Sodium Bisulfite , or NaHSO3,is a chemical sanitizer, preservative and water dechlorinator. It is a combination of sodium, hydrogen, sulfur and oxygen. It is also called sodium hydrogen sulfate, and is classed as a sulfite, or sulfur-based chemical. Its natural form is a white crystalline powder, but turns yellow in solution. It is acidic, considered corrosive, and is a powerful reducing agent used in water treatment, textile dye preparation and film development, but most people are more familiar with its use as a food additive.