Sodium dithionite is a whitish to light yellow crystalline solid having a sulfur dioxide-like odor. It spontaneously heats on contact with air and moisture. This heat may be sufficient to ignite surrounding combustible materials. Under prolonged exposure to fire or intense heat containers of this material may violently rupture. It is used in dyeing and to bleach paper pulp. Sodium dithionite is an inorganic sodium salt that is the disodium salt of dithionous acid. It has a role as a reducing agent and a bleaching agent. It contains a dithionite(2-).