Sodium metabisulfite is white or yellow crystalline powder or small crystal, with strong smell of SO2, specific gravity 1.4, soluble in water, the aqueous solution is acidic, contact with strong acid will release SO2 and generate the corresponding salts, a long time in the air, oxidation into Na2S2O6, so this product can not be long-term storage. Above 150 degrees Celsius, SO2 is broken down.