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. Louis XVI created a Consultative Commission for Units to devise a new decimal-based system of measurement. This royal commission, which included such aristocrats as Antoine Lavoisier, founded the very beginnings of the “metric system”, which later evolved into the contemporary International System of Units (SI).

In 1793 a new, decimal series of weights was introduced by the French Revolutionary government. The series of weights (milligravet, centigravet, decigravet, gravet, centigrave, decigrave, grave, centibar, decibar, bar [1]) contained three root unit names without a prefix: gravet, grave, and bar. Of these, the grave was the central unit with a definition. It was the weight of one cubic decimeter of pure water at the melting temperature of ice.

In 1795, the three root unit names were replaced by a single new name: the gram. 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).[2][3] The regulation of trade and commerce required a “practical realisation”: a single-piece, metallic reference standard. The kilogram was more convenient as a standard than the gram. A brass cylinder was made that served as the prototype of the provisional 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.[4][5] 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. ↑ This 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)
  2. ↑ 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
  3. ↑ Decree relating to the weights and measurements
  4. ↑ L’Histoire Du Mètre, La Détermination De L’Unité De Poids, link to Web site here.
  5. ↑ History of the kilogram
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