170 GENERAL SCIENCE 



With hard coal, coke, and charcoal, as well as with wood or soft 

 coal, after the flame has burned out no air should be admitted over 

 the fire. 



In most cooking ranges, and in some heating stoves and furnaces, 

 there is a damper which permits smoke from the firebox to pass 

 directly to the chimney without passing through the heating flues. 

 One should learn how such a damper operates and keep it closed, 

 except possibly when first starting up the fire. Opening this damper 

 will often make the fire burn more briskly, but most of the extra heat 

 thus produced is usually lost up the chimney. In summer, however, 

 when extra heat is not desired, this damper may be left open to allow 

 heat to escape up the chimney. 



QUESTIONS 



1. Why is water gas more dangerous to use than coal gas or 

 " city gas "? 



2. How many tons of coal are required to heat your home? 



3. How many Btu. are given off? 



4. What is the cost per million Btu.? 



5. How many cubic feet of gas would be required to obtain 

 the same number of Btu.? 



6. What would be the difference in cost in heating your home 

 with gas as compared with coal? 



7. Find the price of wood in your town, and compute the cost of 

 heating your home with wood? 



NOTE. In all cases of fuels, use the selling price as you find it in your locality. 



8. Why should great care be taken to regulate the drafts of a 

 coal fire? 



9. Why does a blue flame appear over a coal fire when the stove 

 door is opened? 



10. How may heat be saved during cooking processes? 



11. Why should the gas be turned down low after water is 

 boiling? 



12. Why is heat lost if water boils violently and steam escapes 

 around the cover? 



