Potassium Metabisulfite contains an amount of K2S2O5 equivalent to not less than 51.8 percent and not more than 57.6 percent of SO2. Potassium Metabisulfite occurs as white or colorless, free flowing crystals, crystalline powder, or granules. It gradually oxidizes in air to the sulfate. It is soluble in water, but it is insoluble in alcohol. Its solutions are acid to litmus.