Properties.—Pure ammonia gas is colourless, with a strong, irritating, pungent odour, forming white fumes of ammonic chloride, if exposed to hydric chloride vapour, and turning red moist litmus-paper strongly blue. By intense cold, or by a pressure of 61⁄2 atmospheres at the ordinary temperature, the gas is readily liquefied; the liquid ammonia boils at 38°; its observed specific gravity is ·731; it freezes at -57·1°. Ammonia is readily absorbed by water; at 0° water will take up 1000 times its own volume, and at ordinary temperatures about 600 times its volume. Alcohol also absorbs about 10 per cent. Ammonia is a strong base, and forms a number of salts. Ammonia is one of the constant products of the putrefaction of nitrogenous substances; it exists in the atmosphere in small proportions, and in everything that contains water. Indeed, water is the only compound equal to it in its universality of diffusion. The minute quantities of ammonia thus diffused throughout nature are probably never in the free state, but combinations of ammonia with hydric nitrate, carbon dioxide, &c.
§ 92. Uses.[115]—A solution of ammonia in water has many applications in the arts and industries; it is used in medicine, and is an indispensable laboratory reagent.
[115] Sir B. W. Richardson has shown that ammonia possesses powerful antiseptic properties.—Brit. Med. Journal, 1862.
The officinal caustic preparations of ammonia are—ammoniæ liquor fortior (strong solution of ammonia), which should contain 32·5 per cent. of ammonia, and have a specific gravity of ·891.
Liquor ammoniæ (solution of ammonia), specific gravity ·959, and containing 10 per cent. of ammonia. There is also a liniment of ammonia, composed of olive oil, 3 parts, and ammonia, 1 part.
Spiritus Ammoniæ Fœtidus (fœtid spirit of ammonia).—A solution of assafœtida in rectified spirit and ammonia solution, 100 parts by measure, contains 10 of strong solution of ammonia.
Strong solution of ammonia is an important ingredient in the “linimentum camphoræ composita” (compound liniment of camphor), the composition of which is as follows:—camphor, 2·5 parts; oil of lavender, ·125; strong solution of ammonia, 5·0; and rectified spirit, 15 parts. Its content of strong solution of ammonia is then about 22·6 per cent. (equivalent to 7·3 of NH3).[116]