The Ptolemaïc or lesser Alexandrian talent had been divided into 60
minás of 12 ounces; these either 100 drachmæ or 12 × 12 carats of 3·1616
grains. The carat was an ancient Eastern weight, originally the flat
seed of the caroub or locust-tree, _Ceratonia siliqua_, and in Greek
_keration_. Throughout North Africa and in other Moslem countries there
are two usual lesser units of weight:
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.
THE 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.
_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_
Public-domain text, read in full here on John Shaqi.
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