a white crystalline compound, Na2SO4, usually known as the anhydrous compound (orthorhombic; ...) or the decahydrate (monoclinic; ...). The decahydrate is known as Glauber's salt. A metastable heptahydrate (Na2SO47H20) also exists. All forms are soluble in water, dissolving to give a neutral solution. ... Sodium sulphate may be produced industrially by the reaction of magnesium sulphate with sodium chloride in solution followed by crystallization, or by the reaction of concentrated sulphuric acid with solid sodium chloride. ...