64 Rankin and Wrigh t — Tern ary System Ca 0-Al 2 O-Si O n _. 



There are, therefore, five boundary curves of this type, R'-4: 7 

 9-7, D-16, 18-17 and 18-16, along each of which crystallization 

 curves of the several different types described for boundary 

 B'-4: will proceed. These different types of crystallization 

 curves are : (1) a crystallization curve which, proceeding to a 

 boundary curve along which one solid phase partially disap- 

 pears while the other crystallizes ends at the quintuple point 

 for that boundary ; (2) a crystallization curve which, proceeds 

 in the same manner as (1) to a quintuple point, but at that 

 point one solid phase entirely disappears and the crystallization 

 curve proceeds along a boundary to another quintuple point ; 

 (3) a crystallization curve which proceeds to a boundary along 

 which one solid phase wholly disappears before a quintuple 

 point is reached, wherefore it leaves the boundary and crosses 

 a field to another boundary curve along which it proceeds to a 

 quintuple point. 



Which one of these three types of crystallization curves any 

 given solution when cooled will follow depends, as has been 

 shown, on the original composition of the solution. We will give 

 here merely the areas (fig. 17) which represent the composi- 

 tions of solutions for each of these types of crystallization curve 

 and the particular solid phases in order as they appear or dis- 

 appear from a cooling solution. 



(1) There are 4 areas which represent the compositions of 

 solutions which on cooling have crystallization curves of 

 type (1). (a) Triangle C 3 S 9 -C 2 AS-C a S; from solutions whose 

 crystallization curves intersect boundary i?'-4 there will appear 

 consecutively pure C a S; C,S and C 3 S, together; and finally 

 CJS, C 3 S, and 2 AS. (b) Triangle OAS 2 -AS-A ; from solu- 

 tions whose crystallization curves intersect boundary 9-/ there 

 will appear consecutively pure A ; A and AS; and finally 

 A, AS and CAS,, (c) Triangle O.S-Z-1S in which there will 

 appear consecutively CJS\ C[S and 3 S ; and finally C^S, 3 S 

 and 3 A. (d) Triangle C&O-X- C 3 A ; from those solutions 

 whose curve intersects boundary 18-17 there will appear con- 

 secutively : CaO ; CaO and 3 S and finally CaO, C 3 S and 3 A 

 and from those which intersect boundary 17- D, CaO ; CaO and 

 C 3 A and finally CaO, C 3 A and CJ3. 



(2) There are 8 areas which represent the compositions of 

 solutions which exhibit crystallization curves of type (2). 

 (a) Triangle 3 S 2 -0 2 AS-4:; from those solutions whose crys- 

 tallization curves intersect boundary B'-k there will appear 

 consecutively: pure GJS\ C 2 S and C 3 S 2 ; C 2 S, C 3 S 2 and C 2 AS; 

 C& and CjAS find finally C 3 S„ C 2 AS said OS. (b) In triangle 

 OAS-9-AS from those solutions whose crystallization curves 

 intersect boundary 9-7 there will appear consecutively : pure 

 A ; A and AS', A, AS nnd OAS 2 ; CAS 2 und AS; and finally 



