RESPIRATION. 



51 



III. CARBON DIOXIDE IN EXPIRED AIR. 



a. Breathe through a tube into a glass of lime-water. 



b. What occurs ? Explain and write the reaction. 



c. What occurs when hydrochloric acid is added ? 



d. What does this prove? 



IV. TEST THE AIR OF AN ORDINARY ROOM FOR CAR- 



BON DIOXIDE. 



Use a bottle with a rubber stopper 

 fitted with two pieces of glass tubing, 

 each bent at a right angle. One piece 

 of the tubing should reach nearly to 

 the bottom of the bottle, the other just 

 below the stopper. (See Fig. 6.) 



a. Fill the bottle half full with lime- 

 water. 



b. Draw the air out of the bottle 

 through the short tubing. 



c. What happens? Why? 



FlG. 6. Apparatus for 

 testing ail- for car- 

 bon dioxide. 



C. Experiments on the Student's Body. 

 Apparatus. A watch. A tape-measure. 



I. THE NUMBER OF RESPIRATIONS. 



Count the number of respirations in a minute under 

 ordinary conditions. Count the number after running. 



II. THE SIZE OF THE CHEST DURING RESPIRATION. 



Measure the chest by passing a tape across the chest 

 and around just under the arms to the middle of the back. 



