THE ATMOSPHERE 



85 



the corpuscles of the blood. The purpose of respiration 

 is to oxidize the materials of the body that are constantly 

 wearing out into a form of waste that may be removed 

 from the body more readily. 



The results of oxidation in the body are : energy, which 

 is created in the form of heat ; carbon dioxide, formed as 

 a result of the union of the carbon in the waste products 

 with oxygen ; and waste matter, in forms which may 

 be easily 'disposed of. Part of the heat energy is used 

 in the body and part of it escapes as heat. This oxi- 

 dation of the body is constantly changing it. 



Nitrogen. Air is approximately one fifth oxygen 

 and four fifths nitrogen. Oxygen cannot be taken di- 

 rectly from the air. Nitrogen, however, may be obtained 

 from the air by burning 

 out the oxygen from a 

 limited quantity of it. 



Experiment 24. Place a 

 small quantity of red phos- 

 phorus on a slice of cork. 

 Support the cork by a wire 

 held upright by sticking it into 

 a large rubber stopper. Place 

 in a pan and surround by two 

 inches of water (Figure 86). 



Light the phosphorus and place over it a quart jar. Water will 

 rise in the jar as the oxygen is used in the combustion of the 

 phosphorus. When the white smoke, phosphorus oxide, has dis- 

 solved in the water, slip a piece of glass under the jar and set it 

 upright on the table. Test the nitrogen in a number of ways in 

 which oxygen was tested. 



Nitrogen does not readily unite with other elements. 

 Its principal value in the air is to dilute the oxygen, which 

 would otherwise be too active for many of its uses. Nitf o- 



FIG. 86. 



