31 \ Rankin and Merwin — 



that the intersection point P represents a maximum 

 temperature on the boundary 4-(i. 



It is upon such indirect evidence that point 6 is desig- 

 nated as a eutectic. 



Table 15. 



Queuchings which show the course of the crystallization curves which pass 



through quintuple points (not eutectics) - anil 4. and that cross the 



field of tiie ternary compound \ cordierite) near point 3. 



Comp. Weight 



Per 



cent 



Temp. 



Time 

 in 



Phases Point 



1 



MgO AL0 3 



SiO, 





hours 





100 240 



660 



1438 



10 



Glass (2) 







14:55 



1-0 



Glass 4- AlA.SiO, 







1428 



10 



Glass + AlA-SiOj -f cordierite 







1425 



10 



Glass -j- SiO., (tridymite) -4- cordierite 



160 350 



490 



1465 



20 



Glass 4- ALQ,.Si0 2 (3) 







1457 



1-0 



Glass -j- ALOj-SiOo -f- cordierite 







1450 



40 



Glass -j- spinel -4- cordierite 



260 230 



510 



1378 



10 



Glass (4) 







1376 



10 



Glass -j- spinel 







1375 



•5 



Glass -j- 2MgO.SiO, + cordierite 



Following is 



a list of 



the 7 quintuple points giving 



composition in weight percentages of MgO, A1 2 3 , Si0 2 

 and the corresponding temperatures as determined by 

 quenches. The numbers assigned to each quintuple point 

 correspond to the numbers in fig. 1. 



Point 1 is the eutectic for MgO.SiO,,, SiO„ and the 

 ternary compound (MgO 20-3, A1 2 3 18-3, Si0 2 614). 

 Its melting point (1345° ±5°) is based on the values 

 obtained from various compositions as given in Table 16. 



Table 16. 



Melting temperature: Quintuple point 1 for MgO.SiCX, Si0 2 and ternary 



compound as determined from various compositions. 



[MgO 200 18-9 250 200 250 



Composition, weight, per cent \ AL0 3 190 241 180 180 200 



[SiO., 610 570 570 620 55-0 



Temperature 1348 1340 1340 1345 1345 



Point 2 is the quintuple point for Si0 2 , ternary com- 

 pound and Al 2 3 .Si0 2 (MgO 10-0, A1 2 3 23-5, Si0 2 66-5). 

 Its melting temperature (1425° ±5°) is based on the 

 values obtained from compositions given in Table 17. 



Table 17. 



Melting temperature: Quintuple point 2 for SiO., ternary compound and 

 ALO :! .Si0 2 as determined from various compositions. 



[MgO 12-4 100 100 90 



Composition, weight, per cent \ AL0 3 31-6 30-0 240 240 



[SiO. 560 600 660 670 



Temperature 1425 1425 1425 1425 



