EXPLOSIVE MECHANISM

in botany, (1) in flowers, an arrangement for the transference of pollen to sn inseci-visitor by a sudden movement of floral organs. (2) In fruits, an arrangement for the fercible expwsion of seeds from a fruit brought about in yarious ways (see SLING-FRUITS). Ths spores of Ferns, ascospores, and some conidia are also liberated explosively. EXPLOSIVES. An explosive is a substance or mixture of substances which, by the action of a blow or of heat, can be converted very easily and suddenly into a more stable substance or substances, usually gaseous, with the simultaneous liberation ofa larg amount of heat. Explosives are divided into cla es according to the uses to which they are put, but the line of demarcation is not always very clear. The industrial and blasting powders may be either low or high explosives. A ‘low’ explosive explodes by the application of heat, and burns more or le uniformly and slowly, and projects neighbouring objects to a distance. A ‘high’ explosive explodes under a blow, and the whole of the substance is instantly transformed, and instantly exerts its maximum pre ure, creating a violent disturbance in a limited area without nece arily projecting substances to any great distance. Service explosives, for naval and military purposes, are divided into propellants and high explosives. Sporting powders are specially modified propellant powders. Examples of these cla es of explosives, with notes on their composition, are given below. Low Explosives. 'The best examples of the low explosive are gunpowder and similar mixtures. The constituents of the ‘gunpowder’ explosives are generally not explosive alone, but only when mixed. A ‘gunpowder’ mixture contains carbon or carbonaceous matter like wood-meal, hydrocarbons, starches, and sugars, ., which burn owing to the presence of highly oxy-genated substances like peroxides, chlorates and perchlorates, nitrates, permanganates, chromates 360 EXPLOSIVES and dichromates, all of which convey the nece ary oxygen. In addition, there usually is;resent some very sasily ignited substance like sulphur or sulphides, or phosphorus or phosphides, . As compared with other expl sives, gunpowder or black powder has certain advantages. It is cheap, easily ignited, insensitive to shock, and stable at mcderately lbigh temperature; ic burns regularly, and its residue is non-corrosive. But it is weak in power, and produces much smoke. It is excellent for armour piercing shell and for rings of time fuses. Gunpowder made in different eountries varies in composition, but for rifle, cannon, and sporting powders it usually contairs 74 to 75 parts of saltpetre, 9 to 14 parts of sulphur, 12 ty 16 parts of chircoal. For blasting powders le saltpetre and more charcoal is used. Charcoal is made by the carbonization of wood. in England dogwood, aider, and willow woods are used; in Germany alder and willow are used; in France black alder and also white elder, roplar. aspen, birch, and hazel; in Switzerland hazel wood; in Spain oleander, yew, willow, hemp stems, and vine; in Italy hemp stems. The wood is generally carbonized in iron retorts. The pr-duct is allowed to cool out of contact with air, else it may inflame. Wood Lurnt for ordnance powders gives a > ield of 20 to 30 per cent charcoal; that for smallerms gives a yield of 40 per cent. The charcoal contains from 68 to 85 per ce it carbon, from 2-8to 5-7 percent hydrogen, from 1? to 27 per cent oxygen, and ma* have up to a per cent ash. The saltpetre is found naturally in Chile, India, and in ot»er countries, and is refined by crystallization from water. It is a colourle , crystalline solid. Sulphur, a pale-yellow solid, melting-point 113° C., boiling-point 444-5° C., is found in nature, and is refined to a purity of 99-5 per cent and over. It has a low ignition temperature of 261° C., an 1 makes the powder burn more readily. Under the pre ure of the pre and the incorporating mill it flows and cements the minute particles of charcoal and _ saltpetre together. The three ingredients are ground, mixed, sieved, incorporated or mixed in drums or mills, broken down, and then pre ed, corned or granulated, and glazed. Cannon powders receive an addition of graphite to reduce the rate of burning. The powder is then dried in a stove, finished in a recl to get rid of the last traces of dust, and blended. In the United States powder for blasting contains sodium nitrate instead of pota ium nitrate. The powder is eheaper and stronger, but is hygroscopic. Sprengsaltpetre is largely used in Sta furt salt-mines, where a mild explosive is required, and consists of 75 parts by weight of sodium nitrate, 10 j arts by weight cf sulphur, and 15 parts by weight of brown coal. It is cheap, and ¢ oes not produce poisonous fumes. lobbinite is largely.1sed in coal-mines. It is black powder with ammonium and copper sulphates, po ibly also starch and paraffin wax. When gunpowder explodes, the product consists of 43 per cent gases, 56 per cent solids,a dtherest water. The composition of other industrial end blasting powders is given in the sequel. Propellant Explosives. The chief propellants are nitrocellulose, alse called nitrocotton or guncotton, and nitroglycerine. WNitrocellutose. The chief sources of cellulose are wood and cotton. When cotton is plentiful, nitrocellulose is meade as follows. Cotton-waste is handpicked to get rid of string, wood, .; it is opened out by a teasing-machine, which tears off small portions at a time, and the cotton is then dried to about 0-5 per cent moisture content. The cotton is then nitrated with ‘mixed acid’—a mixture of about 16 per cent nitric and 75 per cent sulphuric acid and about 8 per cent water—at 15° to 25° C. After the nitration, the acid is removed and the nitrocotton boiled up in water to stabilize it. Generally nitrocotton contains about 12 to 13 per cent. of nitrogen. Wet nitrocotton is quite safe although it can be detonated, but dry nitrocotton is very dangerous. To-day, paper is usually made from wood-pulp, and when the cotton supplies of Germany were stopped during the European War, nitrocellulose had to be made from woodpulp via a form of paper crépe prepared by the Germans from the pulp. For propellant purposes the nitrocotton is ‘gelatinized,’ either alone or mixed with nitroglycerine, and is then worked up into different forms, such as wire, rods, grains, or tape, when it becomes controllable at will, so that the firing is not dangerous. Nitroglycerine. Mixed acid, containing 41 per cent nitric acid and 57-5 per cent sulphuric acid, is brought to 22° C. by cooling coils*of brine, ang pure glycerine is injected into the acid at such a rate that no glycerine accumulates unchanged, and that the temperature is kept between 15° and 22°C, When all the glycerine has been added, the liquid is allowed to stand, and the nitroglycerine rises to the surface. It is run off to the wash-house, where it is washed free from acid and settled. The proce is a dangerous one, and great care must be taken at every stage of the manufacture. The floors of the plant must be free from grit 361 EXPLOSIVES and dirt, no accumulation of liquid should be allowed anywhere, special clothing and rubber boots must be worn, no metallic implements may be used, and the plant should not be handed over for repairs except under the supervision of a responsible person. Nitroglycerine, when absorbed in a porous earth called ‘ Kieselguhr,’ is calied dynamite. Kieselguhr, or simply guhr, absorbs twice its weight of nitroglycerine; cork charcoal abcorbs nine times its weight. Dynamite cartridges are generally exploded by detonators. Preparation of Cordite; Nitrocellulose Tape (N.C.T.); Ballistite; é . For cordite, the nitro-cotton, freed from moisture, is mixed with nitroglycerine, and the paste or the cotton itself, if N.C.T. is to be made, is incorporated into a uniform dough with ether and alcohol. Some mineral jelly is added to render the explosive more stable. The dough is pre ed through different sizes of dies according to the product desired. For rifle powder fine cords are used; for artillery, thicker cords or flat ribbons of varying thickne es are required. The cords or tapes from the dies are cut into suitable lengths, the solvents driven off, and the products blended to obtain uniform ballistic quality. For ballistite the nitrocellulose is beaten up with nitroglycerine in water. The paste is freed from water, dried, and worked into byrn-like sheets by means of rollers. High Explosives; Picric Acid. At the outbreak of the European War the chief high explosive of the Entente Powers was ly ddite (in France, mélinite), also called trinitrophenol or picric acid. It is a bright-yellow solid, melting point 122° C., sparingly soluble in water, and forms easily exploded metallic salts. It is now displaced by trinitrotoluene. Picric acid is made from phenol or carbolic acid. Phenol is obtained from coal-tar, or made synthetically from benzene. The phenol is sulphonated with strong sulphuric acid, and the phenol-sulphonic acid resulting is nitrated with strong nitric acid at about100°C. Picric acid separates, and is washed free from mineral acid and dried. It may also be made from benzene without converting it into phenol thus: The benzene is chlorinated and gives chlor-benzene. This is nitrated into dinitrochlor-benzene, and is then treated with caustic so#a to give dinitrophenol. This is then further nitrated into trinitrophenol or picric acid. Picric acid has a high melting point, it must be used pure, is di olved by water, it attacks metals forming dangerous compounds, and requires troublesome plant for its manufacture. Hence it has been displaced by more suitable substances, notably by trinitrotoluene. Trinitrotoluene (T.N.T.). This compound may now be made in a eontinuous plant. Mono nitro tolu ens is put in at one end of the plant and comes out as trinitrotoluene. Mixed nitric and sulphuric acid is put in at the end where the T.N.T. is obtained, and emerges, where mono nitrotoluene is put in, as waste acid. T.N.T. in the past has also been made discontinuously thus: The toluene is nitrated by mixed acid into either mono or dinitro toluene, which is then tri nitrated. The conversion into mono nitrotoluene was used in the United Kingdom, France, Germany, Canada, and America; the conversion into dinitro toluene was used in Italy. The T.N.T. emerges liquid, and is pa ed over a rotating drum internally cold water cooled. A knife strips the thin congealed skin of T.N.T. off. This T.N.T. is only grade 3, and for conversion into grade 1 it must be purified. Formerly this was done by means of an organic solvent, but this dangerous and expensive method has been displaced by treatment either with phenol or sodium sulphite, whch gives a grade 1 product. T.N.T. is a very pale yellow solid, melting-point 80:2? C.,and therefore, melted by hot water, almost insoluble in water, burns quickly in the air, is inert, and comparatively safe to handle. It has displaced picric acid owing to its superiority, physically and chemically, over that substance. Jetryl or C.E. (Composition Exploding). Tetryl, also called tetra nitro dimethylaniline, or more correctly tri nitro phenylmethyl nitramine, is a powerful high explosive, and is thus obtained. One part of dimethylaniline is di olved in 10 parts of strong sulphuric acid, and the solution allowed to flow into strong nitric acid. The temperature should be kept below 40° C., else decomposition may occur. After nitration the yellow tetryl separates out, and is filtered off and water-washed till free from acid. It is then dried in hot-air stoves. Tetryl] is much more dangerous than T.N.T., and is also more poisonous to handle. No other nitro-bodies were made in England on the large scale during the European War, but on the Continent, owing to the scarcity of raw materials, dinitrobenzene, dinitro toluene, and nitro naphthalenes, and even le important nitro-bodies, were made. Their manufacture is similar to that of those already described. Probably none of these nitro-bodies so pre ed into use is as good as T.N.T. Detonating Substances. Though modern explosives are not easily exploded by a blow, they are sensitive 362 EXPLOSIVES to shock of given intensity, and le er or different shocks will not suffice. The ‘detonator’ to produce the shock is set into the explosive. A complete shell carries two detonators. One, in the percu ion cap, sets off the propellant charge which expels the projectile; the other, in the fuse in the nose of the shell, is ignited by the discharge of the gun, and detonates the high-explosive filling at a set interval after the discharge of the shell. Therefore, the shell can be exploded either in its flight when it is used as shrapnel shell, or on its arrival at its objective when it can be used for small-calibre artillery shell for field-guns, ., or after its arrival when it is used for heavy howitzer and armour-piercing shell for destroying entrenched works, armoured forts, or ships. The manufacture of detonators is a very dangerous and delicate operation. Some substances (the copper acetylides) explode by a scratch, some (nitrogen iodide) by the touch of a feather or the tread of a fly, some explode even in solution when poured from one ve el into another (diazo benzene perchlorates). Mercury fulminate is more often employed in the detonator, and is prepared from mercury, alcohol, and nitric acid. It is expensive, and most modern detonators consist of lead azide or salts of styphnic acid, with a layer of T.N.T. in a narrow aluminjum cylinder. The following is a list of the more important explosives, the different groups not being mutually exclusive:-— Coal-mine Explosives American. Aetna Coal-mine Powder A, B, O: nitroglycerine explosive. Black Diamond: 2A, 3A, 6L.F are nitroglycerine explosives; 5, 7, 8, ammonium nitrate explosives. Carbonite: nitroglycerine 26, barium nitrate 4, pota ium nitrate 29, wood-meal or starch flour 40, calcium carbonate 0:25. A DuPont Permi ible: nitroglycerine, ammonium nitrate, common salt. sounaia:nitroglycerine and hydrated salt. Monobel: ammonium nitrate, nitroglycerine, wood-meal, alkali chloride. Red H1-7: ammonium nitrate explosives. 7 Trogan Coal Powder: contains nitro starch.; Austrian and Hungarian. ‘ Chloratit: during war was used in coal-mines.; Dynammon: ammonium nitrate, pota ium nitrate, red charcoal. Pannomite:nitroglycerine,collodion cotton, ammonium nitrate, dextrin, glycerine, nitrotoluene, alkali chloride. Titanite: Ammonium nitrate, trinitrotoluene, curcuma charcoal. Belgian. Alsilite: ammonium nitrate, trinitrotoluene, ferrosilicon-aluminium, salt. Baelluite: ammonium-nitrate, trinitrotoluene. Densite: alkaline nitrates, trinitrotoluene, dinitro toluene, and ammonium chloride. Favier Explosives: mixtures in varying proportions containing ammonium nitrate, nitro naphthalene, paraffin, and resin; higher nitrated naphthalenes, pota ium nitrate, and tetry] may be present. Manufactured by the French Government as Explosifs N or Favier or Grisounites. Grisounites-couche for coal-mines have theoretical explosion temperatures of 1500°C.Grisounites-roc he of 1900°C. Ammonite, Westfalite, Bellite, Roburite are explosives of this type; other ammonites, Bellite Nos. 2and 4, Faversham powder, and negro powder have ammonium or sodium chloride added. British. Ammonite: Favier type; ammonium nitrate 75, dinitro naphthalene or other nitro-body, salt 20. Bellite: ammonium nitrate meta dinitrobenzene; starch may be added. Bobbinite: the only gunpowder explosive allowed in England, not allowed in foreign mines; alkali nitrate, carbohydrates, wax may be added. Shatters coal le than high explosives. Cambrite: a Nobel carbonite plus 8 per cent of a cooling agent. Denaby Powder:ammonium unit rate, alkali nitrate, T.N.T., ammonium chloride. Dynobel: nitroglycerine 15, collodion cotton 0-5, nitro body 3, ammonium nitrate 46, woodmeal 5-5, salt 29-5, magnesium carbonate 0:5. Limit charge, 18 to 30 ounces. Swing of ballistic pendulum, 2:35 inches. Mon arkite: ammonium and sodium nitrate, nitroglycerine, nitrocotton, starch, mineral jelly, salt. Monobel: ammonium nitrate, nitroglycerine, wood-meal, salt, alkali chloride, magnesium carbonate; nitro-body may be present. Negro Powder: Grisounite type; ammonium nitrate 88, T.N.T. 10, graphite 2. Rex Powder: nitroglycerine 1%, salt 20, wood-meal 8, ammonium nitrate 60. Charge 20 ounces. Swing of pendulum, 2-61 inches. Rippite (Super): nitroglycerine, nitrocotton, pota ium nitrate, borax, alkali chloride. and salt and 363 EXPLOSIVES 360 Bygr uri ammonium nitrate 61, T.N.T. 16, salt 23. Stomonal: nitroglycerine, ammonium nitrate, sodium nitrate,woodmeal, wheat-flour, salt, ammonjum oxalate. Thames Powder: Similar to above. Danish. Aerolite: ammonium nitrate 78-1 per cent, pota ium nitrate 7:5 per cent, sulphur 8:75 por eent, tar 2:5 per cent, sago-meal 1:25 per cent, manganese dioxide 1-25 per cent, resin 0-6 per| cent. Poudre Blanche Cornil: ammonium nitrate, alkali nitrate, nitro naphthalene, lead chromate. French, Favier xplosives.