406 The Economic Production of Artificial Heat. 



borne acid ; and the flame seen at the top of a chimney is due to 

 the same cause. Perforating the furnace door partially prevents 

 this waste. Since the elements of coal, coke, etc., exist in the 

 solid form, in changing to ths gaseous state they absorb a large 

 amount of the heat derived from previous combustion ; and the 

 gaseous products of combustion carry off so much heat, that it is 

 believed their volatilization consumes as much of it as is given 

 out by their combustion : hence, there is reason to doubt that 

 the effect of any coal containing hydrogen is greater than that 

 of its carbon ; and it has been found that coal containing the 

 smallest quantity of gases, is, practically, the most effective as 

 a heat-producer. When coal contains hydrogen, the resulting 

 water forms double its volume of steam. 



We may err by having too great as well as too small a 

 supply of air. If the latter is in excess, the heat being dispersed 

 through a greater quantity of matter, the temperature obtained 

 is less than it should be. When twice the proper quantity 

 of air is admitted, the temperature of the products of com- 

 bustion will be only about 2300°, or little more than half 

 what might be expected; yet five, and even ten times the 

 proper amount is often supplied to the fuel. We must not, 

 however, confine ourselves to the theoretical quantity, since 

 only about two-thirds of what is sent into the furnace comes 

 in contact with the combustibles. 



Various means have been devised for the consumption of 

 smoke. It is not enough to increase the height of the chimney : 

 this would indeed augment the draught, but would produce little 

 other effect than the diffusion of the nuisance over a wider 

 space. Among the most effective means that have been 

 employed, is mixing air with the smoke. When fuel is put on 

 the dead plate, so that it may be coked, and its volatile consti- 

 tuents mixed with air may pass over the fuel which is at a 

 high temperature, air is required above the fuel. If this is cold, 

 on account of bein^ drawn directly from the atmosphere, not 

 only is the bottom of the boiler lowered in temperature, and the 

 generation of steam in consequence diminished, but the smoke 

 is not all destroyed. It has been attempted to obviate these 

 inconveniences by supplying the required air through tubes 

 passing down within the chimney ; but this, by cooling the con- 

 tents of the latter, diminishes the draught, and thus affects the 

 supply of the supporter of combustion. When, as with coke, 

 or cinders of any kind, the combustion is confined to the fuel 

 on the grate, air is not required above ; yet such is the neglect, 

 not unfrequently observed, that the same draught may be some- 

 times found with every kind and quantity of fuel. 



When the waste steam was first thrown into the chimney 

 of locomotives, it was found that the draught was enormously 



