apothecaries' scale

mass The traditional, and in the USA contemporary, scheme used by apothecaries, with units distinguished, where necessary, by the trailing qualifier ap. in the USA, apoth. in the UK, e.g. oz ap.

Unlike the more usual avoirdupois scale with its pound of 16 ounces and 7 000 grains (making its ounce 437.5 gr), the apothecaries' scale, like the troy scale, has a pound of only 12 ounces each of 480 grains, giving a total of 5 760 grains, the grain being the one unit common to all three scales. The distinctive scale for apothecaries' units is shown in Table 2.

BI-apoth, US-C-ap	Internat values:	SI	US-C-av
grain	…	…	…	64.8~ μg	1 gr
20	scruple	…	…	1.30~ g	20 gr
60	3	drachm, dram	…	3.89~ g	60 gr
480	24	8	ounce	31.1~ g	1.10~ oz
5 760	288	96	12  pound	373.~ g	13.2~ oz

As with the avoirdupois units, the apothecaries' units have for centuries been very close to their current international value, probably the same to at least six significant figures. Current values are based on the international grain, adopted in 1959, of 64.798 91 mg.

This scale was removed entirely from UK measures in 1970.The UK Weights and Measures Act 1985 explicitly excluded from use for trade the bushell, cental, chain, drachm, dram, fluid drachm, furlong, grain, hundredweight, ounce apoth., peck, pennyweight, quarter, quintal, rood, scruple, stone, ton, the square mile, cubic inch, cubic foot, cubic yard, and the term ‘metric ton’. However, the legal status of the bushell, fluid drachm, and peck had been repealed, along with all apothecaries' units and troy units other than ounce, by Order in 1970. Besides the remaining BI units and the simple SI units, the Act included the kilometre, decimetre, centimetre and millimetre, the square metre, square decimetre, square centimetre and square millimetre, the hectare and decare along with the are, the cubic metre, cubic decimetre and cubic centimetre, the hectolitre decilitre, centilitre and millilitre, the tonne (or ‘metric tonne’), kilogram, hectogram, milligram and carat (metric). All had been included in the similar Act of 1963, but with some variation of name: -gram was -gramme, decare was dekare, the tonne appeared only as metric ton.