Calorie, 491 converting between units

There is a fixed relation between the measure of a quantity of work and that of the quantity of heat obtained from it by complete conversion. If these- two measures are expressed in terms of the erg and the calorie respectively as units, there will also be a relation between the erg and the calorie. Heat, considered as a form of energy, may be measured in ergs, i.e., in work units, and to convert the measure of a quantity of heat expressed in calories into the measure. of the same quantity expressed in ergs, we must find the number of times the erg is contained in the calorie, and multiply this by the measure of the given quantity of heat in calories. It is a relation between units which is involved. 

In dealing with Boussinesq s problem, Lord Rayleigh used the amount of heat H (measuring unit calorie) as one of the then used base dimensions. Only since the introduction of SI (Systeme International d Unites) it was required to make no distinction between heat and mechanical energy, because both were considered to be equal. In order to comply with this requirement, the Joule equivalent of heat J [M L2 T2 H-1] had to be introduced as a natural constant in the relevance list. If we proceed from the assumption of an inviscid , ideal liquid, no mechanical heat can be converted into heat. In this case, J is irrelevant. 

By detinition, one calorie (International Table) is exactly 4.186 8 absolute joules which converts to 1.055 056 X 10 joules for one Btu (International Table). Also, by definition, one calorie (thermochemical) is exactly 4.184 absolute joules which converts to 1.054350 X 103 joules for one Btu (thermochemical). A mean calorie is TSOth of the heat required to raise the temperature of one gram of water at one atmosphere pressure from 0°C to 100°C and equals 4.19002 absolute joules. In all cases, the relationship between calorie and British thermal unit is established by 1 cal/(g. °C) = 1 Btu/(lb. 6SF). A mean Btu, therefore is 7So h of the heat required to raise the temperature of one pound of water at one atmosphere pressure from 32°F to 212°F and equals 1.055 87 X 103 joules. When values are given as Btu or calories, the type of unit (International Table, thermochemical, mean, or temperature of determination) should be given. In all cases for this table, conversions involving jou S are based on the absolute joule. 

In all previous JANAF Thermochemical Tables, the standard-state pressure was one atmosphere (101 325 Pa) and the unit of energy was the thermochemical calorie (4.184 J). For this publication, the standard-state pressure is changed to one bar (100 000 Pa) and the energy unit to the joule. The values from previous JANAF tabulations have been converted as described below. This information is provided not only to make clear the correspondence between this publication and previous JANAF Thermochemical Tables but also to assist the reader in making comparisons with other tables. This information is the same as that provided in The NBS Tables of Chemical Thermodynamic Proper-... 

Table 15.1 summarizes the relationships between calories, nutritional Calories, joules, and kilojoules (kj) and the conversion factors you can use to convert from one unit to another. 

The unit of heat used throughout this article is the calorie. Historically the calorie is defined as the specific heat of water. As soon as more accurate measurements were possible, it was found that the specific heat of water varies by as much as Va% between 0 and 100° C. For a more precise definition the temperature of the water had to be specified. Soon after 1900 practically all precision calorimetry was ultimately linked to the more convenient and accurate electrical measurement of oiergy. Out of habit most measurements were, however, still converted to calories, so that finally an artificial calorie was defined. The present value of this defined calorie is ... 

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