Okay, here's the skinny on the history of the grain as measure of weight - don't blame me for posting it. It IS, however, at least the SECOND time I've posted it this year, so perhaps it ought to be made into a sticky.
Quote -
At least since
antiquity, grains of
wheat or
barley were used by
Mediterranean traders to define units of mass; along with other seeds, especially those of the
carob tree. According to a longstanding tradition, 1
carat (the mass of a carob seed) was equivalent to the weight of 4 wheat grains or 3
barleycorns. Since the weights of these seeds are highly variable, especially that of the cereals as a function of moisture, this is a convention more than an absolute law.
The history of the modern British grain can be traced back to a royal decree in thirteenth century England, re-iterating decrees that go back as far as
King Offa (eighth century).The
tower pound was one of many monetary pounds of 240
silver pennies.
By consent of the whole Realm the King's Measure was made, so that an
English Penny, which is called the Sterling, round without clipping, shall weigh Thirty-two Grains of Wheat dry in the midst of the Ear; Twenty pennies make an Ounce; and Twelve Ounces make a Pound.
—
Tractatus de Ponderibus et Mensuris.
The pound in question is the
Tower pound. The Tower pound, abolished in 1527, consisted of 12
ounces like the troy pound, but was 1⁄16 (≈6%) lighter. The weight of the original sterling pennies was 22½ troy grains, or 32 "Tower grains".
Physical grain weights were made and sold commercially at least as late as the early 1900s, and took various forms, from squares of sheet metal to manufactured wire shapes and coin-like weights.
The troy pound was only "the pound of Pence, Spices, Confections, as of Electuaries", as such goods might be measured by a
troi or small balance. The old troy standard was set by King Offa's
currency reform, was in full use in 1284 (Assize of Weights and Measures, *King Edward I), but was restricted to currency (the pound of pennies) until it was abolished in 1527. This pound was progressively replaced by a new pound, based on the weight of 120 silver
dirhems of 48 grains. The new pound used a barley-corn grain, rather than the wheat grain.
Avoirdupois (goods of weight) refers to those things measured by the lesser but quicker balances: the bismar or auncel, the Roman balance, and the
steelyard. The original mercantile pound of 25 shillings or 15 (tower) ounces was displaced by variously the pound of the Hanseatic League (16 tower ounces) and by the pound of the then-important wool trade (16 ounces of 437 grains). A new pound of 7680 grains was inadvertently created as 16 troy ounces, referring to the new troy rather than the old troy. Eventually, the wool pound won out.
The
avoirdupois pound was defined in prototype, rated as 6992 to 7004 grains. In the Imperial Weights and Measures Act of 1824,
the avoirdupois pound was defined as 7000 grains exactly. The act of 1855 authorised Miller's new standards to replace those lost in the fire that destroyed the
Houses of Parliament. The standard was an avoirdupois pound, the grain being defined as 1/7000 of it.
The division of the carat into four grains survives in both senses well into the early twentieth century. For pearls and diamonds, weight is quoted in carats, divided into four grains. The carat was eventually set to 205 milligrams (1877), and later 200 milligrams. For touch or fineness of gold, the fraction of gold was given as a weight, the total being a solidus of 24 carats or 96 grains.
*King Edward I [AKA 'Longshanks because of his prodigious height of around 6ft 5", when most adult males were almost a foot shorter], was NOT a 'British king'. He was an English king. The term 'British' had yet to be taken into common usage - both Scotland and Wales were in the throes of becoming an unwilling 'partnership of nations' that eventually morphed into the United Kingdom and Ireland was a 'place over there, as yet not understood yet suffered'. With the
Acts of Union 1707 it became the official name of the new state created by the union of the
Kingdom of England (which then included Wales) with the
Kingdom of Scotland, forming the
Kingdom of Great Britain.
