AMMONIA, in chemistry. Volatile al kali, in its purest form, sulisists in a state of gas, and was thought, till the late expe riments of Mr. Davy, to be composed of azote and hydrogen. It may be obtained in the following manner : put into a retort a mixture of three parts of quick-lime and one part of sal ammoniac in powder. Plunge the beak of the retort below the mouth of a glass jar filled with mercury, and standing inverted in a ba.sin of mer cury. Apply the heat of a lamp to the retort : a gas comes over, which displaces the mercury and fills the jar. This gms is ammonia. It was known by the name of volatile alkali ; it was also called harts horn, because it was often obtained by distilling the horn of the hart ; spirit of urine, because it may be obtained by the same process from urine; and spirit of sal ammoniac, because it may be obtained &on' that salt. Dr. Black first pointed out the difference between ammonia and car bonate of ammonia, orammonia combined with carbonic acid ; and Dr. Priestley dis covered the method of obtaining. it, in a state of purity, by the process already described. Ammonia, in the state of gas, is transparent and colourless like air ; its tmste is acrid and caustic like that of the fixed alkalies, hut not nearly so strong, nor does it like them corrode those animal bodies to which it is applied ; its smell is remarkably pungent, though not unplea sant when sufficiently diluted. Its use as a stimulant to prevent fainting is well known. Animals cannot breathe it with out death, When a lighted candle is let down into this gas, it goes out three or four times successively ; but at each time the flame is considerably enlarged by the addition of another flame of a pale yel low colour, and at last this flame descends from the top of the vessel to the bottom. Its specific gravity, according to the ex periments of Kirwan, is 0.60, that of air being 1.00; while Mr. Davy, whose gas was probably purer, found it 0.55. At the temperature of 60°, a hundred cubic inches of this gas weigh. according to Kirwan, 18.16 grains, according to Davy, 17.068. Hence it is to common air nearly as 3 to 5. When exposed to a cold of —4 5°it is condensed into a liquid, which again assumes the gaseous form, when the temperature is raised. When passed
through a red hot tube of porcelain or glass, it is totally decomposed, and con verted into hydrogen and azotic gas. It combines very rapidly with water. When a bit of ice is brought into contact with this gas, it melts, and absorbs the ammo nia, while at the same time its tempera ture is diminished. Cold water absorbs this gas almost instantaneously, and at the same time heat is evolved, and the specific gravity of the water is diminish ed. Water is capable of absorbing and condensing more than a third of its weight of ammoniacal gas. It is in this state that ammonia Is usually employed by Chemists. The term ammonia almost always means this liquid solution of am monia in water. When heated to the temperature of about 130°, the ammo nia separates under the form of gas. When exposed to the temperature of — 46°, it crystallized; and when sud denly cooled down to — 68°, it assumes the appearance of a thick jelly, and has scarcely any smell. It follows, from the experiments of Mr. Davy, that a satura sed solution of ammonia is composed of 74.63 water. 25.37 ammonia.
• '100.00 Charcoal absorbs ammoniacal gas, but does not alter its properties while cold. But when the gas is made to pass through red hot charcoal, part of the charcoal combines with it, and forms a substance known by the name of prussic acid. Am monia is not acted on by raote ; but it combines rapidly with muriatic acid; the two gases concreting into the solid salt called muriate of ammonia. Ammonia does 'not combine with the metals ; but it changes some of them into oxydes, and then dissolves them. Liquid ammonia is capable of dissolving the oxydes of sil ver, copper, iron, tin, nickel, zinc, bis muth, and cobalt. When digested upon the oxydes of mercury, lead, or mangan ese, it is decomposed, water is formed by the union of the hydrogen of the ammo nia with the oxygen of the oxydes, and azotic gas is emitted. If a considerable heat be applied, nitric acid is formed at the same time with water. Several other oxydes are also partly deoxidized, when ammonia is poured into their solutions in acids. See ALKALI, CIIEMISTRI,