GUMS. 368 GUNCOTTON. flaky iragacanth of commerce; vermicelli and common tiagacanth are cheaper varieties. Traga- eanth is dull, translucent, horn-like, and has a white or ^yellowish color. It contains both arabin and bassorin; when the gum is treated with v.ater, the portion containing arabin goes into .solution, forming a mucilaginous liquid, while the bassorin remains undissolved. Tragacanth has a soothing action when applied to a sore throat. It also tinds considerable application in the arts, being muel) valued as a stiffening ma- terial for various textile fabrics. The following gums are more or less closely allied to gum tragacanth: liassora gum, which is used to adul terate tragacanth; uood gum, which is derived from the birch, ash, oak, willow, etc. (3) Chtrrii-lree gum is a colorless or yellow gum used for stiflening hats. It swells with water, forming a slimy paste. In contains a con- siderable amount of the insoluble substance cerasin. t'iugar-hcet gum, Irisli-moss gum, and a few other gums contain substances which dift'er some- what in their properties and reactions from the arabin, bassorin, and cerasin mentioned above. Sugar-beet gum contains pararabin; Irish-moss gum contains lichenin. A substance named animal gum has been ex- tracted from the salivary and mucous glands. It is a carbohydrate closely resembling the vege- table gums; soluble in water, insoluble in alcohol. Like the vegetable gums, it is transformed into sugar when boiled with dilute acids. Gum Rksixs. These are the dried exudations of various plants. The gura resins are mixtures containing one or more gums and one or more resins. When they are rubbed with water, the gum generally dissolves, while the insoluble resin forms an enuilsion. Alcohol, on the contrary, dissolves the resin, leaving an insoluble residue of gum. It thus requires both water and alcohol to dissolve a gum resin completely. The group includes: Ammoniac, asafoctida, galbanum. gam- hoge, myn-h, and srainnwng. all of which are in- cluded in the United States Pharraacopceia, and are described in special articles under their names. Other gum resins are the following: Bdellium, which resembles myrrh, and was highly esteemed by the ancients for its medicinal properties. The Indian variety is mentioned in the Bible; the African variety is used by French druggists in making plasters. Euphoi-bium. an acrid substance formerly used in medicine: it is derived from the Euphorbia officinarum. growing in Xorthwestern Africa. Sagapenum. formerly used in medicine. Gum Sue.stiti'tes. These are made from wheat-starch, potato-starch, and other feculas, by baking or roasting, so as to convert the .starch into dextrin. They are employed as substitutes for the real gums, which are more expensive. For some purposes, the gum substitutes are su- perior to the real gums. GUMTI, gum'te. A river of India, remarkable for its windings. It rises in a small lake in the District of Shahjehanpur in the United Provinces of Agra and Oudh, and after a southeastern course of 4S2 miles, enters the Ganges near Benares (Map: India, D 3). It is navigable for inland craft to Lucknow. more than 300 miles above its conlluence with the Ganges. GUM-TREE. A name applied to many very distinct trees that exude gum or resin of some kind. In the United States, one of the best known from New York to Texas is the sweet gum {Liquidambar styntciflua, order Hamamelidea') , sometimes called the American stora.x, a large, handsome tree, with deeply five- to seven- lobed smooth and shining leaves, which in autunui become brilliant scarlet. The rather fine-grained wood is used to a considerable ex- tent for furniture, and the bark, which is deeply furrowed, is valued in domestic medicine in the treatment of dysentery. Several species of Xyssa, a genus of the order Cornacea>, are known as gum-trees. The best known is the black or sour gum {Xyssa multiflora) , found from jMaine to Texas, a large tree with tough, close-grained wood which, since it splits with difficulty on ac- count of its cross-grained and interlacing fibres, is valuable for hollow woodenware. Other spe- cies are conunon through the Southern States, where they are better known as tupelo. Xyssa riipitata. of rather limited range in South Caro- lina, Georgia, and Florida, is known as the ogeeehee lime from the appearance of its edible fruit. Burstra gummifcra. of Florida, is known as gum elenii, and Bumelia lanuginosa, the shit- timwood, indigenous from Illinois to Texas and Jlexi<"0, is locally known as gum elastic. In Australia the name gum-tree is applied with various modifications to many of the species of Eucalyptus (q.v. ). Sfi/raj; Soisoi'n is called gum- tree in the East Indies, and in Europe a number of other trees are similarly designated. GUN. A heavy piece of artillery or ordnance designed for direct fire, in which it differs from howitzers and mortars, which use high-angle fire. See Artillery ; Guns, Naval ; Ordnance^ Field Artillery; Machine Gun; Mortar; Siege Guns. GUNBOAT. A small vessel of light draught, designed for service in harbors, rivers, and in- shore waters. Modern gunboats are much larger than their prototypes. In the United States Xavy the vessels of the Yorktoicn class of 1700 tons displacement are styled gmiboats, though their proper designation is that of cruiser, for they are sea-going ships. Gunboats have always been useful auxiliaries in ofTensive and defensive warfare, but by themselves they have very little fighting value. GUN-CARKIAGE. The vehicle or support by which artillery or heavy ordnance is brought into action or manoeuvred. The modern gun- carriage is a result of the great improvements made in recent years, chiefly due to better me- chanical design, and the introduction of pneu- matic and hydraulic cylinders to check the recoil, combined with powerful springs to throw the gim back to its firing position, after recoil. For more detailed information, see Artillery; Field Ar- tillery; Coast Artillery; Guns. Naval ; Ma- chine Guns; Mountain Artillery; Siege Guns ; and Ordnance. GUNCOTTON. A name applied to certain cellulose products of the action of nitric acid on cellulose, discovered by Schonbein in 1840. The molecular formula of cellulose (q.v.) is some un- known multiple of C„H,„0„ and the action of nitric acid results in the substitution of a vary- ing number of NO, groups for hydrogen atoms in the doubtless complex molecule of cellulose. The
