. As a purgative, 120 gr. to 1/2 oz., or more; in combination, from 60 gr. upwards; as a diuretic, 20 gr. to 60 gr.

Adulteration. When made from bittern it contains chloride of magnesium and sodium; it then deliquesces, and gives off hydrochloric acid fumes with sulphuric acid; it also precipitates nitrate of silver.