16 HOW CROPS GROW. 



Exp. 2.— If a splinter of dry pine wood be set on fire and the burning 

 end be gradually passed Into the mouth of a narrow tube (see figure 1), 

 whereby the supply of air is cut off, or if it be thrust into 

 sand, the burning is incomplete, and a, stick of charcoal re- 

 mains. 



Carbonization and Charring are terms used to 

 express tKe blackenitg of organic bodies by heat, 

 and are due to the separation of carbon in the free 

 or uncombined state. 



The presence of carbon in animal matters also is 

 shown by subjecting them to incomplete com- 

 bustion. 



£XP. 3.— Hold a knife-blade in the flame of a tallow candle ; 

 the full access of air is thus prevented, — a portion of carbon 

 escapes combustion, and is deposited on the blade in the form 

 of lamp-black. 



Oil of turpentine and petroleum (kerosene) contain so 

 much carbon that a portion ordinarily escapes in the free 

 state as smoke, when they are set on fire. 



When bones are strongly heated in closely-covered iron 

 pots, until they cease yielding any vapors, there remains 

 in the vessels a mixture of impure carbon with the earthy 

 matter (phosphate of lime) of the bones, which is largely 

 used in the arts, chiefly for refining sugar, but also in the 

 manufacture of fertilizers under the name of aninial char- 

 coal, or bone-black. 



Lignite, bituminous coal, anihradte, coke — the porous, 

 hard, and lustrous mass left when bituminous coal is 

 heated with a limited access of air, and the metallic ap- 

 pearing ^as-carJow that is found lining the iron cylinders 

 in which illuminating coal-gas is prepared, all consist 

 largely or chiefly of carbon. They usually contain more 

 or less incombustible matters, as well as a little oxygen, 

 hydrogen, nitrogen, and sulphur. 



The different forms of carbon possess a greater or less 

 degree of porosity and hardness, according to their origin 

 and the temperature at which they are prepared. 



Carbon, in most of its forms, is extremely indestructi- 



