Apothecaries' system
Historical medical weight and volume system used by apothecaries.
The apothecaries' system, a historical framework for measuring mass and volume, was employed by physicians, apothecaries for prescriptions, and occasionally by scientists. Its English variant shares the pound and grain with the troy system used for precious metals, but divides a pound into twelve ounces, an ounce into eight drachms, and a drachm into three scruples of twenty grains each. This specific structure was standard in the United Kingdom and persisted in some former colonies well into the twentieth century. Medical recipes were long written in Latin, often employing unique symbols for these weights and measures. Across Europe, from the decline of the Roman Empire until metrication, it was common to have separate weight systems for different purposes, such as a commercial system for general trade and another for precious metals. The apothecaries' system frequently used the same ounce as the precious metals system, though the pound might contain a different number of ounces. Its specialized units derived from Roman general-purpose weights, transmitted through influential Greek medical texts. In the nineteenth century, most European countries or cities maintained at least two distinct systems. The Irish pharmacopoeia of 1850 attempted to replace the troy pound with the avoirdupois pound, dividing it into sixteen ounces, each subdivided into eight drachms of three scruples, to unify purchase and sale units. This innovation was not widely adopted. British legislation in 1858 prescribed the avoirdupois system for the United Kingdom, and the 1864 pharmacopoeia recommended the imperial avoirdupois pound of 7000 grains and ounce of 437.5 grains, discontinuing the drachm and scruple. However, the old apothecaries' system based on the troy pound remained common until the Weights and Measures Act 1976 abolished it for most uses, allowing it only for precious metals and stones. Apothecaries' units became obsolete in the UK with mandatory metric drug measurements from January 1, 1971. In the United States, the system was official until abolished in 1971 in favor of the metric system. English-speaking countries also employed a corresponding system of fluid volume units, originally using terms and symbols similar to those for solid weights.
- field
- Historical weights and measures
- known_for
- System of mass and volume units for medical prescriptions
- related_system
- English troy system
- key_units
- Pound (12 ounces), ounce (8 drachms), drachm (3 scruples), scruple (20 grains)
Lore & Background
The apothecaries' system, a historical system of mass and volume units, derived its specialized divisions from the Roman general-purpose weight system, transmitted through the influential medical writings of the Greek physicians Dioscorides and Galen. In its English form, the system was closely tied to the troy system: the pound and grain were identical in both. However, the apothecaries' pound was uniquely divided into 12 ounces, each ounce into 8 drachms, each drachm into 3 scruples, and each scruple into 20 grains. This specific arrangement was used in the United Kingdom and persisted in some former colonies into the 20th century. A parallel system of volume units, based on the fluid ounce, also existed. For centuries, medical prescriptions were written in Latin, often employing special symbols for these weights and measures. The use of multiple, purpose-specific weight systems was common across Europe from the decline of the Roman Empire until metrication, driven by international trade and the need to match target market standards. In many regions, a commercial system (like avoirdupois) existed alongside a system for precious metals (like troy), and the apothecaries' system often shared the same ounce as the precious metals system, though the pound division differed. This overlap created ambiguity in trade, as it was not always clear which system governed transactions between merchants and apothecaries. In the 19th century, the Irish pharmacopœia attempted to unify units by adopting the avoirdupois pound, divided into 16 ounces, for apothecary use, but this was not widely accepted. British legislation later mandated the avoirdupois system for pharmacy, though the traditional apothecaries' divisions remained in common practice until the Weights and Measures Act 1976 restricted their use. The system became obsolete in the UK with mandatory metric drug measurements in 1971, and the United States abolished its official use the same year.
Reader's Guide
The apothecaries' system represents a key example of the historical fragmentation of measurement systems in Europe, where different systems coexisted for commerce, precious metals, and medicine. Its significance lies in its long use for medical prescriptions, influencing pharmacopœias and medical practice for centuries. The system's gradual replacement by the avoirdupois and later metric systems reflects broader trends toward standardization in the 19th and 20th centuries. The Irish and British attempts to reform the system highlight the practical challenges of unifying weights used by apothecaries for purchase and sale. The system's legacy persists in the continued use of troy weights for precious metals and in the distinct US and UK fluid ounce systems derived from apothecaries' volume measures.
Did You Know?
- The apothecaries' pound and grain were identical to the troy pound and grain.
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