GUNPOWDER AND HIGH EXPLOSIVES CHAPTER I COMBUSTION, EXPLOSION, DETONATION Ordinary Combustion. In all explosions, the changes that occur may be considered the direct results of ordinary combustion, the manifestations of which, such as heat, light, etc., are universally known. In their relation to combustion, all substances may be classified, first, as combustibles, or substances which burn, e. g., wood, coal, fats, oils, gas, etc.; and incombustibles, or substances who do not burn, e. g., glass, porcelain, earthenware, grae, etc.; secondly, as supporters of combustion, or thos substances which aid or sustain combustion, e. g., air, oxygen (a gas), etc.;1 and non-supporters of combustion, or those substances which retard combustion, e. g., nitrogen (a gas), etc. In order that combustion may occur, or a substance burn, a combustible and a supporter of combustion must be brought together, and the temperature of the combustible raised to a point at which it may unite with the supporter of combustion. 2 The temperature at which a combustible begins to burn 1The most energetic supporter of combustion is oxygen (a colorless, odorless, transparent gas). Air, the most common supporter of ordinary combustion, is such only by reason of the oxygen it contains, air being composed of 23 parts of oxygen and 77 parts of nitrogen (approximately). 2 What actually occurs is, the elements of which the combustible is composed unite chemically with the oxygen of the supporter of combustion, forming new and entirely different products. This disintegration and union is generally brought about by the action of heat. is called its "point of ignition," and this point varies between very wide limits; thus, phosphorus ignites at 150° F., sulphur at 480° F., while several substances require a temperature over 1,000° F. for their ignition. Combustion may be started, or a substance ignited in various ways; e. g., by contact with a heated body (such as a flame), by friction, percussion, concussion, an electric spark or current, etc. The combustion of a substance may be promoted or increased by intimately mixing the combustible and supporter of combustion. Thus, in order to kindle a fire rapidly, the wood is cut into small pieces or shavings. In the same way sawdust, if the particles be separated or suspended in the air so that they may be surrounded by or thoroughly mixed with it, burns far more energetically or intensely than the wood from which it was obtained. The principal manifestations of combustion are heat, light, and gas, the first two being always perceptible to the senses, the latter being sometimes visible in the form of smoke, and at other times invisible. Of these accompanying phenomena, the most important, from an explosive point of view, is the last mentioned, gas, and next in importance is the heat which causes the gas to expand. Recapitulation.-1. Combustion is an example of chemical change, in which the combustible unites with the oxygen of the supporter of combustion. 2. In ordinary combustion the oxygen is supplied by the air. 3. The most energetic supporter of combustion is pure oxygen. 4. To ignite a combustible, or cause a substance to burn, its temperature must be raised to its point of ignition, and this may be done in various ways. |