karat
[Etymology: Arabic: ‘carob’, the plant Ceratonia siliqua] mass
Internat 1907, UK 1913 As agreed by the 4th CGPM and as metric carat (CM), = 200 mg (3.086 5~ gr) - a deprecated unit under the SI.
Internat 1877, UK 1877 = 205.3 mg (3.168 3~ gr).
goldsmiths' (USA usually karat) Measure of proportion, against a maximum of 24, notably to express purity of gold. Within practical tolerances, 24-karat gold is absolutely pure while 14-karat gold has 14 parts gold to 10 parts other metal(s). Terminology appears to relate to a gold/copper coin (the mark) that weighed 24 goldsmiths' carats of 12 gr = 288 gr (18.662~ mg).
