PREPARING THE MIXTURE FOR THE KILN. 419 



are still of interest, as they resulted in a high-grade, though expensive, 

 product. 



At the Empire plant the marl and clay are obtained from a swamp 

 about three fourths of a mile from the mill. A revolving derrick with 

 clam-shell bucket was employed for excavating the marl, while the 

 clay was dug with shovels. The materials are taken to the works over 

 a private narrow-gauge road, on cars carrying about three tons each, 

 drawn by a small locomotive. At the mill the cars were hauled up 

 an inclined track, by means of a cable and drum, to the mixing floor. 



The clay was dried in three Cummer "salamander" driers, after 

 which it was allowed to cool, and then carried to the mills. These mills 

 were of the Sturtevant " rock-emery" type, and reduced the clay to 

 a fine powder, in which condition it was fed, after being weighed, to the 

 mixer. The marl was weighed and sent directly to the mixer, no pre- 

 liminary treatment being necessary. The average charge was about 

 25 per cent clay and about 75 per cent marl. 



The mixing was carried on in a mixing pan 12 feet in diameter, in 

 which two large rolls, each about 5 feet in diameter and 16-inch face, 

 ground and mixed the materials thoroughly. The mixture was then 

 sampled and analyzed, after which it was carried by a belt conveyor 

 or two pug-mills, where the mixing was completed and the slurry formed 

 into slabs about 3 feet long and 4 to 5 inches in width and height. These 

 on issuing from the pug-mill were cut into a number of sections, so 

 as to give bricks about 6 inches by 4 inches by 4 inches in size. The 

 bricks were then placed on slats, which were loaded on rack cars and 

 run into the drying tunnels. The tunnels were heated by waste gases 

 from the kilns and required from twenty-four to thirty-six hours to 

 dry the bricks. 



After drying, the bricks were fed into dome kilns, twenty of which 

 were in use, being charged with alternate layers of coke and slurry 

 bricks. The coke charge for a kiln was about four or five tons, and 

 this produced 20 to 26 tons of clinker at each burning, thus giving a 

 fuel consumption of about 20 per cent, as compared with the 40 per 

 cent or so required in the rotary kilns using wet materials. From 

 thirty-six to forty hours were required for burning the charge. After 

 cooling, the clinker was shoveled out, picked over by hand, and reduced 

 in a Blake crusher, Smidth ball mills, and Davidsen tube mills. 



