Minor Constituents of Air 249 



of fish be kept in a limited quantity of water, they soon 

 die, since they quickly remove the dissolved oxygen and 

 the water becomes too foul for their continued existence 

 to be feasible, just as a closed room in which a number 

 of people are living becomes unfit for habitation unless 

 some method of supplying fresh air be adopted. 



QUESTIONS 







1. Suggest a method of determining roughly the percentage 

 volume of carbon dioxide in respired air. 



2. The air of a deep well or mine is sometimes tested before 

 men go down by lowering a lighted candle at the end of a rope. What 

 information concerning the state of the air is obtained by this 

 means ? 



3. How would you try to show that the air of a living-room 

 contained a larger proportion of carbon dioxide than the outside air ? 



4. The density of carbon dioxide is If times ; and that of nitrogen 

 |> that of oxygen. Explain why the atmosphere is not composed 

 of a layer of carbon dioxide near the Earth's surface, with con- 

 secutive layers of oxygen and nitrogen above. 



5. Give an account of the part played by each of the various 

 constituents of the air in plant and animal life. 



6. Describe a process of estimating the proportion of oxygen 

 in a sample of air which neither involves the direct oxidation of iron 

 nor of phosphorus. 



7. Name the five principal constituents of ordinary air, and 

 describe experiments by means of which the presence of any two 

 of them in air may be shown. 



8. How can the presence of water-vapour in the air be accounted 

 for? 



9. What do you understand by the statement that iron is an 

 element ? Classify the following bodies as elements or compounds : 

 tin, water, chalk, nitrogen, argon, iron rust. 



10. The specific gravity of nitrogen is that of oxygen. Using 

 the percentage volumes given in Chapter xin, find the percentage 

 weights of nitrogen and oxygen in air. 



