MINERAL INDUSTRIES LIME AND LIMESTONE. fq 



or, if the limestone used for making quicklime contains magnesia, the follow- 

 ing equation is appropriate: Magnesian quicklime plus water becomes slaked 

 or hydrated magnesian lime — 



Ca0.Mg0-fH20-Ca(0H)2.Mg0. 



Commercially the term "hydrated lime" is restricted to the dry powder 

 prepared by treating quicklime with just enough water to combine with all 

 the calcium oxide present. In the preparation of hydrated lime two materials 

 only are used — fresh caustic lime and water. The general method of prep- 

 aration is first to reduce the lumps of lime by crushing to about Vs-inch size. 

 In some plants this reduction is carried further by grinding the lime to 

 about the fineness of granulated sugar. The crushed or granulated Hme is 

 then treated with sufficient water to combine chemically with the calcium 

 oxide in the lime, care being taken that the quantity is neither too Httle to 

 satisfy the chemical requirements nor so great as to leave the hydrated mass 

 wet or even damp. In practice, an excess of water is used, but this excess 

 is driven off by the heat generated in the slaking or hydrating of the Hme. 

 The object of crushing the product is to produce a larger surface for the 

 action of the water, and, moreover, large lumps would be rather unwieldy 

 in the hydrater. The lime comes from the hydrater as a fine, dry powder, 

 which must be screened to remove any coarse or overburned lime that would 

 not slake. From the screens it goes to the storage bin, where, if the 

 capacity is available, it is at some plants allowed to age for 30 days. Finally, 

 the product is fed into bags for shipment. The equipment of the hydrating 

 plant generally includes two elevators, one to take the Hme from the crusher 

 to the bin over the hydrater and one to take the hydrated lime from the 

 hydrater to the storage bin. Most mills include, also, a machine for grinding 

 the oversize from the screens. This material consists of unburned stone, 

 overburned lime, lime which is not fully hydrated, and even pieces of brick 

 from the kilns, and coal ashes. When ground, the tailings may be sold for 

 fertilizer. The methods of manufacture most extensively employed in thi? 

 country are the batch process, the continuous process, and modifications of 

 these two processes. 



LIMESTONE. 



In addition to that used in making lime, limestone is produced 

 in Florida for other purposes as follows : Broken limestone used 

 for railroad ballast, concrete and road material, and ground lime- 

 stone for application to soils. A limited amount of limestone 

 was probably also used in building, although not reported. The 

 quantity of limestone produced for the various purposes men- 

 tioned are as follows: Railroad ballast, 93,750 tons, valued at 

 $37,500; concrete, 123,506 tons, valued at $72,432; road material, 

 rock valued at $156,589; ground for application to soils, 16,908 

 tons, the total production amounting to $156,589.00. 



The following is a list of firms reporting the production of 

 limestone in Florida during 1913: 



