Rankin and Wright — Ternary System CaO-Al n O % -SiO n _. 69 



Thus in a solution of the composition CaO 53, Al o 3 4, Si0 2 43 

 at a temperature of 1420°, 2CaO.Si0 2 crystallizes; at 1415° 

 the crystallization curve has reached the boundary B'-± where 

 2CaO.Si0 2 disappears and 3Ca0.2Si0 2 separates; at 1410° the 

 2CaO.Si0 2 has all disappeared and the crystallization curve has 

 left the boundary B'-± and entered the field B'-4:-6-B in 

 which pure 3CaQ.2SiO., separates. 



THE APPLICATION OF EQUILIBRIA WITHIN THE SYSTEM CaO, 

 Al,0 3 , Si0 2 TO PROBLEMS INVOLVING THESE THREE OXIDES. 



It is not our purpose to discuss, here, all the possible appli- 

 cations of the equilibrium diagram for CaO, A1 2 3 and Si0 2 to 

 problems involving these three oxides. We merely wish to 

 show how this diagram may be applied, and to consider briefly 

 its application to the study of portland cement clinker and 

 certain geological inquiries.* 



In order to obtain this diagram it has been necessary to 

 determine experimentally the equilibrium conditions for the 

 existence of the components, pure or in mixtures, and of the 

 various compounds. These equilibrium conditions have been 

 presented in diagrams which have shown principally the con- 

 ditions at the liquidus ; in other words, we have shown the 

 conditions under which the solid components and compounds 

 exist in equilibrium with solutions. The diagram (tig. 17) 

 illustrates how these components and compounds crystallize 

 from solutions ; that is, it enables us to state the order in which 

 they crystallize, and to specify the final product obtained when 

 the solutions have completely crystallized. 



These final products of crystallization of solutions of CaO, 

 A1 2 3 and Si0 2 , which are the only essential data required to 

 elucidate most of the problems in which this system is con- 

 cerned, are given in fig. 19, which, it will be seen, is composed 

 of a large number of triangular areas. Each of these triangles 

 represents all possible mixtures of those three compounds 

 whose compositions are represented by the apices of the tri- 

 angle. Though three certain, definite compounds can exist 

 together in only one triangle, yet, as can be seen in the dia- 

 gram, any one of these three compounds may be found in a 

 number of different triangles. 



In applying the data presented in fig. 19 to any problem 

 involving a part or all of this diagram, it must be remembered 

 that this diagram represents equilibrium conditions, that is, this 

 diagram represents the components and compounds as they 

 would occur together in mixtures if time were allowed for all 



* Each of these applications will be taken up more fully in papers to be 

 published in the near future. 



