Expanding System of Projectiles. See [Projectiles, Rifle].
Expedient. A stratagem in warfare.
Expedition. Is an enterprise taken by sea or by land against an enemy, the fortunate termination of which depends on the rapidity and unexpected nature of its movements. It is usually intrusted to a commander of acknowledged talents and experience.
Expense Magazines. Are small powder-magazines containing ammunition, etc., made up for present use. There is usually one in each bastion.
Experiments. The trials or applications of any kind of military machines in order to ascertain their practical qualities and uses.
Expiration of Service. The termination of a soldier’s contract of enlistment.
Explode. To burst with a loud report; to detonate, as gunpowder, or a shell filled with powder or the like material.
Explosion. The sudden enlargement of the volume of a body by its conversion into gas or vapor. (See [Explosives].) The explosion of powder may be divided into three distinct parts, viz.: [ignition], [inflammation], and [combustion], all of which see under their proper headings.
Explosives. Substances the elements of which under certain conditions suddenly undergo a chemical rearrangement into gases, giving rise to great pressures on surrounding bodies. Modern writers recognize two different kinds of explosions,—explosions of the 1st order, or [detonations], and explosions of the 2d order, or rapid [combustions]. Detonating explosions are practically instantaneous. The explosion is supposed to be propagated by a vibration throughout the mass. Ordinary explosions are propagated by inflammation. [Gunpowder], which may be taken as a type of explosives of the 2d order, burns at a certain rate, depending upon the density. When a charge is fired the inflammation spreads from the point of ignition to all parts of the charge,—each grain is successively enveloped and burned from surface to centre. The velocity of inflammation is the greater in proportion to the degree of confinement from the increased tension of the gases. The velocity of combustion is the rate at which the solid grains are burned. It is measured by the distance passed over by the burning surface (the line being taken perpendicular to the surface) in the unit of time. Time thus enters into the explosion of gunpowder and gives it its peculiar value as a ballistic agent.
In the detonating explosives, the case is very different. These bodies may be supposed to be made up of molecules containing so many atoms of carbon, oxygen, nitrogen, etc., so placed as to be held in a state of equilibrium by their mutual attractions and repulsions, but this equilibrium is unstable; that is to say, each atom has only a very small arc of vibration in which the molecule is stable. If by any cause an atom is forced beyond this limit the equilibrium of the whole mass is destroyed, and the elements instantly rearrange themselves under the influence of the chemical affinities which obtain under the particular conditions of the explosion. This kind of explosion is brought about in various ways,—by percussion, concussion, heat, etc.,—some bodies being susceptible to one mode of firing more than another. The theory which offers the best explanation of the various phenomena is that the molecular balance is peculiarly susceptible to overturn by certain vibrations. The vibrations given out by the explosion of the fulminates seem to have the widest range in bringing about the detonation of different substances. For this reason the fulminate of mercury is the universal detonating agent. Its own susceptibility to explosion by heat, percussion, and the electric spark especially fits it for this work. Wet gun-cotton requires in addition to the fulminate a “primer” of dry gun-cotton.