8 BULLETIN" 459, U. S. DEPARTMENT OF AGRICULTURE. 



verting it all into heat, by burning the substance, and measuring the 

 heat produced. Various units have been employed in measuring heat, 

 but the one used in this bulletin is the therm. 



A therm 1 is the quantity of heat required to raise the temperature 

 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 tem- 

 perature 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. 2 



Therms. 



Timothy hay 175. 1 



Clover hay 173. 2 



Oat straw 171. 



Wheat straw 171. 4 



Corn meal 1 70. 9 



Oats 180. 6 



Wheat bran 175. 5 



Linseed meal 196. 7 



UTILIZATION Of ENERGY. 



But the value of a fuel depends also upon how much of the chemical 

 energy which it contains can be used. Hard coal contains plenty of 

 energy, but it would, not be of much use to run a gasoline engine. 

 Wheat straw contains fully as much chemical energy as corn meal, 

 but much of that energy can not be utilized by the animal machine. 



Two causes combine to affect the utilization of the chemical energy 

 contained in feeding stuffs. 



First, more or less of the feed escapes from the body unburned. 

 If a coal is of such quality that portions of it drop through the grate 

 unconsumed, and if smoke and combustible gases are carried off 

 through the stack, it is evident that a ton of it will supply far less 

 heat to the boiler than it would if the combustion were perfect. The 

 case of the feeding stuff is similar. Much of even the best feeding 

 stuffs escapes digestion and is excreted in the dung, carrying with it 

 a corresponding quantity of the chemical energy of the feed. More 



1 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, the unit so used being the large or kilogram calorie, as distinguished from the 

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

 thus used 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 necessary 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 large calories, available data, such, for example, as those in Farm- 

 ers' Bulletin 22, can be readily given expression in the new unit. The use of the word therm, with the 

 abbreviation t., has also been proposed as the equivalent of the small (or gram) calorie, but it has not come 

 into general use. 



2 With 15 per cent moisture. 



