PHYSICAL STATES OF MATTER 65 



68. Exercises. 



1. When the glass stopper of a bottle "sticks," we can often loosen 

 it by heating the neck of the bottle. Why? 



2. If you heat water in a thick glass bottle over a flame, the bottle 

 usually breaks, while a thin glass flask does not. Why? 



3. Why do telephone wires sag in summer and become taut in winter? 



4. Alcohol boils at 78 C.; what temperature is this on the Fahren- 

 heit scale? The room temperature is 70 F. ; what is this on the 

 Centigrade scale? 



5. How could you make an air thermometer, that is, one using the 

 expansion of air instead of that of mercury? 



6. Which feels colder in a room, oilcloth or carpet? Wood or 

 metal? Is there any real difference of temperature? Explain. 



7. Why can ice cream be carried in a paper box through heated air, 

 and yet not melt? Would a tin box be better? 



8. Which feels hotter, the handle of a silver spoon, or that of an 

 iron spoon, if the bowl of each is in boiling water? Why? 



9. Why does air enter a stove at the bottom, and go out at the top? 



10. Where should steam pipes be put to heat a room? Where 

 should pipes of cold water be placed in a cold storage room in order to 

 cool the room? 



11. Why are houses built with double walls having air spaces be- 

 tween them? 



12. How is a "fireless cooker" made? Why is the heat not given 

 off? How is it like a Thermos bottle (cf. 57)? 



69. Physical States of Matter; Solids. If we believe 

 that matter is broken up into molecules ( 61), we can 

 understand the differences between solids, liquids, and 

 gases, the three physical states, or forms, of matter. The 

 two causes at work upon the molecules are cohesion and 

 heat. Cohesion represents the attraction of the molecules 

 for one another; heat is the energy of the molecules. 

 Cohesion draws the molecules together; heat causes them 

 to fly apart. 



