Note 5 — Chapter IV · COLLECTING THE GEMS

According to Gardner Williams the South African carat is equivalent to 3·174 grains. In Latimer Clark’s Dictionary of Metric and other Useful Measures the diamond carat is given as equal to 3·1683 grains = 0·2053 gramme = 4 diamond grains; 1 diamond grain = 0·792 troy grain; 151·5 diamond carats = 1 ounce troy.

Webster’s International Dictionary gives the diamond carat as equal to 3⅕ troy grains.

The Oxford English Dictionary says the carat was originally ¹/₁₄₄ of an ounce, or 3⅓ grains, but now equal to about 3⅕ grains, though varying slightly with time and place.

The Century Dictionary says the diamond carat is equal to about 3⅙ troy grains, and adds that in 1877 the weight of the carat was fixed by a syndicate of London, Paris, and Amsterdam jewellers at 205 milligrammes. This would make the carat equal to 3·163 troy grains. A law has been passed in France ordaining that in the purchase or sale of diamonds and other precious stones the term “metric carat” shall be employed to designate a weight of 200 milligrammes (3·086 grains troy), and prohibiting the use of the word carat to designate any other weight.