CHAPTER VII 



CARBON AND ITS COMPOUNDS 



117. Carbon as an Element. We all know carbon as 

 it exists in soot, coal, charcoal, and in the " black lead" 

 of our pencils. It is a black solid; it does not dissolve in 

 water; and even powerful chemicals, such as acids and 

 bases (cf. 214), do not change it to any great extent. 

 When it is heated to the right temperature, it burns, 

 forming carbon dioxide (cf. 51). It is hard to believe 

 that the bright, hard, and lustrous diamond (Fig. 75, 95) 

 is a form of the same element as the black graphite (' ' black 

 lead") and charcoal, yet it is true. If a pure sample of 

 each of these substances is completely burned in oxygen, 

 it gives nothing but carbon dioxide. If a diamond is heated 

 in a tube containing no oxygen, it is changed to graphite. 



Carbon is of great importance for all life upon the earth. 

 Living things are made up of wonderfully constructed 

 compounds containing carbon. Proteids, sugar, starch, 

 and fats are such compounds. When compounds of car- 

 bon are heated, and can get plenty of oxygen, they usually 

 burn. But when they are heated without sufficient air, 

 or too rapidly, nearly all of them char, or "turn to car- 

 bon." We have all seen this happen when sugar or milk 

 has been spilled upon a hot stove, and when toast or 

 meat has been "burned" by overheating. 



118. Coal. All of the many different kinds of coal 



no 



