EPSOM SALTS, small, colourless, needle-shaped crystals, white when powdered, used as a purgative. Chemically the salt is heptahydrated magnesium sulphate, the magnesii sulphas of pharmacy. It occurs dissolved in sea water and in most mineral waters, especially in those at Epsom (from which place it takes its name), Seidlitz, Saidschutz and Pullna. It also occurs in nature in fibrous excrescences, constituting the mineral epsomite or hairsalt; and as compact masses (reichardite), as in the Stass furt mines. It is also found associated with limestone, as in the Mammoth Cave, Kentucky, or with gypsum, as at Montmartre. Epsom salts form orthorhombic crystals, being isomorphous with the corresponding zinc and nickel sulphates, and also with magne sium chromate. It is used in the arts for weighting cotton fabrics, as a top dressing for clover hay in agriculture, and in dyeing. In medicine it is frequently employed as a hydragogue purgative, specially valuable in febrile diseases, in congestion of the portal system, and in the obstinate constipation of painters' colic. In the last case it is combined with potassium iodide, the two salts being exceedingly effective in causing the elimination of lead from the system. It is also very useful as a supplement to mercury, which needs a saline aperient to complete its action. It possesses the ad vantage of exercising but little irritant effect upon the bowels. Its nauseous bitter taste may to some extent be concealed by acidi fying the solution with dilute sulphuric acid, and in some cases where full doses have failed the repeated administration of small ones has proved effectual. (See MAGNESIUM.)