208 



PALEOBOTANY 



pressure from beds of rock and the 

 temperatures normally jjrevailing a few 

 liundred feet below the surface. For 

 this reason, many of our coal deposits 

 are still in an early stage of coalifica- 

 tion, or "low rank," although they have 

 been buried for millions of years. A 

 few coal deposits, however, were 

 situated where profound movements of 

 the rocks in the earth's crust occurred 

 during periods of mountain building. 

 This rock movement generated much 

 additional heat and pressure, produc- 

 ing our "high-rank" coals, such as 

 medium- and low-volatile bituminous 

 coal and anthracite. Occasionallv the 

 movement of molten rock oozing from 

 the deep, hot regions of the earth into 

 its outer crust transformed the adjacent 

 coal beds into coke. 



***«#« 



Most anthracite has a somewhat lower 

 heating value than the highest-grade 

 bituminous coals, but its lack of soot 

 and the fact that it will burn longer 

 without attention make anthracite an i 

 ideal domestic fuel, and much of it is 

 used for space heating. 



THE CHEMISTRY OF COAL 



Coal, like wood, is made up of the 

 elements carbon, hydrogen, oxygen, 

 nitrogen, a little sulfur, and other ele- 

 ments in minute quantities. The pro- 

 portions in which the major elements 

 are mixed differ greatly in different 

 kinds of coal, and the chemistry of 

 coal is extremely complicated. 



Bituminous coal is the most abund- 

 ant and widespread rank of coal in the 

 United States. It is the coal used most 

 commonly for industrial, power, rail- 

 road and heating purposes. Bitumi- 

 nous coals may be either coking or non- 

 coking. This property is not based on 

 the rank of the coal, but rather on 

 whether it will produce a coke when 

 processed in a coke oven. Nearly all 

 eastern bituminuos coals have coking 

 properties, but many of the western 

 bituminous coals are noncoking or free- 

 burning. 



*«***# 



Anthracite, sometimes called hard 

 coal, has a brilliant luster and a uni- 

 form texture. If you handle anthracite, 

 it will not soil your fingers as does coal 

 of lower ranks. Anthracite has a higher 

 percentage of fixed carbon and a lower 

 percentage of volatile matter than the 

 lower-rank coals. It burns slowly, with 

 a pale-blue flame free from smoke. 



THE USES OF COAL 



You can burn coal; if it is a coking 

 coal you can make coke from it; or 

 you can convert it into gas. Tliese are 

 its three primary uses at present. To 

 them a fourth— the commercial pro- 

 duction of synthetic liquid fuels— may 

 some day be added in the United 

 States. Coal already has been used for 

 this purpose in some countries that 

 have little or no oil and a good supply J 

 of coal, notably England and Ger- " 

 many. 



As fuel, coal is used as a source of 

 heat energy for many things, includ- 



ing- 



1. Producing steam for power by 

 electric power plants, industrial plants, 

 and some steam vessels and railroads. 



2. Industrial and commercial heat- 

 ing and cooking, such as store and 

 plant heating, bakeries, etc. and coke 

 production. 



3. Domestic heating and cooking. 



4. Firing ceramic products— brick, 



