124 CHEMISTRY OF RESPIRATION. 



sure of the outside air pushes water up into the jar to take 

 the place of the oxygen that has been removed. The clear 

 gas left when the cloud disappears is nitrogen. What part 

 of the jar is occupied by the nitrogen ? What part of the air 

 is oxygen ? Of course this experiment will not show these 

 proportions very accurately. 



EXPERIMENT 2. After the gas remaining in the jar has 

 become clear, carefully lift the plate and jar, and lower them 

 into a pail of water until the mouth of the jar is well under 

 the water. Hold the jar with one hand, and let the plate and 

 lead sink. Slip the palm of the hand over the mouth of the 

 jar, and invert the jar and set it on the table, keeping the 

 hand firmly over the mouth of the jar. Slowly lower a lighted 

 taper into the jar. The flame is extinguished. Quickly cover 

 the jar and repeat the experiment. The nitrogen does not 

 support combustion. If an animal were put into a jar of 

 nitrogen, it would soon die ; not because the nitrogen injures 

 it in any way, but simply because nitrogen does not support 

 respiration. 



Nitrogen makes up four-fifths of the air and oxygen one- 

 fifth. 



EXPERIMENT 3. Into a jar of oxygen lower a splinter 

 with a live coal at the end (left after blowing out the flame). 

 The coal is kindled into flame. This shows the chief prop- 

 erty of oxygen ; that is, its power of supporting combustion. 



EXPERIMENT 4. Into a jar of carbon dioxid lower a 

 lighted taper. It is at once extinguished. 



Carbon dioxid may easily be generated by such means as 

 are at hand in every kitchen. Baking-powder liberates carbon 

 dioxid freely when water is added to it. Put some baking- 

 powder into a tumbler, and pour water upon it. The carbon 

 dioxid may be poured into another tumbler and tested. Better 

 put the baking-powder into a bottle, or Florence flask, fitted 



