296 DOMESTIC ANIMALS, DAIRYING, ETC. 



a great variety of feeding stuffs from which it has to extract its sup- 

 ply of fuel, and even the materials which it actually burns up are 

 of various sorts. 



These fuel materials are not all of equal value. A pound of 

 good anthracite coal, for example, is, other things being equal, about 

 14 per cent more valuable as fuel than the same weight of alcohol, 

 while a pound of fat in the food has over twice the fuel value of a 

 pound of starch. Evidently, it will greatly simplify comparisons 

 of different feeding stuffs and rations as sources of fuel material to 

 have some simple method by which we can learn not only the amount 

 of fuel material which the feed contains, but also the quality of that 

 fuel. Such a basis of comparison is afforded by a study of the 

 energy values. 



Measurement of Energy. Anything which has the capacity to 

 do work is said to possess energy. Hence we say that the fuel of the 

 engine and the feed of the animal possess energy, since they enable 

 the engine or the body to do work. They hold this energy stored 

 up in the "latent" or "potential" form of chemical energy. When 

 they are burned in the engine or the body, this chemical energy is 

 set free, part of it being converted into work and the rest escaping 

 as heat. 



Plainly, then, the value of a fuel, or of a feeding stuff so far as 

 it serves as fuel, depends, in the first place, on how much chemical 

 energy it contains. This can be measured without difficulty by 

 converting it all into heat, by burning the substance, and measur- 

 ing the heat produced. Various units have been employed in meas- 

 uring heat, but the one used in this article is the therm. 



A therm* is the quantity of heat required to raise the tempera- 

 ture of 1,000 kilograms (2,204.6 pounds) of water 1 C. A pound 

 of good anthracite coal would produce heat enough to raise the 

 temperature of about 3,583 kilograms of water 1 C. Consequently, 

 the chemical energy contained in the coal is 3.583 therms per pound. 

 In precisely the same way the amount of chemical energy contained 

 in many feeding stuffs has been measured. The following are the 

 results of a few such determinations : 



Chemical Energy in 100 Pounds (With 15 per cent moisture.) 



Therms. 



Timothy hay 175.1 



Clover hay 173.2 



Oat straw 171.0 



*In the nutrition investigations and studies of foods and feeding stuffs made 

 by this Department and by the State agricultural experiment stations, the results, 

 so far as energy or fuel value is concerned, have been expressed in calories. 

 There is consequently a large mass of available data so expressed. The calorie 

 is the amount of heat required to raise 1 kilogram of water 1 C. (approximately 

 1 pound of water 4 F.). The small size of the unit has made it necessarv to 

 use inconveniently large numbers to express the fuel values of foods and feeding 

 stuffs, a difficulty which is obviated by the use of the therm. As the latter unit 

 is equivalent to 1,000 calories, available data, such, for example, as those in 

 Farmers' Bulletin No. 22, can be readily given expression in the new unit. The 

 use of the word therm, with the abbreviation *., has also been proposed as th 

 equivalent of the small (or gram) calorie, but it has not come into general use, 



