PROBLEM I . Hoiv to Choose Foods Wisely 



169 



Fig. 190 What was the original source of the 

 egg eaten by the skunk, and the ?nilk lapped up 

 by the cat? What is the source of all the food 

 eaten by animals? (johnson, Schneider and 



SCHWARTZ, GEHR) 



To measure anything there must be 

 a unit of measurement. Scientists have 

 agreed on a i^mit for heat energy. They 

 call it a 4^alo£ie[^ (k;al'-(>r5€TnT"'ir'the 

 amomi t^ of J ^p-^r rpqjiir ed to r aise the 

 temperature__jif_mTe kilogramTa"' little 

 FeUian one quart) of water one de- 



g ree c entigiadj&>--Thus jtJa£x:i^TTes_^ 

 to measure the am^mnt-o f heat by meas- 

 urin^g^'^with a thermometer the rise in 

 temT 

 tei 



ire o f pure water. When the 



risen 7 ° C, we say 7 Calories of h eat en- 

 ergy liad been addgd^-If you can do Ex- 

 ercise 2, you understand something 

 about the measurement of heat. 



Measuring the energy in food. To find 

 out how much heat is produced when a 

 food compound is oxidized, some of the 

 pure substance is weighed so that the 

 experimenter knows exactly how much 

 is going to be burned. The substance is 

 then placed inside a chamber in which 

 it can be oxidized. This chamber is sur- 

 rounded by a jacket containing pure 

 water which catches every bit of heat 

 produced. The outside of the jacket is 

 covered with asbestos or some other ma- 

 terial that prevents escape of heat. The 

 temperature of the water is taken before 

 and after the oxidation. The amount of 

 water in the jacket is known. And, since 

 the experimenter knows how much the 

 temperature of this water rises, it is easy 

 to determine how many Calories were 

 produced by the burning (oxidation) of 

 that amount of food. In this way scien- 

 tists have determined the amount of heat 

 energy to be obtained from a known 

 amount of protein, carbohydrate, and 

 fat. The apparatus used is called a calo- 

 rimeter (cal'o-rim'e-ter). 



Besides burning known amounts of 

 pure proteins, carbohydrates, and fats, 

 scientists have also tested most of the 

 common foods for their energy value. 

 For example, a thick slice of white bread 

 may be burned. If the thermometer 

 shows that the temperature of 1 1 kilo- 



