310 Shepherd, Rankin, Wright — Binary Systems of 



52.22# 



A1 2 3 



53$ Al 3 O s 



Time 

 f 30min. 



I 60 " 

 L 30 (i 



55% A1 2 3 { 



57% A1 2 £ 



Al 2 O s 



T 

 1565° 

 1513° 

 1484° 

 1454° 

 1424° 

 1394° 



1544° 

 1513° 

 1484° 

 1454° 

 1427° 

 1431° 

 1385° 



1394° 

 1424° 

 1458° 

 I486 

 1513° 

 1544° 



Glass 



II 



Time 

 30 min. 



45 " 



30 " 



120 " 



30 

 | 180 

 I 120 



3CaO. 

 IB A1 2 3 5Ca0.3Al 2 O s 



CaO . Al 2 O a 



T 

 1394 c 

 1428° 

 1454° 

 1484° 

 1513° 

 1544° 



1544° 

 1513° 

 1513° 

 1513° 

 1454° 

 1424° 

 1424° 

 1394° 



Glass 



IB 



5CaO . 3ALO s 



tr 



CaO . Al a Oi 



tr 



Examination of this series of quenchings shows that the 

 biref racting phase, which was found to be homogeneous at 52*22 

 per cent A1 2 3 , is not present as a stable phase. It appears in 

 small amounts (indicated by IB) in certain quenchings and not 

 in others. It usually occurs in mixtures where a large charge 

 is taken from the furnace and air-cooled. It appears in the 

 same charge along with the stable phase, but disappears when 

 the mass is baked at 1300°, passing into the stable form. The 

 heat effects due to this unstable form occur irregularly both 

 as to temperature and time of development. They are 

 destroyed by holding the charge just below JSTO for a time 

 before making the heating curve. 



The spinel analogue CaO.Al 3 8 melts at 1587°. It has a 

 density of 2*981. It is a birefracting crystalline substance, 



