BOILERS, FUELS AND FLUES 201 



ers with this particular end in view. In 

 buying a boiler the safe plan is to purchase 

 a style which has fully established itself on 

 the market and which is made by a thorough- 

 ly reliable firm. Such boilers will have passed 

 the experimental stage and repairs may be 

 secured quickly and reasonably. 



Essentials of a Boiler. The function of 

 the boiler is to extract the latent heat from 

 the fuel and transfer it to the water or steam, 

 which may be circulated when needed. The 

 essentials are, a grate on which the fuel is 

 burned and a watertight receptacle, so ar- 

 ranged as to present a large amount of sur- 

 face (known as fire surface) to the fire or 

 burning gases. The problem of the manu- 

 facturer is to so arrange and proportion the 

 fire surface and the grate surface that the 

 heat of the burning fuel may be most econ- 

 omically absorbed and distributed. 



Grate Surface. For best results the 

 amount of grate surface should be large 

 enough, so that the fire will not have to be 

 forced. In small and medium-size boilers 

 the rate of combustion should not exceed 

 from five to seven pounds of coal per square 

 foot of grate per hour. In larger boilers the 

 rate of combustion of fuel may be as high as 



