AMMO'NIA (Gk. anyurtaK6v, ammoniakon, rock-salt), A colorless, pungent, gaseous compound of nitrogen and hydrogen. It was known to the ancients as volatile alkali, and is said to have been called vehement odor by Pliny. Its name is believed to be derived from Zeus Ammon, near whose temple in Libya, Upper Africa, it was first produced by horning camels' dung. Others derive it from Ammonia, a Cyre naic territory. In 1774 Priestley obtained it by boiling its aqueous solution and collecting the gas, which he termed alkaline air, over the mer curial pneumatic trough. Scheele showed that it contained nitrogen, and Iferthollet, in 1785, demonstrated its composition. Free ammonia does not occur in nature, but its salts are found in the atmosphere and in rain-water, in mineral and sea waters, in most. plants, and as a product of the decay of nitrogenous organic bodies.
It may be made by heating.ammonium chloride with lime. The principal commercial source of ammonia is from the destructive distillation of coal in gas making. In the distillation of coal in a retort, there is obtained, first, illuminating gas, and, secondly, a liquor which contains ammo nia. Allowing this liquid to settle, the aqueous portion separates, from which free ammonia is first expelled by means of steam, after which the liquor is treated with lime and further steam to expel the fixed ammonia. The steam, ammo
nia, and other gases are passed through strong sulphuric acid in lead tanks, and the crystals of ammonium sulphate which then form are re moved from time to time by means of ladles, while the free ammonia is collected in water yielding aqueous ammonia or hartshorn, a trans-. parent, colorless, and strongly alkaline liquid with an acrid, caustic taste and pungent odor. When exposed to the air, it loses ammonia, and when reduced to minus 40° C. it freezes.
Liquid ammonia has been used for motive power, and its evaporation is the basis for the Carre and Linde processes for the production of artificial cold. It is also used in pharmacy, dyeing, calico printing, and in the preparation of coloring matters, and many chemicals.
Ammonium sulphate, which is a white crys talline compound, is largely used both alone and in mixtures as an artificial fertilizer; it is also used in the manufacture of alum, and in the preparation of other ammonium salts. Ammo nium chloride, called also sal ammoniac, is used in pharmacy, in dyeing, and as a convenient source of ammonia. Ammonium carbonate, called also sal volatile, is used for scouring wool, for dyeing, and as a baking powder. Consult: Arnold, A ammonia and A n»non ia Compounds (London, 1889) ; and Lunge, Coal Tar (London, 1882).