CLAY WORKING INDUSTRIES. 181 



variations would be in the state of the atmosphere and the closeness of 

 the setting of the ware in the kiln. In a compound stack, the draft 

 varies greatly according to the number of kilns on full fire at once, and 

 the burner, unless he is a man of intelligence and good judgment, is likely 

 to have constant trouble from this cause, and no matter how good judg- 

 ment he may possess, the more judgment required, the more frequent 

 will the failures be. 



2d. One stack permits of more easy regulation than two or more. 

 One damper affects all parts alike, while in multiple stacks the number 

 of conflicting currents prevents the burners from securing very accurate 

 regulation. 



On the other hand, it may be urged in favor of the compound stack, 

 that the heat of one kiln, just finishing or cooling off, gives powerful 

 assistance to the draft of another which is just starting and whose draft 

 is therefore in the weakest condition. This assistance is of great benefit 

 in getting through the drying out and heating up stages of the burn, but 

 as previously shown, it becomes a source of danger when the vitrifying 

 stage is attained. Also in favor of multiple stacks it may be urged that 

 they are cheaper to construct than one stack of any pretensions, and also 

 they have the great advantage of using no yard room, being built in the 

 circumference of the kiln walls, and thus affording greater economy of 

 space and convenience of arrangement than can be attained with either 

 single or compound stacks. 



In producing the draft of square kilns, the conditions vary somewhat 

 from those of round kilns. By a square kiln is meant a rectangular one; 

 not one of equal length and breadth. In fact the square kilns in use, are 

 usually eighteen feet wide, by seventy or eighty feet long. In kilns of 

 this size, it is impossible to devise any plan which shall enable one stack 

 to reach the various parts of the kiln with equal efficienc}^. Therefore, 

 a multiplicity of stacks is a necessity in this type of kiln. But they may 

 still be arranged so as to be under as much control as the single stack on 

 the round kiln or they may be arranged at such frequent intervals along 

 the sides as to produce entirely different effects. 



The most excellent burning that was seen in the state in a rectangu- 

 lar kiln was accomplished in one which was about thirteen feet wide by 

 thirty feet long. The stacks were arranged at both ends of the kiln and 

 the main central flue connected each stack. This flue was divided by a 

 horizontal partition into a top and bottom compartment. The bottom 

 compartment, opened only into the central third of the kiln's length, the 

 top parts drained the two end thirds of the kiln, each to its own stack; 

 by dampers the whole draft or any part of it could be directed to either 

 end or the center. By such an arrangement, where control is possible, 

 two or more stacks are an advantage ; in fact, in long kilns they are almost 

 a necessity to secure anything like the best work. By the use of a large 

 number of small stacks built in the kiln walls the problem is somewhat 



