32 HOW CROPS GROW. 
Expr. 2.—If a splinter of dry pire 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 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 
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 illuminate 
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 
