GLUTEN; (Colle Vegetale, Fr.; Kleber, Germ.) was first extracted by Beccaria from wheat flour, and was long regarded as a proximate principle of plants, till Einhof, Taddei, and Berzelius, succeeded in showing that it may be resolved by means of alcohol into three different substances, one of which resembles closely animal albumine, and has been called Zymome, or vegetable albumine; another has been called Gliadine; and a third Mucine. The mode of separating gluten from the other constituents of wheat flour, has been described towards the end of the article [Bread].
Gluten when dried in the air or a stove, diminishes greatly in size, becomes hard, brittle, glistening, and of a deep yellow colour. It is insoluble in ether, in fat and essential oils, and nearly so in water. Alcohol and acetic acid cause gluten to swell and make a sort of milky solution. Dilute acids and alkaline lyes dissolve gluten. Its ultimate constituents are not determined, but azote is one of them, and accordingly when moist gluten is left to ferment, it exhales the smell of old cheese.
GLYCERINE, is a sweet substance which may be extracted from fatty substances. If we take equal parts of olive oil, and finely-ground litharge, put them into a basin with a little water, set this on a sand bath moderately heated, and stir the mixture constantly, with the occasional addition of hot water to replace what is lost by evaporation, we shall obtain in a short time, a soap or plaster of lead. After having added more water to this, we remove the vessel from the fire, decant the liquor, filter it, pass sulphuretted hydrogen through it to separate the lead, then filter afresh, and concentrate the liquor as much as is possible without burning upon the sand bath. What remains must be finally evaporated within the receiver of the air-pump. Glycerine thus prepared is a transparent liquid, without colour or smell, and of a syrupy consistence. It has a very sweet taste. Its specific gravity is 1·27 at the temperature of 60°. When thrown upon burning coals, it takes fire and burns like an oil. Water combines with it in almost all proportions; alcohol dissolves it readily; nitric acid converts it into oxalic acid; and according to Vogel, sulphuric acid transforms it into sugar, in the same way as it does starch. Ferment or yeast does not affect it in any degree.
Its constituents are, carbon 40; hydrogen 9; oxygen 51; in 100.
GNEISS, is the name of one of the great mountain formations, being reckoned the oldest of the stratified rocks. It is composed of the same substances as granite, viz. quartz, mica, and felspar. In gneiss however they are not in granular crystals, but in scales, so as to give the mass a slaty structure. It abounds in metallic treasures.
GOLD. (Eng. and Germ.; Or, Fr.) This metal is distinguished by its splendid yellow colour; its great density = 19·3, compared to water 1·0; its fusibility at the 32d degree of Wedgewood’s pyrometer; its pre-eminent ductility and malleability, whence it can be beat into leaves only one 282,000th of an inch thick; and its insolubility in any acid menstruum, except the mixture of muriatic and nitric acids, styled by the alchemists aqua regia, because gold was deemed by them to be the king of metals.
Gold is found only in the metallic state, sometimes crystallized in the cube, and its derivative forms. It occurs also in threads of various size, twisted and interlaced into a chain of minute octahedral crystals; as also in spangles or roundish grains, which when of a certain magnitude are called pepitas. The small grains are not fragments broken from a greater mass; but they shew by their flattened ovoid shape, and their rounded outline, that this is their original state. The spec. grav. of native gold varies from 13·3 to 17·7. Humboldt states that the largest pepita known was one found in Peru, weighing about 12 kilogrammes (261⁄2 lbs. avoird.); but masses have been quoted in the province of Quito which weighed nearly four times as much.
Another ore of gold is the alloy with silver, or argental gold, the electrum of Pliny, so called from its amber shade. It seems to be a definite compound, containing in 100 parts, 64 of gold, and 36 of silver.
The mineral formations in which this metal occurs, are the crystalline primitive rocks, the compact transition rocks, the trachytic and trap rocks, and alluvial grounds.
It never predominates to such a degree as to constitute veins by itself. It is either disseminated, and as it were impasted in stony masses, or spread out in thin plates or grains on their surface, or, lastly, implanted in their cavities, under the shape of filaments or crystallized twigs. The minerals composing the veins are either quartz, calc-spar, or sulphate of baryta. The ores that accompany the gold in these veins are chiefly iron pyrites, copper pyrites, galena, blende, and mispickel (arsenical pyrites.)