48 



On the arrival of the raw materials at the mill the clay is 

 often dried, in order to simplify the calculation of the mixture. 

 The reduction of the clay is commonly accomplished in a dis- 

 integrator or in edge-runner mills, after which the material is 

 further reduced in a pug mill, sufficient water being here added 

 to enable it to be pumped readily. It is then ready for mixture 

 with the marl, which at some point in its course has been screen- 

 ed to remove stones, wood, etc., so far as possible. The slurry 

 is further ground in pug mills or wet grinding mills of the disk 

 type ; while the final reduction takes place commonly in wet tube 

 mills. The slurry, now containing 30 to 40 per cent, of solid 

 matter and 70 to 60 per cent, of water, is pumped into storage 

 tanks, where it is kept in constant agitation to avoid settling. 

 Analyses of the slurry are taken at this point, and the mixture 

 in the tanks is corrected if found to be of unsatisfactory com- 

 position. After standardizing, the slurry is pumped into the 

 rotary kilns. Owing to the large percentage of water contain- 

 ed in the slurry the fuel consumption per barrel of finished ce- 

 ment is 30 to 50 per cent, greater, and the output of each kiln 

 correspondingly less than in the case of a dry mixture. 



It may be of interest, for comparison with the above descrip- 

 tion, of the wet process with rotajry kilns, to insert a description 

 of the semi-wet process as carried on a few years ago at the 

 dome kiln plaint of the Empire Portland Cement Company at 

 Warners, N. Y. The plant has been remodeled since that date, 

 but the processes formerly followed are still of interest, as they 

 resulted in a high-grade though expensive product. 



At the Empire plant the marl and clay were obtained from a 

 swamp about three- fourths of a mile from the mill. A revolv- 

 ing derrick with clam-shell bucket was employed for excaivat- 

 ing the marl, while the clay was dug with shovels. The mater- 

 ials were taken to the works over a private narrow-gauge road, 

 on cars, carrying about three tons each, drawn by a small loco- 

 motive. At the mill the cars were hauled up an inclined 1rack, 

 by means of a cable and dlrum, 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 re- 

 duced 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 preliminary treatment being neces- 



