Matter & Energy

Matter is composed of atoms or groups of atoms called molecules. The arrangement of particles in a material depends on the physical state of the substance. In a solid, particles form a compact structure that resists flow. Particles in a liquid have more energy than those in a solid. They can flow past one another, but they remain close. Particles in a gas have the most energy. They move rapidly and are separated from one another by relatively large distances.


Ammonia, colorless, pungent gas, highly soluble in water. A saturated aqueous (water) solution of ammonia contains 45 percent ammonia by weight at 0° C (32° F) and 30 percent at ordinary room temperatures. On solution in water, ammonia becomes ammonium hydroxide, NH4OH, which is strongly basic and similar in chemical behavior to the hydroxides of the alkali metals (see Acids and Bases; Alkalies).

Ammonia was known to the ancients, who derived both the name and the substance from sal ammoniac, which was produced at the Temple of Jupiter Ammon in Libya by the distillation of camel dung. During the Middle Ages in Europe ammonia was obtained by heating the horns and hoofs of oxen and was called spirits of hartshorn. Free ammonia was obtained by the German alchemist Basil Valentine; its composition was determined by the French chemist Comte Claude Berthollet about 1777.

In the 19th century the principal source of ammonia was the destructive distillation of coal; it was an important by-product of the manufacture of fuel gases (see Gases, Fuel). Today most ammonia is produced synthetically from hydrogen and nitrogen (see Nitrogen Fixation). Ammonia is an important refrigerant (see Refrigeration) and is widely used in the chemical industries, especially in the manufacture of fertilizer, nitric acid, and explosives.

Ammonia melts at -77.7° C (-107.9° F), boils at -33.35° C (-28.03° F), and has a density of 0.68 at its boiling point and 1 atmosphere (1,013 millibars) of pressure.