Sodium metabisulfite appears as a white crystalline or powder solid with a slight sulfur odor. Toxic by inhalation . Strongly irritates skin and tissue. Noncombustible, but may decompose to emit toxic oxide fumes of sulfur and sodium when heated to high temperature. A corrosive acid when mixed with water. Used as a food preservative and as a laboratory reagent. Sodium disulfite is an inorganic sodium salt composed of sodium and disulfite ions in a 2:1 ratio. It has a role as a food antioxidant. It contains a disulfite.