PRECIOUS METALS—GOLD AND SILVER Gold.—Gold is probably the earli est known of the metals, and one of the most widely distributed. It is among the heaviest, softest, and most malleable. It occurs in nearly all the great mountain ranges and in sea water. United States gold coin con sists of 90 parts pure gold and 10 parts copper and silver alloy. Silver as an alloy gives a pale shade to gold, and copper a reddish color. Thus the red gold of watch chains and jewelry is alloyed with copper. These alloys are harder than pure gold, which is too soft to wear well in coin or orna ments. The amount of alloy in jew elry varies from 10 per cent to 50 per cent or more. The ratio between gold and its alloys indicates its fine ness, and may be expressed either in thousandths or karats. Pure gold is 1,000 fine, or 24 karats fine. United States gold is 900 fine.
The karat is a weight of 3.17 grains troy, and is the standard used in weighing precious stones. As em ployed to express the fineness of gold, it represents 5lr part of the pure metal. This is the older form still used by jewelers and the British mint. On this basis equal parts of gold and other metals is said to be 12 karat fine. Sixteen parts of alloy make an 8 karat gold, and so on. Common gold jewelry is usually 14 karat fine, but a better quality is 18 karat. The for mer is usually of a darker shade, due to the larger percentage of copper.
Pure gold is more than nineteen times as heavy as water. One cubic inch of pure gold weighs 10.12883 ounces troy, and is valued at $209.38. In calculating the value of bullion, 387 ounces troy are considered to be worth $8,000, hence 1 ounce is worth $20.6718 +.
Gold is extremely malleable, as is shown by the fineness of gold leaf used in gilding. Gold does not rust or tarnish by exposure to weather or to gases, and is very difficult to dis solve. Ornaments found in ancient tombs remain unchanged. Gold may be dissolved in chlorine, or a mixture of nitric and hydrochloric acids. This is known as aqua regia, or the " royal liquid," as gold was called by the al chemists " the royal metal," and this mixture was thought by them to be the only solvent capable of attack ing it.
Gold is sometimes alloyed with the rare metal palladium, and with plati num. These give a hard and very
elastic alloy. Mercury unites freely with gold to form an amalgam. The value of gold as money rests not only on its beauty and durability, but also upon the fact that it cannot be ob tained without a certain amount of human labor, and this fact helps to determine its value and establish a re lation between it and other commodi ties. Hence gold is at once a measure of the labor performed and the re ward of labor. Enormous amounts of gold are used in the arts and con sumed by the wear of coin and jew elry. Approximately one sixth of the annual production of gold is estima ted to be used for purposes other than coinage.
Gold Leaf.—One ounce of gold may be beaten out so thin as to cover 189 square feet of surface, but this is not customary, 1,000 square feet to the ounce troy being the usual measure. Ordinary gold leaf is so thin as to require 282,000 sheets to make a pile an inch high. At this thinness it transmits a light somewhat the same as would be given by a piece of green glass. One grain of gold may be drawn into a wire 500 feet long. Gold leaf is used in gilding and by dentists in filling teeth.
The art of gold beating is known to but few. For dentists' use the gold is perfectly pure, but for gilders' use various alloys of silver and copper are added, according to color. The gold is first rolled into ribbons, of which 700 are required to make an inch in height, and then placed be tween the leaves of a little book made of parchment, which is laid on a stone anvil and beaten by workmen with a 16-pound round hammer having broad, round face. Several other proc esses are required, all of which are done by hand. When completed, the gold leaf is placed in books or tissue paper 3i inches square, the leaves of which are rubbed with red ocher to prevent the gold from sticking. Each of these holds 25 leaves or 5i grains of gold. Torn gold leaf may be mended by laying another torn leaf on the top of the first and making a cut near the center by means of a thin, sharp strip of reed. The leaves unite along the line of the cut by their own weight, and if skillfully done no trace of the welding is visible.