Apothecaries' system

The apothecaries' system, or apothecaries' weights and measures, is a historical system of mass and volume units that were used by physicians and apothecaries for medical prescriptions, and also sometimes by scientists. The English version of the system is closely related to the English troy system of weights, the pound and grain being exactly the same in both. It divides a pound into 12 ounces, an ounce into 8 drachms, and a drachm into 3 scruples of 20 grains each. This exact form of the system was used in the United Kingdom; in some of its former colonies, it survived well into the 20th century. The apothecaries' system of measures is a similar system of volume units based on the fluid ounce. For a long time, medical recipes were written in Latin, often using special symbols to denote weights and measures.
The use of different measure and weight systems depending on the purpose was an almost universal phenomenon in Europe between the decline of the Roman Empire and metrication. This was connected with international commerce, especially with the need to use the standards of the target market and to compensate for a common weighing practice that caused a difference between actual and nominal weight. In the 19th century, most European countries or cities still had at least a "commercial" or "civil" system for general trading, and a second system for precious metals such as gold and silver. The system for precious metals was usually divided in a different way from the commercial system, often using special units such as the carat. More significantly, it was often based on different weight standards.
The apothecaries' system often used the same ounces as the precious metals system, although even then the number of ounces in a pound could be different. The apothecaries' pound was divided into its own special units, which were inherited from the general-purpose weight system of the Romans. Where the apothecaries' weights and the normal commercial weights were different, it was not always clear which of the two systems was used in trade between merchants and apothecaries, or by which system apothecaries weighed medicine when they actually sold it. In old merchants' handbooks, the former system is sometimes referred to as the pharmaceutical system and distinguished from the apothecaries' system.

English-speaking countries

Weight

Pound	Drachm	Scruple	Grain
1	16 ℥	128 ʒ	384 ℈	7,000.00 gr.
	1 ℥	8 ʒ	24 ℈	437.50 gr.
		1 ʒ	3 ℈	54.68 gr.
			1 ℈	18.22 gr.
453.6 g	28.3 g	3.5 g	1.2 g	64.8 mg

From pound down to the scruple, the units of the traditional English apothecaries' system were a subset of the units of the [|Roman weight system], although the troy pound and its subdivisions were slightly heavier than the Roman pound and its subdivisions. Similar systems were used all over Europe, but with considerable local variation described below under [|Variants]. The traditional English apothecaries' system of weights is shown in the first table in this section: the pound, ounce and grain were identical to the troy pound, ounce and grain The confusing variety of definitions and conversions for pounds and ounces is covered elsewhere in a table of pound definitions.
The Irish pharmacopœia of 1850 rejected the use of the troy pound and instead adopted the use in its formulae of the avoirdupois pound, divided into 16 avoirdupois ounces, with the avoirdupois ounce subdivided into eight drachms, each of three scruples. This innovation was intended to unify the units used by apothecaries for sale with the avoirdupois units that they used for purchase, and that were used by other professions such as manufacturing chemists. To allow effective use of the new system, new weight pieces were produced. Since an avoirdupois ounce corresponds to 28.35 g, the proposed system was very similar to that in use in Portugal and Spain, and in some locations in Italy. But it would have doubled the value of the avoirdupois drachm. Therefore, it conflicted with other non-standard variations that were based on that nearly obsolete unit.
The Irish proposal was not widely adopted, but British legislation, in the form of the Medical Act 1858, was more radical: it prescribed the use of the avoirdupois system for the United Kingdom, with none of the traditional subdivisions. This innovation was first used in the United British pharmacopœia of 1864, which recommended the adoption in pharmacy of the imperial avoirdupois pound of 7000 grains and ounce of 437.5 grains, and discontinuation of the drachm and scruple. In practice, however, the old apothecaries' system based on divisions of the troy pound, or of the troy ounce of 480 grains, was still widely used until it was abolished by the Weights and Measures Act 1976, since when it may only be used to measure precious metals and stones.
Apothecaries' units of any kind became obsolete in the UK with the mandatory use of metric drug measurements from January 1, 1971.
In the United States, the apothecaries' system remained official until it was abolished in 1971 in favour of the metric system.

Volume

English-speaking countries also used a system of units of fluid measure, or in modern terminology volume units, based on the apothecaries' system. Originally, the terms and symbols used to describe the volume measurements of liquids were the same as or similar to those used to describe weight measurements of solids. A volume of liquid that was approximately that of an apothecaries' ounce of water was called a fluid ounce, and was divided into fluid drachms and sometimes also fluid scruples. The smallest unit of liquid volume was traditionally a drop. Although nominally defined as a sixtieth of the fluid drachm, in practice the drop was a not a standardized unit of volume but was measured by means of releasing literal drops of liquid from the lip of a bottle or vial.
The 1809 London Pharmacopoeia introduced modified terminology for apothecaries' measurements of liquid volume. New terms and symbols introduced by the London College of Physicians were subsequently adopted by the Pharmacopoeias of the United States and Dublin. The pint was given the Latin name octarius and represented by the symbol O, thus distinguishing its Latin name and symbol from that of the pound. The terms for fluid ounce and fluid drachm were distinguished from weight measures by the prefix fluid- or in abbreviations by the prefixed letter f. The smallest unit of volume was standardized as precisely a sixtieth of a fluidrachm and given the name minim. Along with the new name of minim, the London Pharmacopoeia of 1809 prescribed a new method of measuring the smallest unit of volume using a graduated glass tube.
Before introduction of the imperial units in the U.K., all apothecaries' fluid measures were based on the unit of the wine gallon, which survived in the US under the name liquid gallon or wet gallon. The wine gallon was abolished in Britain in 1826, and this system was replaced by a new one based on the newly introduced imperial gallon. Since the imperial gallon is 20% more than the liquid gallon, the same is true for the imperial pint in relation to the liquid pint. Accordingly, in the new imperial system, the number of fluid ounces per pint was adjusted from 16 to 20 so that the fluid ounce was not changed too much by the reform. Even so, the modern U.K. fluid ounce is 4% less than the US fluid ounce, and the same is true for the smaller units. For some years both systems were used concurrently in the U.K.
As a result, the Imperial and U.S. systems differ in the size of the basic unit, and in the number of fluid ounces per pint.
Apothecaries' systems for volumes were internationally much less common than those for weights.
There were also commonly used, but unofficial divisions of the Apothecaries' system, consisting of:

Glass-tumbler 8 fl. oz.
Breakfast-cup about 8 fl. oz.
Tea-cup 5 fl. oz.
Wine-glass 2 fl. oz.
Table-spoon fl. oz.
Dessert-spoon 2 fl. dr.
Tea-spoon 1 fl. dr.

In the United States, similar measures in use were once:

Tumblerful — ƒ℥ viii
Teacupful — ƒ℥ iv
Wineglassful — ƒ℥ ij
Tablespoonful — ƒ℥ ss
Dessertspoonful — ƒʒ ij
Teaspoonful — ƒʒ j

Remington's Pharmaceutical Sciences states: "In almost all cases the modern teacups, tablespoons, dessertspoons, and teaspoons, after careful test by the author, were found to average 25 percent greater capacity than the theoretical quantities given above, and thus the use of accurately graduated medicine glasses, which may be had now at a trifling cost, should be insisted upon."
Apothecaries' measures eventually fell out of use in the U.K. and were officially abolished in 1971. In the U.S., they are still occasionally used, for example with prescribed medicine being sold in four-ounce bottles.

Medical prescriptions

Until around 1900, medical prescriptions and most European pharmacopoeias were written in Latin. Here is a typical example from the middle of the 19th century.
The letters "ss" are an abbreviation for the Latin "semis" meaning "half", which were sometimes written with a ß. In Apothecaries' Latin, numbers were generally written in Roman numerals, immediately following the symbol. Since only the units of the apothecaries' system were used in this way, this made it clear that the civil weight system was not meant.

Variants

Diversity of local standards

The basic form of the apothecaries' system is essentially a subset of the Roman weight system. An apothecaries' pound normally consisted of 12 ounces. In the south of Europe and in France, the scruple was generally divided into 24 grains, so that one ounce consisted of 576 grains. Nevertheless, the subdivision of an ounce was somewhat more uniform than that of a pound, and a common feature of all variants is that 12 ounces are roughly 100 drachms and a grain is roughly the weight of a physical grain.
Image:Apothecaries weights 1800.png|thumb|300px|Map showing examples of the weight of 1 apothecaries' ounce in grammes around 1800, before metrication and the Prussian weight reform. The dashed lines indicate three different ways to subdivide the ounce.
It is most convenient to compare the various local weight standards by the metric weights of their ounces. The actual mass of an ounce varied by ±17% around the typical value of 30 g. The table only shows approximate values for the most important standards; even the same nominal standard could vary slightly between one city and its neighbour. The range from 25 g to 31 g is filled with numerous variants, especially the Italian range up to 28 g. But there is a relatively large gap between the troy ounces of 31 g and the Habsburg ounce of 35 g. The latter is the product of an 18th-century weight reform.
Even in Turkey a system of weights similar to the European apothecaries' system was used for the same purpose. For medical purposes the tcheky was divided in 100 drachms, and the drachm in 64 grains. This is close to the classical Greek weight system, where a mina was also divided into 100 drachms.
With the beginning of metrication, some countries standardized their apothecaries' pound to an easily remembered multiple of the French gramme. E.g. in the Netherlands the Dutch troy pound of 369.1 g was standardized in 1820 to 375.000 g, to match a similar reform in France. The British troy pound retained its value of 373.202 g until in 2000 it was legally defined in metric terms, as 373.2417216 g.