88 



Dr. Thomson on the Composition of 



[Aug. 



turning their attention to economizing this most important 

 article conceiving that they gain as much upon the whole by 

 the tendency which their increased consumption has to raise the 

 price of coals, as they lose by that increased consumption. But 

 though this mode of reasoning may, perhaps, apply to the present 

 race of iron smelters in this neighbourhood, it certainly will not 

 to their successors. Greater attention to the economy of this 

 important article would probably contribute to the improvement 

 of the iron trade upon the whole. 



I converted the different species of coal into coke by exposing 

 given weights of each to a strong red heat for about an hour in 

 a covered platinum crucible. The following table exhibits the 

 results of these experiments : 



The reader will be able to form a more accurate conception of 

 the quantity of coke which each of these species of coal yields 

 from the following table, in which we have supposed the original 

 weight of the coal before coking to be 1000. 



From this table it is evident that the Newcastle coal yields by 

 far the greatest quantity of coke, while the cannel coal yields the 

 smallest quantity. The reason of this will be evident as soon as 

 I have given the constituents of which each of these species con- 

 sists. The coak from all the species of coal has a good deal of 

 the metallic lustre, is much lighter than the coal, and has a 

 silvery aspect. The coke from caking coal is split into columns, 

 having much the appearance of basaltic columns, or rather 

 bearing a close resemblance to the shape which starch assumes 

 when it is allowed to dry by the manufacturer. 



