Fire and Heat 69 



the aid of the facts illustrated experimentally, explain draft in a 

 chimney. 18. How is draft controlled in heating appliances? De- 

 scribe a modern range and show location and purpose of dampers and 

 other devices for control of draft. 19. Why does a fire smoke some- 

 times when first started in a range or stove? 20. Mention several 

 conditions in which forced draft is necessary. 21. By what means 

 may it be secured? 



22. Is there any known energy which is not derived from the sun? 

 Explain. 23. How can the heat from coal or wood be the stored-up 

 energy derived from the sun? 24. Give an idea of the amount of 

 heat that the earth receives from the sun. 25. What is the importance 

 to us of this received solar energy? 26. By what devices have men 

 sought to utilize directly the sun's energy? 



SUGGESTIVE QUESTIONS 



1. How could you make a fire in the forest without paper and 

 matches? 2. What is the most effective fuel, taking into considera- 

 tion cost, cleanliness, and convenience? 3. A fireplace smokes badly 

 whenever the fire is burning. How would you remedy it ? 4. What 

 important factor in the climate is typified by the draft in a chimney? 

 5. How could you make direct use of the sun's heat in warming water 

 for the household? 6. Mention several industries in which heat from 

 fuel is indispensable. 7. Mention several uses of the sun's heat 

 energy made directly by us in our daily life. 8. Have you read of 

 any people who did not know of fire or make use of it? What prog- 

 ress had such a people made in the arts and crafts of civilization ? 



II. WHY FIRE BURNS 



33. Early theories. Although great advance had been 

 made in the use of fire for heating and lighting, and in the 

 industries and arts, there was practically no understanding 

 of the conditions, process, and products of combustion, before 

 the latter part of the eighteenth century. It had been gen- 

 erally imagined that when anything burns, such as wood or a 

 candle, some substance escapes. This substance was supposed 

 to resemble the air or be " ethereal," and it was named by the 

 scientists of that age " phlogiston." No further knowledge 

 of what makes a fire burn and what happens in burning was 



