RESPIRATION AND EXCRETION 297 



Method b. Breathe on the bulb of a thermometer. 



1. What are your observations ? Conclusions ? 



Method c. Breathe through a glass tube into a test tube 

 half filled with lime water. 



What takes place ? Conclusion ? 



Method d. Place a small lighted candle in a bottle, and 

 after the flame has gone out, insert a flaming splint. 



What takes place ? 



Observation. Pour into the bottle two or three tablespoon- 

 fuls of lime water, and shake it. 



What is the result ? 



Conclusions. 1. What was formed by the burning candle ? 



2. Will this gas support combustion ? 



Review note. Carbon dioxide is produced by the union of 

 oxygen of the air with carbon which may be either in candles, 

 wood, coal, or the fats and carbohydrates stored in your body 

 or in foods. 



3. What goes on in your body, as indicated by the last two 

 tests ? 



Method e. Hold a tin cup half filled with cold water over a 

 small burning candle so as not to interfere with the flame arid 

 not so near as to heat the cup. What do you observe ? 



Conclusions. 1. What is another of the results of oxidation 

 of a candle ? 



2. What similar process goes on in your body ? 



3. Which is the more intense, the heat of oxidation of 

 the candle, or the heat of oxidation of the body ? In which 

 case is oxidation the more rapid ? Which requires the greater 

 supply of oxygen ? 



4. What is the purpose of a draft in a stove or furnace ? 

 How is the oxygen supplied for oxidation in the body ? 

 Where does the carbon come from ? 



b. Air in Room 



Method. Fill a large bottle with water, and take it into a 

 room containing many people. Pour out the water. What is 



