The Ammonium thiosulphate has the chemical formula: (NH4)2S2O3. It is used in modern photographic fixer.

Photographic processing is the chemical means by which photographic film or paper is treated after exposure to produce a negative or positive image. Photographic fixer is a mix of chemicals used in the final step of the photographic processing. The fixer stabilises the image removing the unexposed silver bromide on the photographic film or paper. By fixation, the film or paper is insensitive to further action by light. Without fixing, the remaining silver bromide cause fogging of the image. Fixation may be achieved by treating with sodium thiosulphate solution commonly called Hypo. The modern quick fixture is ammonium thiosulphate. After fixation, washing is important to remove the exhaused chemicals. The chemical steps of reactions : silver bromide+ ammonium thiosulphate solution= silver ammonium thiosulphate complex +ammonium bromide.

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