234 THE POPULAR SCIENCE MONTHLY. 



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 fur- 

 nace, 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 oxidation, i. e., good 

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

 temperature, and that high temperature of fuel does not produce com- 

 bustion until oxygen is introduced : therefore we can have a high tem- 

 perature of fuel, without rapid combustion, provided we control and 

 limit the supply of oxygen. If we have thoroughly grasped these 

 elementary facts, we shall be in a position to understand the points to 

 be aimed at in the construction of a fireplace. 



My attention was first directed to the question of waste of fuel at 

 the time of the coal-famine some twelve years ago. I read in the 

 " Times," and acted upon the suggestion, to economize coal by insert- 

 ing an iron plate on the grid under the fuel so as to cut off all draught 

 through the fire. This undoubtedly induced slow combustion, and 

 economized fuel, but the fire was dull, cold, and ineffective. The plan 

 was abandoned. It taught me, however, the fact that combustion 

 could be controlled by cutting off the under-draught, but I did not 

 then see why combustion was spoiled. The reason was that the 

 under surface of the fire was chilled, and the fuel lost its incandes- 

 cence owing to the rapid loss of heat through the iron toward the 

 open-hearth chamber. To some persons even now "slow-combustion 

 stoves " are an abomination, and are supposed to by synonymous with 

 bad combustion. 



The next stage in my fireplace education was the adoption of the 

 Abbotsford grate. I thereby learned that the reason why an Abbots- 

 ford grate was an advance upon the iron plate lay in the fact that the 

 solid fire-brick bottom stored up heat and enabled the fuel to burn 

 more brightly resting upon a hot surface not upon a cooling iron 

 plate. But Abbotsford grates, and the other class of grates with solid 

 fire-brick bottoms, the Parson's grates, have disadvantages. They are 

 apt to become dull and untidy toward the end of the day, and do not 

 burn satisfactorily with inferior coal. There is a better thing than a 

 solid fire-brick bottom, and that is the chamber under the fire closed 

 in front by an " Economizer." 



The history of the next, the most important stage of my fireplace 

 education, was as follows : 



Some five years ago I made, somewhat accidentally, the discovery 

 that the burning of coal in an ordinary fireplace could be controlled 

 and retarded by the adoption of a very simple and inexpensive con- 



