Gold(redirected from Auric (Ion))
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gold,metallic chemical element; symbol Au [Lat. aurum=shining dawn]; at. no. 79; at. wt. 196.96657; m.p. 1,064.43°C;; b.p. 2,808°C;; sp. gr. 19.32 at 20°C;; valence +1 or +3.
Gold is very ductile and is the most malleable metal; it can be beaten into extremely thin sheets of gold leaf. Only silver and copper, which are above it in Group 11 of the periodic tableperiodic table,
chart of the elements arranged according to the periodic law discovered by Dmitri I. Mendeleev and revised by Henry G. J. Moseley. In the periodic table the elements are arranged in columns and rows according to increasing atomic number (see the table entitled
..... Click the link for more information. , are better electrical conductors. Gold is chemically inactive. It is unaffected by moisture, oxygen, or ordinary acids but is attacked by the halogenshalogen
[Gr.,=salt-bearing], any of the chemically active elements found in Group 17 of the periodic table; the name applies especially to fluorine (symbol F), chlorine (Cl), bromine (Br), and iodine (I).
..... Click the link for more information. . Aqua regia (a mixture of nitric and hydrochloric acids that liberates chlorine) is so named for its ability to dissolve gold, the "king" of the metals. Gold forms both aurous (univalent) and auric (trivalent) compounds; auric chloride and chloroauric acid are its most common compounds.
A relatively soft metal, gold is usually hardened by alloying with copper, silver, or other metals. White gold, a substitute for platinum, is an alloy of gold with platinum, palladium, nickel, or nickel and zinc. Green gold, also used by jewelers, is usually an alloy of gold with silver. Alloys of gold with copper are a reddish yellow and are used for coinage and jewelry. Gold is often found in nature alloyed with other metals; when more than 20% of silver is present the alloy is called electrum. The gold content of an alloy is commonly stated in carats, a carat being 1-24 part by weight of the total mass. Pure gold is therefore 24 carats fine; an alloy that is 75% gold is 18 carats fine. Fineness is sometimes expressed in terms of parts per thousand; thus gold containing 10% of other metals is said to have a fineness of 900.
Gold is widely distributed on the earth; although large amounts are present also in seawater, the cost of current methods for recovering it exceeds its value. Most gold is found in the metallic state in the form of dust, grains, flakes, or nuggets. It occurs, usually in association with silver or other metals, in quartz veins or lodes so finely disseminated that it is not visible. It is found also in alluvial placer deposits, which are worked by panning, dredging, and hydraulic mining. Gold is extracted from its ores by mechanical means and separated from other metals by chemical processes, notably the cyanide processcyanide process
method for extracting gold from its ore. The ore is first finely ground and may be concentrated by flotation; if it contains certain impurities, it may be roasted.
..... Click the link for more information. , the amalgamation processamalgamation process
, in particular, a method to extract gold and silver from ores. The ore is crushed and treated with mercury, in which the metal dissolves. The amalgam is heated and the mercury evaporates, leaving pure gold or silver.
..... Click the link for more information. , and the chlorination process (in this the ore is oxidized and chlorinated and the gold precipitated with hydrogen sulfide). It also occurs in compounds, notably telluride minerals.
Gold has been known from prehistoric times and was possibly the first metal used by humans. It was valued for ornaments (see goldworkgoldwork,
ornaments, jewelry, and vessels created from gold. Such works have figured in almost every stage of civilization as symbols of wealth and power. The Ancient World
The earliest-known fine goldwork is from Ur in Mesopotamia. Dating from c.3000 B.C.
..... Click the link for more information. ), and magical efficacy was attributed to it. In the Middle Ages alchemists sought to transmute baser metals into gold. The quest for gold stimulated European explorations and conquests in the Western Hemisphere, and its discovery has led to many a gold rushgold rush,
influx of prospectors, merchants, adventurers, and others to newly discovered gold fields. One of the most famous of these stampedes in pursuit of riches was the California gold rush.
..... Click the link for more information. . Much of the gold now extracted is used for jewelry. The chief producers are China, Australia, the United States (especially in Nevada and Alaska), South Africa, Peru, Russia, Indonesia, and Canada. For a discussion of the monetary function of gold, see bimetallismbimetallism
, in economic history, monetary system in which two commodities, usually gold and silver, were used as a standard and coined without limit at a ratio fixed by legislation that also designated both of them as legally acceptable for all payments.
..... Click the link for more information. ; coincoin,
piece of metal, usually a disk of gold, silver, nickel, bronze, copper, aluminum, or a combination of such metals, stamped by authority of a government as a guarantee of its real or exchange value and used as money.
..... Click the link for more information. ; international monetary systeminternational monetary system,
rules and procedures by which different national currencies are exchanged for each other in world trade. Such a system is necessary to define a common standard of value for the world's currencies.
..... Click the link for more information. ; moneymoney,
term that actually refers to two concepts: the abstract unit of account in terms of which the value of goods, services, and obligations can be compared; and anything that is widely established as a means of payment.
..... Click the link for more information. .
Until the mid-1700s tradition dictated that the British monarch offer gifts of frankincense, gold, and myrrh at the Chapel Royal on Epiphany. Heralds and knights of the Garter, Thistle, and Bath accompanied the king on his royal pilgrimage. Under the unstable King George III (1760-1820) the procession was abandoned, although the monarch's gift of gold, frankincense, and myrrh is still sent to the Chapel Royal by proxy. A similar royal offering was at one time customary in Spain.
Gold has been considered rare, valuable, and beautiful throughout history. In addition to its beauty and brightness, gold has some unusual properties. It is nearly indestructible, and yet it is also the most malleable of metals. A single ounce of gold can be beaten into a sheet of gold leaf that measures approximately 200 feet on each side. Gold does not tarnish or corrode, and is extremely resistant to wear. Finally, it is often found in a nearly pure state. These qualities enhance its value, versatility, and mystery.
Coughenour, Robert A. "Gold." In Paul J. Achtemeier, ed. HarperCollinsBible Dictionary. Revised edition. San Francisco, Calif.: HarperSanFrancisco, 1996. Crippen, Thomas G. Christmas and Christmas Lore. 1923. Reprint. Detroit, Mich.: Omnigraphics, 1990. Peattie, Donald Culross. "Gold, Frankincense, and Myrrh." Saturday Eve-ning Post 264, 6 (November 1992): 56. Gospel Accounts of Christmas
(Latin, Aurum) Au, a chemical element in Group I of the Mendeleev periodic system. Atomic number, 79; atomic weight, 196.9665. A heavy yellow metal. Gold has one stable isotope, 197Au.
Historical survey. Gold was the first metal known to man. Golden articles are found in cultural layers of the Neolithic epoch (fifth to fourth millennium B.C.). In ancient states—Egypt, Mesopotamia, India, and China—the mining of gold and the manufacture from it of ornaments and other objects existed as early as 3000–2000 B.C. Gold is mentioned often in the Bible, the Iliad, and the Odyssey, and in other ancient literary monuments. The alchemists called gold the king of metals and designated it by the symbol for the sun . The chief object of alchemy was to discover ways of transmuting base metals into gold.
Distribution in nature. The average content of gold in the lithosphere is 4.3 × 10−7 weight percent. Gold is scattered in magma and magmatic rocks, but hydrothermal gold deposits (quartz gold-bearing veins, and so forth), which are important industrially, are formed from hot waters in the earth’s crust. In ores, gold occurs mainly in the free (native) state and only very rarely forms minerals with selenium, tellurium, antimony, and bismuth. Pyrites and other sulfides frequently contain an admixture of gold, which is extracted in the processing of copper ore, complex ores, and others.
In the biosphere, gold migrates in complexes with organic compounds; in river suspensions, it migrates mechanically. One liter (l) of river or sea water contains about 4 × 10−9 g of gold. In some parts of gold ore deposits the underground water contain about 10−6 g/l of gold. This gold migrates in soils; from the soil it enters plants, some of which (for example, Equisetatum and Zea mays) concentrate gold. The destruction of endogeneous gold deposits results in the formation of gold placers, which are of industrial importance. Gold is mined in 41 countries, the main reserves being concentrated in the USSR, the republic of South Africa, and Canada.
Physical and chemical properties. Gold is a soft, very plastic, and ductile metal (it can be hammered into leaves as thin as 8 × 10−5 mm and drawn into wire that weighs as little as 1 gram for every 2 km). It is a good conductor of heat and electricity and it is extremely resistant to chemical action. The crystal lattice of gold is a face-centered cubic array; a = 4.704 angstroms (A). Atomic radius, 1.44 Å; ionic radius of Au1+, 1.37 Å. Density (at 20°C), 19.32 g/cm3; melting point, 1064.43°C; boiling point, 2947°C; thermal coefficient of linear expansion, 14.2 × 10−6 (0°-100°C); specific thermal conductivity, 311.48 watts/m-°K[0.744 cal/cm-sec-°C]; specific heat, 132.3 joules/ (kg · °K) [0.0316 cal/(g · °C)] (at 0°-100°C); specific electric resistance, 2.25 × 10−8 ohm · m (2.25 × 10−6 ohm · cm) (at 20°C); electric resistance temperature coefficient, 0.00396 (0–100°C). Modulus of elasticity, 79 × 103 meganewtons (MN) per m3 (79 × 10−2 kilograms-force [kgf] per mm2). For annealed gold the tensile strength is 100–140 MN/m2 (10–14 kgf/mm2); the relative elongation, 30–50 percent; and the necking, 90 percent. After cold plastic deformation the tensile strength rises to 270–340 MN/m2 (27–34 kgf/mm2). The Brinell hardness is 180 MN/m2 (18 kgf/mm2) (for gold annealed at about 400°C).
The outer electron configuration of the gold atom is 5d106s1. In compounds the valences of gold are 1 and 3. (Complex compounds are known in which gold is bivalent.) Gold does not react with nonmetals (except for halogens). It forms halides with halogens; for example, 2Au + 3Cl2 = 2AuCl3. Gold dissolves in a mixture of hydrochloric and nitric acids to give chloroauric acid H[AuCl4]. In solutions of sodium cyanide (NaCN) or potassium cyanide (KCN) with simultaneous access of oxygen, gold is converted to sodium auricyanide 2Na[Au(CN)2] (univalent gold). This reaction, discovered in 1843 by P. R. Bagration, found practical application only at the end of the 19th century. Characteristic of gold is its ready reducibility from compounds to metal and its complexing ability.
The existence of a univalent gold oxide, that is, aurous oxide (Au20), is doubtful. Univalent aurous chloride AuCl is obtained by heating the chloride of trivalent gold, auric chloride:
AuCl3 = AuCl + Cl2
Auric chloride AuCl3 is obtained by treating thin gold leaf or spicules with chlorine at 200°C. With water, the red needles of AuCl3 give a brown-red solution of complex acid:
Aucl3 + H2O = H2[AuOCl3]
Treatment of a solution of AuCl3 in water with caustic alkali precipitates an amphoteric yellow-brown hydroxide of trivalent gold, Au(OH)3, with mainly acidic properties; for this reason, the hydroxide is called auric acid and its salts, aurates. Heat converts auric hydroxide (trivalent gold) to auric oxide, Au2O3, which decomposes above 200°C:
2Au2O3 = 4Au + 3O2
The reduction of gold salts by stannous chloride
2AuCl3 + 3SnCl2 = 3SnCl4 + 2Au
leads to formation of an extremely stable purple colloidal gold solution (Cassius’ purple). This reaction is used analytically to detect gold. The quantitative determination of gold is based on its precipitation from aqueous solutions by reducing agents (FeSO4, H2SO3, H2C2O4) or by fire assay.
Extraction and refining. Gold can be extracted from placer deposits by washing, thanks to the great difference in density between the gold and the barren rock. This method, used even in remote antiquity, involves large losses. Its place was taken by amalgamation (known as early as the first century B.C. and used in America beginning in the 16th century) and by cyanide treatment, which came into widespread use in America, Africa, and Australia in the 1890’s. At the turn of the 20th century the main source of gold became primary deposits. Gold-bearing rock is first crushed and concentrated. The gold is extracted from the resultant concentrate with a solution of sodium cyanide or potassium cyanide. The gold is precipitated from the complex cyanide solution with zinc, which also precipitates any impurities. In the electrolytic refining of gold (Wohlwill process, 1896), anodes cast from impure gold are immersed in a bath of a hydrochloric acid solution of AuCl3; a sheet of pure gold serves as the cathode. When a current is passed through the solution the impurities precipitate (anode sludge, slime) and gold not less than 99.99 percent pure is deposited at the cathode.
Use. Under conditions of commercial production, gold serves as money (see the section below on economic significance). Technical use is made of gold alloyed with other metals, which increases its strength and hardness and makes it possible to economize on its use. The gold content of alloys used to make jewelry, coins, medals, and dental prosthesis-production intermediates is expressed as fineness. The usual addition is copper (the so-called alloying element). Alloyed with platinum, gold is used to make chemically resistant equipment; alloyed with platinum and silver, it is used in electrical engineering. Gold compounds are used in photography for toning.
S. A. POGODIN
Artistic use. Since ancient times gold has been used in the jeweler’s art (ornaments, religious and palace utensils) and for gilding. Because of its softness, malleability, and ductility, gold lends itself to particularly fine working by chasing, casting, and engraving. It is used to create various decorative effects (from the smooth surface of a yellow polished surface with liquid plays of light to complex textural juxtapositions with a rich play of chiaroscuro) and for the finest filigree work. Gold is often variously colored by adding other metals. It is used also in conjunction with precious and semiprecious stones, pearls, enamel, and niello.
Medical use. Gold preparations are used as a suspension in oil (the Soviet preparation krizanol, the foreign Myocrisin), or as water-soluble preparations (the foreign preparations Sancrisin and Solganal), for injection in treating chronic rheumatoid arthritides and lupus erythematosus, often in conjunction with hormonal and other preparations. Gold preparations often evoke side effects (rise in body temperature, irritation of the intestines or kidneys). Contraindications to the use of gold preparations include serious forms of tuberculosis, sugar diabetes, and affections of the cardiovascular system, liver, kidneys, and blood.
Radioactive gold (usually 198Au) is introduced into the tissues as needles or pins in gamma therapy and in the form of colloidal solutions for beta therapy. It is used in the treatment of tumors, usually in conjunction with surgery and drugs, and it is used for diagnostic purposes in the form of colloidal solutions to study the reticuloendothelial system, liver, spleen, and other organs. it is used for diagnostic purposes in the form of colloidal solutions to study the reticuloendothelial system, liver, spleen, and other organs.
REFERENCESPlaksin, I. N. “Zoloto.” In Kratkaia khimicheskaia entsiklopediia, vol. 2. Moscow, 1966.
Remy, G.Kurs neorganicheskoikhimii, vol. 2. Moscow, 1966. Pages 439–51. (Translated from German.)
Ullmanns Enzyklopddie der technischen Chemie, 3rd ed., vol. 8. Munich-Berlin, 1957. Pages 253–307.
Magak’ian, I. G. Rudnye mestorozhdeniia, 2nd ed. Yerevan, 1961.
Russkoe zolotoe i serebrianoe delo 15–20 vekov. Moscow, 1967. (Bibliography, pp. 289–93.)
Rosenberg, M. Geschichte der Goldschmiedekunst auf technischer Grundlage. Frankfurt am Main, 1918.
Economic significance. Under conditions of commercial production, gold has the function of a universal equivalent. “The first function of gold is to give the commercial world a material by which to express value, that is, to express the value of goods as homonymous variables that are qualitatively identical and quantitatively comparable” (K. Marx, in K. Marx and F. Engels, Soch. , 2nd ed., vol. 23, p. 104). Expressing the value of all other goods, gold as a universal equivalent takes on a special use value and becomes money. “Gold and silver are not by nature money, but money is by its nature gold and silver” (K. Marx, in K. Marx and F. Engels, Soch., 2nd ed., vol. 13, p. 137). The commercial world chose gold as money because it has the best physical and chemical properties for a monetary commodity: uniformity, divisibility, preservability, portability (high value for low volume and weight), and ready workability. A considerable amount of gold is used to make coins or is kept in the form of ingots as a gold reserve of central (state) banks. Gold is used widely for industrial purposes (in radio electronics, instrument-making, and other progressive branches of industry) and in jewelry-making.
Originally gold was used solely in making ornaments; later it began to serve as a means of holding and accumulating wealth and as a means of exchange (initially as ingots). Gold was used as money as early as 1500 B.C. in China, India, Egypt, and the Mesopotamian states, and in the seventh and eighth centuries B.C. in ancient Greece. The first coins in history were minted in Lydia (which was rich in gold deposits) in the seventh century B.C. The name of the Lydian king Croesus (who reigned circa 560–546 B.C.) became synonymous with incalculable wealth. In the territory of the USSR (in Armenia) gold coins were struck in the first century B.C. But in antiquity and the Middle Ages gold was not the chief metal of currency. Copper and silver fulfilled this function along with it.
The quest for gold and the passion for enrichment were causes of numerous colonial and trade wars, and during the period of the great geographical discoveries they stimulated the search for new lands. After the discovery of America the flow of precious metals to Europe was one of the sources of the primary accumulation of capital. Mainly gold (97–100 percent of the importable metal) was imported before the mid-16th century from the New World into Europe, but after the discovery of the richest deposits of silver in Mexico and Peru (after the second third of the 16th century) it was mainly silver (85–99 percent). In Russia at the beginning of the 19th century new gold deposits in the Urals and Siberia started to be worked, and for three decades the country had the highest output in the world. In the middle of the 19th century rich gold deposits were found in the USA (California) and Australia, and in the 1880’s, in the Transvaal (South Africa). The development of capitalism and the expansion of intercontinental trade strengthened the demand for currency metals and, although the gold output rose, in all countries silver continued to be used extensively as money along with gold. At the end of the 19th century there was a sharp drop in the value of silver because of improvements in the methods of extracting it from complex ores. The increase in the world gold output, particularly the flow of gold to Europe and the USA from Australia and Africa, accelerated the displacement of depreciating silver and created conditions for a changeover of most countries to monometallism (gold) in the classic form of the gold monetary standard. Great Britain, at the end of the 18th century, was the first to go over to a gold monometallism. Toward the beginning of the 20th century gold currency was established in most countries of the world.
Reflecting the relations of people under conditions of uncontrolled commercial production, the power of gold appears on the surface as a relation between things; this power seems to be a natural, internal property of gold and gives rise to gold and money fetishism. The passion to accumulate gold wealth grows without limit; it is an incentive to monstrous crimes. The power of gold grows particularly in capitalism, where manpower becomes a commodity. The formation of a world market in capitalism has extended gold’s sphere of circulation and made it a universal money.
The gold standard is undermined during a period of general capitalist crisis. Paper money and bank notes that are not convertible to gold predominate in the internal circulations of capitalist countries. The export and the buying and selling of gold are restricted or prohibited altogether. Because of this, gold ceases to fulfill its function as a medium of currency and payment, however, appearing ideally as a measure of value and retaining its significance of a means of forming treasuries and world monies, it remains the basis of monetary systems and the chief means of definitively regulating the mutual monetary demands and obligations of capitalist countries. The size of gold reserves is an important index of the stability of capitalist currencies and the economic potential of individual countries. The buying and selling of gold for industrial consumption and for private hoarding goes on in special gold markets. The fall of gold out of free interstate market circulation caused the reduction of its share in the currency system of the capitalist world and, above all, in the currency reserves of the capitalist countries (from 89 percent in 1913 to 71 percent in 1928, 69 percent in 1958, and 55 percent in 1969). An increasingly large part of newly mined gold goes for hoarding and industrial use (in the modern chemical industry for rocket construction and space technology). Thus, from 1960 to 1970 private hoarding of gold rose 3.3 times and its use for jewelry and industry rose almost 2.3 times, while the gold stocks of capitalist countries remained at practically the same level ($41 billion).
Under socialist economic conditions, gold is also a universal equivalent, used as a measure of value and a scale of prices. The gold content of the Soviet ruble was established at 0.987412 g pure gold on Jan. 1, 1961. The same amount of gold was made the basis of the exchange ruble, the international socialist currency of countries belonging to the Council for Mutual Economic Assistance (Comecon). In the world socialist market gold is used as the universal money.
REFERENCESMikhalevskii, F. I. Zoloto v period mirovykh voin. [Moscow] 1945.
Mikhalevskii, F. I. Zoloto v sisteme kapitalizma posle vtoroi mirovoi voiny. Moscow, 1952.
Borisov, S. M. Zoloto v ekonomike sovremennogo kapitalizma. Moscow, 1968.
A. I. STADNICHENKO
What does it mean when you dream about gold?
This metal suggests that a bright event in the future may hold one of life’s finest rewards. The color gold also represents a high state of illumination.