668 



CEMENTS, LIMES, AND PLASTERS. 



Table 250 contains the analysis of a number of European slag cements, 

 as given by various authorities. It will be seen that, despite the appar- 

 ently great variations in practice, the ultimate composition of the finished 

 cement falls within quite narrow limits. The range in composition of 

 a good slag cement may be considered to be about : SiC>2, 22 to 30 per 

 cent; Al 2 03+Fe 2 O3, 11 to 16 per cent; CaO, 49 to 52 per cent; MgO, 

 less than 4 per cent; S, less than 1.5 per cent; ignition loss, 2.5 to 7.5 

 per cent. 



TABLE 250. 

 ANALYSES OF EUROPEAN SLAG CEMENTS. 



*CaS. 



t CaS0 4 . 



Physical Properties. 



Specific gravity. The specific gravity of slag cements usually ranges 

 from 2.7 to 2.9, as compared with the 3.15 which may be considered 

 a fair average for the specific gravity of a good Portland cement. The 

 slag cements are, therefore, appreciably lighter than Portlands, and 

 more bulk is obtained for the same weight. The following determi- 

 nations of the specific gravity of three American slag cements have 

 been made at Philadelphia: 



Toltec 2.861 



Climax 2 . 888 



Penn 2 . 831 



Aside from its use as a method of distinguishing slag cements from 

 Portlands, the determination of the specific gravity of the cement is 

 of little engineering importance. A point which is of engineering impor- 

 tance, however, appears to have been overlooked by experimenters. So 

 far as the writer knows, the relative specific gravities of set briquettes, 

 composed of neat-slag cement and neat-Portland cement respectively, 

 have never been determined. A knowledge of the two values would 

 be of service, at times, in selecting the type of cement to be used. For' 



