SOURCES OF CARBON DIOXIDE 



83 



you finally see any change? 



d. Now repeat (b.) and (c.), counting the number 

 of times it is necessary to squeeze the bulb in order to 

 obtain the same result. Divide the number of times it 

 takes indoors by the number of times required out of 

 doors. The result will show about how much more car- 

 bon dioxide there is indoors than out of doors. If the 

 room is properly ventilated there should be little differ- 

 ence. Is the schoolroom properly ventilated? 



