NUTRITIVE VALUE OF FEEDING STUFFS 45 



the feeding stuff, and may be used by animals for maintenance and 

 production. 



Various units have been employed for measuring the heat of 

 combustion. The common unit is a Calorie, which represents the 

 amount of heat required to raise the temperature of one kilo- 

 gram of water one degree Centigrade, or that of a pound of water 

 very nearly four degrees Fahrenheit. A therm, as proposed by 

 Armsby, means 1000 Calories, the amount of heat required to raise 

 the temperature of 1000 kilograms of water (or 2204.6 pounds) 

 one degree Centigrade. This unit has been quite generally adopted 

 of late and will be used in the following pages. 



The various components of feeding stuffs contain certain 

 amounts of oxygen and are, therefore, partially oxidized. Carbo- 

 hydrates thus contain about 50 per cent of oxygen, fats 10 to 12 per 

 cent, protein 22 per cent (pp. 9, 12, 14) . The amount of heat evolved 

 in the combustion of any organic material depends on the propor- 

 tion of oxygen it requires for complete oxidation of the carbon, 

 hydrogen, nitrogen, and other chemical elements contained therein. 

 This amount can be calculated in the case of substances of known 

 composition, and directly determined in a so-called calorimeter. 



The Calorimeter. This apparatus consists of a well-insulated, 

 double-walled compartment, into which a platinum shell or bomb 

 is introduced and submerged in water. A weighed small amount 

 of the substance whose heat of combustion is to be determined is 

 introduced into this shell with compressed oxygen, and ignited 

 by means of an electric spark. By noting the rise in temperature 

 in the surrounding water the amount of heat given off by the sub- 

 stance on complete combustion can be calculated. 



Chemical Energy. It has been found by direct experiments 

 that the chemical energy of different classes of nutrients and feed- 

 ing stuffs is as follows : 



Chemical Energy in 100 Pounds, in Therms 



Pure nutrients 

 Protein : Carbohydrates : 



Wheat gluten 272 Starch, cellulose 190 



Gliadin, serum albumen . . . 268 Glucose 170 



Egg albumen, pure lean Sucrose, lactose, maltose. . 179 



meat 259 Fats : 



Blood fibrin 256 Steers and swine 425 



Sheep 427 



Corn oil 421 



Common feeding stuffs 



Flaxseed meal 267 Alfalfa hay, mixed hay and 



Linseed oil meal 194 oat straw 173 



Corn meal 171 Rice meal . 170 



