calorie
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calorie
Calorie
a unit of heat that is not part of a system of units. Designation, cal. In addition to the calorie, the kilocalorie (also known as the large calorie) is widely used; 1 kcal = 1,000 cal.
Originally, the calorie was defined as the quantity of heat necessary to raise the temperature of 1 g of water by 1°C. Neither the temperature interval within which the heating was performed nor its conditions had been defined prior to the late 19th century. Various calories have therefore been used: the 0°, 15°, 20°, and 25° calories as well as the average calorie and the thermochemical calorie. The 20° kilocalorie was used in the USSR from 1934 to 1957. This kilocalorie was equal to the quantity of heat (with an accuracy of up to 0.02 percent) required to heat 1 kg of water from 19.5° to 20.5°C.
The First International Steam Table Conference (London, 1929) introduced the international calorie, defined as 1/861.1 of the international kilowatt-hour (kW-hr). The InternationalSteam Table Conferences in 1954 and 1956 accepted the decisionon transition from the calorie to a new unit, the absolute joule(J), which subsequently was included in the International Sys-tem of Units. The following relationship was established betweenthe calorie and the joule: 1 cal = 4.1868 J (exactly). The 20°calorie is equal to 4.181 J. The calorie used widely in thermo-chemistry is equal to 4.1840 J.