NO. I FUEL ECONOMY — MITMAN 5 



vides an insulation which will cut the absorptive power over 

 25 per cent. The flues should be cleaned in the case of anthracite at 

 least every few weeks and in the case of bituminous coal practically 

 every day. Other defective developments commonly met with are in 

 the form of leaky settings, cracks, warped castings, and the like. 

 These, however, communicate their ill effects chiefly in the matter of 

 draft control and may therefore be considered under that head. 



In this latter connection, two general deductions are to be derived 

 from what has been said in the preceding pages. First, that air enter- 

 ing the furnace above the fuel bed is objectionable in that it serves 

 to lower the temperature within precisely as the influx of cold air 

 lowers a room temperature. Second, an undue amount of air beyond 

 that required for combustion, even when fed through the fuel bed, is 

 open to the same objection. Accordingly, the common practice of 

 opening the coaling door or even the slide in the door to check the 

 fire is, in general, bad and should be resorted to only when absolutely 

 necessary; similarly, holes or cracks admitting air above the fuel 

 bed should be sealed as soon as they develop. 



As too much air passing through the fuel bed has the same general 

 effect as air fed over the bed, it follows that the further practice 

 commonly met with of opening the ash pit door to obtain full draft 

 is scarcely less objectionable than opening the coaling door, and 

 leaky settings, cracks, etc., leading into the ash pit, in their general 

 effect, are not unlike similar defects in the combustion chamber. 

 So far as possible, the control over the furnace should be accomplished 

 with the check damper, supplemented by the opening of the ash pit 

 damper only to a sufficient degree and for a sufficient time to stimulate 

 combustion. In this way excess air with its consequent cooling effect 

 is cut to a minimum and the course of the gases is retarded, giving 

 the maximum opportunity for the heat to be absorbed. One of the 

 commonest practices met with combines about everything that has 

 been pointed out as objectionable. This is the practice of banking the 

 furnace at night leaving the coaling door open, to be followed in the 

 early morning by opening up everything down below. This means 

 the complete loss of the heat generated by combustion during the 

 night followed by the cooling effect of excess draft throughout at 

 least the early part of the day. 



The value of having a coal uniformly suited to the requirement will 

 be discussed in some detail later. It may be well here, however, to 

 touch briefly on the important bearing that the size of coal exerts. 

 The case comes to mind of a householder accustomed to using nut 



