82 CHEMISTEY. 



for certain substances in separating the'm from others, as, 

 for example, in separating the coloring substance from ale, 

 and also that which gives it its bitter taste. 



98. Coal. All the different varieties of coal anthracite, 

 bituminous, etc. are carbon, more or less mixed with 

 compounds of hydrogen and carbon called hydrocarbons. 

 Anthracite burns without smoke, and when fully ignited 

 without flame, for it is destitute of the volatile hydrocar- 

 bons that are present in bituminous coal. The reason of 

 the difference is that these volatile substances have been 

 driven off by heat in the formation of the anthracite. When 

 the anthracite is burned the carbon all passes upward, unit- 

 ed with the oxygen of the air, forming carbonic anhydride. 

 The impurities combined with this carbon in the coal fall 

 below, making the ashes. The bituminous coal is used in 

 making illuminating gas. What is left after the volatile 

 matters are driven off is a very impure charcoal called coke. 



99. Graphite. Graphite, or plumbago, sometimes called 

 black-lead, contains not a particle of lead, but is crystallized 

 carbon, having commonly a very little iron mingled with 

 it. It is a grayish black substance having a metallic lus- 

 tre. It is used for making the so-called lead-pencils, and for 

 giving a polish to stoves and other iron articles. When 

 powdered it is so soft and lubricating that it is added to 

 grease for the prevention of friction in wheels and machin- 

 ery. It is a very incombustible article, and therefore the 

 coarser kinds are manufactured into crucibles, or melting- 

 pots. There are famous mines at Cumberland, in England, 

 and in Siberia, which furnish very fine graphite for pencils. 

 It is quite a common mineral in this country, appearing in 

 many localities. At Ticonderoga, in New York State, an 

 extensive deposit occurs, most of which is worked up into 

 crucibles and stove-polish. 



100. The Diamond. In the diamond we have pure carbon 



