Alumina with Silica, Lime and Magnesia. 



311 



attacked slowly by cold water and readily by hot. The 

 densities of all of these aluminates were determined in dry 

 turpentine at 25° and reduced to water at 25°=1. Hydro- 

 chloric acid dissolves all of these compounds. 



The entectic CaO.Al 2 3 — 3Ca0.5Al 2 3 is located at -about 

 67*5 per cent A1 2 3 . The liquidus falls but slightly from 65 

 per cent to 67'5 per cent, the temperature of the eutectic being 

 1580°. 



At 75*22 per cent the preparation is homogeneous. The 

 melting point, determined optically, is : 



Al 2 8l ... 75-22 



CaO _.. 24-78 j \ 



Millivolts 



•452 



•455 



452 



452 



T 

 1710 ( 



There is a second crystal form of the 3Ca0.5Al 2 3 compound 

 which shows different optical properties and a specific gravity 

 of 3*05, determined by flotation. It seems probable that the 

 relation of the two is monotropic, though the speed with which 

 this higher form changes into the lower, together with the 

 high temperature, makes quenching experiments unsatisfactory. 

 Crystals of the low form usually show indications of having 

 inverted during cooling, while preparations quenched from 

 above line GP do not. GP is an inversion point, and as it 

 extends to R, indicates that the 75*22 compound is unstable at 

 its melting point. In the iridium furnace, the 75*2 per cent 

 A1 2 3 preparation seems to melt before the 76*5 per cent. 

 This means either that the 3Ca0.5Al 2 3 is unstable at its 

 melting point or that the eutectic is so close to the maxi- 

 mum that the necessarily crude method will not determine it. 

 The evidence indicates the former relation and we have 

 adopted it. The 76*5 per cent A1 2 3 shows free alumina, as 

 do all preparations between this and 100 per cent A1 2 3 . 



Table II. —Invariant System CaO + 3CaO . A1 2 3 . (Line SLB, Fig. 6) 



Percentage in 

 of Al a 8 



15 20 



25 



28 



31-29 



35 



37-78 



41 



42 



43 



Eutectic 





















melts. __ 1526° 



1524° 1530 e 



1536° 1531° 



1535° 



1534° 



1535° 



1543° 



1529° 



1535° 



28 



26 30 



35 



30 



35 





35 



42 



31 



34 





28 



26 29 



36 



31 



35 



33 



34 



35 



31 



35 





28 



26 29 



36 



32 



35 



33 



36 



35 



33 



34 





28 



26 



29 



36 



32 



35 



34 



33 



35 



33 



34 





27 



26 



29 



36 



32 



35 



33 



34 



34 





34 





-- 





-- 



-- 



33 

 34 



38 

 37 



33 

 35 



33 



-- 



-- 



35 



Mean 



1528 



,1526 1529 



1536 



1532 !l536 



1534 |l534 1537 



1531 



1534 



