138 AMMONIA. 



AMETHYST. (Amethyste occidentale, Fr. ; Amethyst, Ger.) One of the vitreous 

 varieties of quartz, of a clear purple or bluish-violet tint ; but the colour is frequently 

 irregularly diffused, and gradually fades into white. The colour is supposed to b 

 due to the presence of a small per-contage.of manganese, but Hointz attributes it to a 

 compound of iron and soda. The amethyst, from the beauty of its colour, has always 

 been esteemed and used in jewellery. It was one of the stones called by the ancients 

 afjiiQuaros, a name which they conferred on it from its supposed power of preserving 

 the wearer from intoxication. The most beautiful specimens are procured from 

 India, Ceylon, and Persia, where they occur in geodes and pebbles : it is also found 

 at Oberstein, in the Palatinate ; in Transylvania ; near Cork, and in the Island of 

 May, in Ireland. H. W. B. 



AMETHYST, ORIENTAL. (Amethyate orientate, Fr. ; Demantspath, Ger.) 

 This term is applied to those varieties of corundum which are of a violet colour. See 

 CORUNDUM. H. W. B. 



AMIANTHUS is the name given to the whiter and more delicate varieties of 

 asbestos, which possess a satin-like lustre, in consequence of the greater separation of 

 the fibres of which they are composed. A variety of amianthus (the amianthoide of 

 Haiiy) is found at Oisans, in France, the fibres of which are in some degree elastic. 

 The word amianthus (from afitav-ros, undefilod) is expressive of the easy manner by 

 which, when soiled, it may be cleansed and restored to its original purity, by being 

 heated to redness in a fire. See ASBESTOS. 



AMIDE. This term and amidogen are applied to a class of substances which 

 contain ammonia deprived of an atom of hydrogen. 



AMIDINE. A name given to the soluble portion of starch. 



AMIDON. The name for starch on the Continent. 



AMINES. Chemical substances resembling Amides, but containing basic radicals. 

 See Watts's ' Dictionary of Chemistry.' 



AMMONIA. NH*. at. wt. 17. (Ammoniaque, Fr. ; Ammoniak, Ger.) The name 

 given by Bergman in 1782 to the gas prepared by treating sal-ammoniac with lime or 

 a caustic alkali. It was first isolated by Dr. Black in 1756, and distinguished by 

 him from its carbonate, with which it had been previously confounded. The aqueous 

 solution had been long known, and is mentioned by Raymond Lully in the thirteenth 

 century. Ammonia being a product of the putrefactive decay, as well as of the 

 destructive distillation of organic substances containing nitrogen, is widely diffused 

 in nature, but, from the very circumstances of its formation, it is rarely, if ever, 

 evolved in a free or uncombined state. It exists in the atmosphere, though the relative 

 quantity is small ; according to Liebig, if all the ammonia were collected at the level 

 of the sea and had a density corresponding to the atmospheric pressure there, it would 

 form a stratum less than a quarter of an inch in depth ; yet he believes that the 

 nitrogen of plants is derived entirely from this source. The opinions of chemists 

 are, however, divided upon this point ; Liebig's view is supported by Boussingault 

 and opposed by Mulder and Ville. The ammonia present in the air is carried down 

 by rain, sometimes partly in the form of nitrite or nitrate ; ths maximum amount 

 of combined nitrogen found in numerous analyses by Lawes, and Gilbert, and Way, 

 being 0'032 part in 100,000 parts of rain-water. Recent experiments by Dr. R. 

 Angus Smith have shown that the proportion of ready-formed ammonia varies with 

 the locality; thus, at Valentia, on the west coast of Ireland, it was as low as - 018, 

 whilst from the burning of coals and other causes, and the diminished area of ab- 

 sorbent soil and vegetation, it rises in large towns, London giving 0'345 and Glasgow 

 even 0'910 in 100,000. In addition there are certain nitrogenous bodies capable of 

 yielding ammonia, designated by Dr. Smith 'albumenoid ammonia,' since it is formed 

 when these bodies are treated with the same chemical reagents which evolve ammonia 

 from albumen. 



Ammonia is found in many mineral and brine springs, some kinds of rock salt, in 

 deep well-water, river-, and sea-water. In volcanic districts its salts are at times 

 exhaled in such quantity as to form an article of commerce. The eruption of 

 Vesuvius in 1794 produced so much sal-ammoniac that the peasants collected it by 

 hundredweights ; in an eruption of Hecla in 1845 a similar phenomenon was observed ; 

 also at Etna it is sometimes found in sufficient abundance to create a profitable trade. 

 Dr. Daubeny is of opinion that the volcanic ammonia is produced by the action of 

 water upon mineral nitrides (perhaps the nitrides of silicon), similar in properties to 

 the nitrides of titanium and boron, which have been recently more carefully ex- 

 amined by M. St. Claire Deville. The suffioni of Tuscany yield, besides boracic acid 

 and several different salts, sulphate of ammonia as an important by-product. All 

 cultivable soils, especially those of ferruginous or argillaceous nature, contain an 

 appreciable quantity of ammonia, and a considerable evolution of its salts has been 

 observed recently on meadow-land being overflowed by a stream of lava. Tho 



