Page:The American Cyclopædia (1879) Volume VII.djvu/42

 EXPLOSIVES ropes. This, too, is sometimes employed as a powerful mechanical force, as by inserting wedges of wood into cracks, or into holes drilled for the purpose in rocks, and then cov- ering the wood with water. As this is absorbed, the wood slowly expands, exerting a steady pressure of surprising force. The presence of moisture in the atmosphere is ascertained by instruments based on this principle. (See HY- GEOMETEY.) For the effect of expansion of steam, see STEAM. EXPLOSIVES. An explosion may be occasioned by the sudden removal of resistance to an ex- panding force, as in the case of steam boilers ; but it is more frequently the result of a sudden generation of energy by chemical reactions. Most explosions of this kind are instances of rapid combustion ; and an explosive compound, as distinguished from a merely inflammable one, may be defined as one which contains with- in itself the elements of combustion or other chemical change, liberating mechanical energy. Thus the fire damp of coal mines, when pure, is inflammable ; but mixed with a certain pro- portion of atmospheric oxygen, it becomes ex- plosive. The ingredients of an explosive com- pound remain inert unless the condition of chemical reaction is supplied. This is usually heat, produced by the direct contact of a heated body, or by pressure or percussion. In some instances, however, the introduction of a new substance, or the change of aggregate condi- tion in one or more of the ingredients, may occasion explosion. The number of explosives known to chemists is considerable. Chiefly those which are employed in the arts will be considered in this article. Gunpowder. Of these, gunpowder is the most widely employed, partly because the longest known, but mainly because it is not liable to spontaneous change, or explosion from other causes than a very high temperature (that of a spark or flame, for example), and because the manufacture can be cheaply carried on to any required extent, and can be so varied as to control the qualities of the product according to the proposed use. Gunpowder presents to the eye a mass of grains, usually angular and of uniform size, dark color, and polished surface. The different varieties range from 0-5 to 4*5 mm. in diameter of grain. Its specific gravity is 1-8 to 2*0. It explodes when rapidly heated above 300 C. It is composed of charcoal, sulphur, and nitre, the two former being the combustible ingre- dients, and the latter, by the surrender of its oxygen, supporting their combustion. Ac- cording to the theory formerly held, the nitre is reduced during the combustion of rifle powder to nitrogen and potassium, the latter forming with sulphur potassium sulphide, while all the oxygen combines with the carbon of the charcoal to form carbon dioxide (carbonic acid). The formula expressing this reaction would be 2KNOt+8+80=80O+K8+SN; and the proportions of ingredients in 100 parts would be: nitre, 74-84; sulphur, 11-84; char- coal, 18'32. From blasting powder, on the other hand, carbonic oxide as well as carbonic acid is formed, and the theoretical reaction is shown in the equation KN"0 8 + S + 2C=KS + N + C0 2 + CO, requiring the proportions : nitre, 64'4; sulphur, 20'4; carbon, 15'2. How near- ly these formulas are adhered to will appear from the following tables of analyses : I. MlLITAEY POWDEB. VARIETIES. Char- coal. Sul- phur. Nitre. Authority. Theoretical proportions Austrian 13-32 13-1 15-0 13-42 14-22 13-7 15-0 12-5 12-5 18-5 17-7 14 (or 15) OB SP 14-4 12-5 17-0 14-0 12-0 13-5 15-5 11-27 18-2 12-0 3LA8TIS 15-2 21-36 18-00 15-00 18-00 20-48 21-87 19-43 12-00 20-95 16-70 15-83 11-84 11-3 10-0 12-80 8-63 10-1 10-0 12-5 12-5 11-5 11-7 10-0 ORTING 9-9 7-8 8-0 8-0 10-0 9-6 10-5 9-84 8-6 8-0 ro Pov 20-4 18-45 20-00 20-00 13-40 26-44 16-56 16-24 18-00 11-75 16-60 15-83 74-84 75-6 75-0 73-78 77-15 76-2 75-0 75-0 75-0 75-0 70-6 76 (or 75) POWD 75-7 79-7 75-0 78-0 78-0 76-9 74-0 78-99 78-2 80-0 n>EB. 64-4 60-19 62-00 65-00 73-60 63-12 61-94 64-82 70-00 67-20 66-70 68-34 Linck. Lottner. Karolyi. Ure. Otto. Combes. Magnus. Gottlieb. Meyer. Ordnance Man- ual EE. Otto. Combes. Otto. Bevue de l'Ar- tillerie. Bunsen. PrechtL Eziha. Eziha. Combes. Eziha. Lottner. Dingier. Eziha. " ordnance " small arms. . English French Prussian Eussian United States. . II. ElFLE American. English. . ? 4 K French 11 (1 T> 11 German Italian Eussian . III. 1 Theoretical proportions Austrian French " round " French " ordinary " . . . Freiberg "double" Hartz, coarse, strong... " medium " weak, fine Italian Mansfeld Russian. Westphalian These variations are due partly to the variable quality of the ingredients, particularly the charcoal, which always contains water and ash. The best coal (from light non-resinous wood, like poplar, black alder, or willow) rarely contains over 83 per cent, of carbon. The composition of powder has been also varied from the theoretical formulas to ob- tain a variety in its effects, and the researches of Bunsen, Shishkoff, Karolyi, Craig, and Fe- dorow have shown that the simple reactions upon which the formulas were based do not take place ; that the products of combustion, which vary somewhat with the pressure under which ignition takes place, comprise, among the gases, small quantities of carbonic oxide, hydrogen, sulphuretted hydrogen, and free ox- ygen, and, in the smoke and residue, chiefly the sulphate and carbonate, not the sulphide, of potassium. Bunsen found the gases from rifle powder to be but 31 '4 per cent, of the weight. The pressure generated by the com-