The Story-Book of the Fields 



this condition it forms four-fifths of the 

 common air that we breathe. The other 

 fifth consists of a second gas called oxygen, 

 also without colour or smell. Oxygen only 

 is able to support respiration and combustion. 

 It is that alone which acts upon us so as to 

 consume the material of our blood and to 

 produce natural heat. That alone in com- 

 bustion dissolves carbon, phosphorus, sulphur 

 and other substances, producing a compound 

 which we call carbonic acid gas, when it is 

 derived from carbon, or phosphoric acid if it 

 comes from phosphorus. In a word, all the 

 properties that we have hitherto considered 

 as belonging to the air, really are properties 

 of oxygen. As for nitrogen, it plays no 

 part in the atmosphere, except to modify 

 the excessive energy of oxygen. 



Nitrogen is necessary for all plants. It is 

 needed by the wheat to form the grain in its 

 ear ; by the pea, the bean and the lentil, to 

 fill their pods ; by the grass of the pasture 

 and by the hay of the meadow, to prepare 

 the food which the sheep will convert to 

 meat, and the cow to milk. We ourselves 

 need phosphorus, since it enters into the 

 composition of our bones ; still more do we 

 need carbon, which is the chief fuel for the 



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