![]() 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. The amount depends on the atmospheric pressure and the starting temperature, and different choices of these parameters have resulted in several different precise definitions of the unit. The "small" calorie is broadly 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, a gradation of one percent of the interval between the melting point and the boiling point of water). The alternate spelling calory is archaic. The small calorie was originally part of the metric system (SI), but it was officially deprecated by the ninth General Conference on Weights and Measures in 1948 in favor of the joule. The small calorie (cal) was recognized as a unit of the cm-g-s system (cgs) in 1896, alongside 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. This usage was adopted by Wilbur Olin Atwater, a professor at Wesleyan University, in 1887, in an influential article on the energy content of food. In 1879, Marcellin Berthelot distinguished between gram-calorie and kilogram-calorie, and proposed using "Calorie", with capital "C", for the large unit. He proposed calling the "large" unit "kilocalorie", but the term didn't catch on until some years later. physician Joseph Howard Raymond, in his classic 1894 textbook A Manual of Human Physiology. The same term was used for the "small" unit by Pierre Antoine Favre (Chemist) and Johann T. The term (written with lowercase "c") entered French and English dictionaries between 18. The term "calorie" was first introduced by Nicolas Clément, as a unit of heat energy, in lectures on experimental calorimetry during the years 1819–1824. The precise equivalence between calories and joules has varied over the years, but in thermochemistry and nutrition it is now generally assumed that one (small) calorie ( thermochemical calorie) is equal to exactly 4.184 J, and therefore one kilocalorie (one large calorie) is 4184 J, or 4.184 kJ. However, this unit is not officially part of the metric system (SI), and is regarded as obsolete, having been replaced in many uses by the SI unit of energy, the joule (J). In physics and chemistry the word calorie and its symbol usually refer to the small unit the large one being called kilocalorie. Some authors recommend the spelling Calorie and the symbol Cal (both with a capital C) to avoid confusion however, this convention is often ignored. It is generally used in publications and package labels to express the energy value of foods in per serving or per weight, recommended dietary caloric intake, metabolic rates, etc. In nutrition and food science, the term calorie and the symbol cal almost always refers to the large unit. ![]() Thus, 1 large calorie is equal to 1000 small calories. The small calorie or gram calorie was defined as the amount of heat needed to cause the same increase in one gram of water. The large calorie, food calorie, or kilogram calorie was originally defined as the amount of heat needed to raise the temperature of one kilogram of water by one degree Celsius (or one kelvin). ![]() For 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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