SLAG CEMENT. REQUISITES AND TREATMENT OF THE SLAG. 651 



head at the upper end of the drier. The material is picked up by 

 buckets or carriers fastened to the inner surface of the outer cylinder, 

 and is carried partly around during the rotation of the drier. On 

 dropping from these buckets it is caught by flights fastened to the outer 

 surface of the inner cylinder. These flights carry the material partly 

 around and then drop it on the outer cylinder, when the cycle of opera- 

 tions commences again. While the movements of the material are 

 occurring, it is being dried both by the heated-air current which flows 

 through the space between the two cylinders, and by contact with the 

 warm outer surface of the inner cylinder; and it is also being carried 

 slowly toward the lower or discharge end of the machine. 



The following table shows working results obtained in the use of 

 the Ruggles-Coles drier on blast-furnace slag at various slag-cement 

 plants : 



TABLE 245. 

 WORKING RESULTS OF RUGGLES-COLES DRIER. 



The Hoist drier is used at Donjeux and Mallstadt, and consists 

 essentially of a sheet-iron cylinder 9 meters long and 0.8 meter in diam- 

 eter, into which the slag is fed automatically by a screw feed. In the 

 cylinder a helical screw revolves on a hollow central shaft, causing the 

 slag to advance slowly through the cylinder. The fireplace is below 

 and near one end of the cylinder and the heat is caused to pass under 

 the cylinder to the other end, thence through the hollow shaft to the 

 stack in a direction contrary to that in which the slag is moving. The 

 cylinder is protected from the direct flame by brickwork. This appa- 



