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Indiana University Studies 



when set. It is also cheaper to add some foreign substance, 

 whicli material can always be cheaper than the lime itself. The 

 most common material used for filler in mortars is sand. Any 

 type of sand grain is superior in hardness to the set lime, and 

 when the lime mortar cements these hard grains together the 

 resulting mortar is hard and durable. In the production of 

 mortars any inert substance which does not shrink nor de- 

 teriorate may be used. Ground or rough crushed limestone 

 may be used and will give equally good results. Crushed stone, 

 being rough edged, gives the lime more chance to adhere, and 

 thus the resulting mortar is very durable. Dolomitic limes are 

 more durable and show less shrinkage than high calcium limes. 

 (See also Beyer, loc. cit.) 



A long series of tests of the proper percentage of lime and 

 foreign material for the strongest mortar, and the type of lime 

 best adapted to the manufacture of mortars has been conducted 

 by the Iowa Geological Survey and the results of these tests are 

 published in the seventeenth annual Report of that Survey for 

 the year 1906 (pp. 106-146). 



Lime Burning. The reaction by which limestone or car- 

 bonate of hme is broken up into lime oxide or quicklime and carbon 

 dioxide takes place above the temperature of 850 Centigrade or 

 1,562 Fahrenheit. This reaction will go on to completion only 

 in a current of heated air to carry away the carbon dioxide as 

 fast as formed. Dr. Thorp in his Outlines of Industrial Chemistry 

 says (p. 175) : 



Calcium carbonate begins to decompose below a red heat into calcium 

 oxide and carbon dioxide, but the decomposition is not complete until a 

 bright red heat (800 to 900 Centigrade) is reached. The temperature should 

 not rise above 1,000 to 1.200 Centigrade, as there is danger of overheating 

 the hme. [For successful burning], it is essential that the gases escape 

 freely from the kiln, the draught usually being sufficient to remove them as 

 thej' form. This escape may be accelerated by blowing steam or air into 

 the kiln during the burning, or even by wetting the carbonate as it is in- 

 troduced. 



The amount of heat required to produce this change of limestone 

 to quicklime is 373.5 calories for one kilogram of calcium carbonate 

 changed. This amount of heat is equivalent to 747 B.T.U. 

 These are the figures given by Gruner, while Eckel gives the heat 

 requirements as 784 B.T.L^. The above figures are quoted from 

 Vol. Ill of the West Virginia Geological Survey (p. 358). 



Lime kilns are of two general classes: periodic and continuous. 



