=AMMONIA.= NH_{3}. _Syn._ AMMONIA GAS, AMMONIACAL GAS, ANHYDROUS AMMONIA, TERHYDRIDE OF NITROGEN; AMMONIAQUE, Fr.; AMMONIAK, Ger. At the present day the ammonia of commerce is chiefly prepared from the ammoniacal liquor of the gas-works and the manufactories of ivory black, animal charcoal, &c. Lant or stale urine is also an important source of ammonia. In these places a large quantity of crude ammoniacal liquor is produced; to which either sulphuric or hydrochloric acid is added, by which it is converted into a salt, which may be obtained nearly pure by evaporation, and one or more crystallisations, and, in the case of the hydrochlorate and carbonate, subsequent sublimation. Other sources and processes have been sought out and occasionally adopted for the preparation of the principal salts of ammonia (its sulphate, carbonate, and hydrochlorate); some of which have been patented, but few of them have got into general use, or have been carried out on the large scale. For many years the manufacture of ammonia and its compounds has incessantly engaged the attention of European chemists. Many unsuccessful attempts have been made to directly convert the nitrogen of the atmosphere into ammonia. Of these we may mention one which consisted in passing a mixture of nitrogen, carbonic oxide and steam over red-hot hydrate of lime, whereby ammonia and carbonic acid are formed. A plan for the indirect application of atmospheric nitrogen in the preparation of ammonia was suggested by Margueritte, in which it was proposed that cyanide of barium should be prepared, and its nitrogen converted into ammonia by the aid of a current of superheated steam at 600° C. According to the description of this process in a patent, not, however, in practice, native carbonate of baryta is calcined with about 30% of coal-tar, for the purpose of rendering the mass porous as well as more readily converted into caustic baryta at a lower temperature. The carbonaceous mass is, after cooling, placed in a retort, and kept at a temperature of 300° C., while air and aqueous vapour are forced in, the result being the formation of ammonia in considerable quantity, and carbonate of baryta, which is again used. Ammonia is evolved from ball soda while cooling; during the formation of cyanogen and cyanide of potassium in blast furnaces; and the formation of sal-ammoniac in the process of iron smelting.