Page:Encyclopædia Britannica, Ninth Edition, v. 17.djvu/564

Rh 520 N I T N I T in the juice of flesh. Volhard prepared it synthetically by the successive realization of the following two reactions : (1) (2) CH 3 C1. Chloracetic acid Metliylamine. 2 . NH(CH 3 ). COOH ; Methyl-amido-acetic acid. (sarkosine). CH 2. NH(CH 3 ). COOH + (CX)XH 2 Savkosine. Cyanamide. N(CH 8 ). [CH 2. COOH]. Crcatine. Betaine and Neurinc, two bases derived from trimethylamme, are of great physiological importance. Neurine (CH 3 ) 8 -N-(OH) CH. CH 2 was discovered by Liebreich as one of the congeners of a complex substance contained in the brain. By oxidation it is converted into betaiue (CH 3 ).,-N -, - CH,.CO.O which Scheibler discovered in the juice of the sugar-beet. Both bases can be produced synthetically, the betaine by first unit ing triniethylamine with chloracetic acid into a chloride, C1CH,.COOH + N(CH 3 ) 3, and then replacing the Cl by OH by means of oxide of silver and water. The hydroxide X-[OH]&amp;lt; (CH,), CH 2 .COO[H] formed spontaneously loses the bracketed [OH] and [H] as water, and becomes trimethyl-glycocoll, which is betaine. Native Alkaloids. These may be divided into (1) bodies consisting of carbon, nitrogen, and hydrogen only, generally volatile liquids (of which nicotine may be quoted as an example) ; and (2) such as contain oxygen in addition to the three elements named (quinine, morphia, strychnine, &c.). The more important of these bases are noticed in separate articles. The Albumenoids. This class comprises those substances known as albumin, fibrin, casein, &c., which, conjointly with carbo hydrates and fats respectively may be said to form the basis of vegetable and animal life. They consequently are the most important of all nitrogenous carbon compounds ; but unfortunately we know little of their chemical constitution. They are all solids containing 53 to 547 per cent, of carbon, 7 1 to 7 2 of hydrogen, 15 6 to 15 8 of nitrogen, and 1 7 to 1 8 of sulphur. Glutin and chondrin (glue) are closely allied to them. See the special articles. Analysis. In regard to general methods for the determination (or detection) of the element, see CHEMISTRY, vol. v. p. 546-7. But it may be added that the method there given as that of Dumas, for combustible carbon compounds, can be made to apply to metallic nitrates by simply substituting finely divided metallic copper for the oxide of copper as a burning agent, and that Varrentrapp and Will s method applies&quot; as it stands to metallic nitrides and amides, to metallic cyanides, and to all metal-amines. We confine ourselves here to the more important methods for the detection of certain classes of nitrogen compounds. 1. Ammonia-salts and most acid-amides and amin-acids, when treated with aqueous potash, give off their nitrogen as ammonia gas, which, if sufficient in quantity, is easily detected by (a) its pungent smell, (b) its action on turmeric or red-litmus paper, (c) its forming dense clouds of sal-ammoniac when brought into contact with a glass rod moistened with muriatic acid. Should the vapours of ammonia be too highly attenuated to be thus identified, condense them in dilute muriatic acid, and to the distillate obtained (afte neutralization of the free acid by potash or soda) apply &quot; Nessler s reagent&quot; (a solution of the salt HgL.2KI in aqueous caustic potash or soda ; see MERCURY, vol. xvi. p. 34). The least trace of ammonia, if present, assumes the form of iodide of mercur- ammonium, which, if too little to come down as a precipitate, will announce itself by imparting to the liquid an intense brown or yellow colour. One-hundredth of a milligram of ammonia dif fused throughout 50 c.c. of liquid (i.e., five million times its weight) can thus be detected with unerring certainty. 2. Nitrous and Nitric Acid. We assume the acids to be given as solutions of their alkaline salts, and may well do so because othei metallic salts of either acid can easily be brought into this form by suitable operations. A solution of alkaline nitrite, when mixed with aqueous sulphuric acid, gives off brown fumes (of N 2 3 and N 2 4 ) if it is sufficiently concentrated. In more dilute solutions the liberated nitrous acid breaks up into nitric acid and nitric oxide gas, which latter forms brown fumes (of N 2 4 ) as soon as it comes into contact with the air. In still more dilute solutions the .iberated nitrous acid remains undecomposed, but is readily detected t&amp;gt;y a sufficiency of a strong solution of ferrous sulphate or chloride, which reagents liberate nitric oxide from it and dissolve it with formation of an inky-black solution. This is the most character istic and a highly delicate test. But in the latter respect it is far surpassed by &quot; Gries s reagent,&quot; a solution of sulphate of meta- diamido-benzol in dilute sulphuric acid. When this solution is added to even the most dilute solution of nitrous acid, a yellow coloration is developed which attains its maximum of intensity after about fifteen minutes standing. This test is fully as delicate as Nessler s for ammonia. A nitrate solution, when mixed with aqueous sulphuric acid or that acid and ferrous salt, exhibits no visible change. But when the solution is mixed with its own volume of (concentrated) oil of vitriol, so as to not only liberate but also dehydrate the nitric acid, and a strong solution of ferrous sulphate is cautiously poured on the top of the mixture, nitric oxide is eliminated which dissolves in, and strikes an inky-black colour with, the ferrous salt layer. This is the test for nitrates. When a solution containing nitrates or nitrites is distilled with concentrated caustic potash or soda and aluminium foil or zinc- foil and iron filings (or any metal or combination which, with the pure alkali-solution, would give off hydrogen), the nitrogen is gradually eliminated as ammonia, which can be condensed, and, however little it may amount to, detected by Nessler s reagent, as above explained. (W. D. ) NITROGLYCERIN (synonymes Glonoin, Glonoin Oil, Dynamites, Blasting Gelatin}^ C 3 H 5 N 3 O = C 3 H 5 (NO 2 ) 3 O ;!, was discovered by Sobrero in 1846, and soon afterwards was more thoroughly investigated by Railton and by De Vrij. It is formed by the action of concentrated nitric acid, in the presence of strong sulphuric acid, upon gly cerin at a low temperature, and may be readily prepared upon a small scale by dropping the glycerin into the mixed acids, the mixture being kept artificially cooled, and afterwards poured into a large volume of water. The nitroglycerin then separates as a heavy liquid (sp. gr. 1 6), generally pale yellow, but quite colourless when pure. It is inodorous, and has a sweet pungent aromatic flavour; if it be touched with the tongue or even brought into contact with the skin severe headache ensues, but this effect does not recur after a while with those who habitually handle it, nor is their health premanently injured by working with it. Nitroglycerin is applied medicinally, in very minute doses, in cases of heart disease, but if taken even in small quantities it operates as a violent irritant poison. If a thin layer be spread upon a hard surface and struck sharply with a hammer it explodes violently ; under favourable conditions it is more sensitive to explo sion by a blow than even mercuric fulminate. It freezes (or crystallizes, in six-sided prisms) at about 40 F., and slowly liquefies again at 50. When frozen it is less sensitive to explosion; in the United States, where nitro glycerin is extensively used, as such, in mining operations, it is transported in the frozen state for greater safety. Under some circumstances, however, the readiness with which nitroglycerin and its preparations freeze is a source of danger; they have generally to be thawed, by applying heat, before use in cold weather or after they have been frozen for some time, and disastrous explosions have re sulted from this being carelessly done. Nitroglycerin is very slightly soluble in water, but is readily taken up by many solvents, especially by methyl-alcohol or Avood- spirit. This solution being non-explosive, in the early days of application of nitroglycerin it was transported in that form ; but if the spirit became weakened by evapora tion, an explosive layer of nitroglycerin containing some spirit would separate, and, in cool weather, nitroglycerin would crystallize out of the solution. The dangers attend ing the use of nitroglycerin were therefore not much diminished by the use of the solvent. Unless very carefully freed from acid and from unstable impurities, nitroglycerin will decompose more or less rapidly, especially in warm climates, and the heat developed