GANGUE

A word derived from the German gang , a vein or channel. It signifies the mineral substance which either encloses or usually accompanies any metallic ore in the vein. Quartz, lamellar carbonate of lime, sulphate of baryta, sulphate and fluate of lime, generally form the gangues; but a great many other substances become such when they predominate in a vein. In metallurgic works the first thing is to break the mixed ore into small pieces, in order to separate the valuable from the usele parts, by proce es called stamping, picking, sorting. See Metallurgy and Mines . GARNET ( Grenat , Fr.; Granat , Germ.); is a vitreous mineral of the cubic system, of which the predominating forms are the rhomboidal dodecahedron and the trapœzohedron; specific gravity varying from 3·35 to 4·24; fusible at the blowpipe. Its constituents are, silica, 42; alumina, 20·0; lime, 34·0; protoxide of iron, 4. Garnets are usually di eminated, and occur in all the primitive strata from gnei to clay slate. The finer varieties, noble garnet or Almandine, and the reddish varieties of Gro ulaire (E onite), are employed in jewellery; the first are called the Syrian or oriental; the others, hyacinth. In some parts of Germany garnets are so abundant as to be used as fluxes to some iron ores; in others, the garnet gravel is washed, pounded, and employed as a substitute for emery. The garnets of Pegu are most highly valued. Factitious garnets may be made by the following composition:—Purest white gla , 2 ounces; gla of antimony, 1 ounce; powder of ca ius, 1 grain; manganese, 1 grain. GAS (Eng. and Fr.; Gaz , Germ.); is the generic name of all those elastic fluids which are permanent under a considerable pre ure, and at the temperature of zero of Fahrenheit. In many of them, however, by the joint influence of exce ive cold and pre ure, the repulsive state of the particles may be balanced or subverted, so as to transform the elastic gas into a liquid or a solid. For this most interesting discovery, we are indebted to the fine genius of Mr. Faraday. The following table exhibits the temperatures and pre ures at which certain gases are liquefied. | Name of the gas. | Becomes liquid | Calculated boiling point; Barom. = 30 inches. | | At | Under a pre ure of | | Sulphurous acid | 59 | ° | F. | 3 | atmospheres. | - | 4 | ° | Fahr. | | Chlorine | 60 | | 4 | | - | 22 | | | Ammonia | 50 | | 6 | ·5 | - | 64 | | | Sulphuretted hydrogen | 50 | | 17 | | - | 142 | | | Carbonic acid | 32 | | 36 | | - | 229 | | | Hydrochloric or muriatic acid | 50 | | 50 | | - | 249 | | | Deutoxide of azote | 45 | | 50 | | - | 254 | | Liquid carbonic acid becomes solidified, into a snowy-looking substance, by its own rapid evaporation. Oxygen, hydrogen, and azote, have hitherto resisted all attempts to divest them of their elastic form. For this purpose, it is probable that a condensing force equal to that of 650 atmospheres, will be required. The volume of any gas is, generally speaking, inversely as the pre ure to which it is exposed; thus, under a double pre ure its bulk becomes one-half; under a triple pre ure, one-third; and so on. For the change of volume in gaseous bodies by heat, see Expansion . Ammonia, carbonic acid, carburetted hydrogen, chlorine, muriatic acid, sulphurous acid, sulphuretted hydrogen, are the gases of most direct interest in the arts and manufactures. Their detailed examination belongs to a work on chemistry.