=Ammonium, Sesquicarbonate of.= Probably 2NH_{4}HCO_{3} + NH_{4}NH_{2}CO_{3}, _i. e._ a mixture or compound of bicarbonate of ammonium and carbamate of ammonium. _Syn._ (CARBONATE OF AMMONIA, AMMONIÆ CARBONAS. B. P.). CARBONATE D’AMMONIAQUE, Fr.; KOHLENSAURES AMMONIAK, Ger. It is prepared on a very large scale commercially as follows:——Sal ammoniac or sulphate of ammonia, and chalk, equal parts, both dry and in powder, are mixed as before, and sublimed from a series of iron retorts or iron pots, into a well-cooled and capacious receiver lined with lead or earthenware; or, more generally, into such a receiver connected, by iron or lead pipes, with a second and similar one containing a stratum of water, to absorb the free ammonia evolved during the process. The so-called “Volcanic Ammonia” is evolved during the manufacture of borax, from carbonate of soda and boracic acid. It is largely used in pharmacy. _Prop._ The carbonate of ammonia, of commerce, usually occurs in the form of white, fibrous, translucent, or semi-translucent cakes, generally about two inches thick. It is less volatile and pungent than the neutral carbonate; soluble in 4 parts of water at 55° Fahr., 3·3 parts at 62°, 2·5 parts at 96°, and 2 parts at 120°; boiling water and alcohol decompose it, with the evolution of carbonic acid gas and ammonia; by age or exposure to air, the surface assumes an opaque white colour, from its carbonate flying off, and the remaining bicarbonate being less volatile. Unlike the carbonate, it can neither be resublimed nor digested or distilled with either alcohol or water, without suffering decomposition. Sp. gr. 0·966. The exact composition of this salt varies, according to its method of preparation.