3. The Carat and the Grain
(A) The Carat
One would hardly recognise the golden Solidus of Rome in the French Sol, the brass halfpenny with the effigy of Louis XVI, current within my memory, or in the bronze Sou by which sums under three francs are still reckoned in France.
The Solidus, Aureus, or Exagium solidi, was so called because, representing the As, or unit of money, it was the gold-unit of which the semissis was the half and the tremissis the third.
Weighing 70·1 grains (under Constantine) it was 1/6 of the Roman mint-ounce = 420-2/3 grains, or 1/72 of the As libralis. Its weight was equal to 24 siliquæ, afterwards called Carats = 2·921 grains, and its third, the tremissis, weighed nearly 24 grains, the troy pennyweight. Hence pure gold was considered as solidus or ‘entire’ of 24 carats, and the quality or ‘touch’ of gold would be denoted by the number of carats of pure gold it contained out of 24. The carat of fineness was divided into 4 assay-grains, and these again into fourths. English gold coins are 22 carats fine since the time of Henry VIII, but the Plantagenet gold coins were usually 23 carats 3-1/2 grains fine, that is 191/192 = nearly 995 in 1000.
Thus the carat was 1/24 Solidus or 1/144 ounce.
When the Arab caliphs had conquered Egypt and the greater part of the Mediterranean countries, they followed Roman imperial customs and replaced the gold Exagium solidi, 1/72 of the As, by the gold mithkal, 1/72 of the Libra or Egypto-Roman pound. The Mithkal was then 1/6 of the Egypto-Roman ounce = 437 grains, so that it weighed 72·7 grains. It was divided like the Roman coin into 24 qirát, each = 3·035 grains and divided into 4 hubba or light grains, meaning corn-grains.
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
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.
This is medieval rubbish. As John Greaves, Professor of Astronomy at Oxford, in his ‘Discourse of the Roman foot’ (1647) wisely said:
I cannot but approve the counsel of Villapandus who adviseth such as will examine measures and weights to begin with the greater and not the lesser.... The most curious man alive with the exactest scale that the most skilful artisan can invent, shall never be able, out of the standard of one grain, to produce a weight equal to the weight of ten thousand grains.
While the subdivision of linear measures and of weights usually stopped at some familiar quantity named after a seed, yet efforts were sometimes made to get at an ultimate atom as the term of the series. The Hindus who began, or ended, a series of weights with one of the motes or fine particles of dust visible in a sunbeam, were imitated by the English moneyers who continued the 20-dwt. and 24-grain series by dividing the grains into 20 Mites, each of 24 Droits, each of 20 Periots, each of 24 Blanks, the blank being 1/230400 of a grain.
So our mint expressed the weight of a Stuart silver penny, not as 7-23/31 grains (all the silver coins having then a fraction of 31sts); that would have been too simple—but as 7 grains, 14 mites, 20 droits, 2 periots, 12 blanks. Even then the statement was not exact; one or two more infinitesimal units would have had to be added to the series.
It may be noted that 7-23/31 grains is simpler than the modern decimal equivalent 7·74193548, &c.
The origin of these mint-terms is obscure; the ‘N.E.D.’ casts no light on it. I consider their source to be—
Mite—mijt, a small Dutch coin.
Droit—a corruption of the Dutch duit, Sc. ‘doit,’ a fraction of a farthing. It was more properly written ‘dwit’; perhaps the r was inserted to avoid confusion with ‘dwt.’
Periot—a period or full stop; perhaps influenced by ‘iota’ and ‘jot.’
Blank—as the blank in dominoes, still lower than the ace, point, or full stop, the Dutch As; perhaps influenced by ‘point-blank,’ in which the bull’s eye, at first the ‘point,’ became the blank or white.
It has been seen, under Troy weight, that there are two classes of grains:
The heavy grain 1/(20 × 24) = 1/480 ounce as in English Troy.
The light grain 1/(24 × 24) = 1/576 ounce as in French Troy.
The ounce of 576 light grains was used in France, some Italian states, Spain and Portugal. Elsewhere, throughout Europe, the mint and medicinal ounce was 480 heavy grains, the scruple being 20 grains.
The heavy and light grains have been connected respectively with the barley-corn and the wheat-corn. They may have been so originally, but it is more probable that the grain, at first a seed-weight, came to mean a division of the scruple into either 20 or 24 parts.
In Dutch mint-weight the Troy ounce was of 20 dwt. or Engels, each of 2 mail, 4 vierling, 8 troisken, 16 deusken, 32 azen or aces. The Aas was the wheat-corn of our mint-legend. In the Spanish Netherlands the Engel was increased to make the ounce 24 × 24 grains. The Engel thus became (Antwerp 1580) = 28·8 grains = 1-1/5 English dwt. The word Engel means ‘angel,’ not the angel coin weighing 3 engel 10 azen, but Angle—‘Angli, non Angeli.’