with the label "Contains Sulfites" in the US. It is used as a reducing agent to break sulfide bonds in shrunken items of clothing made of natural fibres, thus allowing the garment to go back to its original shape after washing It is used as a SO2 source (mixed with air or oxygen) for the destruction of cyanide in commercial gold cyanidation processes. It is used as a SO2 source (mixed with air or oxygen) for the precipitation of elemental gold in chloroauric (aqua regia) solutions. It is used in the water treatment industry to quench residual chlorine. It is used in tint etching iron-based metal samples for microstructural analysis. It is used as a fungicide for anti-microbe and mould prevention during shipping of consumer goods such as shoes and clothing. Plastic stickers and packaging (such as Micro-Pak™) containing the anhydrous, sodium metabisulfite solid active ingredient are added prior to shipping. The devices absorb moisture from the atmosphere during shipping and release low levels of sulfur dioxide. It is used for preserving fruit during shipping. It is used as a solvent in the extraction of starch from tubers, fruit, and cereal crops. It is used as a pickling agent to treat high pressure reverse osmosis and nanofiltration water desalination membranes for extended storage periods between uses. Safety Sodium metabisulfite, despite not being flammable, decomposes in 150°C of heat releasing toxic gasses when decomposed. It is corrosive when dissolved in water. Harmful if swallowed, it is corrosive to metals and should be stored safely. References External links International Chemical Safety Card 1461 The surprisingly elusive crystal structure of sodium metabisulfite CDC - NIOSH Pocket Guide to Chemical Hazards Metabisulfites Sodium compounds Food additives Disinfectants Homebrewing E-number additives