26 INTRODUCTION. 



Fahrenheit thermometer. The inventor of the latter instru- 

 ment, Fahrenheit, commenced counting not from the freezing- 

 point, but 32 below it, which causes the freezing-point to be at 

 32, the boiling-point at 180 above it, or at 212. (Fig. 3.) 



Specific heat. Equal weights of different substances require 

 different quantities of heat to raise them to the same tempera- 

 ture. For instance : The same quantity of heat which is suf- 

 ficient to raise one pound of water from 60 to 70, will raise 

 the temperature of one pound of olive oil from 60 to 80, or 

 two pounds of olive oil from 60 to 70. Olive oil consequently 

 requires only one-half of the heat necessary to raise an equal 

 weight of water the same number of degrees. Specific heat is 

 therefore the heat required to raise a certain weight of a sub- 

 stance a certain number of degrees, compared with the heat 

 required to raise an equal weight of water the same number of 

 degrees. 



The heat required to raise one pound of water one degree 

 centigrade, is usually taken as the unit of comparison. On 

 thus comparing olive oil, we find its specific heat to be J. If 

 we say the specific heat of mercury is ^, we indicate that equal 

 quantities of heat will be required to raise one pound of water 

 or 32 pounds of mercury one degree centigrade, or that the heat 

 which raises one pound of water one degree will raise one pound 

 of mercury 32. 



QUESTIONS. 



11. What two kinds of divisibility of matter do we distinguish, and 

 by what actions are they accomplished ? 



12. Explain the term molecule. 



13. Mention one of the facts which prove that a gas consists of parti- 

 cles with intervals between them. 



14. State the Law of Avogadro. 



15. Mention the effects produced by increased velocity of the mole- 

 cules of a mass. 



16. Give an explanation of the expressions latent heat, free heat, 

 and specific heat. 



17. Explain the construction of a mercury thermometer. 



18. How many degrees of Fahrenheit are equal to 50 C. ? 



19. How many degrees of centigrade are equal to 167 F. ? 



20. What is distillation, and what is sublimation ? 



