In military mining and especially in gallery work careful attention must be given ventila tion and drainage. A pressure-blower, worked by hand or power, is among the essential items of a mining equipment. If water shows itself or is suspected, dead-level galleries must be avoided, and all slopes should fall toward a point or points where the water can be disposed of.
A satisfactory explosive for the purposes of military engineering must be: (1) Stable as to its constitution and characteristics for a long period. (2) Unaffected by ordinary varia tions of temperature and moisture. (3) In sensible to shock of handling, transportation, projectiles and neighboring explosions. (4) Not too difficult of detonation. (5) Quick enough to give good results when not confined and slow enough to give good results when con fined. (6) Convenient in form and consistency for packing and loading and for making up charges of different weight. These conditions point to a high explosive of medium strength of granular or plastic consistency, put up in waterproof cylindrical cartridges of standard size and length. The detonating compound in general use is fulminate of mercury, and all methods of firing involve the explosion of a small quantity of fulminate enclosed in a cap or fuse and placed in the charge. Bickford or safety fuse is used to ignite the fulminate when electricity is not available. This fuse may be used in wet holes, but for underwater use it should have a continuous rubber coating; when a total blast is divided into a number of charges it is important that all should go at the same instant. In simultaneous ignitions by electricity, the fuses are connected in series: that is to say, they are all placed in the same circuit. A lead from the firing apparatus is connected to one wire of a fuse on one flank. The other wire of this fuse is connected to a wire of the next fuse, and so on, until the last fuse is reached, the second wire of which is connected back by a lead to the firing point. It may be assumed as sufficiently exact that charges of the same explosive develop total energies directly proportional to their weights. This energy is exerted in all directions in com pression of the surrounding medium. The distance at which this disturbance remains sufficient to destroy galleries is called the radius of rupture and the surface joining the ends of these radii is called the surface of rupture. The relief of pressure on one side shortens all radii of rupture which have a component in that direction, but does not appreciably affect those which have no such component. Hence, when material is displaced the surface of rup ture is ellipsoidal; when no material is dis placed it is spherical. Land mines are usually formed by excavating from the surface and are designed to be exploded at the moment the enemy is over them. ' They are usually em ployed in front of defensive positions and in connection with visible obstacles. The charges are placed deep enough only to avoid artillery projectiles. If no artillery fire is to be expected they may be pliced just under the surface. If a bore hole is sufficient the charge is placed at the bottom and the hole well tamped. If an open pit is dug the mine chamber should be in firm ground at one side and the hole back-filled and well rammed.
In siege operations mining is done at close quarters, and is, or should be, opposed by countermining by the enemy. There is then a double purpose in view; to reach the original objective by placing the charge where intended and firing it, and while so doing to detect and circumvent any attempt of the enemy to inter fere, or to prosecute any enterprise of his own.
Demolitions.— Military demolitions have for their purpose to destroy or make unservice able any object in the theatre of war the preser vation of which would be unfavorable to the army or favorable to the enemy, excepting always objects neutralized by international con vention or the laws of war. Demolition is permissible only under a military necessity. They may be made by fire, by mechanical means or by explosives. Fire is the only agent when absolute destruction is necessary, as in case of food supplies, munitions of war, structural ma terials, etc. Soluble matter, as gunpowder, sugar, salt, etc., might be destroyed in water, but this method is laborious. Burning is equally effective and much easier. For quick results with slow-burning materials a quantity of highly combustible stuff must be collected. In the destruction of railroads, operations may be directed against rolling stock, bridges, cul verts, tunnels, track or accessories, such as water stations, telegraphs, etc. Locomotives are temporarily disabled by removing valves or other small vital parts; permanently, by building a fire in a dry boiler or by detonating a charge of explosive in the boiler. In haste, piston or connecting rods, links, etc., may be destroyed by explosives, or a hole may be blown in the bottom of the tender tank. Cars may be burned or wrecked by collisions or derailment. The best places are in deep cuts or tunnels. Wooden bridges may be burned or small ones may be pried qff their seats by levers or dragged off with tackle. Track may be destroyed by taking it up, burning the ties, heating the rails on the fires and twisting them with bars through the bolt holes, with a chain and lever, or a hook and lever. Telegraph lines are tensporarily disabled by breaks, in which the wires are cut, grounds in which the wires are connected to the ground and crossed in which a metallic connection is made between the wires. A ground may be made by connecting a wire to the rail or to a bar or plate of metal in damp earth. Copper is best. To destroy a telegraph line cut down and burn poles, cut and tangle wires and break insulators. To disable guns, smash the sights and firing gear; endeavor to dent or burn the corners of the breech-closing wedge and damage the elevating gear. Unscrew the striker plug and take it out: fire one or two rifle bullets into the opening. The degree of success attained in demolitions with explosives depends upon the experience of the powder men doing the work. The explosive adopted for the United States service is triton (tri nitrotoluene, trinitrotoluol, trotyl, TNT). It may often become necessary to use whatever explosive is at hand; for this reason data for their use is given. There are many uncer tainties attending the military use of explosives, and local conditions frequently raise a doubt as to the efficiency of the application of for mulated methods. Where a lifting effect is desired, gunpowder should be used: but, when a cutting or shattering effect is necessary, a high explosive is better, such as triton, dyna mite, gun cotton, etc. Each company of engi neers carries on each of its two tool wagons a demolition outfit and supplies, consisting of earth and wood augers, pinch bars, magneto exploders, sledge hammers, picks, shovels, firing wire, caps, fuses, etc., and 200 pounds of ex plosive. In addition it has two pack demolition outfits, each with demolition tools and supplies, including 45 pounds of explosive. Each squad ron of cavalry has a pack demolition outfit with demolition equipment and supplies, including 80 pounds of explosive.