July 1. 1892.] 



KNOWLEDGE 



137 



liigh temperature gunpowder takes fire, or, if the con- 

 ditions be suitable, explodes. In the combustion of gun- 

 powder the carbon burns to carbonic acid ( a gas) , the sul- 

 phur burns to sulphurous acid (a gas), and other gaseous 

 products are also formed in considerable quantity. 



The heat developed by the chemical reaction raises the 

 temperature of the gases, which causes them to expand 

 rapidly and occupy a large volume. If the burning of the 

 gunpowder takes place in a confined space, the force of 

 expansion of the gas is resisted by the walls of the en- 

 closure, and if the latter are not of sufficient strength, the 

 obstacles are overthrown. If, however, the enclosure be 

 sufficiently strong and furnished with no outlet (as in 

 certain experiments where very small charges are fired 

 inside strong bombs), the gases formed are kept compressed 

 in a small volume, and no disruption takes place. 



Here we have the fact of explosion, without its usual 

 striking accompaniments. 



When a cartridge is tired in a gun-barrel, the gases, 

 whose force of expansion would be sufficient to burst the 

 steel of the barrel, find in one direction no great resistance, 

 and expanding rapidly in this direction propel before them 

 the bullet, which thus leaves the muzzle of the gun en- 

 dowed with a high velocity. 



Explosives are compounds or mixtures, which contain 

 in themselves elements capalile of taking up a new mole- 

 cular arrangement forming fresh compounds, one or more 

 of the new compounds being gases, and the formation of 

 these compounds being accompanied by an evolution of 

 heat. The formation of gases, and the development of 

 heat in the reaction, are essential to the production of an 

 explosion. 



When we come to enquire what is the condition gene- 

 rally necessary to produce the explosion of an explosive 

 body, we find that it is the rapid vibration of the particles. 

 Such \'ibration may be generated by heat, by shock, or 

 by friction, but in general the condition most favourable 

 to explosion is one of rapid vibration, which may be 

 produced by a sudden blow which will" serve to detonate 

 dynamite without appreciably heating it. The liability 

 of the occurrence of explosion under such circumstances 

 does not depend only on the /aire of the blow, but on 

 the nature of the striking body with which the blow is 

 given. Thus, a force of blow which would cause explosion 

 if the blow were one of steel against steel might be harm- 

 less if produced by wood against wood. In this case the 

 explosion is determined, not by the amount of heat pro- 

 duced, but by the rapidity of the vibration. It is well 

 known that a tuning-fork struck against steel yields a 

 higher note (i.e., a sound of more rapid vibration) than if 

 struck against wood. 



When explosion occurs the chemical atoms are sliakvii 

 iiut of one combination to fall into another. This process 

 takes place much more readily when the explosive is warm. 



Although explosions are often produced independently 

 of heating eil'ects, yet it must be borne in mind that at a 

 sufficiently high temperature all explosives will detonate. 



In the study of phenomena connected with explosives 

 we often meet with occurrences at variance with the old 

 . dog-Latin dogma, musa aquat ert'ectiiiii. The pulling of the 

 trigger, followed by the rush of the bullet from the gun, is 

 a familiar example ; the work done in pulling bears no 

 proportion to the energy developed by the explosion. 

 Another case in point is afforded by the manner in which 

 explosions are sometimes caused in the incorporating mills, 

 in which the component materials of gunpowder are mixed 

 together. The presence of a small hard body, such as a 

 naU, or even a hard piece of grii, may cause sufficient 

 local heating to start an explosion of the whole mass. 



Both shocks and local heating are most carefully guarded 

 against in gunpowder factories. Charcoal possesses a 

 property (that of condensing air in its pores) which some- 

 times leads to local heating and mduces spontaneous com- 

 bustion. 



Li grinding the sulphur there is another source of danger. 

 Sulphur is a highly electric body, and in the process of 

 grinding a large amount of electricity will often accumu- 

 late, sometimes giving rise to sparks, the passing of which 

 may produce serious consequences. The danger from this 

 source is, however, to a great extent overcome by con- 

 necting the sulphur mills to earth by means of copper 

 wires, and thus continually drawing off the charge of 

 electricity produced by friction in the grinding process. 



In the' pressing of the gunpowder, hydraulic machines 

 fui-nished wuth ebonite plates are frequently employed. 

 Ebonite is a convenient material for the purpose, being 

 tough, elastic, smooth, and sufficiently hard. Unfortunately, 

 ebonite is a highly electric material, and the upper and 

 lower plate, with the cake of powder between them, form 

 practically an electric pile. A passing thunderstorm may 

 induce a discharge of sparks from the ebonite, igniting the 

 gunpowder and producing, as has happened in several 

 cases, fatal accidents. 



In spite of all precautions, explosions are liable to occur 

 in the mixing of the materials for gunpowder, and it is 

 well to provide, as far as possible, for the safety of the 

 ,mph_iii>'s and of the building. A good protector for the 

 workmen is a curtain of ships' hawsers, which offer the 

 kind of resistance which is most efiectual in the case of an 

 explosive outburst of gas. 



By having a light roof, secured only by one or two 

 wooden pins, an outlet is obtained for the gases produced 

 in a factory explosion. The roof is simply lifted off, and 

 the outlet thus given prevents the pressure inside the 

 building from becoming sufficiently great to damage 

 seriously the main portions of the building. 



Turning now from the explosive mixture gunpowder to 

 the nitro cum pounds, such as gun-cotton and nitro-glycerin, 

 we find that the nitro bodies explode more readily under 

 shock, and also at a lower temperature. Nevertheless, in 

 the hands of properly- trained workmen, the manufacture 

 of nitro-glycerin and dynamite is accompanied by fewer 

 casualties than that of gunpowder. Gun-cotton is prepared 

 by the action of strong nitric acid and sulphuric acid upon 

 cotton-wool. Most of the processes are carried out in pre- 

 sence of a large excess of water, though this is, of course, 

 not the case during compression, in which operation great 

 care has to be exercised. 



Nitro-glycerin, prepared by acting upon glycerin with a 

 j mixture of nitric and sulphuric acids, is liable to explode 

 both by heat and by shock. 



Dynamite is produced by absorbing three parts of nitro- 

 glycerm by one part of kiesulguhr, a finely-divided siliceous 

 earth capable of absorbing a large quantity of liquid 

 without becoming pasty. Dynamite only explodes when 

 subjected to special treatment, bemg unafi'ected by moderate 

 heat or by an ordinary blow, but detonating under the 

 sharp shock given by a percussion fuse of fulminating 

 mercury. The kiesulguhr plays no part in the actual 

 explosion, so that dynamite, as an explosive, must be 

 classed along with gun-cotton and the other compouwh, 

 rather than with explosive mixtures such as gunpowder. 



The smokeless gunpowders now coming into general use 

 are prepared from gun-cotton, or fi'om gun-cotton and 

 nitro-glycerin. 



A special class of explosives are required for tiUhig per- 

 cussion caps and detonators. Fulminate of mercury is the 

 mist important of these highly dangerous substances, the 



