GUM. A vegetable product, distin guished by solubility in water, and in solubility in alcohol ; it is tasteless and inodorous. Gum-arabic, which is the produce of the Acacia vera, may be taken as a sample of the _purest form of gum. It is imported from Barbary and Morocco. Its specific gravity is 1.45. Its solution is viscid, and is termed mucilage. Gum is used as a demulcent in medicine, and for giving a gloss to linens, silks, &c. It consists of carbon 41.4, oxygen 52.09, hydrogen 5.51; or, in other terms, of 4P4 charcoal and 58.6 water.
Guerin has analyzed several varieties of gum. Arabia, which constitutes the greater portion of gum-arabic, is com posed of Carbon 43 81 Oxygen 49-85 Hydrogen 620 Azote '14 100.00 Gnm-arabic is found to consist of Arabin 79.40 Water 17.60 Ashes 300 100 00 Messrs. Gay-Lussac and Thenard found its composition to be : Arabin 8416 Water 1313 Ashes 100 00 The difference of water found depended stpon the different methods of analysis. The dried root of the blue-bell contains mucilage, very similar to gum-arabic. Gum. senega is less soluble than gum arable, and deeper in color. GUM-RESIN. An exudation from many trees, composed of n mixture of gum and resin, or of a substance inter mediate between the two.
GUN. Under this general term most of the species of fire-arms are included, the pistol and mortar being almost the only exceptions. Great guns, or cannon, began to be used as military engines about the middle of the 14th century ; but small guns, or muskets, appear to have been introduced nearly two centuries later, namely, 1521. They were first used by the Spanish infantry at the siege of Rhege. Muskets were at first of a very clumsy construction, being so heavy that they could not be levelled and fired from the shoulder ; accordingly the soldier was provided with a rest, which it was ne cessary to carry along with him and plant in the ground in order to support the weapon before it could be used. The gun was generally fired with a match ; sometimes by means of sparks gene rated by the revolution of a notched wheel of steel, placed directly above the pan containing the priming. Muskets with rests were employed so lately as the civil wars in the time of Charles I. ; afterwards a lighter matchlock musket came into use ; and about the beginning of the last century the troops through out Europe were armed with firelocks.
Small guns were invented by Swartz, a German, about 1378 ; brought into use by the Venetians, 1382. Cannon were first used at the battle of Cressy, 1346 ; first used in England at the siege of Ber wick, 1405 ; first cast in England, 1544 ; used in shipping by the Venetians, 1539; before they were only used to batter walls. Mohammed, at the siege of Con
stantinople, employed some of the larg est guns ever made use of before or since. One of his cannon was of such enormous size as to require 70 yoke of oxen to draw it, and 2000 men to man it. It discharged a ball of the weight of 300 lbs. The report was heard to a great distance, and the country shaken to the distance of 40 furlongs.
The barrel forms the essential part of the gun ; and the first requisite to a good barrel is toughness in the material of which it is made, for safety in using it depends mainly on this quality. The best iron for the formation of musket barrels is that which has been much worn, and toughened by the loss of its fiery particles; and, accordingly, old horse stub-nails are much in request for this purpose, and sold at a high price to the barrel-forgers. Formerly the best gun barrels were made in Spain ; and their superiority was attributed to the excel lency of the iron made use of, which consisted almost exclusively of stub-nails, and the old shoes of horses and mules : but the barrels now made in this coun try are not inferior to those of any coun try in the world. The method of mak ing the barrel is this : the iron is first formed into a thin flexible bar, some thing like a cooper's hoop, and when heated is plied or twisted round a man dril, much in the same manner as a rib bon of leather is turned round the handle of a whip. For the best barrels the breadth of the bar does not exceed half an inch; and it is turned round the man dril in such a manner that the edges are brought close together, but do not over lap. In this position it is wedded by horizontal strokes with the hammer. But in common guns a broader bar is em ployed; and its edges, which are placed so as to overlap considerably, are welded down on each other. The Damascus barrels, prized for their beauty, though inferior in strength, are composed of iron and steel in certain proportions laid crossways, and hammered together the whole length of the barrel. After the barrel has been forged, the inside is ren dered smooth and perfectly cylindrical by boring it with a bit, or rather bits of different sizes used in succession. In ri fles a certain number of parallel grooves, either straight or slightly twisted, are cut in the inside of the barrel, of equal depth and fineness, and through its whole length. The exterior is smoothed by turning it on a lathe.