HEAT AND EXPANSION 111 



ing plants, described in Chapter VIII, where ice is manufac- 

 tured by means of the expansion of ammonia which is the 

 most economical gas to liquefy. 



Questions 



1. When is a body hot? 



2. When metals begin to melt, they liquefy at once. Why? 



3. Why is ice packed in sawdust? 



4. Why does a draft extinguish a flame? 



5. Which will heat more quickly, rough or polished surfaces? 



6. Why does sprinkling a shop floor cool the air? 



7. Why are steam cylinders polished on the inside? 



8. Why are glass tumblers broken by pouring hot water into 

 them? 



9. What is the basis of all cooling mixtures? 



10. Explain why so much energy is lost in steam engines. 



11. Is temperature a measure of the amount of heat in a body? 



12. Explain why railroad engines have a polished sheet iron 

 jacket around the cylinder and boiler. 



13. What becomes of the cloud which forms about a blowing 

 locomotive whistle? 



14. Why are expansion joints added to long lines of steam pipes? 



15. Place a ball through a ring, then heat the ball in an alcohol 

 or Bunsen flame and try to pull it back through the ring. 



16. Why do mechanics who work in a warm room wear flannel 

 shirts to keep cool in the summer and warm in the winter? 



17. Why is felt a better conductor of heat when firmly packed 

 than when loosely packed? 



18. Ducts and pipes are frequently covered with felt or asbestos. 

 Why? 



Problems 



1. Change the following Fahrenheit readings to Centigrade 

 readings: 56; 75; 5; 0; -23; 45; 54. 



2. Change the following Centigrade readings to Fahrenheit 

 readings: 0; 68; 44; -17. 



