HEALTH AND FOOD STANDARDS 91 



128. Units of energy. To measure the energy expended by 

 the body, or to measure anything else, we must have a unit. 

 We measure length in inches or yards or miles. In a similar 

 manner we are able to measure energy by work done. But as 

 different forms of energy do different kinds of work, it is 

 necessary to find some common unit for measuring. For 

 example, motion can be measured by the quantity of matter 

 moved and the distance through which it is moved, as one 

 ton raised five inches, three pounds raised two feet. The unit 

 of measuring this kind of work may be the foot pound, or the 

 amount of energy it takes to raise one pound of matter one foot. 



If a pint of water at room temperature (about 18 C., or about 

 65 F.) is placed in a pan over a burner, it will gradually be- 

 come warmer, until it reaches the boiling point. It takes a cer- 

 tain quantity of heat to change the temperature of the water 

 from 65 to 212 (the boiling temperature of water). For a 

 quart of water it would take twice as much heat to do the 

 required work. As a unit of heat energy we might use, for 

 example, the pint degree. The unit adopted among engineers 

 is the quantity of heat necessary to raise one kilogram of water 

 (a little more than a quart) from the temperature of o to the 

 temperature of i C. This unit is called a calorie. 



In dealing with fuel or the conversion of fuel energy into other 

 forms, it is customary to record energy in terms of calories. In deal- 

 ing with mechanical work it is customary to record energy in terms of 

 foot pounds, or horse-power hours. 1 



1 The fuel values of proteins, fats, and carbohydrates are as follows : 



From these figures it will be seen that a given quantity of fat contains more 

 than twice as much latent energy as the same quantity of protein or carbohy- 

 drate, and that the latter two classes of compounds have the same fuel value. 



