Transportation on Land 315 



Boiling temperature varies with the pressure. 



The heat (972 B. T. U. per Ib.) which disappears when water is 

 converted into steam is the latent heat of steam. It reappears when 

 the steam condenses. 



The same disappearance and reappearance of heat occur in evap- 

 oration and condensation in nature. 



The steam engine depends on the relative volumes of equal weights 

 of steam and water, and on the ability of steam to expand. 



The heat energy of steam is used in part in the simple steam en- 

 gine, but more fully in multiple expansion engines. 



Distillation depends on the difference in the boiling temperatures 

 of substances. 



REVIEW QUESTIONS 



1. Mention several uses of steam. 2. Explain the singing of a 

 teakettle.. 3. What important facts are to be observed in the boiling 

 of water? 4. Is steam visible? Why? 5. How does the temperature 

 of steam compare with that of boiling water ? 6. Does the application 

 of a hotter flame to the boiling water increase its temperature or its 

 rate of boiling? 7. How can you demonstrate that the boiling tem- 

 perature of water rises with increase in pressure? 8. How can you 

 demonstrate that the boiling temperature of water falls with decrease 

 in pressure? 9. What are some of the practical uses made of the 

 change in boiling temperature due to change in pressure? 



10. Which has the greater heating effect, steam or water, at the 

 same temperature? How could you prove your answer? 11. What 

 is meant by heat of liquid ? 12. Heat energy that enters a body and 

 produces no rise in temperature is called by what name? 13. The 

 heat which disappears when water boils is used in performing what 

 tasks among the water particles? 14. Distinguish between evap- 

 oration and boiling by mentioning two points of similarity and two 

 of difference. 15. Explain the influence upon the weather of conden- 

 sation and evaporation. 



16. Steam heating of buildings depends upon evaporation and 

 condensation. Explain. 17. How much heat is required to warm 

 a pound of water from the freezing to the boiling point? 18. How 

 much to vaporize it? 19. How much heat is given out by the con- 

 densation of the pound of steam? 20. How much is given out in 

 the cooling of the pound of water to freezing point? 



21. Compare the volume of a pound of water with the volume of 

 the 'same weight of steam. 22. Why does the pressure increase in a 



