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LEFT GTJMMERE 428 GUN POWDER GUMMERE, ERAITCIS BARTON (gum'e-re), an American teacher and author; born in Burlington, N. J., March 6, 1855. He was instructor in Harvard College from 1881 to 1882; and in 1887 became Professor of English at Haver- ford College, Pa. Besides miscellaneous papers in Germanic philology and Eng- lish literature, he has written: "The Anglo-Saxon Metaphor" (1881) ; "Hand- book of Poetics" (1885) ; "Germanic Origins" (1892) ; "Old English Ballads" (1904); "The Popular Ballad" (1907). GUN. See Automatic Gun; Firearms; Ordnance; Artillery; Machine Gun; Explosives. GUN BATTERY, in fortification, the emplacement of two or more pieces of ar- tillery, destined to act on the offensive or defensive. It may be: En echarpe, hav- ing a line of fire oblique with the object. En revers, playing on the rear of the enemy. Crossfire, several batteries hav- ing a converging fire on an object. Case- mate, when protected by a bomb-proof chamber, and firing from embrasures. Barbette, firing over a parapet. Ricochet (smooth bores only), when the balls, with a low charge, traverse the inner face of the enemy's work, and rebound and roll along the same. Mountain, light pieces adapted to be dismounted and, with their dislocated carriages, carried on mules. Some of these have been made in two pieces, which unscrew for ease in trans- port. In field-artillery, the tactical unit of field-artillery, consisting of six or eight field guns under one command, to- gether with the oflicers, men, horses, wagons, and stores. GUN COTTON, pyroxylin. Trinitro- cellulose, C,,H7(NO-.)305, more probably a nitric ether of cellulose, Ci2H,4(ONOl.)o04, as by the action of reducing agents as hydric potassium sulphide, KHS, and iron and acetic acid, it is converted into cellulose. Boiled with ferrous sulphate and concentrated hydrochloric acid, it gives off all its nitrogen as N2O2. Gun cotton was discovered by Schonbein in 1845. It is prepared by drying cotton- wool at 100° and then leaving it for 24 hours in a mixture of one volume of nitric acid, specific gravity 1.5, and three volumes of sulphuric acid, specific gravity 1.85, the mixture being cooled to 10°. It is then washed with water, and, if required pure, again with a mixture of one part alcohol and three parts ether to remove the lower nitrates. Gun cot- ton finely divided explodes between 160°- 170°. It keeps best if it is washed with soda. Compressed gun cotton burns like tinder, but is exploded by mercuric-ful- minate. See Explosives. GUNNERY, See GuN POWDER, Ar- tillery, Machine Gun, Rifle, etc. GUNNISON, a river in Colorado, a tributary of the Grand river, and which passes through a remarkable canon 15 miles in length. GUN POWDER, like many other so- called "modern inventions," gun powder appears to have been known to the Chi- nese several centuries before its invention in Europe, whether we ascribe the in- vention to Roger Bacon in the 13th cen- tury or to Friar Schwartz in the 14th. Its earliest well-authenticated use in war- fare was at the battle of Crecy in 1346. Its use was rapidly extended and within a century after Crecy it had driven the bow and arrow from the field and rele- gated the lance and the battle axe to the secondary position of weapons for special emergencies only. It is rather surprising that for more than five centuries, the ingredients first used remained unchanged. These were saltpeter, charcoal and sulphur; — char- coal to furnish the fuel for burning, salt- peter to furnish the oxygen needed to combine with the carbon of the charcoal, and sulphur to accelerate the rate of burning. The products of combustion are carbon dioxide and nitrogen, both gases, and the sulphate and carbonate of potassium, both solids. The expansive force of the gases is due not alone to the change from the solid to the gaseous state, but to the further expansion from the heat released by the change. The solids, being finely divided, produce the dense smoke which marks the firing of a gun loaded with what is now commonly called "black powder" as distinguished from the more modern smokeless powder. Not every explosive substance is suit- able for use as a "propellant" in a gun. To be available for such use, not only must the explosive develop great power but it must develop this power gradually, so that the projectile shall be started from its seat slowly and driven down the bore more and more rapidly as the pres- sure behind it rises to a maximum. If the full pressure were developed instan- taneously, the gun would be ruptured be- fore the projectile was started from its seat. Here we touch upon the difference between "explosion" and "detonation." The explosion of a charge of powder in a gun, sudden as it is, is slow compared with the detonation of the "high explosives," nitro-glycerine, gun-cotton, etc. In one case we have an actual burning, the flame of which passes from grain to grain of the powder, occupying an interval which is perfectly appreciable and can be measured. In the other case we have a