OQQ NEW YOKK STATE MUSEUM 



water at first and add tlie other two thirds later on. Again, as 

 the lean lime gives out much less heat, it is well to keep the 

 mixing pan covered in order to prevent its escaping. Lean lime 

 also slakes better if a certain amount of fat lime is worked in 

 with it. The latter has a sort of contact effect on the former, 

 which is effective and rapid, so that this method is a good one to 

 follow in using overburned lime. 



Depending on the amount and nature of the impurities present, 

 Gilmore divides natural and artificial limes suitable for mortar 

 into five classes.^ 

 " 1 Common or fat limes 



2 Poor or meager limes 



3 Hydraulic limes 



4 Hydraulic cements 



5 Natural pozzuolanas 



The common or fat limes contain less than 10/^ impurities, and 

 a part of the latter are insoluble in water, all the rest of the 

 lime being soluble. They do not harden under water but crumble 

 or slake and increase in volume sometimes threefold. They 

 shrink in hardening, and to prevent this sand must be added. 



Poor or meager limes have from 10 fo to 25/^ of impurities, or 

 sometimes even 39 fc. 



Hydraulic limes are of three kinds: 



a Slightly hydraulic ones with 10^ to 20 fo of impurities 



h Hydraulic limes with 17 fc to 24: fc impurities 



c Eminently hydraulic limes with 20;^ to 35^ of impurities^ 



All hydraulic limes harden under water. Hydraulic cement is 

 an artificial product. It has less lime than the other classes, but 

 not under 2df. 



J^atural pozzuolanas are rocks of igneous origin. They possess 

 hydraulicity and generally under 10 fc of lime. 



It is of course possible to find all intermediate grades between 

 limes and cements. 



^ Gilmore. Limes, hydraulic cements and mortars, p. 69. 

 " *' t. " p. 71. 



