34 COALFIELDS AND COLL1KHIKS OK AUSTRALIA. 



an idea in figures of the injurious effect of the moisture and 

 ash, what volatile matter is wasted in a given furnace, the 

 effect of the size of coal and what heat is lost by a low efficiency 

 of a boiler or improper manipulation of the fire. 



The unavoidable losses of heat may be put down to the 

 heat lost by converting the moisture contained in the coal into 

 steam, also that in the air used in burning it, and in addition 

 heating the steam thus formed to the temperaure at which it 

 leaves the stack. Then there is the heat necessary to raise to the 

 stack temperature, the carbonic acid gas formed by burning 

 the carbon, the sulphurous acid gas from burning the sulphur, 

 the nitrogen of the air after the oxygen has been used up, 

 and the excess of air admitted into the furnace.. Further 

 losses are made through the heat of the ashes removed from 

 the ashpit, as well as from, the carbon remaining in the ashes, 

 and through radiation from boilers and walls, which may !><> 

 reduced by careful construction and covering, but can never 

 be entirely eliminated. The losses that may be more or less 

 avoided are : 



1st. Those due to incomplete combustion as shown by the 

 presence of smoke and carbon mon-oxide in the flue gases, and 

 uii consumed coal in the ashes. The loss resulting from smoke 

 is absolute, it is not only so much fuel gone to waste, but has 

 required a certain amount of heat to raise it to the necessary 

 temperature to escape with the flue gases: the actual waste is, 

 however, comparatively insignificant and not nearly so much 

 as is generally supposed. The loss of efficiency due to the 

 escape of carbon mon-oxide on account of lib. of carbon is the 

 difference between 4400 B.T.TJ. when burnt to carbon mon-ox 

 ide, and 14,650 B.T.U., when one pound of carbon is burnt 

 to carbon dioxide, or 10,100 B.T.TJ. more, i.e., 69.28 per 

 cent. The loss of coal in the ashes may be due to the original 

 small size of the coal, or the subsequent decrepitation, which 

 results in more or less of it dropping through the grate. This 

 may be somewhat reduced by skilful manipulation of the fire. 

 Small quantities of unconsumed hydrogen, or moist gas, may 

 also escape up the stack. 



2nd. Loss from excess of air. Air is composed of: 

 By volume. By weight. 



Oxygen 21.3 28.6 



Nitrogen 78.7 76.4 



100.0 100.0 



1UU.U 1UU.U 



To burn lib. of the following substances requires the cor- 

 responding weight or volume of air: 



