244 



CEMENTS, LIMES, AND PLASTERS. 



Two Davidsen tube mills, running on natural-cement clinker for 

 twenty-six months, turned out 694,522 barrels of cement. During 

 this time nothing was expended for repairs. The mills were only 

 dumped once, and the total loss of screening pebbles amounted to 

 less than one barrel. "The linings, silex and iron, and the bearings 

 were all found in good condition, with little or no wear to speak of." 



FIG. 48. Berthelet separator. 



1. Top view of separator with covers removed. 



2. Side view of separator. 



3. Cross-section of separator. 



4. Front elevation of separating system installed. 



5. Side elevation of separating system installed. 



Another pair of tube mills made a similar excellent record in regard to 

 output and repairs. 



Impact pulverizers. The Stedman disintegrator is described and 

 figured on page 36. It is used in at least one natural-cement plant 

 as a preliminary reducer on hard, partly clinkered material. 



The Williams mill, which is a high-speed pulverizer in which revolv- 



