CARBON 65 



coal is heated away from air, coke is the solid sub- 

 stance that remains. 



The chief use of coke is for fuel for coke ovens, 

 blast furnaces, and steam engines. It is superior to 

 soft coal, because it gives off more heat; but inferior 

 to hard coal, because it burns more rapidly and 

 requires more attention. Because it is a good con- 

 ductor of electricity it is used also in the electrical 

 industry. 



Graphite. Graphite is another form of carbon taken 

 from mines in the earth. The best of these are found 

 in Siberia and Ceylon, though much is mined in Eng- 

 land, California, and New York. Graphite differs from 

 other forms of carbon in that it is very soft. Its uses 

 are many : as a lubricant for machines, as polish for 

 stoves, as a covering to conduct the electric current 

 in electrotyping, and mixed with clay, to supply the 

 "lead" of the lead pencil. 



In the manufacture of lead pencils, graphite is mixed 

 with clay, and worked up into a pasty mass. From 

 this pasty mass the thin rods of the pencil are produced 

 which are finally encased in the wood. The hardness 

 of the pencil depends upon the relative proportions 

 of graphite and clay; the more clay the harder the 

 pencil. 



Diamond. The diamond is pure carbon. It differs 

 from other forms of carbon in its hardness, being the 

 hardest substance known in nature. Because of its 

 rarity it is a very costly gem, its value being deter- 



