EXPLOSION

From Agepedia

EXPLOSION, in natural philosophy; a sudden and violent expansion of an aerial or other elastic fluid, by which it instantly throws off any obstacle in its w^ay. Explosion differs from expansion in this, that the latter is a gradual power, acting uniformly for some time, whereas the former is momentary. The expansions of solid substances do not terminate in violent explosions, on account of their slowness, and the small space through which the expanding substance moves. Thus we find, that, though wedges of wood, when wetted, will cleave solid blocks of stone, they never throw them to any distance, as gunpowder does. On the other hand, it is seldom that the expansion of any elastic fluid bursts a solid substance, without throwing the fragments of it to a considerable distance. The reasons of this may be comprised in these particulars: 1. The immense velocity with which the aerial fluids expand, when affected by a considerable degree of heat. 2. Their celerity in acquiring heat, and being affected by it, which is much superior to that of solid substances. Thus air, heated as much as iron when brought to a white heat, is expanded to four times its bulk; but the metal itself will not be expanded the 500th part of that space. In the case of gunpowder, the velocity with which the flame moves is calculated, by Mr. Robins, to be no less than 7000 feet in a second, or little less than 70 miles perminute. Hence the impulse of the fluid is inconceivably great, and the obstacles on which it strikes are earned off with vast velocity, though much less than that just mentioned; for a cannonball, with the greatest charge of powder, does not move at a greater rate than 2400 feet per second, or little more than 27 miles per minute. The velocity of the ball again is promoted by the sudden propagation of the heat through the whole body of the air, as soon as it is extricated from the materials of which the gunpowder is made, so that it is enabled to strike all at once, and thus greatly to augment the movements of the ball. We may conclude, upon these principles, that the force of an explosion depends, 1. on the quantity of elastic fluid to be expended ; 2. on the velocity it acquires by a certain degreeof heat; and, 3. on the celerity with which the degree of heat affects the whole of the expansile fluid. These three take place in the greatest perfection where the electric fluid is concerned, as in lightning, earthquakes and volcanoes. (See Steam.)