48 AGRICULTURAL CHEMISTRY 



bles and for the linings of furnaces. It is a natural prod- 

 uct and is also produced artificially by dissolving carbon 

 in iron. There are a great many uncrystallized or amor- 

 phous forms of carbon, as lignite and soft coal, lampblack, 

 and charcoal. 



50. Coal. All of the conditions under which coal has 

 been produced are not known. It is supposed to be the 

 result of the joint action of heat and pressure upon pre- 

 historic forms of vegetation. Hard or anthracite coal is 

 the purest form known, and yields the smallest amount 

 of ash and unoxidized volatile products. Bituminous or 

 soft coal is less pure as a larger amount of the carbon is 

 present in chemical combination with the other elements, 

 and when burned, the carbon is not as completely oxi- 

 dized under ordinary conditions as is that of hard coal. 

 Coal may contain a number of impurities, as sulfur and 

 mineral matter. Cannel coal is a variety which contains 

 a large amount of mineral oils. 



Lignite is vegetable matter which has only partially 

 undergone the coal-forming process. It is less pure than 

 soft coal, and is supposed to be an intermediate stage 

 in the formation. Peat is vegetable matter which has 

 undergone chemical changes under water. It is less pure 

 than lignite. 



51. Allotropism. An element which has the power to 

 take on so many different physical forms as has carbon 

 is called an allotropic element. Only a few elements have 

 the properties of allotropism. 



52. Carbon as a Reducing Agent. Carbon is used 

 extensively for the reduction of minerals. The action of 



