134 ELEMENTARY SCIENCE 



By the same means we can test substances of equal tem- 

 perature to determine which contains more actual heat 

 than the other. Thus if equal amounts of iron and lead 

 be tested at equal temperatures it will be found that the 

 iron gives off over three times as much heat as the lead; 

 that is, the specific heat of iron is three times as great as 

 that of lead. 



Calorimeter tests are especially important in determining 

 relative values of fuel, especially of different kinds of coal. 

 They are also important in determining the "fuel-value" 

 to the body of various kinds of heat-producing foods. But 

 such tests as these require a more complicated apparatus 

 than the one described. They require that the substance 

 to be tested be actually burned under water. This is 

 done in a closed vessel by means of electricity and com- 

 pressed oxygen. The heat which they impart to the 

 water is then computed. Of course this is very delicate 

 work, since it is absolutely necessary that all foreign 

 sources of heat gain or loss be either eliminated or else 

 known so accurately that they can be allowed for in the 

 computations. 



QUESTIONS 



1. Explain the principle of the thermometer. 



2. How are thermometers made? 



3. What is the Difference between Centigrade and Fahrenheit ther- 



mometers ? 



4. What kind of thermometer is used on arctic expeditions, and 



why? 



5. Explain Galileo's thermometer. 



6. What is the calory? 



7. What is "specific heat"? 



8. Describe the calorimetw. 



