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Ammonium Thiosulfate
Other Names: Diammonium thiosulfate, Ammonium thiosulphate, ATS

CAS Number: 7783-18-8
Sum Formula: (NH₄)₂S₂O₃
Molar Mass: 148.20 g/mol
Appearance: Colorless to white crystalline solid or aqueous solution (commonly available as a ~60–70% solution)

Ammonium thiosulfate is an inorganic salt composed of ammonium and thiosulfate ions. It is highly soluble in water and primarily used in photographic fixing solutions, metal leaching, and as a sulfur-based fertilizer in agriculture.

Chemical and Physical Properties
Density (solid): ~1.68 g/cm³
Melting Point: Decomposes on heating
Boiling Point: Not applicable (decomposes)
Solubility in Water: Very soluble
Solubility in Other Solvents: Insoluble in alcohols; soluble in ammonium hydroxide
Odor: Slight ammonia-like odor (especially in solution)

Applications
Photography: Used as a fixing agent to dissolve unreacted silver halides from photographic emulsions.
Metal Leaching: Employed in gold and silver extraction as a non-cyanide lixiviant.
Agriculture: Serves as a liquid sulfur and nitrogen fertilizer.
Water Treatment: Occasionally used in dechlorination and chemical neutralization processes.
Analytical Chemistry: Reagent for precipitation or complexation reactions involving metal ions.

Safety
This chemical does not meet GHS hazard criteria for 97.1% (168 of 173) of all reports.

Handling and Storage
Storage Conditions: Store in a tightly closed container in a cool, dry, and well-ventilated area. Protect from heat, acids, and oxidizing agents.
Handling Precautions: Avoid prolonged exposure to moisture or air, especially for dry forms. Use appropriate PPE and avoid generating dust or aerosol.