CHAPTER XIX. 

 COMPOSITION AND PROPERTIES OF NATURAL CEMENTS. 



THE preceding chapters will have failed of their purpose if the 

 reader does not now realize that the cements commonly grouped as 

 "natural cements" differ so widely among themselves as to almost 

 prevent any general statement being made in regard to the group. 

 These differences have appeared in the composition of the various 

 cement rocks, in the degree of burning to which they were subjected, 

 and in the condition of the mass which resulted from this burning. 

 They will appear still more markedly, however, in the composition 

 and properties of the finished products. 



In the present chapter data will be presented bearing on these sub- 

 jects, but they will be treated as illustrating certain points in connection 

 with the processes of manufacture rather than as guides to the testing 

 or uses of the cements. The chemical composition of the natural cements 

 will first be taken up, after which their physical properties will be noted. 



Chemical Composition of Natural Cements. 



A large series of analyses of natural cements, both American and 

 foreign, are given in the following tables. For convenience of reference 

 these analyses are given by States arranged in alphabetical order. The 

 Cementation Index has been calculated for a number of these products, 

 and is given in the bottom line of each table. 



Georgia. The two Georgia brands whose analyses are given in Table 

 112 differ widely in composition and index. The Howard cement is of 

 very low index, much like that from Akron, N. Y., and carries 14 to 20 

 per cent of magnesia. The Chickamauga cement (Dixie brand) is, on 

 the other brand, of medium high index, and runs very low in magnesia, 

 like the natural cements of the Lehigh district and of France. 



Illinois. The Utica cements are quite close in composition to those 

 from the Rosendale district, N. Y., but run somewhat lower in index. 



Indiana-Kentucky. The Louisville cements are of moderate index 

 and average about 11 per cent magnesia. 



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