CHAPTER VI TTHE COMPOUNDS OF NITROGEN WITH HYDROGEN AND OXYGEN

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.

see caption — Fig. 43.—Method of abstracting ammonia, on a large scale, from ammonia water obtained at gas works by the dry distillation of coal, or by the fermentation of urine, &c. This water is mixed with lime and poured into the boiler C″, and from thence into C′ and C consecutively. The last boiler is heated directly over a furnace, and hence no ammonia remains in solution after the liquid has been boiled in it. The liquid is therefore then thrown away. The ammonia vapour and steam pass from the boiler C, through the tube T, into the boiler C′, and then into C″, so that the solution in C′ becomes stronger than that in C, and still stronger in C″. The boilers are furnished with stirrers A, A′, and A″ to prevent the lime settling. From C″ the ammonia and steam pass through the tube T″ into worm condensers surrounded with cold water, thence into the Woulfe's bottle P, where the solution of ammonia is collected, and finally the still uncondensed ammonia vapour is led into the flat vessel R, containing acid which absorbs the last traces of ammonia.

It must be observed that all the complex nitrogenous substances of plants, animals, and soils are decomposed when heated with an excess of sulphuric acid, the whole of their nitrogen being converted into ammonium

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