The grave, abbreviated ''gv'', is the unit of mass used in the first metric system which was implemented in France in 1793. In 1795, the grave was renamed as the

kilogram The kilogram (also kilogramme) is the unit of mass in the International System of Units (SI), having the unit symbol kg. It is a widely used measure in science, engineering and commerce worldwide, and is often simply called a kilo colloquially. ...

Origin

The modern kilogram has its origins in the

Age of Enlightenment The Age of Enlightenment or the Enlightenment; german: Aufklärung, "Enlightenment"; it, L'Illuminismo, "Enlightenment"; pl, Oświecenie, "Enlightenment"; pt, Iluminismo, "Enlightenment"; es, La Ilustración, "Enlightenment" was an intel ...

and the

French Revolution The French Revolution ( ) was a period of radical political and societal change in France that began with the Estates General of 1789 and ended with the formation of the French Consulate in November 1799. Many of its ideas are conside ...

. In 1790 an influential proposal by Talleyrand called for a new system of units, including a unit of length derived from an invariable length in nature, and a unit of mass (then called ''weight'') equal to the mass of a unit volume of water. In 1791, the Commission of Weights and Measures, appointed by the French Academy of Sciences, chose one ten-millionth of the half meridian as the unit of length, and named it ''

metre The metre ( British spelling) or meter ( American spelling; see spelling differences) (from the French unit , from the Greek noun , "measure"), symbol m, is the primary unit of length in the International System of Units (SI), though its pre ...

''. Initially a ''provisional'' value was used, based on the meridian measurement made in 1740 by

Lacaille Abbé Nicolas-Louis de Lacaille (; 15 March 171321 March 1762), formerly sometimes spelled de la Caille, was a French astronomer and geodesist who named 14 out of the 88 constellations. From 1750 to 1754, he studied the sky at the Cape of Good ...

. In 1793 the commission defined the unit of mass as a cubic decimetre of distilled water at 0 °C, and gave it the name ''grave''. Two supplemental unit names, gravet (0.001 grave), and bar (1000 grave), were added to cover the same range as the old units, resulting in the following decimal series of units: milligravet, centigravet, decigravet, gravet, centigrave, decigrave, grave, centibar, decibar, bar. As measured by the customary unit of mass in use in France at the time, the mass of the new unit volume (1 dm³_provisional) of water at 0 °C was determined by

Lavoisier Antoine-Laurent de Lavoisier ( , ; ; 26 August 17438 May 1794),
CNRS ( Haüy to be 18841

grain A grain is a small, hard, dry fruit ( caryopsis) – with or without an attached hull layer – harvested for human or animal consumption. A grain crop is a grain-producing plant. The two main types of commercial grain crops are cereals and legum ...

s. Since a mass standard made of water would be inconvenient and unstable, the regulation of commerce necessitated the manufacture of a ''practical realisation'' of the water-based definition of mass. Accordingly, a provisional mass standard of the grave was made as a single-piece, metallic artefact.

Transition to the kilogram

On April 7, 1795, the

gram The gram (originally gramme; SI unit symbol g) is a unit of mass in the International System of Units (SI) equal to one one thousandth of a kilogram. Originally defined as of 1795 as "the absolute weight of a volume of pure water equal to th ...

was decreed in France to be "the absolute weight of a volume of pure water equal to the cube of the hundredth part of the metre, and at the temperature of melting ice". The law also replaced the three names gravet, grave and bar by a single generic unit name: the gram. The new gram was equal to the old gravet. Four new prefixes (deca, hecto, kilo, and myria) were added to the metric system to cover almost the same range of units as in 1793 (milligram, centigram, decigram, gram, decagram, hectogram, kilogram, myriagram). The brass prototype of the grave was renamed to provisional kilogram. In 1799 the provisional units were replaced by the final ones.

Delambre Jean Baptiste Joseph, chevalier Delambre (19 September 1749 – 19 August 1822) was a French mathematician, astronomer, historian of astronomy, and geodesist. He was also director of the Paris Observatory, and author of well-known books on t ...

and Méchain had completed their new measurement of the meridian, and the final metre was 0.03% smaller than the provisional one. Hence the final kilogram, being the mass of one cubic decimetre of water, was 0.09% lighter than the provisional one. In addition, the temperature specification of the water was changed from 0 °C to the point where the density of water is maximal (about 4 °C). This change of temperature added 0.01% to the final kilogram. At the same time, work was commissioned to precisely determine the mass of a cubic decimetre (one

litre The litre (international spelling) or liter (American English spelling) (SI symbols L and l, other symbol used: ℓ) is a metric unit of volume. It is equal to 1 cubic decimetre (dm3), 1000 cubic centimetres (cm3) or 0.001 cubic metre (m3 ...

) of water. The same decree also defined the litre as follows: "Litre: the measure of volume, both for liquid and solids, for which the displacement would be that of a cube ith sides measuringone-tenth of a metre." Original text: "" Although the decreed definition of the kilogram specified water at 0°C—its highly stable ''temperature'' point—the French chemist Louis Lefèvre-Gineau and the Italian naturalist

Giovanni Fabbroni Giovanni Valentino Mattia Fabbroni (13 February 1752 – 17 December 1822) was an Italian naturalist, economist, agronomist and chemist. He was born in Florence, Italy, the son of Horace and Rosalinda Werner. His mother originated in Heidelbe ...

chose to redefine the standard in 1799 to water's most stable ''density'' point: the temperature at which water reaches maximum density, which was measured at the time as 4°C.Modern measurements show the temperature at which water reaches maximum density is 3.984°C. However, the scientists at the close of the 18th century concluded that the temperature was 4°C. They concluded that one cubic decimetre of water at its maximum density was equal to 99.9265% of the target mass of the provisional kilogram standard made four years earlier.

Kilogramme des Archives

After the definitions were finalized in 1799, an all-platinum kilogram prototype was fabricated with the objective that it would equal, as close as was scientifically feasible for the day, the mass of one cubic decimetre of water at 4°C. It was called the ''Kilogramme des Archives'' as it was stored in the Archives Nationales in Paris. The prototype was presented to the Archives of the Republic in June, and on December 10, 1799 the prototype was formally ratified as the ''Kilogramme des Archives'' (Kilogram of the Archives)Armoire de fer
(in English: Iron chest), vault built in 1790 and used to store kilogram and metre prototypes and the kilogram was defined as being equal to its mass. This standard stood for the next ninety years, until being replaced in 1889 by the platinum–iridium

International Prototype of the Kilogram The International Prototype of the Kilogram (referred to by metrology, metrologists as the IPK or Le Grand K; sometimes called the ''wiktionary:ur-#Prefix, ur-kilogram,'' or ''urkilogram,'' particularly by German-language authors writing in Engli ...

(IPK).

References

Notes

{{DEFAULTSORT:Grave (Unit) Non-SI metric units Units of mass

Origin

Transition to the kilogram

Kilogramme des Archives

See also

References

Notes