clay Working industries. 185 



travelled through covered radial" flues" from the circumference to the 

 central Well hole.' By this' forcing bf the draft td the circumference, 

 only, is it possible to get the outside portions as hard burnt 'as the center, 

 for the circumference is 'constantly' cooled off by radiation and cold air 

 leaking intb the kiln' and perhaps' water, etc., while the center is sur- 

 rounded' by beat on all Sides and'rs bound to become equally hot with the 

 outsides by conduction alone if it is furnished ho draft at all. 



If these' two principles are adopted' in reference' to the arrangement 

 of the bottom', and good' economical fireplaces are used and' a single stack 

 of sufficient size with proper dampers for controlling' it 'are provided, 

 the round down draft kiln cannot fail to be a good 'and satisfactory 

 means of producing' vitrified clay ware.' 'There is another point of 

 importance, which directly influences tie economy of fuel and time,' etc., 

 but it is subsidiary to these ; essentials Without which the highest grade 

 of results are impossible. This point, Which has great influence in 

 assisting the draft to bring the vitrifying temperature down to the floor 

 of the kiln, is the relative height' of the kiln floors and the fireplace 

 floors. The fireplace floor or grateb'ars ought to be plated '36 inches 

 lower than the kiln flobr or as near this as the conformation of the kiln 

 yard and surroundings Will' admit. The reason is twofold; 1st. The 

 lower part of the fireholes' and bags become choked with clinkers dur- 

 ing the progress of a burn and therefore 1 cease to radiate heat to any 

 extent. If the floor of the kiln and the foot of the bag are on 

 the same level, the bricks around the foot of the bag Will not be heated 

 by radiation and the draft will pass them by in a more direct course 

 to the escape points, and a constant 1 percentage of soft material around 

 the bags and walls at the floor may be expected. If however the 

 floor be 18 or 24' Or 36 inches up above, the bag wall is always hot at 

 that point and by' its radiation powerfully assists in drawing 1 the draft 

 away from the center and other favored spots to those which are natur- 

 ally cold. 



; ' 2d. The deeper- the kiln bottom, with its network bf flues is set 

 in 7 the ground, the more trouble from dampness and water from 

 outside and the' more time and more ' fuel are expended in getting 

 the heated currents of gases' to penetrate it and' the 'higher will the stack 

 have to be built, in order to ' obtain the necessary' head to ftvercome this 

 natural reluctance to go down. 



By raising the floor, the^ bottom cah be niade very shallow; and : not 

 only is' the extra expense bf a higher stack saved, but the' draff of the kilns 

 begins earlier in the burn thus heating tip' faster and "saving in' this' Way 

 both time and fuel.' .' . ,' 



" In some situations,' the establishing of a' different' level for the kiln 

 floor and the firing 'floor, is a decided Ihcorivenience— but wherever it 

 can be obtained it is well worth all the inconvenience it cbsts, in the 

 increased ahd regular percentage of hard burnt wares. " ' " ' 



