Dr Fyfe on the Evaporative Power of Coal. 265 



difference in the state of the fire must make a very trifling 

 difference in the total result, where the quantity of fuel em- 

 ployed amounts to several hundredweight. 



Scotch Coal. — 1 conceive it unnecessary to give the result 

 of the numerous trials made with this fuel. They, in general, 

 come very near to each other. I give the particulars of one 

 only, which was conducted with great care, and in the result 

 of which the utmost confidence may be placed. The coal used 

 was from Middlerig, and is considered of good quality. 



In this trial the furnace was supplied with the cwt. of coal 

 at three different stokings. The pressure on the boiler was 

 17 lb. beyond the atmospheric pressure. 



The above table shews, that 784 lb. of fuel were used, and 

 that 488 gallons, that is 4880 lb. of water were evaporated 

 from the temperature 45°, thus giving a result of 6.22 lb. for 

 each pound of coal, at 17 lb. pressure. 



On subjecting the coal used in this trial to analysis, I found 

 it to consist of — 



Moisture, 

 Volatile matter, 

 Fixed carbon, . 

 Ashes, . . 



7.5 

 34.5 

 50.5 



7.5 



100.0 



I may here also state the result of another trial made with 



