SMOKE; ITS CAUSE AND PREVENTION 



97 



to burn the volatile matter as fast as it is produced by the 

 coal. Since it is not convenient to place frequent small 

 charges of coal in the stove, the other method commonly 

 resorted to in smokeless combustion is the gradual and slow 

 distillation of the volatile matter in the soft coal, so that the 

 drafts can furnish oxygen fast enough to consume the volatile 

 matter completely. 



112. How Some Stoves and Furnaces are Constructed to 

 Prevent Smoke. A common device is the HOT BLAST stove. 



FIG. 72. Stove with air blast. FIG. 73. Another form of air blast. 



In this stove the air for the oxygen supply is admitted from 

 above instead of from beneath the grate as in most stoves. 

 By the top-draft arrangement, the volatile matter has a better 

 chance to meet oxygen and hence its complete combustion 

 is more readily accomplished (Figs. 72 and 73). 



In some furnaces the coal is first thrown into a COKING 

 CHAMBER which is heated by the fire in the fire pot. Here slow 

 distillation of the volatile matter takes place. By means of a 

 damper in the coking chamber door, sufficient air can be 

 admitted and a sufficiently high temperature may be main- 



