36 Our Surroundings 



measuring the height to which the water rises in the jar the pro- 

 portion of oxygen that was in the air in the jar may easily be 

 discovered. 



Nitrogen. One important property of nitrogen is its inac- 

 tivity. It does not readily unite chemically with other elements. 

 Like oxygen, it is colorless, tasteless and odorless. Nitrogen is 

 especially useful in the air in diluting or diminishing the power 

 of oxygen to burn other substances. The nitrogen in air serves 

 the same purpose as water does when it is mixed with lemon 

 juice to lessen the sour taste. If air were pure oxygen it would 

 be so active and so powerful that it would destroy all animal and 

 plant life. A fire once started would rapidly oxidize all material 

 with which it came in contact, for even such material as iron 

 will burn in pure oxygen. 



All living things need nitrogen for making the tissue of which 

 their bodies are formed, but most of them are not able to use it 

 as found in the air. It must first be united chemically with other 

 substances. Certain microscopic forms of plant life, called bac- 

 teria, have the ability to take nitrogen from the air and to change 

 it into a form that when in solution the roots of plants can absorb. 

 The plants then make it into a food substance, called protein, 

 which is essential to all living things. 



Carbon Dioxide. As a separate gas, carbon dioxide is heavier 

 than air and therefore tends to settle into its lower layers. It is 

 so heavy that it can be poured from one container to another like 

 water. It will not burn and nothing will burn in it. On this 

 account it is used in fire extinguishers. It sometimes settles in 

 the bottom of wells, mines, or low, unventilated cellars. As 

 one cannot live long breathing carbon dioxide alone, it is dangerous 

 to enter any place where large quantities of it have collected. Its 

 presence may be detected by putting a small pail of lime water 

 into the space where the gas is supposed to be. If it is there, 

 the lime water will assume a milky appearance. A lighted lantern 

 is sometimes used for the same purpose. If present, the gas will 

 cause the light to go out. 



Water Vapor. Water vapor or moisture is usually present 

 in air. Its presence may be detected by placing a pitcher of cold 



