Colorless, pungent gas composed of nitrogen and hydrogen (NH3) in the simplest stable compound of these elements. It was the first complex molecule to be identified in interstellar space. Gaseous ammonia was first isolated by Joseph Priestly in 1774. It is used in the following ways: as a starting material for the production of many commercially important nitrogen compounds, such as in the manufacture of explosives and fertilizers; and as a vapor phase neutralizing/alkalizing agent where it neutralizes effectively but provides no residual alkaline reserve. Ammonia is most often sold as an aqueous solution of ammonium hydroxide.無色、具刺激性氣味之氣體，為氮、氫所組成元素中構造最簡單的穩定化合物(NH3)。是許多商業上重要含氮化合物產品的原料物質。