BOMB, a hollow box, basket or shell, filled with gunpowder, or other explosive set off by means of a time-fuse or other device. For merly the term applied only to the spherical shells thrown by a mortar, but with the use of aircraft in war the missiles dropped from them are called bombs; and the name is also applied to hand grenades and the larger grenades thrown by catapults and trench mortars. The term is also used to designate the infernal machines contrived by common criminals to accomplish murder and destruction of property. The last named are generally an improvised shell of gas or water pipe filled with explosives, and encased in a box so arranged that when the lid is lifted the charge is fired. More elaborate bombs of this sort have clock-work machinery which can be set to fire the bomb at any decided time.
The bombs used by aircraft are of five types: (1) Heavy explosive bombs — for destroying or damaging large structures, like dockyards and ships, munition and factories, railway stations, etc.; (2) hand grenades— for attacking troops in masses, as in camp or on the march; (3) incendiary bombs— for starting fires in oil-yards, store houses or airship sheds; (4) aerial bombs— which have mechanism to change their direc tion from vertical to horizontal after they have fallen a short distance — for attacks upon air ships and balloons; (5) poison gas bombs— for attack upon trenches and troop masses.
In the British air service the Marten-Hale bombs have been most largely used. They are of two types, shrapnel and high-explosive. The first is loaded with 321 to 340 steel balls, which with the fragments of the encasing shell pro duce about 1,000 missiles effective over a space about 100 feet square. Its exploding charge is 4 pOunds ounces of trinitrotoluol. The second carries 6 pounds 33 ounces of the same explosive, and weighs about 20 pounds in all. It produces an enormous shattering effect if dropped from above 200 feet — a fall of that distance being required to bring the primer (by revolving vanes) within acting distance of the charge. These bombs are pear-shaped,
dropping with the large end down. To the upper end is attached a streamer of some textile material which steadies the bomb in falling. In order to overcome the tendency to bury itself in the earth before exploding, when dropped from a great height a small parachute is attached. This is sufficient to modify the speed, and also checks the forward trend im parted by the flying plane, so that it drops almost vertically after release except for the windage. Incendiary bombs, as used by the German air fleet, consist of an outer skin wound about with tarred rope, forming a chamber in which is packed resin, clippings of celluloid and similar combustible material, surrounding a central charge of thermit. An igniter sets off the thermit which burns fiercely. In some of the incendiary bombs dropped in London, which failed to explode, was found amorphous phosphorus, which would not only spread fire, but also produce a cloud of asphyxiating fumes which would prevent the near approach of any one attempting to extinguish the fire.
Poison gas bombs, to be effective in pro ducing either asphyxia or death must nec essarily be filled with a gas at least twice as heavy as air, as otherwise the gas would be too quickly diffused into the atmosphere. Chief among the heavy gases is the vapor of bromine, 5.53 times heavier than air. The effect of bromine is to produce at first spasms of the glottis, with asphyxiation rapidly fol lowing. It is believed that the asphyxiating bombs in use by the German aircraft in the European War were filled with liquid bromine, which was scattered upon the bursting of the bombs. Other gases which may have been used are phosgene, 3.49 times as heavy as air; nitro gen tetroxide (nitrous acid), 3.17 times as heavy as air, chlorine and sulphur dioxide, respectively 2.45 and 2.21 times heavier than air. The effects of all these gases are the same, with the additional certainty of poison ing of the wound if made with a phosphorus bearing bomb. See AMMUNITION; GRENADE; PROJECTILES.