for Manufifiuring Caji Iron. 1 9 



The pit-coal in Scotland may be arranged under the fol- 

 lowing claffes, of each of which there are many varieties : 

 fplint coal, free coal, and bituminous coal. To the former 

 a juft preference has always been given, for the fuperior 

 effects it produces in the blaft-furnace. Free coal feems to 

 partake of the nature of the fplint and the bituminous coal, 

 and is frequently found interfperfed with fmall layers of fplint. 

 It ought therefore to be confidered as the medium ftate of 

 the mineral. Under bituminous coal may be arranged the 

 lighter varieties, known by the names of candle-coal, parrot- 

 coal, &c. Thefe hitherto have been deemed unfit for the 

 manufacturing of crude iron in any profitable fliape. 



As in this place I mean only to convey a juft idea of the 

 materials ufed in the fmelting proccfs, I {hall not enter into 

 a comparative view of the relative effects which the various 

 qualities of coal produce, when ufed in the fmelting or 

 cafting-furnace ; but confine my defcription to that quality 

 which can be ufed for manufacturing crude iron to ad- 

 vantage. Of this kind there are two varieties; the pure 

 fplint and a mixture of fplint and free coal, generally com- 

 pofed of alternate ftrata of each. Both thefe poffefs their 

 advantages derived from local conftruction; the former 

 being the moft preferable, where a fuperiority of mechanic 

 power affords the furnace a heavy and unremitted fupply 

 of air. The latter will be found to poffefs equal advantages, 

 where a deficiency of power in the air machine conveys to 

 the furnace but a fparing column of blaft. The purer and 

 the more approaching to fplint is the coal, the more capable 

 will it be of fupporting unfliaken a current of highly com- 

 preffed air, and of conveying the carbonaceous principle to 

 ihe iron ; which ftamps its utility and value. On the con- 

 trary, the fofter and lei's connected the coal, the lefs capable 

 is it of refilling the force of the blaft, and of fupporting a 

 certain proportion of ore till Inch lime as the metal which 

 it contain imbibes the coally principle, lb eflential to its 

 C * ex 1 1 



