hiw roxx - m!-<i tm 



to lime, and consequently tlio cements are apt 



isfactory. They an i d to improve 



by the addition of Portland cement, after which they can be 



d quit( illy. This class includes those of the Lehigh 



1 he third class is represented by the Roeendale 



brands, which Bet and acquire Btrength Blowly, l>nt which con- 

 tinue to devel«»p it for a long time and eventually arc very str 

 and tough. The fourth includes cements like those of 



5 . which have been, while containing an unusual 

 amount of magnesia, burned so hard that little of the silicates 

 remains undecomposed and uncombined with the lime and mag- 

 nesia, and in consequence they are apt to stand a long time ai 

 use, unless carefully hydrated. The fifth class is one in which 

 the cement is essentially a lightly burned, highly magnesian mate- 

 rial in the preparation of which the heat has not been sufficiently 

 high or prolonged to bring the greater portion of the silica in 

 composition with the lime or magnesia, in this respect being in 

 contrast to the preceding class. The hydraulic principle and 



Dgth are therefore largely due to the magnesia and carbonates 

 rather than to the silicates and aluminates. Examples of this 

 are those cements made at La Salle (111.) The last class gives 

 a cement in which there is rather less magnesia than in the two 

 preceding cli ad less aluminum and iron oxid than in the 



third class. Though they are burned so thoroughly that there 

 is but a small per cent of silicates uncombined, still, as Mr Rich- 

 ardson - 3, all of these cement- will when properly burned and 

 carefully handled givi 3sful results in the large majority 



of c A- a rule natural cement mortar- will acquire a satis- 



factory Btrength with sufficient time, though it may have orig- 

 inally been very weak, or subjected to unfavorable influences due 

 to the conditions under which it was used* 



Portland cement 



Portland cement IS a hydraulic cement, in which the porcont- 

 • alumina and Bilica is aboul as 2 to 1. It seta rapidly 



