118 GENERAL SCIENCE 



making a tight joint whether the bulb is hot or cold, thus allowing no 

 air to reach the filament. An alloy of iron and molybdenum is also used. 

 Examine the place where the wires pass through the glass of an 

 electric light bulb. 



QUESTIONS 



. 1. How much does the air expand in your room when the tem- 

 perature is raised from freezing point to normal temperature? 



2. Why does the thermometer drop when first placed in hot 

 water ? 



3. Why do pipes burst when freezing? 



4. Why do people say pipes burst when they " thaw " out? 



5. Why do fish migrate into deep water during warm weather? 



6. If a tank containing 1000 gallons of water were heated from 

 freezing point to boiling, how many gallons of water would there be 

 in the tank? 



7. Was any money saved by the man who kept his gas meter 10 

 cooler than the surrounding atmosphere by placing over the meter 

 a wet cloth extending from a tub of water? 



8. Why do pipes snap and crackle when the steam is first turned 

 on? 



9. What are expansion joints? Why are they used on steam 

 and hot-water pipes? 



10. Why do little bubbles of air collect on the inside of a glass 

 of water standing in a warm room? j 



11. Why are eggs which are to be used in an angel cake beaten 

 in a cold place? 



12. Why do thick glass tumblers break when hot water is poured 

 into them? 



13. Why do thin glasses seldom break? 



14. Why does not the filling of our teeth fall out when we eat 

 ice cream? 



15. Why does the dentist use a composition of silver, mercury, 

 tin, etc., for so-called silver filling? 



16. Why does paper or bread curl up when heated on one side? 



17. Why does popcorn pop? 



18. Why will it pop better if placed in a cold damp place in the 



