IV.

Uses

The metal has been known and highly valued from earliest times, not only because of its beauty and resistance to corrosion, but also because gold is easier to work than all other metals. In addition, gold was easier to obtain in pure form than the other metals. Because of its relative rarity, gold became used as currency and as a basis for international monetary transactions (see Dollar; Gold Standard). The unit used in weighing gold is the troy ounce; 1 troy ounce is equivalent to 31.1 grams.

The major portion of the gold produced is used in coinage and jewelry (see Metalwork). For these purposes it is alloyed with other metals to give it the necessary hardness. The gold content in alloys is expressed in carats (see Carat). Coinage gold is alloyed with copper or silver. Green gold used in jewelry contains copper and silver; white gold contains zinc and nickel, or platinum metals.

Gold is also used in the form of gold leaf in the arts of gilding and lettering. Purple of Cassius, a precipitate of finely divided gold and stannic hydroxide formed by the interaction of auric chloride and stannous chloride, is used in coloring ruby glass. Chlorauric acid is used in photography for toning silver images. Potassium gold cyanide is used in electrogilding. Gold is also used in dentistry. Radioisotopes of gold are used in biological research and in the treatment of cancer (see Isotopic Tracer).