32 HOW CROPS GROW. 



EXP. 2. If a splinter of dry pine wood be Bet 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 remains. 



Carbonization and charring are terms used to 

 express the blackening 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. 



EXP. 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 l ' ' 

 of lamp-black. 



Oil of turpentine and petroleum (kerosene,) contain so 

 much carbon that a portion 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 animal char- 

 coal, or bone-black. 



Lignite, bituminous coal, coke the porous, hard, and 

 lustrous mass left when bituminous coal is heated with a 

 limited access of air, and the metallic appearing gas-carbon 

 that is found lining the iron cylinders in which illuminat- 

 ing coal-gas is prepared, consist chiefly of carbon. They 

 usually contain more or less incombustible matters, as well 

 as oxygen, hydrogen, and nitrogen. 



The different forms of carbon possess a greater or less de- 

 gree of porosity and hardness, according to their origin 

 and the temperature at which they are prepared. 



Carbon, in most of its forms, is extremely indestructible, 



