EXPLOSIVE

any substance or device that can be made to produce a volume of rapidly expanding gas in an extremely brief period. There are three fundamental types: mechanical, nuclear, and chemical. A mechanical explosive is one that depends on a physical reaction, such as overloading a container with compressed air. Such a device has some application in mining, where the release of gas from chemical explosives may be undesirable, but otherwise is very little used. A nuclear explosive is one in which a sustained nuclear reaction can be made to take place with almost instant rapidity, releasing large amounts of energy. Experimentation has been carried on with nuclear explosives for possible petroleum extraction purposes. This article is concerned with chemical explosives, which account for virtually all explosive applications in engineering. substance or device capable of producing a volume of rapidly expanding gas that exerts sudden pressure on its surroundings. Chemical explosives are the most commonly used, although there also are mechanical and nuclear explosives. A mechanical explosive is one in which a physical reaction is produced, like that caused by overloading a container with compressed air. Nuclear explosives, which produce a sustained nuclear reaction, are by far the most powerful, but their use has been restricted to military weapons, although studies and experiments have been conducted with regard to their controlled use in certain industrial operations. The principal chemical explosives include black powder, nitroglycerin, dynamite, and trinitrotoluene (TNT). A chemical explosive can be either gaseous, liquid, or solid, although the latter two are generally capable of producing more powerful explosions. There are two basic types of chemical explosives: detonating, or high, explosives; and deflagrating, or low, explosives. Detonating explosives, such as dynamite, decompose rapidly and create high pressure, while deflagrating explosives, although they may burn quickly, produce considerably lower pressures. Detonating explosives also are divided into primary and secondary detonators. Primary explosives are detonated by ignitionfor example, a flame or heat-producing impactwhereas secondary explosives require a separate detonator. Black powder, the first chemical explosive, was invented in China some 1,000 years ago. It is a mixture of saltpetre (potassium nitrate), sulfur, and charcoal, and originally was used exclusively for military purposes. Black powder was not used industrially until the 17th century, when it was adapted to blast out mines in Europe. To be detonated, black powder must be ignited by flame or intense heat; the original fuse systems were thin, trailing lines of the powder itself or crude wicks made of straw or other combustible materials combined with sprinklings of the powder. Nitroglycerin and dynamite succeeded black powder as the chief explosives. An Italian chemist, Ascanio Sobrero, discovered nitroglycerin in 1846. The Swedish scientist Alfred Nobel invented dynamite in 1867, the original explosive being a mixture of 75 percent nitroglycerin and 25 percent guhr (a porous, absorbent material that made the product easier to control and safer to use). Nobel developed gelatinous dynamite in 1875 by creating a jelly from the dissolution of a collodion-type nitrocotton in nitroglycerin, producing a more powerful explosive than the straight dynamites and one that proved to be safer. Later, ammonium nitrate was used in dynamite, which made it even more safe to use and less expensive to produce. Other chemical explosives have been developed over the past 200 years, although their commercial uses have been on a considerably smaller scale. Among them are chlorates and perchlorates, Sprengel explosives, liquid oxygen explosives (known as LOX), and those made from nitrostarch and from Nitramon and Nitramex. Later explosives have included ammonium nitratefuel oil mixtures and water gels. Two important developments in the history of explosives were the inventions of the safety fuse and the blasting cap. In 1831 William Bickford of England devised the safety fuse, originally a textile-wrapped cord with a black powder core, which for the first time enabled safe, accurately timed detonations. In 1865 Nobel invented the blasting cap, providing the first safe and dependable means for detonating nitroglycerin and thereby considerably expanding its use for industrial purposes. Electrical firing, first used successfully in the late 19th century, allows greater control over timing. TNT has been the most common conventional military explosive during the 20th century. First used in the Russo-Japanese War in 1905, it became the basis for most of the explosives used in subsequent wars. Other important military explosives include picric acid and ammonium picrate (PETN). Additional reading Encyclopaedic coverage of every aspect of the chemical industry is provided by Herman F. Mark et al. (eds.), Encyclopedia of Chemical Technology, 3rd ed., 31 vol. (197884), formerly known as Kirk-Othmer Encyclopedia of Chemical Technology, with a 4th edition begun in 1991; Ullmann's Encyclopedia of Industrial Chemistry, 5th, completely rev. ed., edited by Wolfgang Gerhartz et al. (1985 ); and Thorpe's Dictionary of Applied Chemistry, 4th ed., 12 vol. (193756). Works specifically on explosives include A.P. Van Gelder and H. Schlatter, History of the Explosives Industry in America (1927), a highly detailed book covering the origin and development of explosives throughout the world up to the date of its publication; M.A. Cook, The Science of High Explosives (1958), an advanced mathematical work devoted almost exclusively to theory, with a brief, interesting section on the history of explosives; C.H. Johansson and P.A. Persson, Detonics of High Explosives (1970), an outstanding book describing the behaviour of high explosives, with emphasis on experimental data; E.I. du Pont de Nemours and Company, Inc., Blasters' Handbook, 15th ed. (1969), a practical discussion of commercial blasting; Institute of Makers of Explosives, Safety in the Transportation, Storage, Handling, and Use of Explosives (1970), a pamphlet primarily designed for the guidance of the consumer; T.L. Davis, The Chemistry of Powder and Explosives, 2 vol. (194143), a general treatment of explosives with excellent coverage of pyrotechnics; T. Urbanski, Chemistry and Technology of Explosives, 3 vol. (1967), an excellent treatment of these subjects, highly recommended; N.B. Wilkinson, Explosives in History: The Story of Black Powder (1966), a popular account, written primarily as a science supplement for high school students; and U.S. Bureau of Mines, Apparent Consumption of Industrial Explosives and Blasting Agents in the United States (annual). Norman Gardner Johnson The Editors of the Encyclopdia Britannica