GEOPHYSICAL LABORATORY. 93 



Portland-cement clinker within the concentration limits set by Richardson, 

 when in equilibrium, may exist in the following combinations, depending 

 primarily upon relatively small changes in the quantity of lime present : 



I. II. III. IV. V. 



Richardson's typical cement corresponds to class II. The relative cement- 

 forming value of the above mixtures has yet to be determined. The more 

 intimate the mixture of the raw material, and the more uniform the heat 

 treatment, the closer will be the approach to equilibrium and therefore to 

 constant relations and the more uniform the behavior of the final product. 

 Classes III and IV are predicted from the general direction of the boundary 

 curves and the quintuple points 14 and 15 (cf. diagram). Class V will occur 

 in cements low in lime and will differ only in the relative amounts of the 

 different phases from pure slag cements whose compositions lie below the line 

 joining the calcium orthosilicate and 2Ca0.x\lo03.Si02 compositions. Type V 

 is dependent on the nature and location of point 13 and is to be regarded as 

 tentative. 



If solid solutions are formed they are very limited in extent and are not 

 sufficient to affect the optical properties of either silicate, the lime or the 

 aluminate. This fact serves to give greater definiteness to the problem and 

 an unexpectedly clear field for studies of the cement-forming quality of 

 clinkers of nearly related composition but different chemical constitution. 

 It therefore seems inevitable that such studies will lead to more reliable 

 standards in cement practice. 



The diagram indicates that the constitution of slag cement will be seriously 

 affected by relatively small differences of composition in the neighborhood of 

 the line joining the compounds calcium orthosilicate and 2CaO.Al203.SiO^. 

 It is, however, unwise to draw positive conclusions about the character of 

 this portion of the diagram until it has been more carefully studied. 



Incidentally, it has been observed that Fe.O., appears not to form solid 

 solutions with CaO, 2CaO.SiOo, or 3Ca0.x'\i263. It does appear to react 

 in some way with 5CaO. 3x^120,, but the nature of this reaction has not yet 

 been studied. Attention should also be called in passing to the important 

 fact that FcoO, dissociates at about 1400° with the formation of FegO^ — a 

 fact which seems to have been overlooked by some investigators. 



Finally, too great importance can not be given to the constant use of the 

 microscope in cement study and practice. It is not improbable that micro- 

 scopic examination will eventually provide much of the information desired 

 about the constitution of test samples, with the advantage over chemical 

 methods of giving immediate results. 



It remains to determine the isotherms of the diagram and to determine 

 whether or not the five typical "clinkers" possess any dift'erences in proper- 

 ties when hydrated to form cement. The work on the isotherms is well 

 under way. 



(2) Recent investigations into the nature of cement at the Geophysical Laboratory, 

 Carnegie Institution of Washington. E. S. Shepherd. Eng. News, 65, 350. 

 1911. 



A briefer presentation of No. i above for the use of engineers. 



