Sodium metabisulfite or SMBS is an inorganic compound of chemical formula Na2S2O5. The substance is sometimes referred to as disodium metabisulfite. In the photographic industry, sodium metabisulfite is used as a fixative ingredient. In the perfume industry, it is used to produce vanillin. Sodium metabisulfite can be used as a preservative in the brewing industry, a coagulant in the rubber industry and a dechlorinating agent after bleaching cotton cloth. It can be used as a reducing agent in the fields of organic intermediates, dyes and leather making.