366 THE APPLE 



correspondingly large ash pits, and large radiating surfaces. As 

 it is necessary to burn a relatively large quantity of fuel in a given 

 time, the size of the grate is made with this end in view. For a 

 kiln floor 20 feet square, or 400 square feet of surface, the grate 

 surface is usually about 3 feet in diameter, containing from 5 to 

 7 square feet. 



As to the most satisfactory length of pipe connecting the fur- 

 nace and chimney, opinions differ. The furnace, with two flanges 

 for attaching the pipe, is placed in the center ; the pipe from each 

 flange is then extended to the side of the room opposite the chim- 

 ney, and from this point the two sections, extending in opposite 

 directions, follow the wall, at a distance of 2 or 3 feet from it, to 

 the chimney. In a kiln 20 feet square some 65 or 70 feet are 

 thus required. Ten-inch pipe is a common size to use for this 

 purpose, and is placed about 3 feet below the kiln floor. 



In kiln evaporators the steam pipes are generally placed in as 

 close proximity to the floor of the drying room as is practicable — 

 within a foot or even closer. That every steam pipe nearest the 

 floor may supply the greatest amount of heat, it should have its 

 own return to the main return of the system. 



One-inch pipe is generally used for such systems. No very 

 definite data are available in regard to the amount necessary to 

 supply the requisite heat. Several kilns, however, which are said 

 to work admirably, have about 650 running feet of pipe for every 

 100 square feet of floor space. One half of this is "riser," the 

 other half " return." 



Fuel. For kiln evaporators using the common type of furnace, 

 hard coal is probably the most satisfactory fuel, and requires less 

 attention than any other. Coke is sometimes used, and if it were 

 as satisfactory as coal, it would be the cheaper fuel ; but it requires 

 much attention, and even with the best of care it is difficult to 

 maintain a uniform degree of heat. A combination of coal and 

 coke is sometimes used with satisfactory results, in which case the 

 faults and advantages of the one tend, in a measure, to equalize 

 those of the other. 



In a steam-heated plant soft coal serves the purpose in a satis- 

 factory way, and in most apple-growing sections is probably cheaper 

 than any other fuel that is readily available. 



