348 Means of increasing the Quantiti:s of Heat 



their accumulating at the bottom of the grate. As the 

 coals go on to consume, the balls mixed with them will 

 naturally settle down towards the bottom of the grate, 

 and the tongs must be used occasionally to lift them up ; 

 and as the fire grows low, it will be proper to remove 

 a part of them, and not to replace them in the grate 

 till more coals are introduced. A little experience will 

 show how a fire made in this manner can be managed 

 to the greatest advantage and with the least trouble. 



Balls made of pieces of any kind of well-burned hard 

 brick, though not equally durable with firebrick, will 

 answer very well, provided they be made perfectly 

 round ; but if they are not quite globular, their flat sides 

 will get together, and by obstructing the free passage of 

 the air amongst them and amongst the coals will pre- 

 vent the fire from burning clear and bright. 



The best composition for making these balls, when 

 they are formed in moulds and afterwards dried and 

 burned in a kiln, is pounded crucibles mixed up with 

 moistened Sturbridge clay ; but good balls may be made 

 with any very hard burned common bricks, reduced to a 

 coarse powder, and mixed with Sturbridge clay, or even 

 with common clay. The balls should always be made 

 so large as not to pass through between the front bars 

 of a grate. 



These balls have one advantage, which is peculiar to 

 them, and which might perhaps recommend the use of 

 them to the curious, even in fireplaces constructed on 

 the best principles : they cause the ^cinders to be con- 

 sumed almost entirely ; and even the very ashes may 

 be burned, or made to disappear, if care be taken to 

 throw them repeatedly upon the fire when it burns with 

 an intense heat. It is not difficult to account for this 



