242 CEMENTS, LIMES, AND PLASTERS. 



and furrows, and the material fed between them is disintegrated rapidly. 

 It is stated that this mill, when working on hard natural-cement clinker, 

 has given very satisfactory results. "The clinker is fed to the mill 

 broken to about the size of 1-inch cubes, and is reduced to about the 

 size of wheat, and from that down to dust, at the rate of 20 tons per 

 hour. This work requires 50 horse-power. In a trial this mill has 

 reduced natural cement (taken direct from the kilns, with the softer 

 portions mixed with the clinker, the latter amounting to about one 

 third of the total) at the rate of 1300 Ibs. pe'r minute, the product pass, 

 ing 50-mesh wire screens. The cost of renewal of the grinding plates 

 has been $10 per month, no other repairs being necessary". Using 

 the data above quoted as bases for calculation, it may be seen that 

 the Cummings grinder, when used as a coarse reducer, taking mate- 

 rial of 1 inch size and reducing it to, say, A inch, requires 2.7 H. P. hours 

 per barrel (300 Ibs.) cement. When used as a complete grinder, taking 

 coarse clinker and reducing it all to pass 50-mesh, it requires 5.2 H.P. 

 hours per barrel of cement. 



Though no direct statement is made by Mr. Ball, it is perhaps fair 

 to assume that the trial noted above took place at the mill of the Cum- 

 mings Cement Company in Akron, N. Y. The following description 

 of the reduction practice there will, therefore, be of interest in this 

 connection. It must be recollected that the cement rock of western 

 New York is of very low index, and that the hard, clinkered portions 

 are therefore very valuable when ground. 



The crushing practice at the Cummings plant at Akron, N. Y., is 

 stated by Ries * to include the following processes: 



"At this works a general system of reduction is used, consisting 

 of (1) Sturtevant crushers; (2) Cummings pulverizers; (3) ten run 

 of 42-inch under-runner millstones faced with chilled-iron plates; (4) ten 

 run of 42-inch Esopus under-runner millstones. The material as it is 

 conveyed from one to another of these sets of crushers is made to pass 

 over screens, whereby such material as has been reduced to proper 

 fineness is separated from the mass and is spouted to a general con- 

 veyor, which finally receives the product from all the grinding machines 

 and conveys it to the packing-house." Each set of crushers, while it 

 furnishes a certain percentage of finished product, reduces the entire 

 material to such a degree that what is fed to the fourth series is about 

 the size of wheat-kernels and very hard to reduce. These harder- 



* Ries, H. Lime and cement industries of New York. Bull. 44, New York 

 State Museum, pp. 836, 837. 



