CARBON AND THE OXIDES OF CARBON 331 



ments of graphite. The amorphous appearance is due to the 

 extreme minuteness of the crystals, which are interspersed, with 

 attendant impurities, through a highly porous mass. 



Chemical Properties of Carbon. 1. Carbon unites vigor- 

 ously with oxygen. With an excess of oxygen it forms carbon 

 dioxide, a gas: 



C + 2 -*C0 2 . 



With a limited supply of oxygen, it forms carbon monoxide, 

 also a gas: 



2C + O 2 -2CO. 



2. In consequence of this tendency to unite with oxygen, 

 carbon is much used as a reducing agent. Thus, when oxide of 

 copper is heated with pulverized charcoal, carbon dioxide is 

 formed, and the metal is liberated: 



In the same way the oxides of tin, of lead, and of many other 

 metals may be reduced. Copper, tin, and lead are manufactured 

 from the ores in this way. 



3. Carbon unites directly with some elements, particularly with 

 sulphur to form carbon disulphide CSj (p. 255) and with certain 

 of the metals. Thus, when dissolved in molten iron, it forms 

 iron carbide Fe 3 C. 



The union with hydrogen is ordinarily too slow to be observed. 

 But when the carbon is mixed with pulverized nickel (contact 

 agent) and hydrogen is passed over the mixture at 250, methane 

 CH4 is formed (99 per cent). The action is reversible and exo- 

 thermal, and is therefore, at higher temperatures, less complete 

 (compare p. 242), at 850 reaching only 1.5 per cent. On the other 

 hand, an electric arc, between carbon poles in an atmosphere of 

 hydrogen, gives traces of acetylene C 2 H 2 , this action being endo- 

 thermal. The other compounds of carbon and hydrogen are all 

 obtained by indirect reactions. 



