(b) The figure depends on the conversion factor between "international joules" and "absolute" (modern, SI) joules. It was later redefined as 4.1840 J exactly. (a) The 'Thermochemical calorie' was defined by Rossini simply as 4.1833 international joules in order to avoid the difficulties associated with uncertainties about the heat capacity of water. This definition was adopted by the Fifth International Conference on Properties of Steam (London, July 1956). (c)ĭefined as 1⁄ 860 "international" watt hours = 180⁄ 43 "international" joules exactly. (c)ĭefined as 1⁄ 100 of the amount of energy required to warm one gram of air-free water from 0 to 100 ☌ at standard atmospheric pressure. The amount of energy required to warm one gram of air-free water from 19.5 to 20.5 ☌ at standard atmospheric pressure. The CIPM in 1950 published a mean experimental value of 4.1855 J, noting an uncertainty of 0.0005 J. (c) Experimental values of this calorie ranged from 4.1852 to 4.1858 J. The amount of energy required to warm one gram of air-free water from 14.5 to 15.5 ☌ at standard atmospheric pressure. The amount of energy required to warm one gram of air-free water from 3.5 to 4.5 ☌ at standard atmospheric pressure. The amount of energy equal to exactly 4.184 J ( Joules) and 1 kJ = 0.239 kcal. Accordingly, several different precise definitions of the calorie have been used. The definition depends on the atmospheric pressure and the starting temperature. The modern (small) calorie is defined as the amount of energy needed to increase the temperature of 1 gram of water by 1 ☌ (or 1 K, which is the same increment). The alternate spelling calory is archaic. Use of the calorie was officially deprecated by the ninth General Conference on Weights and Measures, in 1948. The modern calorie (cal) was first recognized as a unit of the cm-g-s system (cgs) in 1896, Īlongside the already-existing cgs unit of energy, the erg (first suggested by Clausius in 1864, under the name ergon, and officially adopted in 1882).Īlready in 1928 there were serious complaints about the possible confusion arising from the two main definitions of the calorie and whether the notion of using the capital letter to distinguish them was sound. The use of the kilogram-calorie (kcal) for nutrition was introduced to the American public by Wilbur Olin Atwater, a professor at Wesleyan University, in 1887. Berthelot also introduced the convention of capitalizing the kilogram-calorie, as Calorie. In 1879, Marcellin Berthelot distinguished between gram-calorie (modern calorie) and kilogram-calorie (modern kilocalorie). The "small" calorie (modern calorie) was introduced by Pierre Antoine Favre (Chemist) and Johann T. The term entered French and English dictionaries between 18. The calorie was first introduced by Nicolas Clément, as a unit of heat energy, in lectures during the years 1819–1824. 5 Measurement of energy content of food.One calorie is defined as exactly 4.184 J, and one Calorie (kilocalorie) is 4184 J. It has been regarded as obsolete within the scientific community since the adoption of the SI system, but is still in some use. In most countries, labels of industrialized food products are required to indicate the nutritional energy value in (kilo or large) calories per serving or per weight.Ĭalorie relates directly to the metric system, and therefore to the SI system. By convention in food science, the large calorie is commonly called Calorie (with a capital C by some authors to distinguish from the smaller unit). Thus, 1 kilocalorie (kcal) = 1000 calories (cal). The large calorie, food calorie, or kilocalorie ( Cal, Calorie or kcal), most widely used in nutrition, is the amount of heat needed to cause the same increase in one kilogram of water. The small calorie or gram calorie (usually denoted cal) is the amount of heat needed to raise the temperature of one gram of water by one degree Celsius (or kelvin). The calorie is a unit of energy defined as the amount of heat needed to raise the temperature of a quantity of water by one degree Celsius (or kelvin).įor historical reasons, two main definitions of calorie are in wide use. A 710-millilitre (24 US fl oz) energy drink with 330 kilocalories
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