CHAPTERS ON THE CEMENT INDUSTRY 873 



previous grinding or admixture, direct to the kilns. The resulting 

 cement differs from a true Portland in carrying a lower pro- 

 portion of lime (45^-50^) and higher magnesia (5$-10$). The 

 cements will usually pass all Portland requirements, though not 

 so finely ground as the normal Portlands. 



Slag cements. Some time ago the Knickerbocker cement co. was 

 organized for the purpose of making slag cement, the intention 

 being to use the slag from the furnaces of the Poughkeepsie iron 

 co. Operations were suspended, owing to financial difficulties not 

 in any way connected with the cement manufacture itself; and at 

 present no slag cement is made in this state. A brief discussion 1 

 of the technology of this type of cement will be found in a recent 

 issue of Engineering news. 



Notes on Portland cement materials 



Three different combinations of materials are at present in use 

 in New York state; while another may be utilized in the near 

 future. Those now in use are: 



1 Marl and clay 



2 Limestone and clay 



3 Limestone and shale 



To these may be added, as of probable future use 



4 Argillaceous limestone and pure limestone. 



The technology of the industry has been discussed at length by 

 Dr Pies, in the earlier portion of this bulletin; but a brief state- 

 ment of the leading methods and features of the industry, as con- 

 ditioned by the materials used, may be of interest. 



1 Marl and clay. Compared with limestones, the marls are 

 easier to excavate and easier to reduce. They contain, on the other 

 hand, a greater proportion of organic matter and water, per ton of 

 excavated material, than do the limestones. For this reason their 

 transportation and handling, both between bed and mill, and in 

 the mill itself, entail a greater expense for each barrel of finished 



i Eckel, E. C. Slag cement manufacture in Alabama, (see Eng. news. 

 Jan. 23, 1902) 



