Often, Epsom salts. Chemistry, Pharmacology. hydrated magnesium sulfate, MgSO 4 ⋅7H 2 O, occurring as small colorless crystals: used in fertilizers, the dyeing of fabrics, leather tanning, etc., and in medicine chiefly as a cathartic.
Origin
1760-70; after Epsom; so called from its presence in the local mineral water