1886.] on the Princijples of Domestic Firejjlace Construction, 341 



reduction to a mineral residue, but spare heat for driving two 

 60-liorse power engines, and for consuming a reasonable amount 

 of pigs, &c., killed by or on account of disease. 



These three great evils, evils affecting not only individuals, but 

 the community, waste of fuel and heat, production of soot, production 

 of cinders, are a direct result of the violation of the correct principles 

 in fireplace construction. 



Let us next enquire what are the principles which promote good 

 combustion in an open firej)lace — i. e. what are the conditions which 

 are essential to enable fuel to give out to a room " good money's 

 worth in heat." That such a result may be obtained, fuel must 

 burn ivell but not rapidly. Two things in combination are essential 

 to the combustion of fuel — a supply of oxygen, and a high tempera- 

 ture — i. e. plenty of heat around the fuel. If fuel be burned with 

 a hot jacket around it, a very moderate amount of oxygen will 

 sustain combustion, and if the supply of oxygen be moderate, com- 

 bustion is slow. Burn coal with a chilling jacket around it, a 

 rapid conductor like iron, and it needs a fierce draught of oxygen to 

 sustain combustion, and this means rapid escape of actual heat, and 

 also of potential heat in unburnt gases and smoke, up the chimney. 

 This is the key to the whole position ; this is the touchstone by 

 which to test the principles of fireplace construction. 



Few people probably realise the exact conditions of combustion, 

 which may be well illustrated from the process of manufacture of 

 coal gas. In coal we have three kinds of constituents. One mineral, 

 incombustible, seen in the ash residue, which for good coal amounts 

 to barely 3 per cent. The second, volatile, and which, under the 

 influence of heat becoming gaseous, appears in an open fire as tall 

 flame and smoke, and, where combustion is imperfect, produces soot. 

 The third constituent is carbon or charcoal, familiarly known as 

 coke or cinder, and when burning gives a short shallow blueish 

 flame. The carbon and the volatile portions can be raised to a high 

 temperature, and still will not burn unless oxygen be brought into 

 contact with them. 



In the manufacture of gas, coal is raised to a high temperature, 

 and the gases are driven off by roasting the coal in an oven from 

 which air, i. e. oxygen, is shut out. The gases are conducted away, 

 cooled, purified, and stored for future use in a gasometer ; the com- 

 bined carbon and mineral residue, being non-volatile, is cooled down 

 before being exposed to the air, and is sold as coke. Here we have 

 a striking proof of the fact that high temperature in fuel does not of 

 itself involve combustion. If air were admitted to the red-hot coke, 

 or to the gases as they escape in their heated condition from the 

 furnace, they would burn. But when coke has become cold, and the 

 gases are cold, as in a gasometer, no amount of oxygen will of 

 itself start combustion. 



The deduction from all this is, that complete oxydation, i. e. 

 good combustion, is possible only when the fuel and gases are at a 



