294 ORGANIC AGRICULTURAL CHEMISTRY 



by measuring the rise in temperature accurately to .001° C. 

 which takes place in a large volume of water in which the 

 bomb is immersed.^ 



Calorie. — The rise in temperature produced by the com- 

 bustion is calculated in units of heat energy known as calories. 

 A calorie is the amount oj heat necessary to raise the temperature 

 of i.o gram of water 1° C. In the absolute calorie unit this rise 

 of temperature is from 15° C. to 16° C, but the unit may be 

 defined in slightly more general terms, as first given. This 

 unit is small and in practice is multiplied by 1000 ; i.e. it is the 

 heat necessary to raise loco g. of water 1° C. To distinguish 

 these two units they are termed respectively the small calorie 

 or gram calorie, written without capitals, and the large calorie 

 written capitalized or Calorie. Still a third unit has been 

 suggested by Armsby known as the Therm (T.), which is equiva- 

 lent to 1000 Calories or 1,000,000 gram calories. This is used 

 mostly in calculating large feeding rations of domestic animals. 

 In calculating human foods the unit usually employed is the 

 Calorie (large calorie). In English standards the Calorie is 

 approximately equivalent to the amount of heat necessary to 

 raise i pound of water 4° F. 



Thus the Calorie is the unit in which the energy value or 

 food value of a food is expressed. It will often be found referred 

 to in other terms, as we have mentioned, viz. fuel value, calorific 

 value or heat of combustion. All of these terms are, therefore, 

 synonymous as applied to foods, with the corrections which 

 we shall now consider. 



Fuel Values in Calories. — What then are the fuel values in 

 Calories of the three food constituents? While all figures 

 determined do not agree exactly, the ones usually accepted at 

 present are as follows : 



I gram Carbohydrates yields 4.1 Cal. 

 I gram Fats yields 9.45 Cal. 



I gram Proteins yields 5.65 Cal. 



1 A detailed description of this apparatus may be found in U. S. Dept. Agr. 0. E. 

 S. Bui. 21 (1895), or in J. Am. Chem. Soc, XXV, 659 (1903). 



