It was the same with the wool-trade, controlled by the State for revenue purposes. The half-stone of wool became a nail. In 1342 we find _quatuor clavos lanæ_, 4 nails of wool.
But _clavus_, a nail, became confounded with _clavis_, a key, and so in Southern France the nail-weight, introduced from England, became _clau_, a key, instead of _clavèu_, a nail. Thus the nail, Fr. _once_, _ongle_, became clove, Fr. _clou_, L. _clavis_, an iron nail; then in Prov. and Fr. _clau_, L. _clavus_, a key.
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:
