DEMOLITION ( Fr. it moll! 1.at, demo from dentofiri, I1 pill down, from /le, down -1- tao/iri, to !mild). The seitottilie de struction of an enemy's works or property, lit modern \rattan' tile 1f ulat1erial is 1411u (11'10111'd by Military 1'1)11111111 Ildel'S 10 he tO tile sllec•ss Of heir Operations. Tile 111atetia 1 which has been destroyed on varions has included every kind 5vhich itiav be it Ilse 1.0 all army :let 111g either 011 the offellsi 1. or defellSit eases, as ill the fa 111011, raid through the Shenandoah Valley, •a., prac tically everything which it Was though) 'Hight emitribule to the 0r indirectly, of the t'ontederate Arun• destroyed by I:en. cral Sheridan it 11 a t'leW it j111 111'ael icable for the Confederate .\rtny to operate in the valley as it had been doing. .11 the other 1i1. the des' 1110 10l1 wf some single piece of material which nets as a barrier to the ()vol.: rcss of 811 army. .1 tv pica! instance of this kind was the dusiIlttion of a door (hiring the recent hostilities in China. The progress of the trwtqis w:is delayed at one of the gates, t r doors, the approaches to v5 hjvh were ((ell 110'10•191 by the Iiro of the Chinese. A .181111 nese corporal undertook to effeet the 1 1 il)11 of the gal e by an 1•S9h)sion. .1fter he had placed the charge, ignited a fns., and 'withdrawn from its inunc• diate 5 i•inity, the Hanle was extinguished by the hinese. operation having bet's I several time•, he finally drew his '.word after lighting the fuse 1111 .loud over the explosive, permitting himself to be killed by the same ex plosion which broke in the gate.
The principal agents used in demolitions are tire, explosives. mines, and tools. Where time allows and the material to be destroyed is in flammable, as in the ease of crops, frame build ings, wooden bridges, etc., it is burned. In other cases the demolition is effected by the use of explosives, assisted sometimes by the pick, axe, and other tools. The explosives ordinarily used are gunpowder and guncotton. The materials most frequently to be demolished are guns, rail roads, including their bridges and tunnels, walls, doors, telegraph and telephone lines. A large gull is most readily destroyed by removing the breech-block and by exploding a charge on the chase or in the bore. Locomotives and other machinery can likewise quickly be disabled by removing or destroying some vital part. Rail roads have been destroyed by overturning sec tions of the track, removing and burning the ties; the rails can be placed on the piles of burning ties, heated in the centre, and then bent and twisted. If simply bent, it is a comparatively
simple matter to straighten them again. If, however, they are well twisted, the rails must be re-rolled before they can be used again.
Walls and doors, if there is not time for breaking them down with picks and crowbars, can be demolished by exploding charges against them. If gunpowder be used, it is necessary to tamp the charge. If guncotton, the tamping is not essential. The rules governing the amount of explosive to be used are only approximate and must be considered in connection with the class of material to be destroyed. In general the amount of explosive force varies with the square of the thickness of the wall or pier to be de molished; and directly, as its length. For ex ample, a brick wall two feet thick requires about two pounds per running foot of guncotton, while one four feet thick will require about eight pounds per running foot. A steel rail can be cut by the explosion of three-fourths of a pound of guncotton against its web. The destruction of bridges requires judgment in the placing of the charge. In the wooden bridge the destruction can be accomplished by building a fire under one or more pieces, whose failure will eause the entire bridge to drop. Similarly, an iron or steel truss bridge may be destroyed by cutting simultaneous ly with explosives the lower chord of some ten sion member near the centre of the bridge. Arched masonry bridges and tunnels can best be destroyed by exploding the proper sized charge on the top side of the arch near the haunches. When impracticable to reach the top side of the arch, the destruction may be effected by propping, a large charge against the crown of the arch.
Wire entanglements placed as obstacles to the advance of the troop; may be rendered ineffective by cutting with wire nippers, axes, or other edged tools. Telef2r,raph and telephone lines can be destroyed by miffing down and burning the poles; the wires should be removed and twisted or buried. The demolition of material which may subsequently he of service to the friendly army should only he undertaken with great caution. The denial of its use to the hostile army may frequently be accomplished in some other way; for example, a telegraph line may be temporarily disabled by removing some instru ments or establishing faults in the line.