AMMONIA

(NH3), colourless, pungent gas composed of nitrogen and hydrogen. It is the simplest stable compound of these elements and serves as a starting material for the production of many commercially important nitrogen compounds. Pure ammonia was first prepared by Joseph Priestley in 1774, and its exact composition was determined by Claude-Louis Berthollet in 1785. Ammonia is highly soluble in water, forming an alkaline solution called ammonium hydroxide. Moreover, it becomes highly reactive when dissolved in water and readily combines with many chemicals. Ammonia is easily liquefied by compression or by cooling to about -33 C (-27.4 F). In returning to the gaseous state, it absorbs substantial amounts of heat from its surroundings (i.e., one gram of ammonia absorbs 327 calories of heat). Because of this property, it is frequently employed as a coolant in refrigerating and air-conditioning equipment. The chief commercial method of producing ammonia is by the Haber-Bosch process, which involves the direct synthesis of the compound from its constituent elements. Ammonia from the Haber-Bosch process is supplemented by ammonia obtained as a by-product of coke ovens. The major use of ammonia is as a fertilizer. It is most commonly applied directly to the soil from tanks containing the liquefied gas. Additional quantities are converted into ammonium nitrate, ammonium phosphate, and other salts that also are utilized primarily in commercial fertilizers. In the textile industry ammonia is used in the manufacture of synthetic fibres such as nylon and rayon. In addition, it is employed in the dyeing and scouring of cotton, wool, and silk. Ammonia serves as a catalyst in the production of Bakelite and some other synthetic resins. More importantly, it neutralizes acidic by-products of petroleum refining, and in the rubber industry it prevents the coagulation of raw latex during transportation from plantation to factory. Ammonia also finds application in both the ammonia-soda, or Solvay, process, a widely used method for producing soda ash, and the Ostwald process, a method for converting ammonia into nitric acid. Ammonia is used in various metallurgical processes, including the nitriding of alloy sheets to harden their surfaces. Because ammonia can be decomposed easily to yield hydrogen, it is a convenient portable source of atomic hydrogen for welding. Finally, among its minor uses is inclusion in certain household cleansing agents.