174 EXPERIMENTS WITH PLANTS 



ing or oxidation, and since the carbon is the principal 

 substance burned, producing as the final result carbon 

 dioxide, we may measure the carbon dioxide given off 

 by an organism and calculate the amount of carbon 

 burned and consequently the amount of energy used. 

 Thus it has been found by experiment that burning one 

 gram of carbon sets free about eight large Calories 1 and 

 produces about two liters of carbon dioxide. When- 

 ever we find that an organism has given off two liters 

 (or about two quarts) of carbon dioxide, we know that 

 it has set free from the carbon of its food materials 

 about eight large Calories. 2 This energy can be used 

 by the organism in the form of heat, chemical work, 

 mechanical work, etc. If the whole eight large Calories 

 were used in mechanical work they would suffice to 

 raise (8 x 426 =) 3,408 kilograms (= about 7,500 

 pounds) one meter (= about 39 inches or, roughly, 

 1 yard) . 



We may look at the matter in another way. When 

 an organism has produced its own weight of carbon 

 dioxide it has set free from the carbon in its food 

 enough energy to raise itself about 600 miles. A man 



1 A large Calorie is the amount of heat needed to raise the temperature of 

 one kilogram (about a quart) of water from to 1 centigrade. This is roughly 

 the amount needed to raise the temperature of one pound (or one pint) of water 

 through 4 Fahrenheit. 



2 While the amount of energy yielded by burning a gram of carbon differs 

 somewhat, depending on whether the carbon at the start is in the form of char- 

 coal, starch, fat or. proteid, the difference is not large enough to affect the 

 calculation here given. 



