1819.] the different Species of Pit-Coal. 83 



When heated, it breaks into a great number of small pieces. 

 When the heat is raised to a certain point, it melts, and all the 

 fragments are united together into one solid mass. This gives it 

 the name of caking coal. 



It catches fire very easily, and burns with a lively yellow flame ; 

 but in consequence of its caking property, it requires to be 

 frequently stirred to admit the access ot air, otherwise it is extin- 

 guished. 



This species of coal is distinguished by the length of time 

 which it burns, and the great heat which it gives out ; so that 

 when it can be procured at the same price, it is much more 

 economical than any of the other species of coal. 



2. Splint Coal. 



This species of coal constitutes the fifth of the six Glasgow 

 coal-beds, or the lowest bed at present wrought. It is thin, 

 varying in thickness from 30 inches to three feet. It occurs also 

 occasionally in some of the other beds, particularly the second ; 

 but does not constitute the whole of any of the beds except the 

 fifth. It is a well characterized species, and constitutes the 

 most valuable of the Glasgow coals, and always sells at a higher 

 price than the cherry coal or soft coal, as it is also called. It 

 is the only species of coal which is employed in the neighbour- 

 hood of Glasgow for the manufacture of coke. It is found to 

 answer remarkably well for smelting iron, and is solely used for 

 that purpose. Hence, perhaps, the reason why the iron smelted 

 in the neighbourhood of Glasgow is considered as of a better 

 quality, and brings a higher price in the market, than either 

 Welsh or Staffordshire iron. This at least is the case with the 

 iron made at the Clyde iron work, where splint coal alone is 

 employed. 



Colour black, with a slight shade of brown. 



Lustre between glimmering and glistening ; resinous. Lustre 

 of the streak between glistening and shining. It is not uncom- 

 mon to meet with thin layers of cherry coal running through 

 splint coal. Such layers have a much higher lustre, and a much 

 finer black, and, therefore, are easily distinguished from splint 

 coal. 



Principal fracture imperfect curve slaty. Cross fracture fine 

 grained, uneven, and splintery. It is this splintery appearance 

 that seems to have led to the name splint coal. 



Not harder than either caking coal or cherry coal ; but much 

 more difficultly frangible. Hence it is commonly called hard 

 coal. Fragments usually inclining to wedge-shaped. 



Specific gravity, 1-290. 



It requires a much higher temperature to kindle it than is 

 necessary either for caking coal or cherry coal. It burns with 

 flame ; but lasts much longer than cherry coal. In consequence 

 of the high temperature requisite to maintain the combustion, it 



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