‘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.
The Refiner’s Carat
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.
(B) The Grain
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.
Ambroise Paré, in treating of medicinal weights (1582) said:
Every weight arises from some beginning and element. For as our bodies arise from the four first simple or elementary bodies, so all weights arise from the grain, which is tanquam the beginning and the end of the remainder. We understand a grain of barley, neither dried nor mouldy, but well made and of medium fatness. From 10 grains of this sort comes the obolus, from 2 oboli or 20 grains the scruple ... &c.