GOLCON'DA, a fortress of the nizam, situated 7 m. to the n.w. of bis capital, (Hyder abad, stands in lat. 17° 22' n., and in long. 78° 25' east. In its immediate neighborhood are the ruins of an ancient city, once the metropolis of the kingdom of Golconda. The place itself is still strong; but its strength is seriously impaired through its being over topped, within breaching-range, by the yet solid mausolea of its former sovereigns, which form a vast group at a distance of 600 yards. These tombs are dome-crowned structures of gray granite, each having its own mosque, and occupying the center of its own elevated terrace. Golconda is proverbially famous for its diamonds; but, in truth, they are merely cut and polished here, being generally found at Parteall, near the southern frontier of the nizam's dominions.
GOLD (symbol Au, atomic weight 196) has been known and regarded as the most precious of the metals from the earliest ages of the world, and has been universally employed as a medium of exchange. Although the quantity of gold which is found, when compared with that of many other metals, is small, yet there are few parts of the globe in which it does not occur more or less abundantly.
In the native state, it occurs crystallized, the primary form being the •chbe, or in plates, ramifications, or nodules—popularly known as nuggets—which sometimes are of very considerable size. It is almost always alloyed with silver, and sometimes with tellurium, bismuth, lead, etc. It sometimes occurs in small quantity in metallic sul phides, as in galena, iron, and copper pyrites.
The extraction of gold from the substances with which it is associated is effected more by mechanical than by chemical means. See below.
The following are its most important properties. In its compact state, it possesses a characteristic yellow color and high metallic luster, is nearly as soft as lead, and is the most malleable of all metals. It can be beaten into leaves of a thinness.not exceed ing or, according to some authors, of an inch, through which light passes with a green tint; one grain may thus be distributed over 56 sq. in. of sur face; and the ductility of the metal is so great, that the same quantity may be drawn out into 500 ft. of wire. In its tenacity, it is inferior to iron, platinum, copper, and silver; but a wire whose diameter is 0.787 (or rather more than one-third) of a line (which is one twelfth of an inch), will support a weight of about 150 pounds. It fuses at about 2016°, to Daniell's pyrometer, and when in fusion, is of a bluish-green color. It is scarcely at all volatile in the heat of the furnace, but by a powerful electric
discharge, by the concentration of the sun's rays by a powerful burning-glass, or by the oxy-hydrogen jet, it is dispersed in purple vapors. Gold has very little affinity for oxygen; it undergoes no change on exposure to the atmosphere, and is unaffected by hydrochloric, sulphtiric, or nitrie acid, or, in short, by any simple acid except selenic acid; nor do the alkalies affect it. It is, however, dissolved by any mixture which lib erates chlorine, its usual solvent being aqua regia, which is generally prepared by mix ing 1 part of nitric acid with 4 parts of hydrochloric acid. Hydrochloric acid, to which biuoxide of manganese has been added, acts equally well, the gold in these cases being converted int6 a chloride. This metal is one of most perfect conductors both. of heat and of electricity. When precipitated in a finely comminuted state, it is of a brown color; but when suspended in water, and viewed by transmitted light, it appears purple. The specific gravity of this metal is less than that of platinum and iridium, ranging from 19.2 to 19.4, according as it is fused or hammered.
The alloys of gold, or its combinations with other metals, are very numerous, those with copper and mercury being the most important. Copper and gold combine in all proportions without materially affecting the color of the latter, except that it is some what redder. The density of the compound is less than that of gold, but the hardness is greater, and it is more fusible. It is this alloy which is employed in our gold coin age, 11 parts of gold, being combined with one of copper, without which the coin would not be sufficiently hard to stand the wear to which it is exposed. Hence, British stan dard gold contains 8.33 per cent, of copper. In France, and in the United States, stan dard gold contains 10 per cent. of the latter metal. Jewelers alloy their gold with other metals, partly on economical grounds, and partly for the purpose of evolving special tints. Thus, red gold is obtained by combining 75 parts of fine gold with 25 of copper; green gold, by combining 75 parts of line gold with 25 of silver; dead-leaf gold, by combining 70 parts of fine gold with 30 of silver; water-green gold, by combining 60 parts of fine gold with 40 of silver; blue gold, by combining 75 parts of fine gold with 25 of iron.