Calorie

Calorie, the amount of heat required to heat 1 gram of water by 1°C (small C.) or 1 kg (large C.). The small C., or gram-calorie, is essentially a variable quantity throughout the thermometric scale and changes with temperature; strictly speaking, by C. should be understood the amount of heat required to heat by 1° at some specific initial temperature. Often 15° or 20° is taken as this temperature. Then the amount of heat corresponding to the C. is the C. relating to 15° or 20°. This temperature is chosen because for calorimetric experiments it is most convenient to refer all changes specifically to room temperature, and the errors in this case when the temperature of the calorimeter is increased by 1-2° are insignificant. For practical purposes, especially in the field of technology and physiology, the large C., which corresponds to heating 1 kg of water by 1°, is often used instead of the small C. The large C. is 1,000 times larger than the small C. Heating any other substance, taken in an amount of 1 gram or 1 kg, requires a different amount of heat than is the case for water, and the amount of heat required to heat 1 gram of a substance by 1° is usually denoted by the letter C and is called the specific heat of the substance, which for the vast majority of bodies is a fractional quantity. C. can be measured in mechanical units, since heat is equivalent to mechanical work (on the mechanical theory of heat, see Thermodynamics). One large C., when converted into mechanical work, gives 427 kilogram-meters of work. Since the weight of 1 gram is equal to 981 dynes, then 1 kg is equal to 981×10⁸ dynes; 1 kg/m is equal to 981×10⁵ ergs, and therefore one small C. is equal to 981×0.427×10⁵=0.419×10⁸ dynes. The large C. is denoted by a capital, and the small C. by a lowercase letter C.