Grave (unit)

A replica of the prototype of the kilogram at the Cité des Sciences et de l'Industrie, Paris, France

The grave was the original name of the kilogram, in an early version of the metric system between 1793 and 1795.

The modern kilogram has its origins in the pre-French Revolution days of France. In 1790 an influential proposal by Talleyrand called for a new system of units, including a unit of weight equal to the weight of a unit volume of water, and a unit of length derived from an invariable length in nature.[1] In 1791, a Commission for Units appointed by the French Academy of Sciences chose one ten-millionth of the quarter meridian as the unit of length, and named it meter.<ref and named it metre.>Rapport March 17, 1791 Ten millionth of meridian</ref>[2] The commission decided a new measurement of the meridian was required. Lavoisier began refining his method for the precision measurement of the specific weight of distilled water in vacuum at 0°C.

In 1793 the commission proposed defining the unit of weight as a cubic decimeter of water at 0°C, named grave.[3] 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 weights: milligravet, centigravet, decigravet, gravet, centigrave, decigrave, grave, centibar, decibar, bar.[4][5] The government adopted the proposal, and announced that a provisional version of the new system of units, based on an old meridian measurement by Lacaille, would be introduced soon.[6] A prototype of the provisional grave was made in brass. The regulation of trade and commerce required such a practical realisation.

In 1795 a new law replaced the three names gravet, grave and bar by a single generic unit name: the gram.[7] The new gram was equal to the old gravet. Four new prefixes were added to cover the same range of weights as in 1793 (milligram, centigram, decigram, gram, decagram, hectogram, kilogram, myriagram).[8][9] The brass prototype of the grave was renamed to kilogram.

In 1799 the provisional metric units, the meter and the kilogram, were replaced by the final units. The measurement of the meridian by Delambre and Mechant meant the final meter was 0.03% smaller than the provisional meter. Hence the final kilogram, being the weight of one cubic decimeter of water, became 0.09% lighter than the provisional one. In addition, the temperature specification of the water was changed from 0°C to 4°C, the point where the density of water is maximal, to allow greater accuracy. This change of temperature added 0.01% to the final kilogram.[10][11] In 1799 a platinum cylinder was made, and stored in the Archives of Paris, that served as the prototype of the final kilogram. It was called the Kilogramme des Archives, and this standard stood for the next ninety years.

See also

References

  1. ↑ May 1790 Proposal Talleyrand
  2. ↑ Rapport july 11, 1792 Introduction of the names metre, deci-centi-milli
  3. ↑ Rapport january 19, 1793 Name grave and dm^3
  4. ↑ Instructions abrégée sur les mesures déduites de la grandeur de la terre et sur les calculs relatifs à leur division décimale 1793: gravet, bar
  5. ↑ The obsolete unit bar (1000 kg, until 1795) is not to be confused with the newer unit of pressure that was introduced in 1909 (100 kPa)
  6. ↑ Decree of August 1, 1793
  7. ↑ The 7 April 1795 Act: gramme
  8. ↑ Nouvelle instruction sur les poids et mesures, et sur le calcul décimal, adoptée par l'Agence temporaire des poids et mesures. Claude Antoine Prieur, 1795
  9. ↑ Decree relating to the weights and measurements
  10. ↑ L’Histoire Du Mètre, La Détermination De L’Unité De Poids, link to Web site here.
  11. ↑ History of the kilogram
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