230 BULLETIN 12, UNITED STATKK NATIONAL MUSEUM 



The coals incliultHl under this head vary greatly in composition and 

 physical characters, lu general they are soft and dull in luster as com- 

 pared with anthracite. Some of the caunel coals are almost sectile, and 

 are earthy in luster. 



The specific gravity varies, but does not rise above 1.5. The fracture 

 varies from conchoidal to cubic. They kindle easily and burn with a 

 long, yellow, and sometimes smoky llame. Bituminous coals are subdi- 

 vided in several ways, and the following are the principal divisions: 

 Coking, non-coking, canuel, and brown coal or lignite. 



Coking coals are soft and have a nearly cubic fracture. They give a 

 long, yellow flame in burning and make a hot fire. Their chief char- 

 acteristic, however, is that they soften when first heated, and yield a 

 hard, sonorous, cellular coke on continued heating. 



Noncoking coals are bituminous coals, which do not yield a good coke 

 on heating. They are divided into two principal varieties, cherry and 

 splint. Cherry coal generally has a bright luster, but may be dull. 

 It is very black and breaks easily into cubic masses. It ignites easily, 

 burns with a yellow flame, and makes a hot fire. When left undis- 

 turbed pieces retain their shape until entirely consumed. Its specific 

 gravity is 1.20 to 1.30. Splint coal is dull black. It is harder and 

 stronger than cherry, and has a slaty structure. It breaks readily 

 lengthwise, but has a conchoidal cross fracture. It does not kindle 

 easily and makes a dull fire, requiring care in its management. Its 

 specific gravity varies from 1.25 to 1.40. 



Between the coking and non-coking coals there is frequently no chem- 

 ical difierence as shown by the ordinary methods of analysis. There is 

 evidently some chemical difference, but it is not well understood. 



Cannel coal varies from gray to black. It is dull to resinous in 

 luster with a slaty structure, and breaks with a conchoidal fracture. 

 It kindles easily and gives a long, yellow flame, which is frequently 

 smoky. Pieces of it once ignited burn like a candle, whence its name. 

 Its chief characteristic is the large amount of volatile matter that is 

 given off on heating. On this account it is particularly valuable for 

 gas making, and was formerly considered essential for that purpose. 

 Formerly it was also used for the distillation of oils, but has now been 

 replaced by petroleum. Cannel coal frequently contains a large per- 

 centage of ash. 



Brown coal, as its name indicates, is brownish-black in color. It is 

 brittle and breaks with a cubic fracture. It burns easily and makes 

 a good fire. It is more highly oxygenated than any of the other coals 

 and contains 15 to 30 per cent, of oxygen. It occurs in formations 

 more recent than the carboniferous. Lignite is a variety of brown coal, 

 which still retains its woody structure. 



The typical coking coal of this country is that of the Connellsville 

 basin of the Pittsburgh bed in Pennsylvania. The coal and the coke 

 made from it are represented by the following analyses : 



