EXPLOSIVES 



3052 



EXPLOSIVES 



distinct class of explosives, termed 

 the nitric esters, in which the 

 hydroxyl groups (OH) of the raw 

 material are more or less com- 

 pletely replaced by nitrate groups 

 (ONOii) during nitration. 



The molecular arrangement of 

 the product is such that the carbon 

 atoms are linked to the ON0 2 

 groups by hydrogen. The oxygen 

 has the greatest affinity for carbon 

 and hydrogen, but is bound to the 

 nitrogen, resulting in the sub- 

 stances being in an unstable state, 

 and when they are suitably initi- 

 ated, re-grouping occurs in accord- 

 ance with the chemical affinities 

 and with the production of heat. 



Attempts to utilise these new 

 substances commercially showed a 

 number of unexpected difficulties. 

 Many disastrous explosions oc- 

 curred during storage and handling, 

 and, although a spark or flame had 

 been the accepted method of firing 

 gunpowder, these were quite in- 

 adequate for the new explosives, 

 which were easily exploded by 

 percussion. Credit for solving the 

 ignition problem rests with a 

 Swedish chemist, Alfred Nobel, 

 who, in 1864, after years of patient 

 research, evolved a tube containing 

 mercury fulminate which, when 

 exploded by a spark, initiated com- 

 plete detonation in nitroglycerine. 

 Invention of Dynamite 



Fulminate of mercury had 

 previously only been used in per- 

 cussion caps for firing guns, and 

 Nobel's application of it to the 

 initiation of explosives is one of 

 the greatest advances in explosives 

 science, and alone has rendered 

 possible the use of most of our 

 modern high explosives. 



In commenting on the early 

 difficulties with nitroglycerine and 

 nitrocellulose, reference was made 

 to two very important properties 

 of explosives stability and sensi- 

 tivity. Stability is the ability of a 

 substance to remain unchanged 

 during prolonged storage, and early 

 explosives were deficient in this 

 respect. Nitric esters slowly de- 

 compose if minute traces of the 

 nitrating acid remain in the pro- 

 duct, sufficient heat being even- 

 tually generated to explode the 

 mass, and some compounds which 

 would be successful explosives are, 

 inherently, so unstable that they 

 cannot be used. In the case of ex- 

 plosives, sensitivity is always com- 

 parative, and is employed to ex- 

 press the ease with which the com- 

 pound may be exploded by such 

 agencies as heat, friction, per- 

 cussion, etc. Many compounds 

 are known which cannot be used 

 as explosives owing to being ex- 

 cessively or insufficiently sensitive. 

 It is a popular but fallacious belief 



that a successful explosive is sensi- 

 tive and detonates as soon as dis- 

 turbed, whereas the desideratum is 

 one that is so insensitive as to be un- 

 affected by rough usage, but which 

 detonates with great power or 

 violence when suitably initiated. 



Many years of patient work were 

 required to make nitroglycerine 

 and nitrocellulose of commercial 

 value. The former was so sensitive 

 to percussion that soon Nobel was 

 the only worker who persevered 

 with it. He suffered grave family 

 casualties, and accidents were so 

 numerous that many countries 

 prohibited the transport of the 

 substance, but in 1867 he was 

 rewarded by the discovery that 

 kieselguhr would absorb about 

 three times its weight of nitro- 

 glycerine, yielding a plastic mass 

 of sufficient insensitivity. This was 

 christened dynamite and its rapid 

 adoption founded Nobel's fortune. 

 Progress in the use of nitrocellu- 

 lose was equally slow, and at- 

 tended by numerous accidents, 

 much work being done by von 

 Lenk and later by Abel. Improve- 

 ments in manufacture increased its 

 stability, and in 1868 guncotton 

 was made a successful military 

 blasting explosive. Neither of the 

 new explosives, however, was 

 capable of use in guns, being too 

 violent in their action, whilst they 

 were too sensitive for employment 

 as shell fillings. 



In 1867 mixtures of ammonium 

 nitrate with various combustibles 

 were introduced as explosives, but 

 were too insensitive for use until 

 nitroglycerine was added, when 

 they found a certain amount of 

 favour. Another class of explo- 

 sive was invented by Sprengel 

 in 1871, when he employed mix- 

 tures of nitric acid with organic 

 combustibles, the essential feature 

 being that the ingredients were 

 non-explosive until mixed just 

 before use. These have been ex- 

 tensively used for blasting. 

 High Explosives for Shells 



Sprengel also experimented with 

 picric acid or trinitrophenol in 

 1871, but he was not encouraged by 

 the British Government, and this 

 explosive was not taken up until 

 1 885, when Turpin proposed its use 

 for shell filling, and France adopted 

 it. This was the first high explosive 

 which was sufficiently insensitive 

 for this purpose, and belongs to a 

 new class the nitro derivatives of 

 aromatic hydrocarbons. These 

 also are chemical compounds, but, 

 during nitration, hydrogen atoms 

 are displaced by nitryl groups 

 (ONO), which are consequently 

 joined direct to the carbon atoms, 

 and the products are more stable 

 and less sensitive than the nitric 



esters. Aromatic hydrocarbons 

 occur chiefly hi coal tar and petro- 

 leum, which are the raw materials 

 for this class of explosives. 



Smokeless powder became a 

 successful sporting propellant in 

 1865, and a military one in 1884. 

 The successful use of nitrocellulose 

 for this purpose became possible 

 when its structure was destroyed 

 by gelatinisation, its decomposi- 

 tion being then more of the nature 

 of extremely rapid combustion 

 than explosion. 



Picric acid did not prove an 

 ideal explosive for shell filling, as 

 it was liable to form picrates which 

 are sensitive, and in itself proved 

 somewhat too sensitive for use in 

 large guns. Nitration of other 

 aromatic hydrocarbons was there- 

 fore essayed, but did not become 

 a commercial success until the 

 manufacture of cheap, highly con- 

 centrated sulphuric acid was a 

 commercial possibility. Trinitro- 

 toluene then sprang into promin- 

 ence, and was shortly adopted 

 by Germany for military purposes, 

 most other powers following, with 

 the exception of Great Britain 

 and France. 



Explosion and Combustion 



Chlorates became cheap in 1889, 

 and as they contain much available 

 oxygen, attempts were made to 

 employ them in explosive mix- 

 tures. Early attempts to use them 

 in gunpowder had proved disas- 

 trous owing to their sensitivity to 

 percussion and friction, and to 

 avoid such trouble some use was 

 made of porous cartridges of 

 potassium chlorate, which were 

 dipped into a liquid combustible 

 just before use. 



The invention of cheddite (q.v.) 

 was, however, the first completely 

 successful application of chlorates. 

 Ammonium and potassium per- 

 chlorates have also been employed. 

 They contain more available oxy- 

 gen, and are less sensitive than the 

 chlorates, the ammonium salt 

 being the more advantageous as all 

 the products of explosion are 

 gaseous, but for use underground 

 it possesses the disadvantage that 

 the products of explosion contain 

 hydrochloric acid gas, which is 

 poisonous, and if the explosive is 

 to be so used it must contain some 

 metallic or alkaline ingredient to 

 fix this gas. 



The power of an explosive can 

 be increased by raising the tem- 

 perature of the gases evolved, and 

 this effect may be obtained by 

 including a combustible having a 

 high temperature of combustion, 

 and metals are generally em- 

 ployed for this purpose, such ex- 

 plosives being designated Thermit 

 explosives. 



