82 Dr Colquhoun on the Argillaceous Ore of Iron. 



the heat transmitted from the lower part of the furnace. The 

 furnace thus becoming choked up, the free circulation of air 

 through it, which is indispensable to the maintenance of the 

 ignition, would be totally interrupted. To prevent these con- 

 sequences, the whole volatilizable matter is always carefully 

 expelled from the coal, before it is introduced into the fur- 

 nace. 



The coals of this country vary extremely, both in regard to 

 the nature of the coke which they furnish, and to the kind of 

 extraneous ingredients with which they are united. And 

 when attention is given to the purposes which the coke has to 

 serve in the furnace, it will easily appear, that the value of any 

 coal to the iron smelter will be very materially affected by each 

 of these circumstances. A light, open-textured coke would be 

 totally consumed in the continued and intense heat of the blast- 

 furnace, long before it could have time to discharge its impor- 

 tant functions of deoxidizing the ore, liquefying its earthy in- 

 gredients into a glass or slag, and supercarburating the redu- 

 ced metal. A coke of loose aggregation, and liable to shiver 

 into small fragments upon being struck, which is of common 

 enough occurrence, would not only be apt to impede the free 

 passage of air through the furnace, but it would be burnt away 

 with too great rapidity, and it would be incapable of with- 

 standing the mechanical force of the blast. It is essential 

 therefore that the smelter should be careful to 'employ a coke 

 which may, as much as possible, be hard, of compact structure, 

 sonorous when struck, capable of enduring rude treatment 

 without crumbling, and not of a texture that is seamed with 

 numerous clefts. These qualities, unfortunately, are not found 

 united in the coke that is supplied by our most abundant coals, 

 but nevertheless, wherever any of them is very deficient, the 

 coal should be systematically rejected by the ironsmelter as 

 quite unfit for his furnace. 



The extraneous substances which require to be noticed as 

 being usually found in coal may be divided into two classes, 

 iron pyrites, and certain earthy bodies. Nothing can be more 

 injurious to the metallic product of the ironstone than the pre- 

 sence of the sulphur contained by the iron pyrites, which is, 

 unfortunately, very generally distributed among the coals of 



