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AIR 



31. Nitrogen and its Uses. 



As we have learned, about four-fifth of the air is 

 nitrogen. We saw that it was oxygen which supported 

 combustion and that pure oxygen supported combustion 

 much more vigorously than air, because air is only one- 

 fifth oxygen. What do you 'think the effect would be 

 upon fires if all of the air were oxygen? One of the uses 

 of nitrogen, then, is to lessen the effect of oxygen. Where 

 the amount of one substance is reduced by the addition 

 of another we say that the first substance is diluted, and 

 call the process dilution. Nitrogen dilutes the oxygen. 

 Pure oxygen is sometimes inhaled, under the advice of a 

 doctor, by those who have weak lungs. 



For a long time it was thought that nitrogen had no 

 other use than to dilute the oxygen. Now it is known 

 that tiny plants, so small that they are invisible, called 

 bacteria, live upon the roots of some of the larger plants 

 and absorb the nitrogen from the air. This they change 

 into material which is needed by the larger plants. This 

 is one example of the good which bacteria do for us. 

 Later we shall learn that they help us in many ways. 



