Mance: Quarry Industry of Southern Indiana 179 



penetrated by at least five east and west roads and by the Monon 

 running from north to south. 



''Run of mine" and slack coal can be laid down in either town 

 very cheaply since the coal fields are less than forty miles away. 



Methods of Manufacture. There are two general methods 

 of cement manufacture known as the wet and dry method re- 

 spectively. The process adopted in any locality depends upon 

 the deposits to be worked and the economic conditions under 

 which the work is to be carried on. 



In the wet process the clay and chalk or marl are ground 

 in edge runners with heavy rolls till fine. This material is then 

 mixed with about half its weight of water. This slime or "slurry", 

 as it is called, is pumped into buhrstone or tube mills where it 

 is given a thoro grinding. After this wet paste is dried, it is 

 sent to the kilns where it is calcined. The burned clinker is 

 then ground fine to produce the finished product. The Hoffman 

 ring furnace which has already been described in the part of this 

 study treating of lime, is often used in the calcining of cement. 

 Another type of furnace much used is the Dietsch two-storied 

 kiln. This is a continuous kiln, the material being fed in at the 

 top and discharged at the bottom. Tests made on this type of 

 furnace with regard to the fuel consumption give about 7 tons 

 of clinker per ton of coal burned. The Hoffman furnace uses 

 about the same amount of coal per ton of clinker. 



In the dry process the materials, shale and limestone, are 

 ground separately to a good degree of fineness; then they are 

 carefully mixed in predetermined amounts by large mixing 

 machines and this mixed material is charged into the upper end 

 of a long rotating kiln. The fuel is driven into the lower end of 

 the kiln by compressed air and burns as it enters. The hot 

 gases and flame are driven up the kiln and meet the mixture 

 as it rolls down as a result of the rotating of the kiln. The 

 burned clinker drops from the lower end of the kiln where it is 

 picked up by a conveyor, carried to the top of a high tower, and 

 allowed to fall thru space to cool. The fuel charged into this 

 kiln is powdered coal, which gives a very high temperature, on 

 account of the powerful draft produced by the compressed 

 air. 



The cooled clinker is charged into a mill where it is finely 

 ground, and the product is then ready for the storage bins. The 

 shale and the limestone__are_first2 ground by large cruf^hers for 



