124 HOW WE USE HEAT 



IX. Silk fiber: (41) is of animal origin; (42) has a more 

 brilliant luster than any other fiber except rayon; (43) has little 

 scales projecting from its surfaces; (44) is composed of cellulose; 

 (45) is stronger than artificial silk when both are wet. 



X. In washing woolens it is well to use : (46) boiling water ; 

 (47) soap containing free alkali ; (48) little soap but much washing 

 soda; (49) water below boiling point; (50) a small amount of 

 bleaching powder. 



THOUGHT QUESTIONS 



1. Make a list of materials which have a low kindling temper- 

 ature; a high kindling temperature. Which of these would be 

 best to build a fire with? 



2. Find ten ways in which heat insulators are used in your home. 



3. Why is the outside of a teakettle kept bright and smooth 

 while the bottom is dull, black, and rough? 



4. Why does a bicycle tire register greater pressure on a hot 

 day than on a cold day? 



5. Why is it when you fill the radiator of your car full to the 

 brim on a cold day that it begins to run over shortly after you start 

 the car? 



6. You are going to Duluth for your Christmas vacation. 

 What clothes would you take with you, and why? 



7. You are driving from New York City to Florida in March. 

 What clothes would you wear on the trip? Give your reasons. 



REPORTS ON THINGS I HAVE READ, 

 DONE, OR SEEN 



1. Report upon an article related to some topic discussed in 

 this unit. The article may be from a current number of a science 

 magazine or from some popular science book you have read. 



2. Everyday activities involving expansion. 



3. An account of the work of Bunsen or of Fahrenheit which 

 is related to heat. 



4. Uses of heat insulators. 



5. How man's activities and habits vary at different latitudes 

 on the earth. 



SCIENCE RECREATION 



1. Pressure of ice. Fill a small bottle with water. Put a 

 cork in tightly. Be sure there is no air space left inside. Put 

 this either in the ice-cube pan and put into the cooling coil of the 

 refrigerator, or place it outdoors on a day when the temperature 



