EXPLOSIVES. 373 EXPLOSIVES. oiilrr into a chemical reaction accompanied by the production of gases ami the evolution of much heal. History. Nothing definite is known about the origin of explosives, and it is contended by some i the. invention of gunpowder was contempo- raneous with the discover}' of saltpetre. Greek lire, which is believed to have been a preparation et pilch, resin, saltpetre, and sulphur, was first used (lurine the defense of Constantinople about 600, and it is reasonable to believe that gun- powder was a development of this mixture. Manuscripts are in existence showing the use of gunpowder among the Arabs prior to 1250, but its discovery is generally attributed to Roger I ti ii. of Oxford, England, who mentioned it about 1270, and to Berthold Schwartz, of Frei- berg, Germany, who described it in 1328. Its discovery has also been attributed to the Chinese, and a description of its use at the siege of Pian- king and Lo-yang in 1232 is contained in the Chinese Annals, and its invention has been as- cribed to the Hindus in consequence of certain passages in Indian law books, but the authen- ticity of these Oriental descriptions is doubted by modern writers. In 1346 at the battle of t'recy use was made of cannon (see Artillery: and Ordnance) in which gunpowder was em- ployed as a propellant, and its use increased with the subsequent development of firearms, though it remained practically the same until the last century. (See Gunpowder. ) In 1845 SehOnbein, of Basel, discovered the explosive nature of gun- cot ton, and in 1847 Sobrero discovered nitro- glycerin (q.v.). Alfred Nobel invented dyna- mite (q.v. ) in 1800, and to him also is due the production in 1875 of blasting gelatin. The explosive character of nitrated hydrocarbons was indicated by Hermann Sprengel in 1873, and in 1887 it was still further developed by Eugene Turpin, while the now important smokeless pow- ders should be credited to the inventive genius of Vieille, who was the first, in 1880, to produce a really successful military smokeless powder, though previous investigators had been active in this field and had achieved varying degrees of success. See Smokeless Powder. Classification. Explosives are either me- chanical mixtures or chemical compounds. The first class consist of certain chemical substances intimately mixed by mechanical means, which, at an elevated temperature, react upon each other and pass into the gaseous state, causing the explosion. Typical of this class is gun- powder. Another example of this class is a mix- ture of finely divided charcoal and liquid air. A mixture of acetylene and ozone in the liquid state, if it were employed, would constitute one of the most powerful explosives of the same class. A typical example of the second class of explo- sives is nitroglycerin. Other examples of the second class are liquid acetylene and liquid ozone. The further subdivisions of the two classes of ex- plosives include the following groups: Explosive mixtures of the nitrates, explosive mixtures of the chlorates, explosive compounds derived by nitro-substitution, explosive compounds of nitric derivatives, the Sprengel explosives, and fulmi- nates and amides. Theory of Explosions. An explosion may be defined as a chemical reaction which is effected in an exceedingly short space of time with the evo- lution of a large quantity of gas at a high temperature and accompanied by a shock. When this reaction occurs in a body which is confix the expansive action of the heated gases pro duces disruptive effects. The force which is de- veloped by the passage from the solid form to the i eous condition depends upon the ingredients ot the explosive. When the explosion is pro- gressive, that is, starts at an initial point and continues from one group of particles to the next, and so on through the explosive, the action is termed burning and is analogous to ordinary combustion. When, however, the combustion is effected simultaneously throughout the mass in an extremely short space of time, the action is called detonation. The development of an ex- plosion may often be explained as resulting from the transformation of a shock into heat. Thismay be accomplished by the propagation of the shock from particle to particle in an explosive, or by a shock from one explosive bodj to ther not in direct contact. The latter i-, the syn- chronous vibratory theory of Sir Frederick A. Abel, who claims that the originating cause of the detonation of an explosive lies in the syn- chronism between the vibrations produced by the body that provokes the detonation and those that the first body would produce in detonation, just as the string of a musical instrument, re- sounds at a distance in unison with another vibrating cord. Marcellin P. E. Berthelot, on the other hand, contends that an explosion is due to the transformation of mechanical energy into heat, which, during the explosion, is again trans- formed into mechanical energy; that is to say, it is dependent upon the production of two orders of waves, one series of which represents the explosive waves developed in the midst of the matter that detonates, and consists of a con- tinually reproduced transformation of the chem- ical actions into thermal and mechanical actions which transmit equally the sudden pressure all around the centre of the concussion to the ad- joining bodies and thence to a new mass of ex- plosive material. Most explosives consist es- sentially of compounds containing carbon, oxygen, and nitrogen, the last of which is in a state of feeble combination with the whole or part of the oxygen, thus constituting an unstable chemical condition, which is necessary. When the explo- sion takes place the nitrogen gives up its oxygen to the carbon, for which it has a greater affinity, forming carbon dioxide and carbon monoxide gases, the combination being attended by great generation of heat, and the nitrogen is set free. In most explosives the carbon is accompanied by hydrogen, which, by its combustion, produces an extremely high temperature and combines with a part of the oxygen to form water in the state of greatly expanded vapor. Other subordinate ele- ments are often present : thus, for instance, in gunpowder the potassium holds the nitrogen and oxygen loosely together as saltpetre, and there is sulphur, a second combustible whose oxidation evolves even greater heat than carbon. When potassium chlorate i~ present the chlorine acts the same as the nitrogen, and is set free in the gas- eous state. The foregoing description illustrates those explosives in which the decomposition may be considered a process of oxidation, but there are cases in which an explosion occurs by the simple dissociation of a compound without oxi- dation; thus, nitrogen chloride and nitrogen io- dide contain neither carbon nor oxygen, and their
