Grain (unit)

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Grain
Gold grain size comparison.jpg
The small golden disc close to the 5 cm marker is a piece of pure gold weighing one grain. Shown for comparison is a tape measure and coins of major world currencies.
General information
Unit system Troy weight, avoirdupois weight, apothecaries' weight
Unit ofMass
Symbolgr
Conversions
1 gr in ...... is equal to ...
   Troy   15760 troy pound
   Avoirdupois   17000 pound
   Apothecaries'   15760 apothecaries' pound
   SI units   64.79891 mg

A grain is a unit of measurement of mass, and in the troy weight, avoirdupois, and apothecaries' systems, equal to exactly 64.79891 milligrams. It is nominally based upon the mass of a single ideal seed of a cereal. From the Bronze Age into the Renaissance, the average masses of wheat and barley grains were part of the legal definitions of units of mass. Expressions such as "thirty-two grains of wheat, taken from the middle of the ear" appear to have been ritualistic formulas. [1] :27 [2] Another source states that it was defined such that 252.458 units would balance 1 cubic inch (16 cm3) of distilled water at an ambient air-water pressure and temperature of 30 inches of mercury (100 kPa) and 62 °F (17 °C) respectively. [3] Another book states that Captain Henry Kater, of the British Standards Commission, arrived at this value experimentally. [4]

Contents

The grain was the legal foundation of traditional English weight systems, [5] and is the only unit that is equal throughout the troy, avoirdupois, and apothecaries' systems of mass. [6] :C-6 The unit was based on the weight of a single grain of barley which was equal to about +43 the weight of a single grain of wheat. [5] [7] :95 The fundamental unit of the pre-1527 English weight system, known as Tower weights, was based on the wheat grain. [8] The tower "wheat" grain was defined as exactly +4564 (≈+34) of the troy "barley" grain. [1] :74

Since the implementation of the international yard and pound agreement of 1 July 1959, the grain or troy grain (symbol: gr) measure has been defined in terms of units of mass in the International System of Units as precisely 64.79891  milligrams . [6] :C-19 [9] One gram is thus approximately equivalent to 15.43236 grains. [6] :C-13 The unit formerly used by jewellers to measure pearls, diamonds, and other precious stones, called the jeweller's grain or pearl grain, is equal to 14 carat (50 mg; 0.77 gr). [5] The grain was also the name of a traditional French unit equal to 53.115 mg. [5]

In both British Imperial units and United States customary units, there are precisely 7,000 grains per avoirdupois pound, and 5,760 grains per troy pound or apothecaries' pound. [6] :C-6–C-7 It is obsolete in the United Kingdom and, like most other non-SI units, it has no basis in law and cannot be used in commerce. [10]

Current usage

A box of .38 Special (9.1 mm) cartridges that have 148-grain (9.6 g) bullets 148 grain 38 special.jpg
A box of .38 Special (9.1 mm) cartridges that have 148-grain (9.6 g) bullets

Grains are commonly used to measure the mass of bullets and propellants. [11] [12] In archery, the grain is the standard unit used to weigh arrows. [13]

In North America, the hardness of water is often measured in grains per U.S. gallon (gpg) of calcium carbonate equivalents. [14] [15] Otherwise, water hardness is measured in the dimensionless unit of parts per million (ppm), numerically equivalent to concentration measured in milligrams per litre. [14] [15] One grain per U.S. gallon is approximately 17.1 ppm. [14] [note 1] Soft water contains 1–4 gpg of calcium carbonate equivalents, while hard water contains 11–20 gpg. [15]

A five-grain aspirin. The usage guidance label on a bottle of aspirin indicates that the dosage is "325 mg (5 gr)". 5 grain aspirin.jpg
A five-grain aspirin. The usage guidance label on a bottle of aspirin indicates that the dosage is "325 mg (5 gr)".

Though no longer recommended, in the U.S., grains are still used occasionally in medicine as part of the apothecaries' system, especially in prescriptions for older medicines such as aspirin or phenobarbital. [16] [17] For example, the dosage of a standard 325 mg tablet of aspirin is sometimes given as 5 grains. [16] [18] In that example the grain is approximated to 65 mg, though the grain can also be approximated to 60 mg, depending on the medication and manufacturer. [16] [19] The apothecaries' system has its own system of notation, in which the units symbol or abbreviation is followed by the quantity in lower case Roman numerals. [17] [19] [20] For amounts less than one, the quantity is written as a fraction, or for one half, ss (or variations such as ss., ṡṡ, or s̅s̅). [17] [19] [20] [21] :263 Therefore, a prescription for tablets containing 325 mg of aspirin and 30 mg of codeine can be written "ASA gr. v c̄ cod. gr. ss tablets" (using the medical abbreviations ASA for acetylsalicylic acid [aspirin], [21] :34 [22] :8 c̄ for "with", [21] :56 [22] :14 and cod. for codeine). [21] :70 [22] :19 The apothecaries' system has gradually been replaced by the metric system, and the use of the grain in prescriptions is now rare. [19]

In the U.S., particulate emission levels, used to monitor and regulate pollution, are sometimes measured in grains per cubic foot instead of the more usual ppm by volume. [23] [24] This is the same unit commonly used to measure the amount of moisture in the air, also known as the absolute humidity. [25] The SI unit used to measure particulate emissions and absolute humidity is mg/m3. [23] [25] One grain per cubic foot is approximately 2288 mg/m3. [note 2]

History

Approximate weights of grains used for trading in antiquity
GrainApprox. SI mass
carob seed200 mg
barley grain65 mg
wheat grain50 mg

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, one carat (the mass of a carob seed) was equivalent to the weight of four wheat grains or three barleycorns. [7] :95 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. [26] :120–1

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). [27] The Tower pound was one of many monetary pounds of 240 silver pennies.[ citation needed ]

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.

The pound in question is the Tower pound. The Tower pound, abolished in 1527, consisted of 12 ounces like the troy pound, but was 116 (≈6%) lighter. The weight of the original sterling pennies was 22½ troy grains, or 32 "Tower grains". [26] :116

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. [28]

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, and 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 a wheat grain. [29]

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 7,680 grains was inadvertently created as 16 troy ounces, referring to the new troy rather than the old troy. Eventually, the wool pound won out. [29]

The avoirdupois pound was defined in prototype, rated as 6,992 to 7,004 grains. In the Imperial Weights and Measures Act 1824 (5 Geo. 4. c. 74), the avoirdupois pound was defined as 7,000 grains exactly. The Weights and Measures Act 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. [30]

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. [31]

See also

Notes

  1. The exact value of one grain per U.S. gallon is 64.79891/3.785411784 mg/L (ppm). [6] :C-12,C-14
  2. The exact value of one grain per cubic foot is 64.79891/0.028316846592 mg/m3. [6] :C-10,C-14

Related Research Articles

<span class="mw-page-title-main">Carat (mass)</span> Unit of mass

The carat (ct) is a unit of mass equal to 200 mg, which is used for measuring gemstones and pearls. The current definition, sometimes known as the metric carat, was adopted in 1907 at the Fourth General Conference on Weights and Measures, and soon afterwards in many countries around the world. The carat is divisible into 100 points of 2 mg. Other subdivisions, and slightly different mass values, have been used in the past in different locations.

<span class="mw-page-title-main">Imperial units</span> System of measurements

The imperial system of units, imperial system or imperial units is the system of units first defined in the British Weights and Measures Act 1824 and continued to be developed through a series of Weights and Measures Acts and amendments.

<span class="mw-page-title-main">Pound (mass)</span> Unit of mass

The pound or pound-mass is a unit of mass used in both the British imperial and United States customary systems of measurement. Various definitions have been used; the most common today is the international avoirdupois pound, which is legally defined as exactly 0.45359237 kilograms, and which is divided into 16 avoirdupois ounces. The international standard symbol for the avoirdupois pound is lb; an alternative symbol is lbm, #, and or ″̶.

<span class="mw-page-title-main">United States customary units</span> System of units of measurement commonly used in the United States

United States customary units form a system of measurement units commonly used in the United States and most U.S. territories, since being standardized and adopted in 1832. The United States customary system developed from English units that were in use in the British Empire before the U.S. became an independent country. The United Kingdom's system of measures evolved by 1824 to create the imperial system, which was officially adopted in 1826, changing the definitions of some of its units. Consequently, while many U.S. units are essentially similar to their imperial counterparts, there are noticeable differences between the systems.

<span class="mw-page-title-main">Gram</span> Metric unit of mass

The gram is a unit of mass in the International System of Units (SI) equal to one thousandth of a kilogram.

<span class="mw-page-title-main">Troy weight</span> System of units of mass

Troy weight is a system of units of mass that originated in the Kingdom of England in the 15th century and is primarily used in the precious metals industry. The troy weight units are the grain, the pennyweight, the troy ounce, and the troy pound. The troy grain is equal to the grain unit of the avoirdupois system, but the troy ounce is heavier than the avoirdupois ounce, and the troy pound is lighter than the avoirdupois pound. Legally, one troy ounce equals exactly 31.1034768 grams.

The ounce is any of several different units of mass, weight, or volume and is derived almost unchanged from the uncia, an Ancient Roman unit of measurement.

<span class="mw-page-title-main">Avoirdupois</span> System of weights

Avoirdupois is a measurement system of weights that uses pounds and ounces as units. It was first commonly used in the 13th century AD and was updated in 1959.

<span class="mw-page-title-main">Pennyweight</span> Unit of mass

A pennyweight (dwt) is a unit of mass equal to 24 grains, 120 of a troy ounce, 1240 of a troy pound, approximately 0.054857 avoirdupois ounce and exactly 1.55517384 grams. It is abbreviated dwt, d standing for denarius –, and later used as the symbol of an old British penny.

<span class="mw-page-title-main">Bushel</span> Unit of volume with numerous different definitions

A bushel is an imperial and US customary unit of volume based upon an earlier measure of dry capacity. The old bushel is equal to 2 kennings (obsolete), 4 pecks, or 8 dry gallons, and was used mostly for agricultural products, such as wheat. In modern usage, the volume is nominal, with bushels denoting a mass defined differently for each commodity.

The dram is a unit of mass in the avoirdupois system, and both a unit of mass and a unit of volume in the apothecaries' system. It was originally both a coin and a weight in ancient Greece. The unit of volume is more correctly called a fluid dram, fluid drachm, fluidram or fluidrachm.

<span class="mw-page-title-main">Apothecaries' system</span> Historical system of mass and volume units used by physicians and apothecaries

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.

A system of units of measurement, also known as a system of units or system of measurement, is a collection of units of measurement and rules relating them to each other. Systems of measurement have historically been important, regulated and defined for the purposes of science and commerce. Instances in use include the International System of Units or SI, the British imperial system, and the United States customary system.

English units were the units of measurement used in England up to 1826, which evolved as a combination of the Anglo-Saxon and Roman systems of units. Various standards have applied to English units at different times, in different places, and for different applications.

<span class="mw-page-title-main">History of measurement</span>

The earliest recorded systems of weights and measures originate in the 3rd or 4th millennium BC. Even the very earliest civilizations needed measurement for purposes of agriculture, construction and trade. Early standard units might only have applied to a single community or small region, with every area developing its own standards for lengths, areas, volumes and masses. Often such systems were closely tied to one field of use, so that volume measures used, for example, for dry grains were unrelated to those for liquids, with neither bearing any particular relationship to units of length used for measuring cloth or land. With development of manufacturing technologies, and the growing importance of trade between communities and ultimately across the Earth, standardized weights and measures became critical. Starting in the 18th century, modernized, simplified and uniform systems of weights and measures were developed, with the fundamental units defined by ever more precise methods in the science of metrology. The discovery and application of electricity was one factor motivating the development of standardized internationally applicable units.

<span class="mw-page-title-main">Comparison of the imperial and US customary measurement systems</span>

Both the British imperial measurement system and United States customary systems of measurement derive from earlier English unit systems used prior to 1824 that were the result of a combination of the local Anglo-Saxon units inherited from Germanic tribes and Roman units.

Winchester measure is a set of legal standards of volume instituted in the late 15th century (1495) by King Henry VII of England and in use, with some modifications, until the present day. It consists of the Winchester bushel and its dependent quantities, the peck, (dry) gallon and (dry) quart. They would later become known as the Winchester Standards, named because the examples were kept in the city of Winchester.

<span class="mw-page-title-main">Imperial and US customary measurement systems</span> English (pre 1824), Imperial (post 1824) and US Customary (post 1776) units of measure

The imperial and US customary measurement systems are both derived from an earlier English system of measurement which in turn can be traced back to Ancient Roman units of measurement, and Carolingian and Saxon units of measure.

The quarter was used as the name of several distinct English units based on ¼ sizes of some base unit.

The Exchequer Standards may refer to the set of official English standards for weights and measures created by Queen Elizabeth I, and in effect from 1588 to 1825, when the Imperial units system took effect, or to the whole range of English unit standards maintained by the Court of the Exchequer from the 1200s, or to the physical reference standards physically kept at the Exchequer and used as the legal reference until the such responsibility was transferred in the 1860s, after the Imperial system had been established.

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