xxi CARBON AND SOME OF ITS COMPOUNDS 207 



QUESTIONS ON CHAPTER XXI. 



1. Give an account of the different modifications of carbon. How- 

 may it be proved that they all really consist of the same substance ? 



2. What compounds of carbon and oxygen exist ? How may they 

 be obtained, and how may they be mutually converted into one 

 another ? 



3. When carbon dioxide is passed into lime water, the latter 

 becomes first turbid and afterwards clear. Explain the chemical 

 nature of the causes of these changes. 



4. Give a brief account of the part played by carbon dioxide in 

 the economy of nature. 



5. Explain the cause of the blue flames which are frequently seen 

 playing at the top of a coke or charcoal fire. 



6. If a gas containing a mixture of the two oxides of carbon were 

 given you, how could you determine the quantity of each present ? 



7. Describe three experiments to show the high density of carbon 

 dioxide, its effect on combustion, and its action on lime-water. 



8. By what means would you prove the presence of carbon dioxide 

 in atmospheric air and expired air ? 



9. If carbon dioxide be passed over heated iron filings what other 

 product is formed ? How would you collect it, and in what 

 particulars does it differ from carbon dioxide ? 



10. What is the chemical nature of chalk and lime ? How could 

 you obtain lime from chalk and vice versa ? 



11. Describe an experiment to determine the quantity of carbon 

 dioxide which is evolved by the action of acid upon one gram of 

 chalk. 



12. What is marsh gas ? Why is it so called ? What are its 

 properties ? 



13. What is (a) "fire-damp," (6) "after-damp"? What are the 

 dangers due to the presence of much fire-damp in mines ? 



14. By what tests would you ascertain whether effervescence 

 caused by pouring sulphuric acid on a powder was due to the escape 

 of carbon dioxide, sulphur dioxide, hydrochloric acid gas, or 

 hydrogen ? 



15. What is the meaning of hard and soft water ? How would you 

 test to see whether a water is hard or soft ? 



16. Why are some waters "permanently" hard, and others only 

 temporarily so ? Explain clearly what is meant by these expressions. 



17. Rain water is soft, but spring water is generally hard. By 

 what process has the soft rain water, after falling, become hard before 

 issuing as a spring ? 



18. What does coal gas consist of ? What products are formed 

 by its combustion, and how would you endeavour to experimentally 

 prove your answer ? 



19. Describe the apparatus you would use for the production and 

 collection of carbon dioxide gas ; name the materials required, and 

 describe the properties of the gas. 



20. Charcoal burnt in air or oxygen in a bottle containing lime- 

 water produces a white orecipitate in the lime water. The white 



