Rankin and Wright — Ternary System CaO-Al 2 3 -Si0 2 . 73 



being the region of stability of a group of 3. In the triangles 

 in which Si0 2 occurs, it wiil be present either as quartz, tridy- 

 mite or cristobalite, depending on the temperature. 



Summary. 



The foregoing pages are a record of a thorough investigation 

 of the system CaO-Al 2 O s -Si0 2 , an investigation which necessi- 

 tated some 7000 heat treatments and subsequent optical exami- 

 nations of the products. This ternary system proved to be 

 complicated, the equilibrium diagram, which represents the 

 stability relations of components and compounds possible at 

 atmospheric pressure, containing no fewer than 14 separate 

 fields. The mapping of the boundaries of the various fields 

 was possible only by application of the phase rule ; the result 

 shows that this principle is just as applicable to mixtures of 

 oxides, which are liquid only at high temperatures, as it is to 

 ordinary solutions. 



The relations found to subsist between components and the 

 various compounds in each of the three binary systems and in 

 the ternary system are exhibited in a series of temperature- 

 concentration diagrams. A list of these compounds, with 

 their respective compositions, and optical characteristics, inver- 

 sion, melting or dissociation points, and of the co-ordinates (tem- 

 perature and composition) of the various quadruple and quin- 

 tuple points, is appended. From these data the theory of 

 crystallization curves enables one, as we have shown, to pre- 

 dict which substances will separate out from any slowly cool- 

 ing solution containing only CaO, A1 2 3 , and Si0 2 , the order in 

 which they separate, and the corresponding temperatures. 



Moreover, although the diagram exhibiting the final products 

 of crystallization presupposes the continuous attainment of 

 equilibrium, yet it is possible to predict with considerable cer- 

 tainty the final product of reaction in mixtures of the three 

 pure oxides, even when the reaction has not proceeded to com- 

 pletion. This occurs with portland cement clinker, which, if 

 made in the ordinary way from the pure oxides, would be 

 essentially a mixture 'of 3CaO.Si0 2 , 2CaO.Si0 2 , 3CaO.Al 2 3 , 

 with some 5Ca03Al 2 3 , and, possibly, a small amount of free 

 CaO ; a conclusion which has been confirmed by the work of 

 the Bureau of Standards on commercial clinkers. 



