QUANTITY AND TRANSMISSION OF HEAT 147 



10. Why do small bubbles rise in a vessel of water that is being 

 heated long before the boiling point is reached? 



11. Why is scalding by steam more serious than scalding by 

 water at the same temperature? 



12. How do freezing and thawing break up rocks? 



13. If 10 grams of steam at 100 are mixed with 80 grams of 

 water at 0, what will be the resulting temperature ? 



14. Why are stove irons commonly made with wooden handles ? 



15. Why do we wrap ice in blankets to keep it from melting? 



16. Why is woolen cloth warmer than linen? 



17. How may we prove that air goes up over a hot stove? 



18. What is the principle involved in the fireless cooker? 



19. Why is the air inside a hothouse warmer than the air out- 

 side, even if it is not heated artificially? 



20. How may we prove that radiant heat and light travel at 

 the same speed? 



2 1 . Why is there no loss of heat by convection in a thermos bottle? 



Heating and Ventilating of Buildings. All three modes 

 of heat transference are used in the heating and ventilating 

 of our homes and other 

 buildings, but convection 

 is by far the most impor- 

 tant principle involved. 

 Hot-air and hot-water 

 systems are both appli- 

 cations of this principle. 



Hot-air Heating. This 

 system is in quite com- 

 mon use in small build- 

 ings. It consists of a 

 furnace which heats the 

 air in a chamber (Figure 

 127) surrounding the fire 

 box. As the air is heated, convection currents are 

 produced in the pipes leading to the different rooms 



FIG. 127. 

 Diagram of a Hot-air Heating System. 



