Rankin and Merwin — 



Table 6. 



Quenchings which determine limits of field of cordierite 

 (2Mg0.2ALA.5SiO a ) ; see also Table 13. 



Phases present, cordierite -j- glass. . 



Composition Weight Percent Temp. Time 



MgO AL0 3 SiO a in hours 



160 340 500 1450 10 



170 330 500 1460 -5 



160 



330 



510 



1450 



10 



210 



280 



510 



1430 



10 



16-5 



320 



51-5 



1450 



10 



180 



300 



520 



1400 



1-5 



160 



310 



530 



1450 



10 



250 



220 



530 



1370 



•5 



160 



30-3 



53-7 



1450 



1-0 



150 



30- 



550 



1440 



•5 



200 



190 



610 



Table 7. 



1350 



•5 



Quenchings 



which dete 



rmine the limits of the field of ALO ;i 



Phases present, 



glass -f- a Al.O 



, (corundum 



)• 



Composition 



Weight 



Per cent 



Temp. 



Time 



MgO 



Ay}, 



SiO, 





in hours 



100 



700 



200 



1750 01 





100 



650 



250 



1750 01 





140 



470 



390 



1585 



•5 



150 



440 



410 



1575 



•5 



1 Iridium furnace melt. 



While it is not our present purpose to discuss each of 

 these fields at length, it may be well to state here certain 

 special facts concerning the fields and their respective 

 crystalline phases. 



Fields of Stable Compounds. 



The components MgO, A1 2 3 , Si0 2 and the compounds 

 2MgO.Si0 2 , MgO.Al 2 3 and probably Al 2 3 .Si0 2 do not 

 dissociate when melting, therefore the composition of 

 each necessarily lies within its respective field. The 

 accurate determinations of the limits of these fields were 

 in most cases made without difficulty. The limits of the 

 field of MgO and certain portions of the fields of Al o 3 , 

 Al,0 3 .SiO,, MgO.Al 2 3 and 2MgO.Si0 2 , however, could 

 not be determined with extreme accuracy for the reason 

 that the temperatures required are beyond the range of 

 the platinum quenching furnace, 1600°. Due to the pecu- 



