CLAY WORKING INDUSTRIES. 183 



weight of the material to be burnt, while the gases find ready circulation 

 through and beneath this floor, and from this lower level they make their 

 escape to the outside. 



On the arrangement of this lower flue area or "bottom", the effi- 

 ciency of the kiln largely depends. 



There are very few, if any, kiln bottoms in which an adjustable control 

 of the gases is attempted. The only feasible plan seems to adjust the ar- 

 rangement from burn to burn according as the results indicate a need of 

 more or less draft in certain areas. 



In rounds kilns the different kinds of bottoms employed are very 

 numerous. It is impossible to describe all the types, and the variations 

 among these types are innumerable. A few of the most important will 

 be mentioned. 



1st. The main flue from the foot of the draft stack runs to the center 

 of the kiln and is there crossed at right angles by a flue of equal area, 

 running across the entire width of the kiln. The stack flue is covered 

 over; the cross flue is open to the top; the pier walls which support the 

 floor run at right angle to the cross flue and they are usually built of 

 "pigeon work" or checker work to allow free movement of the gases 

 back and forth as well as toward the point of draft outlet. 



The tendency of this bottom is to produce a zone of good burning 

 for a short distance on either side of the cross flue, and best in the center 

 of the kiln, leaving the opposite sides furthest from the center, soft. 



2d. The main flue from the floor of the stack runs into and straight 

 across the kiln. A circular flue or ring flue runs around the inside 

 circumference of the bag walls and communicates with the main flue at 

 the point of entrance, nearest to the stacks. The portions of the 

 straight flue and ring flues nearest to the stack are covered over, wholly 

 or partially ; the pier walls run at right angles to the main flue. This 

 bottom is the main feature of the socalled New Discovery Kiln, which is 

 sold under yard rights and "protected by patents." (?) The trouble with 

 this arrangement is that the draft tends to take the shortest course to the 

 stack and though the front is more or less blockaded to prevent this 

 tendency, still the draft will take the shortest course accessible, to the 

 neglect of the more distant parts of the kiln. The principle of this 

 bottom is therefore less rational than the first described. 



3d. The flue from the foot of the stack goes to the center of the 

 kiln, being open on the top from the circumference to the center. The 

 pier walls are built in a series of concentric circles, each circle being cut 

 by the main flue at one point. The floor bricks are arranged as nearly 

 as possible at right angles to the pier walls and therefore radiate from 

 the center like the spokes of a wheel. 



This bottom besides being very hard to clean and repair, still allows 

 the front half of the kiln to rob the rear half of its fair share of the 

 draft. 



