THE NATURE OF GOLD
The chemical element gold is a heavy, soft metal. Volume for volume, it weighs nearly twice as much as lead. Its hardness varies between 21/2 and 3 on the Mohs' scale . Shiny and deep yellow in color, gold is one of two metals which are not gray or white when pure. (The other is copper.)

Physical Characteristics
Gold is the most malleable and ductile of metals. It may be beaten into gold leaf as thin as 4 millionths of an inch. An ounce of gold may be drawn into a wire more than 40 miles long. Gold is a good conductor of electricity, though it is inferior to silver and Gold mixes, or alloys, readily with other metals. Alloys of gold and silver are soft, malleable, and ductile. Copper is commonly added to harden gold
Atomic and Chemical Properties
In its usual state—atomic mass number 197—gold is stable. However, there are radioactive (unstable) isotopes of mass numbers 186 to 196 and 198 to 203 . Gold normally exhibits a chemical valence of one or three.
Gold is the “noblest” of the noble metals (gold, platinum, palladium, and rhodium), so termed because of their inertness, or reluctance to enter into chemical reactions. Gold will not react with common acids but is attacked by a three-to-one mixture of hydrochloric and nitric acids. This combination is called aqua regia (from the Latin for royal water) because it reacts with the so-called royal metal.
Gold will not combine directly with oxygen, but oxides may be formed indirectly. Gold will also combine with the halogens (fluorine, chlorine, bromine, and iodine) and with the cyanides .The purity of gold is expressed in karats (abbreviated “kt”), on a scale of 24, or in fineness, on a scale of 1,000. Pure gold is 24 karat, or 1,000 fine. An alloy containing 75 percent gold would be described as 18-karat gold, or 750 fine.
The weight of gold is ordinarily expressed in troy ounces of 480 grains. In this article the word ounce means troy ounce. Avoirdupois weight is meant where pounds and tons are mentioned unless other units are specified

THE USES OF GOLD
Eternally attractive to mankind, gold has found its principal use as a store of value. Its beauty has made it popular in decoration. Gold has also become an increasingly important industrial metal.
Because of its rarity and its durability, gold tended to remain relatively stable in value and thus almost universally acceptable as money. In the past the metal was widely used in coins. Until 1934 gold coins could circulate in the United States. They were withdrawn from circulation when a worldwide economic depression forced devaluation of the dollar . For 100 years before 1934, the United States had valued gold at $20.67 per fine troy ounce. In 1934 the price was increased to $35, in 1972 to $38, and in 1973 to $42.22.
With the last devaluation of the dollar, the International Monetary Fund (IMF) reset the exchange rate for gold at $42.22 per ounce. It was then selling for about $65 on the free market. The IMF abolished the “official” price of gold effective April 1978, and by year-end its value rose to $226.37. The market price more than doubled in one year. By mid-January 1980 gold was sold at a record high of $880. Since then the price of gold has slowly declined.