On 2004 Apr 5 , at 3:14 PM, Gavin Young wrote:
For example,
look what happened to the word kilocalorie. In food usage it simply became
Calorie because the orginal calorie unit was too small for use in food
exothermic reactions and people got tired of saying "kilo" in front of the
word "calorie". Now Calorie is often spelled calorie. The SI board eventually
gave up using the kilocalorie and calorie as approved terms.
The calorie was not a shorthand name for the kilocalorie as gavin says above. It was not devised because the calorie was too small. Kilocalorie did not become Calorie; instead, Calorie became kilocalorie.
There were two types of calorie, the "gram-calorie" and the "kilogram-calorie". Both were in use at the same time by different groups of people. The definitions were identical except for one word:
- the definition of the gram-calorie was "the heat needed to raise the temperature of 1 GRAM of water by one degree Celsius at 15�C (specifically from 14.5 �C to 15.5 �C)", while
- the definition of the kilogram-calorie was exactly the same except word KILOGRAM replaced the word GRAM. (CAPS added for emphasis.)
Obviously, the kilogram-calorie is just 1000 times bigger than the gram calorie.
However both units were used and both names were often shortened to just "calorie". The users of the terms simply had to know which one was meant, perhaps by the context or by the source. (In direct dialog, one could always ask.) Sometimes they were called the big calorie and the little calorie. In some (and later "most") quarters, when written, the gram-calorie was spelled "calorie" while the kilogram-calorie was spelled "Calorie"; likewise, their abbreviations or symbols were "cal" and "Cal", respectively. This is still done. (If Calorie is intended, it is not "often spelled calorie" as Gavin wrote above).
I believe the big calorie (Cal.) was used primarily by nutritionists for measuring food energy. And I think most scientists used the little calorie (cal.), although I believe chemists may have used both.
At some point, more and more people got tired of the confusion and realized that a big calorie was just 1000 times the little calorie so that we could have just one calorie (the little one) and could use the metric terminology to call the other one the kilocalorie.
But during the same time (I think) there was growing recognition that heat should be measured in the same unit as other forms of energy, since heat is just a form of energy. (This was NOT understood when calories were first devised.) That SI energy unit is the joule (J). More and more, we are seeing the calorie (in all of its variations*) dropped in favor of using the SI unit, joule (and its multiples and submultiples as convenient). Calories are about 4 joules so anything that was formerly be measured in calories can be conveniently measured in joules and anything formerly measured in Calories (that is kilocalories) can be conveniently measured in kilojoules).
Regards, Bill Hooper Fernandina Beach, Florida, USA <><><><><><><><><><><><> Make it simple; Make it Metric <><><><><><><><><><><><>
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* The definition I gave above (and the similar one for the kilogram-calorie) is the definition of the so-called "15 �C calorie". There are other similar but not identical calories that were (and still are) in use. The BIPM identifies three of them (not as SI units but as non-SI units for which BIPM recognizes specific SI equivalents). They are:
15 �C calorie = 4.1855 J International Table calorie = 4.1868 J thermochemical calorie = 4.184 J
