HEAT LOSSES. 35 



Air in Air in 



Ibs. cub. ft. 

 at 62deg. 



Hydrogen to water 33.9 444 



Carbon to carbon mon-oxide 5.7 75 



Carbon to carbon dioxide 11.3 148 



Carbon mon-oxide to carbon dioxide. . 2.41 32 



Marsh gas to water and carbon dioxide 16.9 222 



Sulphur to sulphurous acid 4.25 56 



For approximate calculation of the weight of air required for 

 combustion of coal the following formula may be used : 



Weight of air-12C +34 (H (0 + 8) ).' 



where C = carbon, H hydrogen and 0= oxygen in the fuel. 

 The + 8 gives the weight in pounds of hydrogen rendered 

 inert by the oxygen of the fuel, and which therefore has to be 

 deducted, for 



H* : O : : 2 : 16, therefore H : : : 1 : 8. 

 When we consider that the oxygen in the air is mixed with 

 nearly four times its volume of nitrogen, which tends to sepa- 

 rate it from the fuel, we cannot expect all the individual atoms 

 of oxygen to unite with their proportion of carbon or hydro- 

 gen in the fuel, so we have to add an excess of air. This 

 excess will vary greatly in different cases from between 50 to 

 300 per cent. The loss due to excess of air will depend on the 

 quantity of unused air that becomes heated and escapes, and 

 also upon the amount of moisture in the air. 



3rd. The loss resulting from too great a temperature oi 

 the escaping gases is one of the most important factors in fuel 

 efficiency. It is largely due to the design of the boiler, etc. ; 

 1)ut is also influenced by the air supply and rate of combustion. 

 To keep the air supply as low as possible so as to obtain the 

 greatest efficiency, requires the greatest care and attention oil 

 the part of the stoker; the fire would be apt to be dull and 

 there would be practical difficulties in maintaining it under 

 varying conditions of demand. 



4th. Loss of heat by removing ashes at too high a tem- 

 perature. This can be greatly reduced with care. 



5th. Loss by radiation. This may be lessened by increas- 

 ing the thickness of walls and covering all exposed portions of 

 the boiler. 



A thin fire increases loss due to excess of air, but de- 

 creases that due to smoke and incomplete combustion. On 

 ihe other hand, a thick fire reduces the excess of air, but in- 

 creases the loss due to smoke and escaping combustible gases. 



Different kinds of coals give best results when burnt under 

 conditions suited to them, consequently when several classes 

 of coal are being tested with a particular boiler, though the 

 -comparative tests may be satisfactory so far as that boiler is 



