THE NECESSITY FOR PURE AIR 87 



amount of carbon dioxide is no more than eight or ten 

 parts in ten thousand. Now 400 is 50 times 8. This 

 means that one breath spoils 50 times that amount of air, 

 not only for others but even for ourselves. For this 

 reason it is very necssary to have a large supply of fresh 

 air. If there are lights burning in the room, such as 

 kerosene lamps or gas, much more air is needed. An 

 ordinary light spoils as much air as four persons in the 

 same time. Electric light does not affect the air. 



Review Questions, 18. 



1. Why does pouring hot water into a glass dish 

 break it? Would there be any difference if the glass 

 were thin? 



2. What is the result of incomplete combustion? 

 Why is it not wise to allow incomplete combustion? 



3. Why should a person not run if his clothing is on 

 fire? What should he do if he is alone? 



4. What kind of clothing is most liable to burn? 



5. What is the composition of the air? 



6. What would happen if there were no nitrogen? 



7. How does carbon dioxide get into the air? 



8. At the ordinary rate of breathing, how much air 

 will twenty pupils breathe in half an hour? How much 

 air will they spoil in the same time? 



9. Find the number of cubic inches of air in your 

 schoolroom and tell how many times it must be changed 

 in every half hour in order to give you enough fresh air, 

 if you were the only person in the room. 



10. Solve Problem 9 for the number of persons in 

 your room. 



