Mance: Quarry Industry of Southern Indiana 137 



breaking. The quarry company furnishes this material free on 

 board the cars at 15 cents per ton. The company has a large 

 belt conveyor to carry the waste from a nearby scabbling machine 

 to the crusher. 



The preparation of the limestone for fertilizing purposes 

 consists simply in pulverizing the stone until it will pass a certain 

 mesh screen. The size of the largest lumps that will be of value 

 upon land is still an open question, but the general idea is that 

 the larger the lumps the more slowly does the sweetening process 

 take place, but the longer can its results be noticed. The stone 

 is usually fed to a large crusher called a breaker, which reduces 

 it to a certain defined size. The largest piece that will pass a 

 given ring is the size by which the product is known. It is 

 then crushed fine in some form of pulverizer, and screened. 

 The fine product is stored, while the material too coarse to pass 

 the screen is returned to the pulverizer and worked over again. 



Rock breakers are of three general types: (1) jaw breakers, 

 in which the motion of the crushing parts is reciprocating; (2) 

 gyrator crushers, in which the motion of the crushing parts is 

 rotary and spiral; (3) roll crushers, in which the motion of the 

 crushing parts is rolling. 



The jaw breakers are of two types according to whether the 

 greatest movement comes on the smaller lumps fed or on the 

 larger. The first kind is known as the Blake type of crusher and 

 the latter kind is known as the Dodge type. Very complete 

 descriptions with sectional drawings of all types may be found in 

 the work of Professor R. H. Richards, of the Massachusetts 

 Institute of Technology, entitled Textbook of Ore Dressing. 



Gyratory crushers are classified on the same principle as the 

 jaw breakers. The type most widely used and the one that will 

 give the best results in the crushing of limestone for fertihzing 

 material is the Gates or the McCully type of breaker. The 

 rolling crushers are known as Forster crushers. 



The jaw breakers are usually selected where the output of 

 the plant is small, on account of their small first cost and the fact 

 that the cost of upkeep depends to a large extent upon the out- 

 put. The cost, per unit of output, of crushing a small quantity 

 is in favor of the jaw crusher. In the selection of a jaw crusher, 

 great care is necessary on account of the great strain that the 

 machine must withstand. The following points should be kept 

 in mind when a selection is to be made: The frame should be 

 heavy and cast in as few pieces as possible. Foundations should 



