Ammonium sulfate (NH4)2SO4), also called diazanium sulfate, diammonium sulfate and sulfuric acid, diammonium salt, is an inorganic salt that appears as an odorless white solid at room temperature. As the salt of sulfuric acid, a strong acid, and ammonia, a weak base, it forms an acidic solution when added to water. The compound occurs naturally as mascagnite and is created in the laboratory by treating ammonia with sulfuric acid.
The main commercial use of (NH4)2SO4 is as a fertilizer for clay soils with high pH. In addition to serving as a nitrogen source, it helps lower soil pH. In the laboratory, (NH4)2SO4 is used to precipitate proteins. It is also a common vaccine additive in the United States, and it is used as a food additive to regulate the acidity of breads and flours. In addition, (NH4)2SO4 is used in the preparation of other ammonium salts and as a component in flame retardant mixtures. A saturated solution of (NH4)2SO4 in heavy water is used as a standard in sulfur NMR spectroscopy.