In Latin the analogous general sense of twelfth belonged to uncia, whether of the foot, of the land-unit, of the pound. The general sense of twenty-fourth attached to the scruple as 1/24 ounce, passed to the qirát, or carat, in the countries influenced by Arab customs, as being 1/24 of the mithkal, the Arab successor of the Roman solidus.
In modern Italy the palmo or span, and the libbra or pound, were both divided into 12 oncie, meaning inches or ounces.
With the general substitution of the 16-ounce pound for that of 12 ounces, the word ‘ounce’ lost its meaning of twelfth. In some of the Romance languages its sense of length extended to the length of any finger-joint, especially to the length of the proximal joint of the thumb. Thus in Southern France the ounço dóu pouce (Fr. once de poulce) was taken as 1/5 of the span or nearly 2 inches.
When our Cwt. was raised to 112 lb. and the 16-lb. stone replaced by that of 14 lb. the term Nail was applied to the half of the new stone, and it was perhaps the divisibility of the new Cwt. into 16 parts of 7 lb. that reconciled people to the unpopular new weight. But for all that, the people held on for centuries to the 16-lb. stone, and call its half, 8 lb., a nail, though it is no longer the sixteenth of a larger unit.
When the half of the 14-lb. stone was legally called a nail, how was this term to be rendered into law-Latin or statute French by the scribes of Plantagenet times ignorant of the origin of the term? Naturally they blundered; they got hold of the wrong nail, rendering it by L. clavus instead of by unguis, and by Fr. clou, cloue, or in the script of the time clove instead of by ongle. This misnomer took; and a statute of 1430 states that a Wey of cheese may contain 32 cloves, every clove 7 lb., making the wey = 224 lb., 2 Cwt. But despite statutes the cheese-trade went on with its 8-lb. clove, of which 32 make 256 lb., the true wey.
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.
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.