CHAPTERS ON THE CEMENT INDUSTRY 865 



As noted below, rotary kilns were installed by this company 

 during 1901, and in consequence changes have been made in 

 the methods of preparation of the materials. The processes 

 formerly followed are given here, as being good examples of high- 

 grade practice at a dome kiln plant. 



The clay was dried in Cummer " Salamander " dryers, three 

 being in use, after which it was carried by conveyors to the mills, 

 being cooled before grinding. These mills were of the Sturtevant 

 " rock emery " type, and reduce the clay to a fine powder, in 

 which condition it is fed to the mixer after weighing. The marl 

 was sent directly to the mixing machine, no preliminary treat- 

 ment being necessary. The marl and clay were weighed, to 

 secure proper proportions. The relative amounts used varied, 

 of course with changes in the chemical composition of the mate- 

 rials, the average charge being about 25$ clay and 75$ 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, with 

 16 inch face, ground and mixed the materials thoroughly. The 

 mixture was sampled and tested, after which it passed, on a belt 

 conveyor, to two pug mills, where the mixing was completed 

 and the slurry was formed into bricks about 3 feet long and 5 

 inches diameter. These bricks were placed on slats, which were 

 loaded on to rack cars, and run into the drying tunnels. These 

 tunnels were heated by waste gases from the kilns, and required 

 24 to 36 hours to dry the bricks. 



After drying, the bricks were fed to the kilns, which were 

 charged with alternate layers of coke and cement mixture. 20 

 kilns, all of the dome type, were in use. The coke charge for a 

 kiln was about four to five tons, and 20 to 26 tons of clinker 

 were produced for each kiln at each burning. From 36 to 48 

 hours were required for burning the charge. After cooling the 

 cement clinker was shovelled out, and sent to the reducing de- 

 partment. It received its first reduction in a Blake crusher. 

 From this it passed to Smidth ball mills, three of which were 



