NITROGLYCERIN (synonymes Glonoin, Glonoin Oil, Dynamites, Blasting Gelatin), C3H6N309 = C8H6(N02)303, was discovered by Sobrero in 1846, and soon afterwards was more thoroughly investigated by Eailton and by De Yrij. 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 wood-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 by the chemical change may lead to spontaneous explosions. But, when manufactured and purified according to the system originated and developed by Nobel, the liquid is possessed of great stability.
The first attempts to utilize the explosive power of nitroglycerin were made by Nobel in 1863; they were only partially successful until the plan, first applied by General Pictot in 1854, of develop-ing the force of gunpowder in the most rapid manner and to the maximum extent, through the agency of an initiative detonation (see "Detonation," art. EXPLOSIVES, vol. viii.), was applied by Nobel to the explosion of nitroglycerin. Even then, however, the liquid nature of the substance, though advantageous in one or two direc-tions, constituted a serious obstacle to its safe transport and storage and to its efficient employment; it was therefore not until Nobel hit upon the expedient of producing plastic solid preparations by mixing the liquid with solid substances, in a fine state of division, capable of absorbing and retaining considerable quantities of it, that the future of nitroglycerin as one of the most effective and convenient blasting agents was secured. Charcoal was the first absorbent used ; eventually the siliceous (infusorial) earth known as " kieselguhr " was selected by Nobel as the best material for pro-ducing DYNAMITE (q.v.), as it absorbs, after calcination, from three to four times its weight of nitroglycerin, and does not part with it easily when the mixture is submitted to pressure or frequent altera-tions of temperature. For work requiring the greatest sharpness and violence of action, the so-called No. 1 dynamite, consisting of about 75 parts of nitroglycerin and 25 parts of kieselguhr, is by far the most extensively used; other inert absorbents have been used at times, and numerous other less violent forms of dynamite (Dynamitis A base action) are prepared by impregnating mixtures of oxidizable substances and oxidizing agents (e.g., of nitrates and charcoal or carbonaceous bodies) with smaller proportions of nitro-glycerin, or by using imperfectly nitrified wood-fibre, or other forms of cellulose, as the absorbent. Lithofracteur, dunlin, glyoxilin, potentite, atlas-dynamite, lignin-dynamitc, are examples. The last-named was employed by the Fenians in the attempted outrages in Glasgow and London iu 1883. The only inert absorbent of nitro-glycerin which compares in efficiency with kieselguhr is magnesia alba, which is extensively used for making dynamite in California. The application of nitroglycerin-preparations to industrial pur-poses, especially for mining, tunnelling, and blasting work in which great cleaving and shattering effects are desired, has developed very rapidly since 1867. Thus, in that year 11 tons were produced at the various works with which Nobel is associated ; in 1870 the yield had increased to 424 tons, in 1877 to 5500 tons, and in 1882 to 9500 tons, while considerable quantities are now manufactured independently of Nobel.
The most recent and most perfect form in which nitroglycerin is now used is called blasting gelatin. This material, also invented by Nobel, is composed of the liquid and of a small proportion of so-called nitro-cotton, which consists chiefly of those products of the action of nitric acid on cellulose which are intermediate between collodion-cotton and gun-cotton (trinitro-eellulose, &c.). If the liquid is gently heated together with 5 to 7 per cent, of the finely-divided nitro-cotton, and the mixture kept stirred, the two gelatinize together, producing a translucent, plastic, and tenacious mass, which becomes hard when cooled to the freezing point of nitroglycerin, and may be kept in water for any length of time without an appreciable separation of nitroglycerin. When properly prepared, blasting gelatin is less sensitive to detonation than dynamite ; and, while its action as an explosive is somewhat more gradual, it is considerably superior to dynamite in explosive power, and even slightly more powerful than pure nitroglycerin, the reason being that the latter contains somewhat more oxygen than is required for the complete oxidation of the carbon and hydrogen, and that this excess is utilized in supplying the deficiency of oxygen existing in the feebly explosive nitro-cotton. Blasting gelatin is rapidly replacing dynamite in some of its applications, and is al-ready extensively manufactured in different countries. (F. A. A.)
The above article was written by: Sir Frederick A. Abel, K.C.B.