214: CEMENTS, LIMES, AND PLASTERS. 



European Natural-cement Rocks. 



As noted later, the European natural-cement industry dates back 

 to 1796, in which year the manufacture of natural cement was com- 

 menced simultaneously in France and England. At present the indus- 

 try is established in practically every country of Europe, though it 

 is of course subject to severe competition from Portland cement on 

 the one hand and the better class of hydraulic limes on the other. Euro- 

 pean natural cements form two fairly distinct classes, which are there 

 called respectively ' 'natural Portlands " and " Roman cements ": 



(1) The natural Portlands, which are described on pages 215-217 in 

 detail, are natural cements of low cementation index (1.05 to 1.15 usu- 

 ally), low in magnesia, and burned at fairly high temperatures. In 

 consequence of the combination of their low index and relatively high 

 burning, these products approach true Portland cements in analysis 

 and physical properties, though they necessarily vary considerably 

 from time to time according to the rock from which they are made. 

 The best of these products will pass low-grade Portland tests, and were 

 formerly largely exported to this country, where they were unloaded 

 on the architects and engineers who specified " foreign Portland cement ". 

 The poorer " natural Portlands " are often adulterated with slag or 

 unburned limestone, in order to make their bulk composition agree 

 on analysis with that of true Portlands. 



While the " natural Portlands " are often useful products, there 

 seems to be no reason for classing them with the true Portlands, for 

 the term Portland is now understood to imply that a very careful and 

 finely ground artificial mixture has been made before burning. 



(2) The Roman cements form the second class of European natural 

 cements. They are usually cements of moderately high index (1.20 

 to 1.60), and are also usually but not invariably low in magnesia. They 

 correspond therefore quite closely, so far as index is concerned, to the 

 best of the American natural cements. In American practice, how- 

 ever, low-magnesia natural cements are quite rare, as can be seen by 

 referring to the tables of analyses on pages 253 to 260, while in Europe 

 high-magnesia cements are very scarce. 



It may be of interest to call attention here to the fact that quick- 

 setting artificial cements of high index (1.20 to 1.60), and very lightly 

 burned, have been made at several points in Europe. These products 

 would correspond in every way with our natural cements, except in that 

 they are made from artificial mixtures and are therefore more expensive 





