Sodium metabisulfite is a white or yellow crystalline powder or small crystal with a strong SO2 odor, a specific gravity of 1.4, soluble in water, and the aqueous solution is acidic. When it is in contact with a strong acid, it releases SO2 to form a corresponding salt. When it is left in the air, it oxidizes. It is Na2S2O6, so the product cannot be stored for a long time. Above 150 degrees Celsius, SO2 is decomposed.
Hang white block white or powder, no bromine or slightly amaranth smell. Soluble in water, slightly soluble in alcohol. Hydrogen sulfide is liberated in the presence of acid and is stable at pH >3. Stable to alkali. Has a strong reduction.