CARBON AND THE OXIDES OF CARBON 337 



Since the molecule of carbonic acid (H 2 CO 3 ) contains two atoms 

 of hydrogen, either one or both of these atoms may be replaced by 

 a metal the acid is dibasic. Thus we may have sodium car- 

 bonate Na 2 CO 3 , or its hydrate, washing soda Na 2 C0 3 , 10H 2 O, and 

 also sodium bicarbonate (baking soda, sodium-hydrogen carbon- 

 ate) NaHCO 3 (see pp. 366-7). 



3. The most marvellous chemical action into which carbon 

 dioxide enters is the action by which plants use the gas as food. 

 This important action is discussed in detail in a later chapter. 



CARBON MONOXIDE 



Preparation. Carbon monoxide CO is most easily prepared 

 in the laboratory by heating formic acid (or sodium formate, a 

 white crystalline solid) with concentrated sulphuric acid. The 

 latter combines with the water, but is not otherwise changed: 



HC0 2 H -> CO + H 2 0. 



When coke, or any form of carbon burns with a limited supply of 

 air, or oxygen, the same gas is produced : 

 2C + 2 -2CO. 



The gas therefore rises from the surface of a coal fire, sometimes 

 escaping unburned, but often burning with a blue flame above 

 the coal. 



Producer Gas and Water Gas. When air is, led through 

 burning coke, the mixture of carbon monoxide (39 per cent) with 

 nitrogen (60 per cent) obtained is called producer gas. It' is 

 combustible, and is used in industrial establishments for heating 

 and to drive gas engines for power. 



Commercially, large amounts of carbon monoxide mixed with 

 hydrogen (water gas), are manufactured by blowing steam over 

 white hot coke or anthracite: 



C + H 2 - CO + H 2 - 29,100 calories. 



