Grave (unité)

The grave (ɡræv, ɡʁav), 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 modern kilogram has its origins in the Age of Enlightenment and the French Revolution. 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. Initially a provisional value was used, based on the meridian measurement made in 1740 by Lacaille. 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 dm3provisional) of water at 0 °C was determined by Lavoisier and Haüy to be 18841 grains. 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. On April 7, 1795, the gram 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.