110 MODERN SCIENCE READER 



elimination of the hydrogen and oxygen altered the cellu- 

 lose of the growing plant to the product of our coal seams. 

 This action is made even more manifest by calculating 

 the analyses so that the carbon is kept as a fixed quantity, 

 which brings into bold relief the gradual elimination of the 

 other constituents of the cellulose. 



THE CONVERSION OF WOODY FIBER TO COAL 



(Percy) 



Hydro- 

 Carbon gen Oxygen 



Wood 100 12.18 88.07 



Peat 100 9.85 55.67 



Lignite 100 8.37 42.42 



Bituminous coal 100 6.12 21.23 



Anthracite (Wales) 100 4.75 5.28 



Anthracite (Penna.) 100 2.84 1.74 



Graphite 100 0.00 0.00 



These changes in composition may also be traced in the 

 calorific value, and show the thermal advantages gained by 

 the elimination of the oxygen during these processes of 

 natural distillation. 



British Thermal 



Calories Units 



Wood 4,771 8,588 



Peat (dry) 5,600 10,080 



Lignite 7,000 12,600 



Bituminous coal 8,446 15,203 



Anthracite 8,677 15,618 



It is not, however, time alone which causes alteration in 

 the character of coal. The factors of temperature and 

 pressure also play so important a part in its composition 

 that it is unsafe to base any far-reaching ideas as to the 

 age of a coal upon the amount of natural carbonization 

 which it has undergone. One may look upon coal as con- 

 sisting of a basis of carbon together with the mineral mat- 

 ters that were mostly present in the sap of the plant, and 

 on the combustion of the coal will remain behind as ash, 

 these forming the solid residue which is left on heating the 



