Fire and Heat 111 



SUMMARY 



Three ways of transferring heat energy are conduction, convection, 

 and radiation. 



A conductor of heat is a substance which readily transmits heat 

 from one part of itself to another. 



Metals are the best conductors, liquids are poor, and gases poorest. 



The warmth of clothing depends mainly on the inclosed air spaces. 



Convection, or the conveying of heat by the movement of the hot 

 body, is illustrated by the rising of hot air from the stove and the 

 movement of heated water in a hot-water system. 



A given weight of water absorbs or gives out more heat for a change 

 of one degree in temperature than any other common substance. 



Water is taken as the standard for heat capacity. 



The winds are convection currents. 



A knowledge of convection is useful in controlling ventilation. 



Radiant energy from the sun comes to us through cold space. 



Good absorbers are generally good radiators. 



REVIEW QUESTIONS 



1. In how many ways is heat transferred? 2. What is the neces- 

 sary condition of heat transfer by conduction? 3. Give the expla- 

 nation of the process of conduction. 4. How would you show the 

 different conductivities of familiar metals? 5. How would you 

 prove that water is a poor conductor? 6. What are the best known 

 conductors?. 7. To what class of substances do they belong? 

 8. What is the best known conductor? 9. What is the poorest 

 conductor named in the list? 10. Give reasons to show that liquids 

 and gases are not heated entirely by conduction. 11. What use is 

 made of our knowledge of the heat conductivity of materials used for 

 clothing? 12. Explain why woolens, fur, feathers, and eiderdown 

 are poor conductors. 13. What use is made of the knowledge of 

 conductivity of different substances in the construction of buildings ? 

 14. Give examples of the use of poor conducting materials in retaining 

 heat or cold in cooking or preserving food. 15. Why do some sub- 

 stances, like wool, feel warm and others, like marble, feel cold to the 

 touch ? 



16. Explain why air when warmed by the heat from a stove moves 

 away from the heat source to other parts of the room. 17. How can 

 you show such circulation of heated air? 18. What use is made of 

 the transfer of heat by air? 19. Trace the course of air from cold- 

 air box to furnace, and thence to rooms and its circulation in a room. 



