LIME AND CEMENT INDUSTRIES 697 



1897 1898 



No Product, bbl. No. Product, bhl. 



Factories using limestone. . . 18 2 282 126 20 3 112 492 



Factories using marl 11 395 649 11 579 792 



29 2 677 775 31 3 692 284 



The essential elements of Portland cement are calcium, silica 

 and alumina. Tlie first is generally supplied by limestones or 

 marl, the two latter by clay. In burning these three elements 

 unite to form silicates of a complex nature, and it is essential 

 that they be combined in proper proportion in order to give the 

 best results. Faija claims'^ that the lime may vary from 58^ to 

 64;^; the silica from 18^ to 24;^; the alumina and iron from 8^ to 



In rare instances it is possible to find a natural limestone which 

 contains the three essential elements in the proper proportion. 

 With marl the expense of crushing and grinding the material is 

 saved, but both have their advantages as well as their disadvan- 

 tages. The chemistry of Portland has been most carefully stud- 

 ied by S. B. and W. B. E'ewberry^ who come to the following 

 conclusions. 



1 The essential constituents of Portland cement are tricalcic 

 silicate with varying amounts of dicalcic aluminate. The com- 

 position is therefore expressed by the formula X (3CaO,Si02) + 

 Y (^CaO,.\l203). From this the proportion is calculated, that 

 is, lime by weight =2.8 SiOg +1.1 AlgOg. 



2 FegOg combines with lime at a high heat and acts like the 

 alumina in promoting the combination of the silica and calcium. 

 For practical purposes the presence of ferric oxid in clay is not 

 to be considered. 



3 Alkalis., judging from the behavior of soda, are of no value 

 in promoting the combination of calcium and silica and probably 

 play no part in the formation of cement. 



* Trans. Am. soc. civ. eng. 30: 43. 



* Cem. and eng. news. 1898, 4: 5. 



