276 Dr Fyfe on the Evaporative Power of Coal. 



67, and in the Scotch coal only 50.5. Now, with regard to 

 the comparative practical evaporative power of the Scotch 

 and English coal, I have stated them as 100 to 133, and as 

 50.5 : 67 : : 100 : 132. 



Again, with regard to the Scotch and anthracite, I have 

 given the evaporative power as 6.66 to 8.73, and 50.5 : 71.4 : : 

 6.66 : 9.41. Thus, not only is the evaporative power in prac- 

 tice in the ratio of the fixed carbon, but there is a very re- 

 markable approximation in the evaporative power to the pro- 

 portion of this ingredient in each. 



In the anthracite the volatile matter, independent of the 

 moisture, was 13.3, in the English it was 29.5, and in the 

 Scotch it amounted to no less than 34.5 per cent. We would 

 therefore naturally expect that the English and Scotch coal 

 would have a greater evaporative power, whereas that which 

 has the least of these volatile ingredients has the greatest. 

 It is evident from this, that, in the combustion of fuel in fur- 

 naces as commonly constructed, the loss of the heat evolved 

 is occasioned in a great measure by the volatile matter ; much 

 of these we know is consumed, but even in the best con- 

 structed furnaces, there is an escape of a considerable pro- 

 portion, owing to the want of a due supply of air, or from 

 want of the pi'oper temperature even though air is present ; 

 indeed it is chiefly owing to the latter, for we never find that 

 the air that has passed up through the fuel is entirely deprived 

 of its oxygen. 



Numerous methods have been recommended for securing 

 the perfect combustion of all the gaseous matter, such as the 

 cautious introduction of the fuel near the front of the furnace, 

 instead of throwing it carelessly over the whole heap in a state 

 of combustion, by which the gradual discharge of the volatile 

 matter is occasioned, and which, being thus expelled and 

 passed over the ignited fuel, should be burned, provided air 

 in suflicient quantity is present. Many others have also been 

 proposed, — such as that patented by Mr Williams of Liver- 

 pool, which consists in allowing air to flow by small streams 

 into the furnace behind the bridge, by which the volatile mat- 

 ter that has escaped combustion is to be consumed. Another 

 is that lately introduced by Mr Ivison of this place. It con- 



