Webster’s Revised Unabridged Dictionary · 1913
Epsom salts
Ep′som salts′ or salt′ (sa̤lt′) . (Med.) Sulphate of magnesia having cathartic qualities; — originally prepared by boiling down the mineral waters at Epsom, England, — whence the name; afterwards prepared from sea water; but now from certain minerals, as from siliceous hydrate of magnesia.