Ammonia, an industrially important chemical compound of nitrogen and hydrogen. At ordinary temperatures and pressures, ammonia is a colorless gas about three-fifths as heavy as air. It is poisonous and has a strong, choking odor. Ammonia dissolves readily in water, alcohol, and ether. In solid form, it is white and crystalline.

Plants use ammonia in the soil as a source of nitrogen, which is needed to build proteins that are essential to their life. Many commercial fertilizers, such as urea and ammonium sulfate, are produced from ammonia. In some cases, pure ammonia is added to the soil as a fertilizer.

Ammonia is used in the manufacture of dyes, explosives, plastics, drugs, nitric acid, and many other chemicals. Ammonia dissolved in water forms ammonium hydroxide. Diluted ammonium hydroxide is household ammonia, which is used for many types of cleaning.

The most important method of producing ammonia commercially is the Haber process, in which nitrogen from the air is combined with hydrogen under high pressure. Ammonia can also be obtained from coal or from animal matter containing protein, such as horns, hooves, and dung. When these materials are heated, ammonia gas is given off.

Ammonia is easily liquefied by being cooled under pressure. When liquid ammonia vaporizes, it absorbs large quantities of heat without changing its temperature. For these reasons, ammonia is widely used as a refrigerant. It is used both for industrial refrigeration and in refrigerators of the gas type.

Ammonium Salts

When ammonia reacts chemically with an acid, an ammonium salt is formed. The salt is composed of ammonium ions (positively charged groups of atoms, each group consisting of one nitrogen atom and four hydrogen atoms) and negative ions derived from the acid. Ammonium carbonate (formed from ammonia and carbonic acid) is used as an ingredient of smelling salts. Ammonium chloride, or sal ammoniac, (from ammonia and hydrochloric acid) is used in dry-cell batteries. Several ammonium salts are important as fertilizers, especially ammonium nitrate, ammonium phosphate, and ammonium sulfate. The nitrate is also used in explosives, the phosphate in flame-proofing wood and textiles, and the sulfate in water treatment and tanning.

Ammonia has the chemical formula NH3. The ammonium ion is NH4+. Ammonium hydroxide is NH4OH; ammonium carbonate, (NH4)2CO3; ammonium chloride, NH4Cl; ammonium nitrate, NH4NO3; ammonium sulfate, (NH4)2SO4.