Rankin and Wright — Ternary System CaO-Al.,O r Si0 2 . 71 



a large extent, those given in the small triangle in which that 

 point occurred ; if, however, other compounds were found one 

 would expect these compounds to be included within adjacent 

 triangles. 



Application to Portland Cement Clinker. — It is a well- 

 known fact that portland cement can be made from the pure 

 oxides CaO, A1,0 3 and SiO a . According to Richardson's data, 

 cement clinker can be made from mixtures of these three oxides 

 whose compositions are represented by points within the area 

 V-X-Z-Y (fig. 19 s ) — an area which lies almost entirely within 

 the triangle CJS-CJS-C S A. Therefore a cement clinker made 

 from pure CaO, A1 2 3 and Si0 2 , burned at a high enough tem- 

 perature for a sufficiently long time, would consist of the three 

 compounds 2CaO.Si0 2 , 3CaO.Si0 2 and 3CaO.Al 2 3 . If, how- 

 ever, equilibrium was approached but not reached we would 

 expect to find, in addition to these three compounds, either free 

 CaO or the compound 5Ca0.3Al 2 3 , or both. 



Commercial portland cement clinker has a CaO, A1 2 3 , Si0 2 

 content of over 90 per cent and is manufactured by methods 

 which one would expect to produce a condition approaching 

 equilibrium ; so that it would seem possible to predict from 

 fig. 19 what compounds of CaO, A1 2 3 and Si0 2 are formed 

 when the raw material for portland cement is burned. From 

 these data we made the prediction that portland cement clinker 

 consists largely of 3CaO.Si0 2 , 2CaO.Si0 2 , 3CaO.Al 2 3 , 5CaO. 

 3A1 2 3 , with, possibly, a small amount of free lime, and the 

 subsequent work of the Bureau of Standards at Pittsburgh has 

 demonstrated the applicability of these criteria to commercial 

 clinkers and has completely borne out this prediction. In mak- 

 ing this prediction as to the probable constitution of portland 

 cement clinker we believed (and it subsequently proved to be 

 so) that the components other than CaO.Al 2 3 and Si0 2 were 

 practically negligible. We do not mean by this that the other 

 components such as MgO, Fe 2 3 , etc., may not be important in 

 cement as cementing material, but that the MgO, Fe 2 3 , etc., 

 are present in such small quantities in the raw cement material 

 that it seemed probable that the clinker would consist largely 

 of compounds of pure lime, alumina and silica. It is not, how- 

 ever, permissible to apply directly the data in fig. 19 to prob- 

 lems involving CaO, A1 2 3 , Si0 2 unless one is sure that the 

 other components present are negligible and that equilibrium 

 conditions were substantially attained. 



Application of the Residts to Certain Geological Inquiries. 



In applying the results of this investigation to problems 

 involving natural minerals composed substantially of CaO, 

 A1 2 3 , and Si0 2 , one must proceed with caution because the 



*The Constitution of Portland Cement, by P. H. Bates. Concrete-Cement 

 Age (cement mill section), 2, 3. 



