472 



CEMENTS, LIMES, AND PLASTERS. 



essentially as combinations of old-style dome kilns and drying-floors. 

 They utilize waste heat for drying the slurry; and are, therefore, more 

 economical in fuel consumption than is the single-dome kiln. They 

 are all based on intermittent working of the kiln, however; and in all, 

 the dried slurry must be charged into the kiln by hand. 



Six Johnson kilns were installed in 1890 at the plant of the Western 



FIG. 108. Plan and section of Johnson kiln. (Engineering News.) 



Portland Cement Company, Yankton, S. D., but have recently been 

 replaced by rotaries. I believe that similar kilns were used in the first 

 plant at Whitecliffs, Ark. 



3. Ring or Hoffmann Kilns. 



The Hoffmann or ring kiln has been used quite extensively in Ger- 

 many for burning Portland cement, lime, and bricks, but has* never 

 come into favor in either England or the United States. It consists 

 essentially of a number of chambers arranged in a circle or ellipse around 

 a central stack. Three flues lead from each chamber to (1) the cen- 

 tral stack, (2) the chamber preceding it in the series, and (3) the chamber 

 following it in the series. Each of these flues may be closed at will 

 by the insertion of a partition of sheet iron. Each chamber also has 

 a door opening to the outside of the kiln and used for charging and 

 drawing. 



Assuming that the kiln is entirely empty (a condition which could 

 occur only in firing up a newly built kiln), the operations would be as 

 follows: Each chamber would be loaded with bricks of dried slurry 

 stacked up as in a brick kiln. Slack or other fine coal is fed in at the 



