Online Encyclopedia

Search over 40,000 articles from the original, classic Encyclopedia Britannica, 11th Edition.

EXPLOSIVES

Online Encyclopedia
Originally appearing in Volume V10, Page 84 of the 1911 Encyclopedia Britannica.
» Make a correction to this article.
» Add information or comments to this article.
Spread the word: del.icio.us del.icio.us it!

EXPLOSIVES , a See also:

general See also:term for substances which by certain treatment " explode," i.e. decompose or See also:change in a violent manner so as to generate force. From the manner and degree of violence of the decomposition they are classified into "See also:propellants " and " detonators," but this See also:classification is not capable of See also:sharp delimitation. In some cases the same substance may be employed for either purpose under altered See also:external conditions; but there are some substances which could not possibly be employed as propellants, and others which can scarcely be induced to explode in the manner known as " detonation." A propellant may be considered as a substance that on See also:explosion produces such a disturbance that neighbouring substances are thrown to some distance; a detonator or disruptor may produce an extremely violent disturbance within a limited See also:area without projecting substances to any See also:great distance. See also:Time is an important, perhaps the most important, See also:factor in this See also:action. A propellant generally acts by burning in,a more or less rapid and See also:regular manner, producing from a comparatively small See also:volume a large volume of gases; during this action See also:heat is also See also:developed, which, being expended mostly on the gaseous products, causes a further expansion. The See also:noise accompanying an explosion is due to an See also:air See also:wave, and is markedly different in the See also:case of a detonator from a real propellant. Some cases of See also:ordinary See also:combustion can be accelerated into explosions by increasing the area of contact between the combustible and the See also:oxygen supplier, for instance, ordinary See also:gas or dust explosions. Neither temperature nor quantity of heat See also:energy necessarily gives an explosive action. Some metals, e.g. See also:aluminium and See also:magnesium, will, in oxidizing, produce a great thermal effect, but unless there be some gaseous products no real. explosive action. Explosives may be See also:mechanical mixtures of substances capable of chemical interaction with the See also:production of large volumes of gases, or definite chemical compounds of a See also:peculiar class known as endothermic," the decomposition of which is also attended with the See also:evolution of gases in large quantity. All chemical compounds are either " endothermic " or " exothermic." In endothermic compounds energy, in some See also:form, has been taken up in the See also:act of formation of the See also:compound. Some of this energy has become potential, or rather the compound formed has been raised to a higher potential.

This case occurs when two elements can be See also:

united only under some compulsion such as a very high temperature, by the aid of an electric current, or spark, or as a secondary product whilst some other reactions are proceeding. For example, oxygen and See also:nitrogen combine only under the See also:influence of an electric spark, and See also:carbon and See also:calcium in the electric See also:furnace. The formation of See also:chlorates by the action of See also:chlorine on boiling potash is a See also:good instance of a complex compound (See also:potassium chlorate), being formed in small quantity as a secondary product whilst a large quantity of See also:primary and simpler products (potassium chloride and See also:water) is forming. In chlorate formation the greater See also:part of the reaction represents a See also:running down of energy and formation of exothermic compounds, with only a small yield of an endothermic substance. Another See also:idea of the meaning of endothermic is obtained from See also:acetylene. When 26 parts by See also:weight of this substance are burnt, the heat produced will warm up 310,450 parts of water 1° C. Acetylene consists of 24 parts of carbon and 2 of See also:hydrogen by weight. The 24 parts of carbon will, if in the form of pure See also:charcoal, heat 192,000 parts of water 1 °, and the 2 parts of hydrogen will heat 68,000 parts of water 1 °, the See also:total heat production being 260,000 heat See also:units. Thus 26 grams of acetylene give an excess of 50,450 units over the amount given by the constituents. This excess of heat energy' is due to some form of potential energy in the compound which becomes actual heat energy at the moment of See also:dissolution of the chemical See also:union. The manner in which a substance is endothermic is of importance as regards the See also:practical employment of explosives. Some particular endothermic See also:state or form results from the mode of formation and the consequent See also:internal structure of the See also:molecule.

See also:

Physical structure alone can be the cause of a relative endothermic state, as in the See also:glass bulbs known as See also:Rupert's drops, &c., or even in chilled See also:steel. Rupert's drops See also:fly in pieces on being scratched or cut to a certain See also:depth. The cause is undoubtedly to be ascribed to the molecular state of the glass brought about by chilling from the melted state. The molecules have not had time to See also:separate or arrange themselves in easy positions. In steel when melted the See also:carbide of See also:iron is no doubt diffused equally throughout the liquid. When cooled slowly some carbide separates out more or less, and the steel is soft or annealed. When chilled the carbides are retained in solid See also:solution. The volume of chilled glass or steel differs slightly from that in the annealed state. Superf used substances are probably in a similar state of physical potential or See also:strain. Many metallic salts, and organic compounds especially, will exhibit this state when completely melted and then allowed to cool in a clean See also:atmosphere. On touching with a little of the same substance in a solid state the liquids will begin to crystallize, at the same time becoming heated almost up to their melting-points. The See also:metal See also:gallium shows this excellently well, keeping liquid for years until touched with the solid metal, when there is a considerable rise of temperature as solidification takes See also:place.

All carbon compounds, excepting carbon dioxide, and many if not all compounds of nitrogen, are endothermic. Most of the ex-See also:

plosives in See also:common use contain nitrogen in some form. Exothermic compounds are in a certain sense the See also:reverse of endothermic; they are relatively inert and react but slowly or not at all, unless energy be expended upon them from outside. Water, carbon dioxide and most of the common minerals belong to this class. The explosives actually employed at the See also:present time include mixtures, such as gunpowders and some chlorate compositions, the ingredients of which separately may be non-explosive; compounds used singly, as See also:guncotton, See also:nitroglycerin (in the form of See also:dynamite), picric See also:acid (as lyddite or melinite), trinitrotoluene, nitrocresols, See also:mercury fulminate, &c.; combinations of some explosive compounds, such as See also:cordite and the smokeless propellants in general use for military purposes; and, finally, See also:blasting and detonating or igniting compositions, some of which contain inert diluting materials as well as one or more high explosives. Many igniting compositions are examples of the last type, consisting of a high explosive diluted with a neutral substance, and frequently containing in addition a See also:composition which is inflamed by the explosion of the diluted high explosive, the See also:flame in turn igniting the actual propellant. Explosive Mixtures.—The explosive mixture longest known is undoubtedly See also:gunpowder (q.v.) in some form—that is, a mixture of charcoal with See also:sulphur and See also:nitre, the last being the oxygen provider. Besides the nitrates of metals and ammonium nitrate, there is a limited number of other substances capable of serving in a sufficiently energetic manner as oxygen providers. A few chlorates, perchlorates, permanganates and chromates almost See also:complete the See also:list. Of these the See also:sodium, potassium and See also:barium chlorates are best known and have been actually tried, in admixture with some combustible substances, as practical ex-plosives. Most other metallic chlorates are barred from practical employment owing to instability, deliquescence or other See also:property. Of the chlorates those of potassium and sodium are the most See also:stable, and mixtures of either of these salts with sulphur or sulphides, See also:phosphorus, charcoal, See also:sugar, See also:starch, finely-ground See also:cellulose, See also:coal or almost any See also:kind of organic, i.e. carbon, compound, in certain proportions, yield an explosive mixture.

In many cases these mixtures are not only fired or exploded by See also:

heating to a certain temperature, but also by quite moderate See also:friction or percussion. Consequently there is much danger in manufacture and storage, and however these mixtures have been made up, they are quite out of the question as propellants on See also:account of their great tendency to explode in the manner of a detonator. In addition they are not smokeless, and leave a ' Not necessarily heat energy entirely. A number of substances —acetylides and some nitrogen compounds. such as nitrogen chloride —decompose with extreme violence, but little heat is produced.considerable See also:residue which in a See also:gun would produce serious fouling. Mixtures of chlorates with aromatic compounds such as the nitro- or dinitro-benzenes or even See also:naphthalene make very powerful blasting agents. The violent action of a chlorate mixture is due first to the rapid evolution of oxygen, and also to the fact that a chlorate can be detonated when alone. A drop of sulphuric acid will start the combustion of a chlorate mixture. In admixture with sulphur, sulphides and especially phosphorus, chlorates give extremely sensitive compositions, some of which form the basis of friction See also:tube and firing mixtures. Potassium and sodium perchlorates and permanganates make similar but slightly less sensitive explosive mixtures with the above-mentioned substances. Finely divided metals such as aluminium or magnesium give also with permanganates, chlorates or perchlorates sensitive and powerful explosives. Bichromates, although containing much available oxygen, form but feeble explosive mixtures, but some compounds of chromic acid with diazo compounds and some acetylides are extremely powerful as well as sensitive. Ammonium bichromate is a self-combustible after the type of ammonium nitrate, but scarcely an explosive.

Explosive Compounds.—Nearly all the explosive compounds in actual use either for blasting purposes or as propellants are nitrogen compounds, and are obtained more or less directly from nitric acid. Most of the propellants at present employed consist essentially of nitrates of some organic compound, and may be viewed theoretically as nitric acid, the hydrogen of which has been replaced by a carbon' complex; such compounds are expressed by M•O•NO2, which indicates that the carbon See also:

group is in some manner united by means of oxygen to the nitrogen group. Guncotton and nitroglycerin are of this class. Another large class of explosives is formed by a more See also:direct See also:attachment of nitrogen to the carbon complex, as represented by M•NO2. A number of explosives of the detonating type are of this class. They contain the same proportions of oxygen and nitrogen as nitrites, but are not nitrites. They have been termed nitro-derivatives for distinction. One of the simplest and longest-known members of this group is See also:nitrobenzene, C6H5NO2, which is employed to some extent as an explosive, being one ingredient in See also:rack-a-See also:rock and other blasting compositions. The dinitrobenzenes, See also:C6H4(NO2)2, made from it are solids which are some-what extensively employed as constituents of some sporting powders, and in admixture with ammonium nitrate form a blasting See also:powder of a " flameless " variety which is comparatively safe in dusty or "gassy" coal seams. Picric acid or trinitrophenol, C6H2.OH•(NO2)3 is employed as a high explosive for See also:shell, &c. It requires, however, either to be enclosed and heated, or to be started by a powerful detonator to develop its full effect. Its compounds with metals, such as the potassium See also:salt, C6H2.OK•(NO2)3, are when dry very easily detonated by friction or percussion and always on heating, whereas picric acid itself will See also:burn very quietly when set See also:fire to under ordinary conditions.

Trinitrotoluene, C6H2•CH3•(NO2)3, is a high explosive resembling picric acid in the manner of its ex-plosion (to which in fact it is a See also:

rival), but differs therefrom in not forming salts with metals. The nitronaphthols, C,,H6.OH•NO2, and higher nitration products may be counted in the list. Their salts with metals behave much like the picrates. All these nitro compounds can be reduced by the action of nascent hydrogen to substances called See also:amines (q.v.), which are not always explosive in themselves, but in some cases can form nitrates of a self-combustible nature. Aminoacetic acid, for instance, will form a nitrate which See also:burns rapidly but quietly, and might be employed as an explosive. By the action of nitrous acid at See also:low temperatures on aromatic amines, e.g. See also:aniline, C6H5NH2, diazo compounds are produced. These are all highly explosive, and when in a dry state are for the most part also extremely sensitive to friction, percussion or heat. As many of these diazo compounds contain no oxygen their explosive nature must be ascribed to the peculiar state of union of the nitrogen. This state is attempted to be shown by the formulae such as, for instance, CsH5'N:N•X, which may be some compound of diazobenzene. Probably the most vigorous high explosive at present known is the substance called hydrazoic acid or See also:azoimide (q.v.). It forms salts with metals such as AgN3, which explode in a peculiar manner. The ammonium compound, NH4N3, may become a practical explosive of great value.

Mercuric fulminate, HgC2N2O2, is one of the most useful high explosives known. It is formed by the action of a solution of mercurous nitrate, containing some nitrous acid, on See also:

alcohol. It is a See also:white crystalline substance almost insoluble in See also:cold water and requiring 13o times its weight of boiling water for solution. It may be heated to 18o° C. before exploding, and the explosion so brought about is much milder than that produced by percussion. It forms the See also:principal ingredient in cap compositions, in many fuses and in detonators. In many of these compositions the fulminate is diluted by mixture with certain quantities of inert powders so that its sensitiveness to friction or percussion is just so much lowered, or slowed down, that it will fire another mixture capable of burning with a hot flame. For detonating dynamite, guncotton, &c., it is generally employed without admixture of a diluent. Smokeless Propellants.—Gunpowders and all other explosive mixtures or compounds containing metallic salts must form See also:smoke on combustion. The solids produced by the See also:resolution of the compounds are in an extremely finely-divided state, and on being ejected into the atmosphere become more or less attached to water vapour, which is so precipitated, and consequently adds to the smoke. The simplest examples of propellants of the smoke-less class are compressed gases. Compressed air was the propellant for the Zalinski dynamite gun. Liquefied carbon dioxide has also been proposed and used to a slight extent with the same idea.

It is scarcely practical, however, because when a quantity of a gas liquefied by pressure passes back again into the gaseous state, there is a great absorption of heat, and any remaining liquid, and the containing See also:

vessel, are considerably cooled. See also:Steam guns were tried in the See also:American See also:Civil See also:War in 1864; but a steam gun is not smokeless, for the steam escaping from the See also:long tube or gun immediately condenses on expansion, forming white mist or smoke. At the earliest See also:stage of the development of guncotton the See also:advantage of its smokeless combustion was fully appreciated (see GUNCOTTON). That it did not at once take its position as the smokeless propellant, was simply due to its physical state—a fibrous porous mass—which burnt too quickly or even detonated under the pressure required in fire-arms of any kind. In the See also:early eighties of the 19th See also:century it was found that several substances would partly dissolve or at Ieast gelatinize guncotton, and the moment when guncotton proper was obtained as a colloid or jelly was the real start in the See also:matter of smokeless propellants. Guncotton is converted into a gelatinous form by several substances, such as See also:esters, e.g. See also:ethyl acetate or benzoate, See also:acetone and other See also:ketones, and many See also:benzene compounds, most of which are volatile liquids. On contact with the guncotton a jelly is formed which stiffens as the evaporation of the gelatinizing See also:agent proceeds, and finally hardens when the evaporation is complete. Whilst in a stiff pasty state it may be cut, moulded or pressed into any desired shape without any danger of ignition. In fact guncotton in the colloid state may be hammered on an See also:anvil, and, as a See also:rule, only the portion struck will detonate or fire. Guncotton alone makes a very hard and somewhat brittle See also:mass after treatment with the gelatinizing agent and complete drying, and small quantities of camphor, See also:vaseline, See also:castor oil and other substances are incorporated with the gelatinous guncotton to moderate this hard and brittle state. All the smokeless powders, of which gelatinized guncottons or nitrated celluloses are the See also:base, are moulded into some conveniently shaped See also:grain, e.g. tubes, cords, rods, disks or tablets, so that the See also:rate of burning may be controlled as desired. The Vieille powder, invented in 1887 and adopted in See also:France for a See also:magazine See also:rifle, consisted of 'gelatinized guncotton with a little picric acid.

Later a mixture of two varieties of guncottongelatinized together was used. In addition to guncottons other explosive or non-explosive substances are contained in some of these powders. Guncotton alone in the colloid state burns very slowly if in moderate-sized pieces, and when subdivided or made into thin rods or strips it is still very mild as an explosive, partly from a chemical See also:

reason, viz. there is not sufficient oxygen in it to burn the carbon to dioxide. Many mixtures are consequently in use, and many more have been proposed, which contain some metallic salt capable of supplying oxygen, such as barium or ammonium nitrate, &c., the idea being to accelerate the rate of burning of the guncotton and if possible avoid the production of smoke. The See also:discovery by A. See also:Nobel that nitroglycerin could be incorporated with See also:collodion See also:cotton to form blasting See also:gelatin (see DYNAMITE) led more or less directly to the invention of ballistite, which differs from blasting gelatin only in the relative amounts of collodion, or soluble nitrated cotton, and nitroglycerin. Ballistite was adopted by the See also:Italian See also:government in 1890 as a military powder. Very many substances and mixtures have been proposed for smokeless powder, but the two substances, gun-cotton and nitroglycerin, have for the most part kept the See also:field against all other combinations, and for several reasons. Nitro-See also:glycerin contains a slight excess of oxygen over that necessary to convert the whole of the carbon into carbon dioxide; it burns in a more energetic manner than guncotton; the two can be incorporated together in any proportion whilst the guncotton is in the gelatinous state; also all the liquids which gelatinize guncotton dissolve nitroglycerin, and, as these gelatinizing liquids evaporate, the nitroglycerin is See also:left entangled in the gun-cotton jelly, and then shares more or less its colloidal See also:character. In burning the nitroglycerin is protected from detonation by the gelatinous state of the guncotton, but still adds to the rate of burning and produces a higher temperature. Desirable Qualities.—Smokelessness is one only of the desirable properties of a propellant. All the present so-called smokeless powders produce a little fume or haze, mainly due to the condensation of the steam which forms one of the combustion products.

There is often also a little vapour from the substances, such as See also:

oils, See also:mineral jelly, vaseline or other See also:hydrocarbon added for See also:lubrication or to render the finished material pliable, &c. The gases produced should neither be very poisonous nor exert a corrosive action on metals, &c. The powder itself should have good keeping qualities, that is, not be liable to chemical changes within ordinary ranges of temperature or in different climates when stored for a few years. In these powders slight chemical changes are generally followed by noticeable ballistic changes. All the smokeless powders of the present See also:day produce some See also:oxide of nitrogen, traces of which hang about the gun after firing and change rapidly into nitrous and nitric acids. Nitrous acid is particularly objectionable in connexion with metals, as it acts as a See also:carrier of oxygen. The fouling from See also:modern smokeless powders is a slight See also:deposit of acid grease, and the remedy consists in washing out the See also:bore of the piece with an alkaline liquid. The castor oil, mineral jelly or camphor, and similar substances added to smokeless powders are supposed to act as See also:lubricants to some extent. They are not as effective in this respect as mineral salts, and the rifling of both small-arms and See also:ordnance using smokeless powders is severely gripped by the metal of the projectile. The alkaline fouling produced by the See also:black and See also:brown powders acted as a preventive of rusting to some extent, as well as a lubricant in the bore. Danger in Manufacture.—In the case of the old gunpowders, the most dangerous manufacturing operation was See also:incorporation. With the modern colloid propellants the most dangerous operations are the chemical processes in the preparation of nitroglycerin, the drying of guncotton, &c.

After once the gelatinizing solvent has been added, all the mechanical operations can be conducted, practically, with perfect safety. This statement appears to be correct for all kinds of nitrated cellulose powders, whether mixed with nitro-glycerin or other substances. Should they become ignited, which is possible by a rise of temperature (to say 180) or contact with a flame, the mixture burns quickly, but does not detonate. As a rule See also:

naval and military smokeless powders are shaped into flakes, cubes, cords or cylinders, with or without See also:longitudinal perforations. All the modifications in shape and See also:size are intended to regulate the rate of burning. Sporting powders are often coloured for See also:trade distinction. Some powders are blackleaded by See also:glazing with pure See also:graphite, as is done with black powders. One See also:object of this glazing is to prevent the grains or pieces becoming joined by pressure; for rods or pieces of some smokeless powders might possibly unite under considerable pressure, producing larger pieces and thus altering the rate of burning. Most smokeless powders are fairly insensitive to See also:shock. All these gelatinized powders are a little less easily ignited than black powders. A slightly different cap composition is required for small-See also:arm cartridges, and See also:cannon cartridges generally require a small primer or starter of powdered black gun-powder. 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 See also:

local strain on the See also:breech near the powder chamber, and more especially that as more and more space is given to the gases by the See also:movement of the projectile up the gun to the muzzle, gas should be produced with sufficient rapidity to keep the pressure nearly See also: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. (W. R. E. H.) See also:Law.—In 186o an act was passed in See also:England to amend the law concerning the making, keeping and See also:carriage of gunpowder and compositions of an explosive nature, and concerning the manufacture and use of See also:fireworks " (23 & 24 Vict. C. 139), whereby previous acts on the same subject were repealed, and See also:minute and stringent regulations introduced. Amending acts were passed in 1861 and 1862. In 1875 was passed the Ex-plosives 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 See also:

Scotland and See also:Ireland, as well as to England, constitutes, with various orders in See also:council and See also:home See also:office orders, a complete See also:code. The act of 1875 was based on the See also:report of a See also:committee of the See also:House of See also:Commons, public See also:opinion having been greatly excited on the subject by a terrible explosion on the See also:Regent's See also:Canal in 1874. Explosives are thus defined: (I) Gunpowder, nitro-glycerin, dynamite, gun-cotton, 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) See also:fog-signals, fireworks, fuses, rockets, percussion caps, detonators, cartridges, See also:ammunition of all descriptions, and every See also:adaptation or preparation of an explosive as above defined. Part i. deals with gun-powder, 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 See also:thirty pounds. The act also prescribes rules for the proper keeping of gunpowder on registered premises. Part ii. deals with nitro-glycerin and other explosives; part iii. with inspection, accidents, See also:search, &c.; part iv. contains various supplementary provisions. By See also:order in council the term " explosive " may be extended to any substance which appears to be specially dangerous to See also:life or property by reason of its explosive properties, or to any See also: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 See also:lays down minute and stringent regulations for the See also:sale of gun-powder, restricting the sale thereof in public thoroughfares or places, or to any See also:child apparently under the See also:age of thirteen; requiring the sale of gunpowder to be in closed packages labelled; it also lays down general rules for See also:conveyance, &c. The act also gives See also: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 Rides and Orders, tit. " explosive substance." The See also:Merchant See also:Shipping Act 1894 imposes restrictions on the carriage of dangerous goods in a See also:British or See also:foreign vessel, " dangerous goods " meaning aquafortis, See also:vitriol, See also:naphtha, benzine, gunpowder, See also:lucifer matches, nitro-glycerin, See also:petroleum and any explosive within the meaning of the Explosives Act 1875. The act is administered by the home office, and an See also: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 manufactureor importation, and appendices containing See also:

information as to accidents, experiments, &c. Practically every See also:European See also:country has legislated on the See also:line of the See also:English act of 1875, See also:Austria taking the See also:lead, in 1877, with an explosives See also: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 PETROLEUM.) (T. A.

End of Article: EXPLOSIVES

Additional information and Comments

There are no comments yet for this article.
» Add information or comments to this article.
Please link directly to this article:
Highlight the code below, right click, and select "copy." Then paste it into your website, email, or other HTML.
Site content, images, and layout Copyright © 2006 - Net Industries, worldwide.
Do not copy, download, transfer, or otherwise replicate the site content in whole or in part.

Links to articles and home page are always encouraged.

[back]
EXPLOSION 		[next]
EXPORTS AND IMPORTS OF THREE SOUTH AMERICAN

Site © 2006 - Net Industries