466 



CEMENTS, LIMES, AND PLASTERS. 



and has, therefore, been already figured and described on pages 36, 37. 

 Of the other impact pulverizers, the Williams mill is the only one ex- 

 tensively used in Portland-cement manufacture. 



Raymond pulverizer. Two Raymond pulverizers, one with three 

 rollers and one with four, are in use at one plant, taking a dry lime- 

 stone-and-shale mixture from dry-pans at about 30-mesh and reduc- 

 ing it to 98 per cent through a 100-mesh sieve. Each of these mills 

 requires about 85 H.P., and delivers about 3^ tons of product (=11| 

 barrels cement). This seems to be a remarkably high figure for power, 

 being equivalent to about 7| H.P. hours per barrel, and it is probable 

 that the pulverizer is not being run up to its true efficiency. 



FIG. 105. View of Williams mill, casing opened. 



Williams mill. The Williams mill is shown in view, with its casing 

 opened, in Fig. 105, and in section in Fig. 106. It will be seen that 

 it crushes by the blows of a series of hammers, rapidly revolving about 

 a horizontal central axis. 



The following record of an actual working test, communicated to 

 me by the chemist of a plant using the Williams mill on its raw mate- 

 rials, will serve to show the percentages on different sieves that are 



