Sodium sulphate is white solid  inorganic compound with formula Na₂SO₄ as well as several related hydrates.

Sodium sulfate is used to dry organic liquids, as a filler in powdered home laundry detergents,as a fining agent which removes small air bubbles from molten glassIn the form of salt cake sodium sulphate is used in making wood pulp by the sulphate process, plate glass, window glass, and bottles, water glass, sodium sulphide, and precipitated barium sul­phate (blank fixe). One of the early patents for ore flotation by the Depart process was based on the use of acid and salt cake.