Ammonium Carbonates

Ammonium carbonates. The commercial salt was formerly known as sal-volatile or salt of hartshorn and was formerly obtained by the dry distillation of nitrogenous organic matter such as hair, horn, decomposed urine, etc., but is now obtained by heating a mixture of sal-ammoniac, or ammonium sulfate and chalk, to redness in iron retorts, the vapours being condensed in leaden receivers. The crude product is refined by sublimation, when it is obtained as a white fibrous mass, which consists of a mixture of hydrogen ammonium carbonate, NH₄?HCO₃, and ammonium carbamate, NH₂COONH₄, in molecular proportions; on account of its possessing this constitution it is sometimes called ammonium sesquicarbonate. It possesses a strong ammoniacal smell, and on digestion with alcohol the carbamate is dissolved and a residue of ammonium bicarbonate is left; a similar decomposition taking place when the sesquicarbonate is exposed to air. Ammonia gas passed into a strong aqueous solution of the sesquicarbonate converts it into normal ammonium carbonate, (NH₄)₂CO₃, which can be obtained in the crystalline condition from a solution prepared at about 30°C. This compound on exposure to air gives off ammonia and passes back to ammonium bicarbonate.