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.

Sodium nitrite is an industrial salt which is a white opaque crystal shaped like salt. Nitrite has sodium nitrite for human body

Harmful, can oxidize methemoglobin in the blood into methemoglobin, lose the ability to transport oxygen and cause tissue hypoxia damage. Nitrite is not only a carcinogen, but also ingestion of 0.2-0.5g can cause food poisoning, 3g can be fatal. Nitrite is a kind of food additive, which plays a role in coloring and antisepsis, and is widely used in animal foods such as cooked meat, enema and canned food. In view of the many beneficial functions of nitrite for meat pickling, it is still allowed to be used in countries around the world to marinate meat, but the amount is strictly limited.