Sodium nitrite

   with chemical formula NaNO2

Sodium nitrite, with chemical formula NaNO2, is used as a color fixative and preservative in meats and fish. When pure, it is a white to slight yellowish crystalline powder. It is very soluble in water and is hygroscopic. It is also slowly oxidized by oxygen in the air to sodium nitrate, NaNO3. The compound is a strong oxidizing agent.

   It is also used in manufacturing diazo dyes, nitroso compounds, and other organic compounds; in dyeing and printing textile fabrics and bleaching fibers; in photography; as a laboratory reagent and a corrosion inhibitor; in metal coatings for phosphatizing and detinning; and in the manufacture of rubber chemicals. It may also be used as an electrolyte in electrochemical grinding manufacturing processes, typically diluted to about 10% concentration in water. Sodium nitrite also has been used in human and veterinary medicine as a vasodilator, a bronchodilator, and an antidote for cyanide poisoning.

   Heated at high temperatures, it decomposes, providing sodium oxide, nitrogen(II) oxide and oxygen. This possibly allowed the crew of the first operable submarine not to die due to the high concentration of the carbon dioxide, as the sodium oxide absorbs the least.

   As a food additive, it serves a dual purpose in the food industry since it both alters the color of preserved fish and meats and also prevents growth of Clostridium botulinum, the bacterium which causes botulism. In the European Union it may be used only as a mixture with salt containing at most 0.6% sodium nitrite. It has the E number E250. Potassium nitrite (E249) is used in the same way.

   While this chemical will prevent the growth of bacteria, it can be toxic in high amounts for animals, including humans. To prevent toxicity, sodium nitrite (blended with salt) sold as a food additive is dyed bright pink to avoid mistaking it for plain salt or sugar.