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Indiana University Studies 



burning them is very great. This is not true of white Hmes. 

 When they are overburned they form a hydrauHc cement, and 

 must be finely ground to be of use. From the above discussion 

 it will be seen that the difference between common hme and a 

 hydraulic cement is only in the amount of clayey material or 

 alumina present, and the percentage of alumina present is the 

 only difference between the hydraulic cement and a true Port- 

 land cement. In fact, these products form a series with the hot 

 or white limes at one end and true Portland cement at the other. 

 The dividing lines are more or less arbitrary, and depend upon 

 chemical composition. The following divisions are commonly 

 made: (1) common or fat lime, (2) hydraulic hmes, (3) hydraulic 

 or Roman cement, (4) Portland cement. 



The main difference between Ipmes on the one hand and 

 cements on the other is that cements are burned at a much 

 higher temperature, contain a much higher percentage of alumina 

 and silica, and must be thoroly pulverized before water will have 

 any great effect upon them. 



The presence of iron or sulphur in a limestone in any amount 

 spoils it for the manufacture of lime. The iron in addition to 

 coloring the lime dark has a fluxing effect. The sulphur darkens 

 the lime and forms sulphates of calcium or magnesium. Organic 

 matter when present in a limestone does not interfere with its 

 lime-making properties because it is completely removed in the 

 process of calcination which the limestone undergoes. 



Mortars made from hot limes harden more quickly than 

 those made from magnesium limes, and tests made at the end of 

 30 or 60 days show the mortars made from hot limes to be harder 

 and more resistant than those made from lean limes. This 

 superiority does not appear to persist, for tests made on mortars 

 after they have been set a year or more shows their resistance 

 to be about equal. 



When water is added to lime, calcium oxide hydrates and 

 changes to calcium hydroxide. On exposure to the air the excess 

 of water is given up. It has been generally held that the set of 

 the lime is complete when all the water disappears from the 

 lime, but it has been determined by Chatelier {West Virginia 

 Geological Survey, Vol. iii, p. 328), that the slaking of lime takes 

 place in four stages: 



1. Simple absorption of water. 



2. The mixture is warmed by contact and by heat of the chemical action 

 taking place, and a portion of the added water is evaporated. 



