CRUSHING AND PULVERIZING MACHINERY. 



465 



TABLE 180. 

 ANALYSES OF FLINT PEBBLES. 



1. Greenland. " Dana" brand. H. S. Turner, analyst. 



2. Havre, France, light. Heiberg and Honey, analysts. 



3. " " : dark. 



4. St. Valerien, France: no. 1. " 



5. " " : no. 2. " " " 



6. Norway: light. " " " " 



7. " rdark. 



From these analyses it will be seen what large variations in com- 

 position occur in different kinds of flint pebbles. Other things being 

 equal, the pebbles highest in silica should give the best results, while 

 lime is a particularly injurious impurity. 



The high cost of flint pebbles for mills situated in the middle and 

 western United States has led to many attempts to secure a domestic 

 substitute for the expensive imported pebbles. Rounded pebbles of 

 shape and character suitable for this use occur only on the shores of 

 great lakes or along the beds of mountain streams. A California mill 

 secures its supply from the American river, where rounded granite 

 pebbles occur in quantity. These pebbles, gathered by Chinamen, 

 cost less than $5.00 per ton at the mill, and are about half as durable 

 as imported flints. For grinding 3000 barrels of cement, 800 Ibs. of 

 granite pebbles were used up, as against 400 Ibs. of imported flint pebbles. 



Flint occurs in several formations in America, but in no case do 

 these formations outcrop along the shore, so that the flint can be obtained 

 only in rough angular masses. Along the north shore of Lake Superior 

 hard quartzite pebbles are said to occur in quantity, and this district 

 may furnish a supply for the American cement trade if any manufac- 

 turer cares to investigate the matter. 



Class 8. Impact Pulverizers. 



The impact pulverizers include all those types of grinding-machines 

 in which the material is broken by a blow, in free space, delivered by 

 a series of rapidly revolving hammers, bars, cups or cages. This group 

 therefore includes the Williams mill, the Raymond pulverizer, the Stur- 

 tevant and Stedman disintegrators, the Cyclone pulverizer, and many 

 other less well-known devices. The Stedman disintegrator is exten- 

 sively used in crushing gypsum or plaster and natural-cement clinker, 



