CHAPTER VI THE COMPOUNDS OF NITROGEN WITH HYDROGEN AND OXYGEN

In ancient times ammonia compounds were imported into Europe from Egypt, where they were prepared from the soot obtained in the employment of camels' dung as fuel in the locality of the temple of Jupiter Ammon (in Lybia), and therefore the salt obtained was called ‘sal-ammoniacale,’ from which the name of ammonia is derived. At the present time ammonia is obtained exclusively, on a large scale, either from the products of the dry distillation of animal or vegetable refuse, from urine, or from the ammoniacal liquors collected in the destructive distillation of coal for the preparation of coal gas. This ammoniacal liquor is placed in a retort with lime and heated; the ammonia is then evolved together with steam. In the arts, only a small amount of ammonia is used in a free state—that is, in an aqueous solution; the greater portion of it is converted into different salts having technical uses, especially sal-ammoniac, NH 4 Cl, and ammonium sulphate, (NH 4 ) 2 SO 4 . They are saline substances which are formed because ammonia, NH 3 , combines with all acids, HX, forming ammonia salts, NH 4 X. Sal-ammoniac, NH 4 Cl, is a compound of ammonia with hydrochloric acid. It is prepared by passing the vapours of ammonia and water, evolved, as above described, from ammoniacal liquor, into an aqueous solution of hydrochloric acid, and on evaporating the solution sal-ammoniac is obtained in the form of soluble crystals resembling common salt in appearance and properties. Ammonia may be very easily prepared from this sal-ammoniac , NH 4 Cl, as from any other ammoniacal salt, by heating it with lime. Calcium hydroxide, CaH 2 O 2 , as an alkali takes up the acid and sets free the ammonia, forming calcium chloride, according to the equation 2NH 4 Cl + CaH 2 O 2 = 2H 2 O + CaCl 2 + 2NH 3 . In this reaction the ammonia is evolved as a gas.