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Rh insensitive to shock. All these gelatinized powders are a little less easily ignited than black powders. A slightly different cap composition is required for small-arm cartridges, and cannon cartridges generally require a small primer or starter of powdered black gunpowder.

It is desired that a propellant shall produce the maximum velocity with the minimum pressure. The pressure should start gently so that the inertia of the projectile is overcome without any undue local strain on the breech near the powder chamber, and more especially that as more and more space is given to the gases by the movement of the projectile up the gun to the muzzle, gas should be produced with sufficient rapidity to keep the pressure nearly uniform or slightly increasing along the bore. The leading idea for improvements in relation to propellants is to obtain the greatest possible pressure regularly developed, and at the same time the lowest temperatures.

Law.—In 1860 an act was passed in England “to amend the law concerning the making, keeping and carriage of gunpowder and compositions of an explosive nature, and concerning the manufacture and use of fireworks” (23 & 24 Vict. c. 139), whereby previous acts on the same subject were repealed, and minute and stringent regulations introduced. Amending acts were passed in 1861 and 1862. In 1875 was passed the Explosives Act (38 & 39 Vict. c. 17), which repealed the former acts, and dealt with the whole subject in a more comprehensive manner. This act, containing 122 sections, and applying to Scotland and Ireland, as well as to England, constitutes, with various orders in council and home office orders, a complete code. The act of 1875 was based on the report of a committee of the House of Commons, public opinion having been greatly excited on the subject by a terrible explosion on the Regent’s Canal in 1874. Explosives are thus defined: (1) Gunpowder, nitroglycerin, dynamite, guncotton, blasting powders, fulminate of mercury or of other metals, coloured fires, and every other substance, whether similar to those above-mentioned or not, used or manufactured with a view to produce a practical effect by explosion or a pyrotechnic effect, and including (2) fog-signals, fireworks, fuses, rockets, percussion caps, detonators, cartridges, ammunition of all descriptions, and every adaptation or preparation of an explosive as above defined. Part i. deals with gunpowder, providing that it shall be manufactured only at factories lawfully existing or licensed under the act; that it shall be kept (except for private use) only in existing or new magazines or stores, or in registered premises, licensed under the act. Private persons may keep gunpowder for their own use to the amount of thirty pounds. The act also prescribes rules for the proper keeping of gunpowder on registered premises. Part ii. deals with nitroglycerin and other explosives; part iii. with inspection, accidents, search, &c.; part iv. contains various supplementary provisions. By order in council the term “explosive” may be extended to any substance which appears to be specially dangerous to life or property by reason of its explosive properties, or to any process liable to explosion in the manufacture thereof, and the provisions of the act then extend to such substance just as if it were included in the term “explosive” in the act. The act lays down minute and stringent regulations for the sale of gunpowder, restricting the sale thereof in public thoroughfares or places, or to any child apparently under the age of thirteen; requiring the sale of gunpowder to be in closed packages labelled; it also lays down general rules for conveyance, &c. The act also gives power by order in council to define, from time to time, the composition, quality and character of any explosive, and to classify explosives, and such orders in council are frequently made including new substances; those in force will be found in the Statutory Rules and Orders, tit. “explosive substance.” The Merchant Shipping Act 1894 imposes restrictions on the carriage of dangerous goods in a British or foreign vessel, “dangerous goods” meaning aquafortis, vitriol, naphtha, benzine, gunpowder, lucifer matches, nitroglycerin, petroleum and any explosive within the meaning of the Explosives Act 1875. The act is administered by the home office, and an annual report is published containing the proceedings of the inspectors of explosives and an account of the working of the act. Each annual report gives a list of explosives at the time authorized for manufacture or importation, and appendices containing information as to accidents, experiments, &c.

Practically every European country has legislated on the lines of the English act of 1875, Austria taking the lead, in 1877, with an explosives ordinance almost identical with the English act. The United States and the various English colonies also have explosives acts regulating the manufacture, storage and importation of explosives. (See also .)

—M. Berthelot, Sur la force des matières explosives (Paris, 1883); P. F. Chalon, Les Explosifs modernes (Paris, 1886); W. H. Wardell, Handbook of Gunpowder and Guncotton (London, 1888); J. P. Cundill, A Dictionary of Explosives (London, 1889 and 1897); M. Eissler, A Handbook of Modern Explosives (London, 1896, new ed. 1903); J. A. Longridge, Smokeless Powder and its Influence on Gun Construction (London, 1890); C. Napier Hake and W. Macnab, Explosives and their Power (London, 1892); G. Coralys, Les Explosifs (Paris, 1893); A. Ponteaux, La Poudre sans fumée et les poudres anciennes (Paris, 1893); F. Salvati, Vocabolario di polveri ed explosivi (Rome, 1893); C. Guttmann, The Manufacture of Explosives (London, 1895 and later); S. J. von Romocki, Geschichte der Sprengstoffchemie, der Sprengtechnik und des Torpedowesens bis zum Beginn der neusten Zeit (Berlin, 1895); Geschichte der Explosivstoffe, die rauchschwachen Pulver (Berlin, 1896); P. G. Sanford, Nitro-explosives (London, 1896); L. Gody, Traité théorique et pratique des matières explosives (Namur, 1896); R. Wille, Der Plastomerite (Berlin, 1898); E. Sarrau, Introduction à la théorie des explosifs (1893); Théorie des explosifs (1896); O. Guttmann, Manufacture of Explosives (London, 1895); E. M. Weaver, Notes on Military Explosives (New York, 1906); M. Eissler, The Modern High Explosives (New York, 1906); Treatise on Service Explosives, published by order of the secretary of state for war (London, 1907). Most of the literature on modern explosives, e.g. dynamite, &c., is to be found in papers contributed to scientific journals and societies. An index to those which have appeared in the Journal of the Society of Chemical Industry is to be found in the decennial index (1908) compiled by F. W. Renant.

EXPRESS (through the French from the past participle of the Lat. exprimere, to press out, by transference used of representing objects in painting or sculpture, or of thoughts, &c. in words), a word signifying that which is clearly and definitely set forth or represented, explicit, and thus used of a meaning, a law, a contract and the like, being specially contrasted with “implied.” Thus in law, malice, for which there is actual evidence, as apart from that which may be inferred from the acts of the person charged, is known as “express.” The word is most frequently used with the idea of something done with a definite purpose; the term “express train,” now meaning one that travels at a high speed over long distances with few intermediate stoppages, was, in the early days of railways, applied to what is now usually called a “special,” i.e. a train not running according to the ordinary time-tables of the railway company, but for some specific purpose, or engaged by a private person. About 1845 this term became used for a train running to a particular place without stopping. Similarly in the British postal service, express delivery is a special and immediate delivery of a letter, parcel, &c., by an express messenger at a particular increased rate. The system was adopted in 1891.

In the United States of America, express companies for the rapid transmission of parcels and luggage and light goods generally perform the function of the post office or the railways in the United Kingdom and the continent of Europe. Not only do they deliver goods, but by the cash on delivery system (see ) the express companies act as agents both for the purchaser and seller of goods. They also serve as a most efficient agency for the transmission of money, the express money order being much more easily convertible than the postal money orders, as the latter can only be redeemed at offices in large and important towns. The system dates back to 1839, when one William Frederick Harnden (1813–1845), a conductor on the Boston and Worcester railway, undertook on his own account the carrying of small parcels and the performance of small commissions. Obliged to leave the company’s service or abandon his enterprise, he started an “express” service between Boston and New York, carrying parcels, executing commissions and collecting drafts and bills. Alvin Adams followed in 1840, also between Boston and New York. From 1840 to 1845 the system was adopted by many others between the more important towns