MANUFACTURE OF NATURAL CEMENTS. 



247 



engineer. The " improved" natural cements of the Lehigh district, 

 most of which are made by mixing Portland and natural cement in 

 various proportions, naturally showed the effect of the very finely ground 

 Portland, and at a few other plants rather fine grinding was prac- 

 ticed. 



TABLE 105. 

 FINENESS REQUIRED BY VARIOUS SPECIFICATIONS. 



The figures given below represent the results obtained * by very 

 careful sizing of three different brands of natural cements. In making 

 these tests Mr. Bleininger used sieves for the coarser sizing and a 

 washing method for the finer work. 



TABLE 106. 

 FINENESS OF THREE BRANDS NATURAL CEMENT. (BLEININGER.) 



Within the past few years some natural-cement manufacturers 

 have realized that if the natural-cement industry is to be maintained 

 in the face of competition from Portland cement the product must 

 be improved. One of the easiest methods of doing this is to increase 

 the fineness of the grinding. This has the effect of making the cement 

 more sound and of increasing its sand-carrying capacity, and therefore 

 its strength when tested as mortar. 



* Transactions American Ceramic Society, vol. 5, p. 100. 



