1819.] the different Species of Pit-Coal. 87 



perform this experiment aright. The muffle mu^t be perforated 

 with holes at its upper extremity in order to occasion a current 

 of air through it, without which the combustion is very- slow 

 indeed. I kept 20 gr. of coal red-hot in a close muffle for eight 

 hours ; but on allowing the furnace to cool, and examining the 

 coal, I found it by no means completely burnt. The following 

 table exhibits the proportion of earthy matter left by 20 gr. of 

 each species of coal tried. 



Grain. Per cent. 



1. Caking coal 0*3 = l - 5 



2. Splint coal 1-9 = 9-5 



3. Cherry coal 2-0 = 10-0 



4. Cannel coal 2-2 = 11-0 



The cannel coal which I used in my experiments was from the 

 Marquis of Anglesea's park, near Coventry. Its colour was 

 brownish-black, and it was interspersed with small particles of a 

 yellowish-brown colour, which burned like the rest of the mass. 



These ashes had a white colour. They contained no lime ; 

 but were chiefly siliceous, mixed, however, with a certain pro- 

 portion of alumina and oxide of iron. There is every reason for 

 believing that this earthy matter is of the same kind with that of 

 which the slate clay which accompanies the coal beds is 

 composed. 



2. Coke yielded by each Species of Coal. 



To determine with precision the quantity of coke which a 

 given species of coal will yield, it is obviously necessary to 

 expose it* to heat in a close vessel ; for when coal is coked in 

 the open air, a much greater loss must be sustained than what is 

 owing merely to the volatile matter dissipated by the action of 

 the heat. Accordingly coking ovens have been found more 

 economical than coking in the open air. But though the iron 

 smelters in the neighbourhood of Glasgow are aware of this 

 circumstance, they prefer the old method of coking the splint 

 coal in the open air. By this process they lose a portion of their 

 coke ; but they find that the quality of the iron is injured when 

 they smelt it with coke prepared in ovens. They assign as a 

 reason that the sulphur which the splint coal contains (under the 

 form of pyrites) is much more completely dissipated when the 

 coal is coked in the open air than when it is coked in ovens. 

 Whether this explanation be satisfactory, I cannot pretend to 

 determine ; but it is considered as a settled point that the 

 quality of the iron is improved when the coal employed to smelt 

 it has been coked in the open air; and this improvement is 

 considered as a full equivalent for the waste of coal that is sus- 

 tained by coking it in the open air. 



The truth seems to be, that as the iron makers in this neigh- 

 bourhood are either great coal proprietors, or at least have leases 

 of large tracts of coal, they have not been much in the habit of 



