Mance: Quarry Industry of Southern Indiana 191 



concrete made from crushed limestone is practically as strong as 

 that produced from any other stone. In the manufacture of 

 concrete the crushed rock should be angular since the resulting 

 aggregate is stronger than with worn particles. 



For any of the above uses the material need only be crushed 

 to about 2-inch size. Thus a single coarse crusher is all that is 

 needed. The most common type used in this work is the Blake 

 jaw crusher. 



Extensive tables on the cost of coarse crushing are given 

 in the chapter on Ground Limestone, and these cost figures will 

 apply equally well to the work on road material because the same 

 machinery is used for rough crushing in both cases. 



The cost of crushing with a Blake type crusher ranges from 

 3 to 63^ cents per ton, depending on the output of the crusher. 

 The power consumed per ton crushed to 2-inch size is about 

 yV of a horse-power per hour. 



Waste Limestone as a Flux for Blast Furnaces. In the 



treatment of iron ore in the production of pig iron it is necessary 

 to add some fusible material of low specific gravity as a means of 

 removing the impurities present in the ore. The present method 

 of ore treatment in use in this country is to feed the ore together 

 with coke and limestone into the blast furnace thru a pair of 

 hoppers closed by means of bells. The object of the double 

 valve is to avoid the escape of the furnace gases. Large quantities 

 of air heated to 600 or 800 degrees Centigrade are forced into the 

 lower part of the furnace at a pressure from 12 to 15 pounds per 

 square inch. This air burns the coke and the heat thus generated 

 melts the charge, and as the material settles to the bottom of the 

 furnace the ore and the slag separate on account of their different 

 specific gravities. The limestone is decomposed by the high 

 temperature, giving up carbon dioxide, and changing to calcium 

 oxide or common lime. 



The large amount of silica and clay or alumina which is 

 contained in the ore unites with the lime formed from the lime- 

 stone to form what is called the slag. This slag is the waste 

 product in the manufacture of iron and usually has the following 

 general composition: 30 to 35 per cent Si02, 10 to 15 per cent 

 AI2O3, and 50 to 55 per cent CaO. The amount of limestone to 

 be used with any ore is determined by the amount necessary to 

 produce an easily fusible slag. 



If the slag is not made use of it is drawn off into large tilting 

 ladle cars and dumped away. In most cases this slag has the 



