LIME AXD CEMENT INDUSTRIES 687 



On treatment with acids, the rock retains its shape, but the 

 clay is dissolved out, and the residue can then be broken down 

 with the fingers. If a coarse rock must be used, the burning 

 should be slow in order to give a combination between the lime 

 and silica every possible chance to take place. 



Manufacture 



The process of manufacture of this class of cements is com- 

 paratively simple. The rock as it comes from the quarry is usu- 

 ally broken into lumps of head size before being charged into 

 the kiln. 



The kilns in use in l\ T ew York state are similar to those used 

 for burning lime (pi. 3). The old type kilns are made of stone, 

 with the interior either round, oval or rectangular in cross-sec- 

 tion, and lined with fire brick. They are open at the top, and 

 taper at the bottom to an opening, through which the burned 

 stone is discharged. When the material is not being drawn, this 

 hole is sometimes kept coi x ered by grate bars. 



At Akron (N. Y.) the kilns have an interior area of 9 x 22 

 feet, or when round a diameter of 9 feet. The hight of all is 

 34 feet. 



The more modern kilns are cylindric in shape, made of boiler 

 iron. They are from 40-45 feet high and lined with fire brick. 



In burning natural cement rock, the fire is first started with 

 wood in the bottom of the kiln, and on this are spread alternating 

 layers of coal and rock. The coal is of pea or chestnut size com- 

 monly. As the burned stone is drawn from the bottom, fresh 

 stone and fuel are added at the top. The kilns are commonly 

 built on a hillside, or where the ground is flat, five, six or more 

 in a row, and in either case tracks are laid on the top to facilitate 

 the delivery of the stone and fuel. The yield of these kilns is 

 large, being from 50-120 barrels of cement 1 per ton of coal. 

 Some patented forms with the Campbell grate, such as is used 



iMin. ind. 2: 104. 



