118 



CARBON AND ITS COMPOUNDS 



If the carbon dioxide and water are brought together 

 under a pressure greater than that of the atmosphere (cf. 

 41), more of the gas dissolves than at ordinary pressure. 

 Water thus " charged 7 ' with carbon dioxide is called 

 ''soda water." When soda water is exposed to the air, 

 it froths, or foams, because the excess of dissolved carbon 

 dioxide escapes. This escape of carbon dioxide causes the 

 effervescing, or frothing, of drinks containing it. Water 

 is often charged with carbon dioxide naturally, below the 

 earth's surface. When such water rises to the surface, 

 the carbon dioxide escapes. 



Carbon dioxide does not burn; neither do burning bodies, such as a 

 candle or match, continue to burn when put into it. The higher 

 animals do not continue to live in carbon dioxide, because they cannot 

 live without free oxygen; they cannot get the oxygen of carbon dioxide 

 away from the carbon. 



127. Carbon Dioxide in the Air. Carbon dioxide gets 

 into the air from all ordinary burning, from the breathing 

 of animals and plants, and from the de- 

 cay of animal and vegetable matter. 

 We can test the air for carbon dioxide 

 by exposing to the air a shallow dish of 

 lime water, which is a solution of slaked 

 lime (cf. 132). Or we can draw air 

 through lime water (Fig. 101). There 

 will be formed a scum, or a precipitate, 

 of calcium carbonate, the substance that 

 makes up marble and limestone. 



We can prove that there is carbon dioxide in the breath 

 by blowing the breath through lime water. The same 

 white precipitate is formed. 



Suction 





FIG. 101. 



Drawing Air through 

 Lime Water. 



