Ammonia

or VouaTILE ALKALI (NH,). Although ammonia does not exist in nature in the free state, ammoniacal salts are widely distributed in the soil, and also occur in the atmosphere; they are characteristic products of the decomposition of organic. substances containing nitrogen. Ammonia itself is.a gaseous substance best pre by heating ammonium chloride (sal ammoniac) with Ammonius. slaked lime, and collecting the product ovei mercury. It is a gas with a very pungent odour, which may be liquefied at 40° C. at the ordinary pre ure of the atmosphere; by the rapid evapora. tion of this liquid ammonia may be still furthe: obtained in white crystals. Ammonia is extremely soluble in water. It combines with acids to form ammoniacal salts, which, as a rule, are colourle and very soluble; the most important are the chloride and carbonate. In medicine it is used as an antacid and a stimulant. Ammoniacum, 2 gum-resin exuding from Dorema Ammoniacum, and D, Aucheri, perennial umbelliferous plants, natives of Irak, in Persia whence the guin is shipped, tid Bombay. It is reddish yellow, opalescent and slightly foetid, and is used as a substitute for the allied a afcetida, ir plasters for tumours, and as an expectorant. Africar ammoniacum, used for fumigation, is obtained fron Ferula ting it an a, a native of Morocco. It is saic to be anti-spasmodic in its action, but is chiefly used to check secretion in chronic bronchitis. Ir the form of a plaster it is also employed external]; to relieve inflamed joints. ‘Ammonites, a group of fo il molluscs related to the living Pearly Nautilus, being like it, tetrabranchiate cephalopods. Armmonite: differ from Nautilus in having the chambers of the i: shells divided by foliated partitions, and in havin; the siphuncle, or tube pa ing through the chambers lateral instead of central. ‘The genus is confined t Secondary rocks, being first found in the Trias and dying out in the Chalk. The species numb several hundreds, and some of them reach diameter of over three feet. As many of the specie: lasted but a very short time, and are fairly abundant they have been used by geologists to divide th Secondary rocks into “zones.” The name is derivec from the resemblance of the shells to the ram’ horns with which Jupiter Ammon was represented Ammonium (NH,), the metal which is supposec to exist in ammoniacal salts; its existence bein; extremely probable in theory, and extremely diff i cult to prove in practice. Under conditions of tem perature and pre ure which do not obtain in ou planet, there is little doubt that ammonium woul be easily obtainable in the metallic state, an further might be incapable of resolution int: NH,+H. The existence of the ammonium com pounds furnishes a strong argument in favour o the a umption that all metals are really comple: in structure. Just as at lower temperatures ant higher pre ures we can conceive of ammonium a an irresolvable metal, so at higher temperature and reduced pre ures we can conceive of ordinar: metals a uming the hypothetical condition nov presented by the ammonium radicle. Alchemist in believing that all metals could be transmute into gold were perhaps not, in the e ence o the thing, such idle dreamers as they are common! supposed.