1911 Encyclopædia Britannica/Carat
CARAT (Arab. Qīrāt, weight of four grains; Gr. κεράτιον, little horn, the fruit of the carob or locust tree), a small weight (originally in the form of a seed) used for diamonds and precious stones, and a measure for determining the fineness of gold. The exact weight of the carat, in practice, now varies slightly in different places. In 1877 a syndicate of London, Paris and Amsterdam jewellers fixed the weight at 205 milligrammes (3.163 troy grains). The South African carat, according to Gardner Williams (general manager of the De Beers mines), is equal to 3.174 grains (The Diamond Mines of South Africa, 1902). The fineness of gold is measured by a ratio with 24 carats as a standard; thus 2 parts of alloy make it 22-carat gold, and so on.