184 GEOLOGY OF OHIO. 



4th. The main flue runs from the stack under cover to a central 

 well hole which is open to the top. From this wall, radiating pier walls 

 run to the circumference. 



By this arrangement, the draft of any one part of the circumference 

 is as good as any other, but the tendency is for the draft to take the 

 shortest cut to the center of the kiln leaving soft bricks all around the 

 circumference. 



5 th. The main flue runs under cover to a center well-hole, which is 

 partly covered with impediments to the draft. From the well-hole a 

 number of flues radiate under cover to points around the the circumfer- 

 ence of the kiln, where they come to the surface with an open top. By 

 this arrangement the draft is equal in all parts of the circumference, and 

 in addition, the excess of the draft which cannot get through the aper- 

 tures above the well-hole is diverted to the circumference of the kiln, 

 by which the most even distribution of the heat can be effected. 



6th. The flue runs under cover to a center well hole which also is 

 nearly covered up by tiles. From the well hole, 8 or 10 flues radiate under 

 cover, to a ring flue which runs with open top around the kiln in front of 

 the bag walls. ' By this arrangement, practically all the draft is made to 

 escape from the kiln from this ring flue. No section can possibly have 

 any advantage over another. And the heat of the kiln being brought to 

 the floor in a zone around the center and near the outside is bound to 

 travel to the center by induction. 



This arrangement is often varied by making the only points for the 

 draft to leave the kiln to be a set of holes between each bag. There is 

 danger in this plan, especially when burning brick, that the outsides will 

 become hot too far in advance of the center and accordingly a little heat 

 is usually allowed to find its way into the well hole direct, without 

 going to the circumference of the kiln and then traveling back to the 

 center under cover. 



7th. The flue system is sometimes arranged as in 5 and 6, under a 

 solid floor; the ends of the flues being marked merely by holes of small 

 size. The small flues are then made of the material to be burnt, by set- 

 ting it with this point in veiw. This kiln has one great advantage. It 

 can be cleaned every burn with no expense, while the others are some of 

 them very expensive to clean from the sand and ashes and brick dust 

 and chippings. The distribution of the heat in this style of bottom is 

 not apt to be as good as in a permanent checker floor. 



There are two principal points which ought to be always provided 

 for in the construction of any round kiln bottom. 



1st. Make all the draft accumulate in the center of the kiln, before 

 conducting by a covered flue to the stack. By this plan only is it possi- 

 ble to give every point of the kiln an equal chance for draft. 



2d. Arrange that the largest part of the draft shall only get to 

 the center, aftei having passed through the floor of the kiln and then 



