Engineering Wonders of the World
Volume I

410 ENGINEERING WONDERS OF THE WORLD. 9'2-INCH gun and barbette on temporary mounting for tests. {Photo, Gale and P olden.) the gun from time to time. Wash can be remedied to a large extent by the means of tight - fitting “ gas-checks,” and, as the bore automatically gets enlarged, by fitting driving bands of extra thickness on the shells. In peace time, to save the bores of large guns, their barrels are fitted with tubes firing a 12- pounder or 6-lb. shell. The sighting apparatus of all guns is placed to one side, and is entirely inde- pendent of the vertical movements of the gun. according to the place they occupy, and are fitted on the outer side in each case with, the mechanism required to operate them. The explosive charge is to-day very different from the old black powder of years ago. The ordinary black cubes were first replaced by prisms of brown material known as “ cocoa ” powder. Then came the demand for energy without smoke. A propelling agent having the character desired was discovered by Professor Abel; it is named “ cordite,” from its resemblance to gray cord. Now, cordite contains no less than 58'3 per cent, of nitro-glycerine, and nothing is so harmful as this compound to the surface of the bore of a gun. Consequently the inner barrels of guns wear out quickly if this powder be used constantly. “ Wear ” falls under two heads —“ erosion ” and “ wash.” Erosion is the eating out of the surface of Erosion the bore pUre Wash and simple- Wash is caused by the rush of gas between the projectile and the bore wherever a space is found. Erosion being due to gas moving rapidly at a very high, temperature and under pressure, the only remedy known is to reline The charge itself is fired by electricity. On a platform so unstable as that of a ship, it will be readily understood that any . Firing delay in discharging a gun a Qun when it bears on an object would probably result in a miss. Electricity, being instantaneous, entirely obviates this difficulty, ’ and firing is now accomplished either by pulling a trigger similar to that fitted to a rifle or by merely pressing a button. In either case an electric circuit is closed in wires which lead to the breech-piece of the gun and terminate in a fine platinum filament of high electrical resistance surrounded by a small amount of fulminate or othei high explosive. The current heats the fila- ment, ignites the fulminate, and through it the main powder charge. This method is eminently suited for the firing of a simul- taneous broadside from a central point of control. As to the mounting of these monster weapons, they are placed in what is called a “ barbette,” and are protected by the “ barbette shield.” The barbette is the modern equivalent to the obsolescent turret. A turret is a thickly armoured circular struc-