Magnesium sulfate

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Colorless, efflorescing crystals that occur in nature as the mineral kieserite. In its heptahydrate form, magnesium sulfate is called Epsom salt, and occurs in nature as needle-shaped crystals in the mineral epsomite. Magnesium sulfate is used to add weight to silk and cotton. It increases the bleaching action of chlorinated lime. Magnesium sulfate is also used in dyeing and fireproofing fabrics and in the tanning of leather.

Synonyms and Related Terms

Epsom salts; bitter salts; magnesium sulphate (Br.)


  • Noncombustible.
  • Used medicinally as a purgative.

Physical and Chemical Properties

Soluble in water, glycerol. Slightly soluble in ethanol.

Composition MgSO4 or MgSO4-7H2O
CAS 7587-88-9

Resources and Citations

  • Richard S. Lewis, Hawley's Condensed Chemical Dictionary, Van Nostrand Reinhold, New York, 10th ed., 1993
  • Matt Roberts, Don Etherington, Bookbinding and the Conservation of Books: a Dictionary of Descriptive Terminology, U.S. Government Printing Office, Washington DC, 1982
  • The Merck Index, Martha Windholz (ed.), Merck Research Labs, Rahway NJ, 10th edition, 1983 Comment: entry 5731