M \v i'OEK BTA1 i: MUSEUM 



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



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



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



etter 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 g 1 one to 



follow in using overturned lime. • 



. the amount and nature of the impurities present, 

 divides natural and artificial limes suitable for mortar 

 into ti\ i -. ! 



" 1 Comm< m or fat limes 

 2 Poor or meager limes 



Bydraulic lis 

 4 Hydraulic cements 



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>' to 25$ of impurities, or 

 sometimes even 39 . 



Hydraulic limes are of three kinds: 



a Slightly hydraulic ones with L0# to 20 r / of impurities 

 b Hydraulic limes with 17/ to 2-K impuriti< 

 c Eminently hydraulic limes with 20$ to 35$ of impurities 2 

 All hydraulic limes harden under water. Hydraulic cement is 

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

 HOI under 29$. 



NTatural pozzuolanas arc rocks of igneous origin. They poe 

 hydraulicity and generally tinder 1"''' of lime. 



It i >urse possible to find all intermediate grades between 



limes and cements. 



• tUmora. Limes, bydraulic cements and mortars, p. 69. 



■ •' " I) 71. 



