The Mithkal = 72·7 grs. of 24 Kharūb or qirát The Dirhem = 48-1/2 „ „ 16 „ „ „
The carat, from a goldsmith’s assay-weight, became the unit for the weight of precious stones, varying slightly in different countries and usually divided into 4 diamond-carats.
Roman siliqua 2·916 grs. 1/4 = ·729 gr. Roman-Egyptian carat 3·035 „ „ = ·758 „ Ptolemaïc „ 3·1616 „ „ = ·790 „ Venetian „ 3·196 „ „ = ·799 „ Egyptian (modern) „ 3·088 „ „ = ·772 „ Spanish (Moorish) „ 3·082 „ „ = ·770 „ Amsterdam (diamond) carat 3·165 „ Hamburg „ „ 3·176 „ = 1/142 Cologne oz. English „ „ 3·177 „ French metric „ 3·086 „ = ·2 gramme
The Eastern qirát has retained all the derived senses seen in the Western carat, 1/24 of a pure gold-unit. A cubit of 28 digits has an alternative division into 24 qirát. The kharūb of Egypt, 16 to a dirhem and 24 to a mithkal, is the weight-counterpart of the digit, 16 to the foot and 24 to the cubit. The density of brine is on a scale of 24 qirát. Points in a competition, shares in a business or ship are reckoned similarly. At Marseilles the ownership of a vessel is divided into 24 qirát as it is in England into sixty-fourths.
‘Ai un queirat sus un navire’: _Calendau_ v. (by Mistral).
Sometimes the 24 qirát are grouped into 4 _rob_ of 6 qirát. _Rob_ is from Ar. _al rabaa_, fourth; cf. _rubaiyat_ = quatrain. In Spain and Portugal the arroba, in Provence the _rub_ (It. _rubbio_) is the quarter-hundredweight.
There is another use of the term Carat, confined to goldsmiths and refiners of the precious metals. The old troy pound was regarded as 24 carats; the carat was 4 grains, each of 4 quarters or of 60 grains. This system was used in the refinery of the Royal Mint up to 1882.
In Germany the Cologne marc (8 ounces) was divided by refiners (1) for gold into 24 carats of 12 grains; (2) for silver into 16 loth (half-ounces) of 18 grains.
It is probable that this system came to England with the Tower pound (12 ounces of the Cologne marc) and was continued with the Troy pound.
The names given to the smaller weights were taken from seeds just as measures of length were named after limb-lengths corresponding roughly to them. The kharoub may be used for a carat-weight. The ruttee or ráti, a scarlet pea with a black spot, is used in India as a goldsmith’s weight = 1·75 grain. Poppy-seeds, mustard-seeds, barley-corns, wheat-corns, have been used for minute weights. The Grain was the Greek _sitatrion_, a wheat-corn. It was perhaps from the custom of saying that 3 poppy-seeds = one mustard-seed, and that 6 of these = one barley-corn, &c., that an idea arose of these seeds being the basis of systems of weight. It has been seen that the definition of the Plantagenet mint-weight was that 32 wheat-corns were the pennyweight. This idea, hallowed in our statutes, is not yet extinct.