140 Introduction to the Study of Science 



ing water gas. Of what two gases is it a mixture ? For what purposes 

 is it used ? 



15. Mention physical changes which take place in the burning 

 candle ; mention chemical changes. 16. What two material products 

 and what two effects do we get from a burning candle? From any 

 fire made of common fuels as wood, coal, gas? 17. Is water obtained 

 from the candle or from the burning of the candle? 18. Distinguish 

 between mixture and compound substances, giving examples of each. 

 19. Mention four common compounds containing hydrogen. 



20. What is smoke? Give at least two reasons why it should be 

 prevented. 21. What are the conditions that favor complete com- 

 bustion of fuel ? 22. What uses are made of lampHack ? Of graphite ? 

 23. How can it b? shown that the diamond is pure carbon? 24. Under 

 what conditions does carbon crystallize to diamond? 



25. How and from what material is charcoal obtained? Coke? 

 26. Mention several common foods that contain carbohydrates. 



27. Give three sources of the carbon dioxid in the air. 28. What 

 substance is purchased for the carbon dioxid it produces and gives 

 up when wet and warm? 29. How does the air that enters the lungs 

 differ from the air which is expelled from the lungs? How can you 

 show this difference? 30. What use is made of the fact that carbon 

 dioxid is soluble in water? That it will not. support combustion? 



31. Why does the percentage of carbon dioxid in the air not increase? 



32. From what source was derived the material which makes our coal 

 seams? By what agency were they formed? 



SUGGESTIVE QUESTIONS 



1. How can you show that expired air contains the same substances 

 as are produced in the burning of a candle, of wood, and coal? 2. De- 

 scribe the changes that occur in burning wood or coal, and state the 

 conditions that bring them about. 3. Explain the difference between 

 rusting, as of metal, and burning, as of oil, coal, or wood. What is 

 the difference between these processes and the use and assimilation of 

 foods in the animal organism? 4. Of what use is nitrogen in the air? 

 In the soil ? In such food substances as beans, meats, etc. ? 5. What 

 reasons can you give to support the statement that the supply of nitro- 

 gen in the air is inexhaustible ? 6. Show in what ways carbon dioxid 

 is essential to human life. 7. With the enormous consumption of 

 carbon dioxid by plants, why is the supply in the air not greatly 

 reduced? 8. Give a suitable name to the white powder formed by 

 the burning of tin. 



