Rankin and Wright — Tern ary System Ca 0-A \ % -Si 0. 2 . 31 



/3 modification is the stable form within the regions 19-20- 

 14-15 and 3-4-8, while in or near the latter region the /3' 

 form occurs with considerable frequency. Within the remain- 

 der of the field the a form is the stable phase. 



Although Ca,Si0 4 shows practically no variation in optical 

 properties over the entire range of this field, yet the inversion 

 /3 < > a takes place at different temperatures depending on the 

 composition of the charge under investigation, as it is evident 

 from Table VI. 



Table VI. 



To show the change of the inversion temperature (3 > a Ca 2 Si0 4 caused by 



the presence of additional solid phases. 



~ . . CaO 65 60 60 55 

 Composition ^ q 



weight per cent ffiAj - 35 35 * 10 



52 58 

 38 33 

 10 9 



Inversion temperature 1420 1415 1395 1395 



1415 1395 



Ca 2 Si0 4 does not take up in solid solution an appreciable 

 amount of any of the compounds with which it is associated in 

 this system. Over the larger part of this field the melting tem- 

 peratures are too high for accurate determination. Those we 

 have determined are given in Table VII. 



Table VII. 



Melting temperature of various compositions within field ,6"-4-l 4-15-1 6-C ; 



primary phase is Ca 2 Si0 4 (M. P. 2130° ±20°). 



Composition 

 Wt. per cent 



CaO 

 A1 2 3 

 -SiO, 



55 



5 



40 



50 

 10 

 40 



50 

 15 

 35 



50- 



17-5 



32'5 



50-7 



22- 



27*3 



51 3 

 29-7 

 19' 



50-9 



30'9 



18-2 



Temperature 

 of melting 





1625 



1400 



1500 



1550 



1625 



1590 



1570 



Table VII (Continued). 



50 



57 



60 



52 



50 



49 



50 



32-8 



30 



27-5 



38 



40 



42 



42 



17*2 



13 



12*5 



10 



10 



9 



8 



1535 



1580 



1600 



1460 



1420 



1390 



1375 



IX. The field of 3Ca0.5Al n 2 . (ll-12-G-H).—ZQnO. 

 5A1 2 3 occurs in two forms, a stable form and an unstable 

 form which is occasionally found in melts. Melting tempera- 

 tures of the stable form are given in Table VIII. 



