PORTLAND CEMENT: PRELIMINARY STATEMENTS. 297 



sidering such products as true Portland cements. Nevertheless, there 

 is absolutely nothing in the definition above quoted that would pre- 

 vent their acceptance; and as a matter of fact at least one of these brands 

 has been submitted, accepted, and used under these specifications. 



The definition above discussed is fairly typical of those now to be 

 found in American cement specifications. 



The definition below has recently (1903-1904) been adopted by 

 the Association of German Portland Cement Manufacturers: 



Portland cement is a hydraulic cementing material with a specific 

 gravity of not less than 3.10 in the calcined condition, and containing 

 not less than 1.7 parts by weight of lime to each one part of silica -f alu- 

 mina + iron oxide, the material being prepared by intimately grinding 

 the raw ingredients, calcining them to not less than clinkering tem- 

 perature, and then reducing to proper fineness. 



In view of the conditions above noted, the writer believes that the 

 following definition will be found more satisfactory than those now in 

 use for insertion as a preliminary requirement in cement specifications. 



" Definition of Portland cement. By the term Portland cement, 

 as used in these specifications, is to be understood the product obtained 

 by finely pulverizing clinker produced by burning to semi-fusion an 

 intimate artificial mixture of finely ground calcareous and argillaceous 

 materials, this mixture consisting approximately of three parts of lime 

 carbonate (or an equivalent amount of lime oxide) to one part of silica, 

 alumina, and iron oxide. The ratio of lime (CaO) in the finished cement 

 to the silica, alumina, and iron oxide together shall not be less than 

 1.6 to 1, or more than 2.3 to 1." 



The ratios of lime to silica, alumina, and iron oxide given in the 

 last sentence of the above definition have been determined by exam- 

 ination of a large series of analyses of standard brands of American 

 Portland cements, and it is very unlikely that any good Portland, as 

 at present made, will have a ratio falling outside the limits above given. 

 Occasionally, however, analyses will come very close to these limits, 

 values of 1.64 and 2.29 respectively having been obtained from good 

 brands. A value as low as 1.6 to 1.7 means a low-testing but abso- 

 lutely safe cement. Values above 2.0 will include the high-testing 

 brands. 



Composition and constitution. Portland cements may be said to tend 

 toward a composition approximating to pure tricalcic silicate (3CaO,Si0 2 ) 

 which would correspond to the proportion CaO 73.6 per cent, SiO2 

 26.4 per cent. As can be seen, however, from the analyses quoted in 

 Chapter XXXVIII actual Portland cements as at present made 



