44 CHEMICAL FERTILIZERS 



lime is so diluted that the cost of carriage becomes pro- 

 hibitive. L,ime kilns can be built on the sloping side of a 

 hill, on which an arch of large limestones is constructed to 

 act as a fireplace for the fuel. The remainder of the kiln 

 space is occupied with a mixture of limestone and fuel. 

 Continuous lime kilns are also used, the fuel being charged 

 in at the top and withdrawn at the bottom. In some of the 

 best works the fuel is chiefly fed down the side of the furnace, 

 so as to avoid mixture with the limestone ; by these means 

 two grades are produced, one pure lime, and the other lime 

 and fuel ash mixed together. Where lime is required for the 

 manufacture of calcium cyanamide, as in the United States 

 Government nitrate plant at Muscle Shoals, Alabama, lime 

 kilns of a rotary form are employed. They are of steel, 

 lined with firebrick, 125 ft. long by 8 ft. diameter, 

 and rotate once in two minutes on an axis inclined three 

 degrees to the horizontal. The limestone is fed into the 

 upper end while a blast of coal dust and air is forced into 

 the lower end. The temperature averages 900 C. and 

 conversion is complete in four hours. The daily consumption 

 is 200 tons of limestone. 



For agricultural purposes lime may be ground in a ball 

 mill to a fair degree of fineness, and bagged and sold as ground 

 lime ; or the lime may be sold as shell lime, or made into 

 slaked lime and sold in that form. All these various forms 

 of lime have their respective advantages for agricultural 

 purposes. Ground limestone will not injure the foliage of 

 any plant, and can be applied at any time to a crop ; on 

 the other hand, ground lime is very active, and is apt to injure 

 foliage, and should, therefore, be only applied either at 

 a time when little vegetation is present or before any seeds 

 are sown. Shell lime has the disadvantage that it is 

 difficult to distribute well, consequently the lumps do not 

 become mixed with the soil for many years. Slaked lime 

 has the advantage that it is a fine, dry powder, easily 

 distributed, that it is not so burning as ground lime, though 

 it is more chemically active than ground limestone. The 

 question of freight must influence the choice that is made 



