478 CEMENTS, LIMES, AND PLASTERS. 



other, the upper rings where the greatest heat occurs being hooped 

 at the joints. The top of each kiln is provided with a cone and a chimney 

 made of sheet iron, 3 feet in diameter and 30 feet in height. The cone 

 has four charging doors, which can be closed by sheet-iron covers as 

 soon as the charging is done. 



At a depth of 12 feet from the top the inner diameter of the kiln 

 is lessened to nearly half its inner horizontal section, and on this zone 

 is provided with a double row of tuyeres to admit compressed air, this 

 arrangement having for its object to burn any carbonic oxide or carbu- 

 retted hydrogen gas arising from below as completely as possible, as 

 well as to concentrate the heat exactly where it is required, viz., on 

 the place where the formation of the clinker is to take place. 



Compressed air is also introduced from below in two places. The 

 pressed air is produced by a ventilator, the pressure being f inch to 1J 

 inches of water. One charge consists of 100 bricks and 65 to 70 Ibs. 

 of coke as fuel; one third of the coke could be rep'aced, if necessary, 

 by anthracite or other small coal. 



As a rule, four kilns are arranged in one set, being provided with a 

 common elevator and a common platform, for all four kilns together. 

 They are surrounded by a scaffolding made of angles and tees, on which 

 the staircase to mount the platform is fixed. At the same time cor- 

 rugated galvanized sheets are riveted on this scaffolding all round, in 

 order to prevent unequal cooling of the furnaces outside in case of rain, 

 wind, or snow. 



The principal advantage of a kiln of this description is that, owing 

 to the continuous and regular cooling from outside, the fritted clinker 

 cannot clog the interior of the furnace, thus ensuring a regular and 

 continuous working of the furnace. The ribs at the same time give 

 strength, and prevent the cast-iron rings from warping. Each fur- 

 nace produces about 25 tons of well-burnt clinker, equal to as much 

 finished cement, in twenty-four hours. 



Reference list for fixed kilns. The design, construction, and opera- 

 tion of vertical or stationary kilns of various types are discussed in 

 many books and papers on Portland-cement manufacture. The most 

 satisfactory of these discussions are included in the following annotated 

 list of references on the subject: 



Butler, D. B. Portland Cement: its manufacture, testing, and use. 1899. 

 Chapter IV of this volume, pp. 71-102, includes descriptions of the 

 dome kiln, Johnson kiln, Batchelor kiln, Dietzsch kiln, and Hoffmann 

 kiln. The discussion of the Johnson kiln and its modifications is par- 

 ticularly valuable. 



