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Indiana University Studies 



Ca(0H)2 is the substance commonly known as slaked lime or 

 the milk of lime. This slaked lime, on exposure to the air when 

 wet, takes up carbon dioxide from the air and again forms calcium 

 carbonate as shown by the following reaction: 



Ca(0H)2 + CO2 = CaCO? + H2O 



Altho the chemical explanation of the above changes has been 

 known but a few decades, nevertheless the fact that such changes 

 took place was known even in the early ages when the Egyptians 

 were engaged in building their great works. In fact, some of 

 their mortars are still to be seen and they are known to be very 

 similar to our present common lime mortars. All the great 

 structures built before the time of the Roman Empire were 

 constructed with lime mortars, but the Romans used a cement 

 made from volcanic ash in many of the great structures built 

 under the Empire. The use of this cement was soon abandoned 

 and the mighty castles of the Middle Ages were constructed with 

 lime mortars. 



Limestones are widely distributed and they differ materially 

 from one locality to another. They are found interbedded with 

 other sedimentary rocks and often grade into them without any 

 perceptible line of change. In purity they may vary from rocks 

 containing but 45 per cent calcium carbonate to hmestones which 

 contain as high as 99 per cent calcium carbonate. The limes 

 of commerce are produced by calcining almost any of these lime- 

 stones, the resulting lime varying in use with its varying purity. 

 The one impurity most often found is magnesium carbonate, 

 and when the percentage of this runs above 20 per cent the rock 

 is called dolomite. Following magnesium carbonate the most 

 common impurities found are silica or sand, alumina or clay, 

 and iron. 



A limestone composed of nearly pure calcium carbonate will 

 furnish a high grade of quicklime. This product is known as 

 Avhite hme, hot lime, or fat lime,- while the product from a Ume- 

 stone containing magnesium is called a cool lime, brown lime, 

 or lean lime. In scientific language the former is called a high 

 calcium hme, while the laticer is known as dolomitic or magnesium 

 lime. 



The hmestones of both the Mitchell and the Salem formations 

 are very free from magnesiuin carbonate, and, in fact, are among 

 the purest hmestones of tjhi§ (Country, so that any lime burned in 



