Systems of measurement are essential. Day-to-day commerce and advancement in areas like science would not exist if not regulated and defined by standards of weights and measures. Systems of measurement presently in use include: the International System of Units (SI), the modern form of the metric system, the imperial system, the apothecaries system and United States customary units.
Apothecaries' Unit
The apothecaries' system or apothecaries' weights and measures is a historical system of mass and volume units used by veterinarians, physicians and apothecaries for medical recipes, and sometimes during scientific investigation. The apothecary system, originated as the system of weights and measures for dispensing and prescribing medications. The English version divided a pound into 12 ounces, an ounce into eight drams/drachms, and a dram into three scruples or 60 grains. This exact form of the system originated in the United Kingdom and continued in some British colonies into the 20th century.
Wholesale druggists and those involved in retail sales involving larger amounts of product (more than an ounce) used the time-honoured imperial weight system and its standard, the 16-ounce pound. Many countries adopted the imperial system, as defined in the British Weights and Measures Act of 1824. The US did so with some modification, primarily to volume units where a US gallon equalled 128 ounces (168 ounce cups) versus 160 ounces imperial (20-8 ounce cups).
The metric system (milligrams, grams, kilograms, liters) now exists in most countries. The US customary system (USCS or USC) emerged from English imperial units, used in the British Empire before the US gained independence. The US overhauled its system, modelling it after the imperial system, yet changing the definitions of some units like volume. France introduced the metric system in 1799. The metric system is a decimal system, making it easier to learn than the non-decimal US system.
The differences caused confusion. Conflicts were not uncommon in business between merchants and apothecaries. If the system used to weigh drugs as the apothecary prepared prescriptions differed from weights used when prescriptions were dispensed, confusion arose as did doubt about practices of unscrupulous apothecary owners. Fortunately, the trust communities developed with doctors, veterinarians and their druggists became golden and constituted a priceless quality that persisted in frontier society.
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.[1][2][3] 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.[4] 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.[5][6] 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.[7] 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.[8][9] In the 19th century, most European countries or cities still had at least a "commercial" or "civil" system (such as the English avoirdupois system) for general trading, and a second system (such as the troy system) for precious metals such as gold and silver.[10] 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 (via influential treatises of Greek physicians such as Dioscorides and Galen, 1st and 2nd century) 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.[11][12] In old merchants' handbooks, the former system is sometimes referred to as the pharmaceutical system and distinguished from the apothecaries' system.[1][13][14]
The traditional English apothecaries' system of weights is as shown in the table, the pound, ounce and grain being identical to the troy pound, ounce and grain.In the United Kingdom, a reform in 1826 made the troy pound the primary weight unit (a role in which it was superseded half a century later by the Avoirdupois pound), but this had no effect on apothecaries' weights. However, the Medicinals Act of 1858 completely abolished the apothecaries' system in favour of the standard Avoirdupois system. The confusing variety of definitions and conversions for pounds and ounces is covered elsewhere in a table of pound definitions. In the United States, the apothecaries' system remained official until it was abolished in 1971 in favour of the metric system.
From the pound down to the scruple, the English apothecaries' system was a subset of the Roman weight system except that 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.[15]
The English-speaking countries also used a system of units of fluid measure, or in modern terminology volume units, based on the apothecaries' system. 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 analogue of the grain was called a minim.
The Imperial and U.S. systems differ in the size of the basic unit (the gallon or the pint, one gallon being equal to eight pints), and in the number of fluid ounces per pint. Apothecaries' systems for volumes were internationally much less common than those for weights.[18] Before introduction of the imperial units in the U.K., all apothecaries' measures were based on the wine gallon, which survived in the US under the name liquid gallon or wet gallon.[19]
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.[20] 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. This explains why the number of fluid ounces per gallon had to be adjusted in the new system 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.[21]
Even in Turkey a system of weights similar to the European apothecaries' system was used for the same purpose. For medical purposes the tcheky (approx. 320 g) was divided in 100 drachms, and the drachm in (16 kilos or) 64 grains.[36][37] This is close to the classical Greek weight system, where a mina (corresponding roughly to a Roman libra) was also divided into 100 drachms.[38]
With the beginning of metrication, some countries standardized their apothecaries' pound to an easily remembered multiple of the French gramme.[39] 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.[40] (At this time its use was mainly confined to trading precious metals.)
In France, at some stage the apothecaries' pound of 12 ounces was replaced by the larger civil pound of 16 ounces. The subdivisions of the apothecaries ounce were the same as in the other Romance countries, however, and were different from the subdivisions of the otherwise identical civil ounce.
The basic apothecaries' system consists of the units pound, ounce, and scruple from the classical Roman weight system, together with the originally Greek drachm and a new subdivision of the scruple into either 20 ("barley") or 24 ("wheat") grains (Latin: grana). In some countries other units of the original system remained in use, for example in Spain the obolo and siliqua. In some cases the apothecaries' and civil weight systems had the same ounces ("an ounce is an ounce"), but the civil pound consisted of 16 ounces. Siliqua is Latin for the seed of the carob tree.
Many attempts were made to reconstruct the exact mass of the Roman pound. One method for doing this consists in weighing old coins; another uses the fact that Roman weight units were derived from Roman units of length similar to the way the kilogramme was originally derived from the metre, i.e. by weighing a known volume of water. Nowadays the Roman pound is often given as 327.45 g, but one should keep in mind that (apart from the other uncertainties that come with such a reconstruction) the Roman weight standard is unlikely to have remained constant to such a precision over the centuries, and that the provinces often had somewhat inexact copies of the standard. The weight and subdivision of the pound in the Holy Roman Empire were reformed by Charlemagne, but in the Byzantine Empire it remained essentially the same. Since Byzantine coins circulated up to Scandinavia, the old Roman standard continued to be influential through the Middle Ages.
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