120 FUEL. 



N. B. The above are the extreme effects ; for practical 

 use let a deduction of -|- be made from the above. 



Combustible matter of fuel. 



The quantity of combustible matter of fuel, if the weight 

 and other circumstances be equal, may be learnt from the 

 ashes, or residuum, left after the combustion. For example, 

 good Newcastle coal contains a greater portion of combus- 

 tible matter than Nova Scotia coal, and leaves behind a 

 smaller amount of earthy and incombustible substance. 

 The heating power, and consequent value, of different kinds 

 of fuel, is affected by this circumstance, though by no means 

 dependent on it. The fitness of fuel for various purposes 

 is furthermore affected by the facility with which it gives 

 off a part of its combustible matter in the form of vapor or 

 gas, which, being burnt in that state, produces flame. For 

 example, the bituminous coals abound in volatile matter, 

 which, when ignited, supports a powerful blaze. On the 

 other hand, the Lehisrh and Khode Island coals are destitute 



3 " 



of bitumen, and yield but little flame. It is from similar 

 causes that dry pine wood produces a powerful blaze, while 

 its charcoal yields comparatively little. A blaze is of great 

 service where heat is required to be applied to an extensive 

 surface, as in reverberating furnaces, ovens, glass-houses, &c. 

 But when an equable, condensed, or lasting fire is wanted, 

 the more solid fuels, which blaze less, are to be preferred. 



