BLACK COAL. ANTHRACITE. 



109 



important, when it saves us from loss of time, expense, and disappoint- 

 ment. 



Common coal is a mineral too well known to require a particular 

 description. Mineralogists divide coal into two species, — Brown 

 coal, and Black coal ; the former, sometimes called wood coal, is 

 chiefly found in alluvial or diluvial ground. It contains, besides 

 charcoal and bitumen, various vegetable principles, and the branches 

 or trunks of trees partially decomposed, which mark the origin of 

 this kind of coal. 



Black coal or common coal, is composed of charcoal, bitumen and 

 earthy matter. The latter forms the ashes which remain after com- 

 bustion : these vary in proportion in different coals, from two to near 

 twenty per cent. The proportion of bitumen varies from twenty to 

 forty per cent., and the charcoal from forty to more than eighty per 

 cent. 



Mineralogists have enumerated many different kinds of black coal : 

 several of these pass by gradation into each other in the same mine. 

 The most important varieties in an economical view are the hard coal 

 like that of Staffordshire, and bituminous or caking coal, called in 

 London Sea-coal. 



Anthracite is a mineral approaching to the state of plumbago ; it 

 consists nearly of pure carbon, is extremely hard and difficult to ignite, 

 ■^and has often a semi-metallic lustre. It occurs in rocks which have 

 generally been regarded as belonging to the transition class, but is 

 sometimes found in small quantities in regular coal strata. The coal 

 in the extensive coal formation of Pennsylvania is called anthracite, 

 because it emits but litde smoke in burning, but is only a variety of 

 common coal, containing but little bitumen. 



Coal strata are frequently accompanied by thin strata of ironstone. 

 This stone has a dark brown or gray color, it has an earthy appear- 

 ance and fracture, and is about three times heavier than an equal 

 bulk of water. Some kinds have the specific gravity of 3*6. 

 Though modern mineralogists call this mineral clay-ironstone, after 

 Werner, from its resemblance to argillaceous stones, on analysis it is 

 found to contain but a very minute portion of alumine or pure clay, 

 sometimes not more than two per cent. It is composed principally 

 of iron combined with oxygen, carbonic acid and water, and a small 

 quantity of silex, and in some instances with calcareous earth. If it 

 be of a good quality, it yields more than thirty per cent, of iron. In 

 some of the beds of clay over coal, detached nodules of ironstone 

 occur, which are also smelted for iron. 



The vast extent and importance of our iron works are well known 

 but their establishment is of recent date. Formerly our furnaces 

 were on a diminutive scale, and wood or charcoal was the only fuel 

 employed, but in the present cultivated state of the country, wood 

 could not be procured in requisite quantity. The application of coal 

 or coke to the smelting of iron is among the most useful of modern 



