gold (Au) [AS, geolu, yellow] , a yellowish soft metallic element that occurs naturally as a free metal and as the telluride AuAgTe4. Its atomic number is 79; its atomic mass is 196.97. Gold has been highly valued since antiquity and has been and is used for currency, for ornamentation, and as a dental restorative material. It is usually hardened by alloying it with small amounts of nickel or copper. It is highly resistive to oxidation but can be dissolved in aqua regia and aqueous potassium cyanide. Gold salts, in which gold is attached to sulfur, are often used in the treatment, or chrysotherapy, of patients with rheumatoid arthritis but cause serious toxicity in about 10% of patients and some toxicity in 25% to 50%. See also chrysotherapy.
