The 12 lb. stone is ordered apparently either as a double of a customary ‘lead-pound’ of 6 lb. or to make the customary fotmal or ‘pig’ of lead, 70 lb. weight, ‘contain 6 stones (of 12 lb.) less 2 lb.’ It also says that the deduction of 2 lb. leaves ‘70 lb. making 5 stones.’ This passage appears to be a subsequent interpolation after the institution of Edward III’s 14 lb. stone.
The fother of lead, of 30 fotmals, would thus be = 2100 lb. But the stone of 12-1/2 lb., evidently intended to be 1/8 of the true hundredweight, and to pave the way for the coming 14 lb. stone, is also applied to lead. How it is not said; but the present fother, = 2184 lb., is almost exactly equal to 30 fotmal, each of 73 lb. = 2190 lb.; and 73 lb. is just 6 stone of 12-1/2 lb. less 2 lb.
The 70 lb. fotmal seems to have disappeared by the seventeenth century, but in the meantime the uncertainty of the fother led to the use of Boole-weight, meaning the weight used at the lead-boles or natural bowls in which lead ore was smelted. The fother, boole-weight, was 30 fotmals of 6 stone of 14 lb. Sometimes it was of 24 fotmals = 2016 lb., that is 18 cwt.
The meaning of Fother is given in Chapter XX.
It is unnecessary to describe or even name the various weights peculiar to trade or local custom. Everyone in the trade knows them; out of it no one need know them. If a person not in the trade buys a cask of wine, a barrel of beer, a sack of flour or a load of potatoes, commonsense prompts him to ask how many gallons or pounds are contained in these units. It is the same in France and other countries of the metric system, where the cask, the sack, the churnful, &c., are trade-units with their peculiar equivalents of litres or kilogrammes. It is indeed by the use of trade-units that manufacturers evade the rigour of the metric system.
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It has been seen that a cubic foot of water is very approximately = 1000 Roman ounces = 62-1/2 lb. of water at the early averdepois standard. There is reason to believe that this cubic foot was our original wine-unit, the wine-bushel, 1/8 of it = 216 cubic inches, being the wine-gallon; and that the cubic foot, increased in water-wheat ratio 1728 × 1·25 = 2160 c.i., was the corn-bushel. The corn-gallon, 2160/8 = 270 c.i., remained at this standard for centuries, 268·8 c.i. being the London measure, and 272-1/4 c.i. the Winchester measure, the slight differences being due to difficulties in casting and gauging shallow metal pans.