534 



SOSMAN AND MERWIN: LIME : FERRIC OXIDE 



The melting point of pure CaO is 2570°, according to Kanolt. 2 

 Its properties have been published elsewhere. 3 



The " transition temperature" at which the compound 

 2CaO. Fe 2 3 dissociates and is in equilibrium with CaO and liquid 

 is 1436°. All mixtures from about 64 molecular per cent (about 

 38 weight per cent) of CaO up to pure CaO liquefy in part at this 

 temperature, leaving pure CaO as the solid phase in excess. This 



1600 

 1500 

 1400 

 1300 



1200 

 1100 



WOO 



CaO + Liquid \ 



CaO + 2.CaO.Fe 2 3 



CaO 



ECaOFe 2 3 



Fe 2 3 



+ Liquid \^CaO.Fe 2 3 + Liquid / + i,q U j d 



zCaO.Fe 2 3 

 + CaO.Fe 2 3 



100 90 80 70 60 50 40 30 20 10 



Molecular Percentage CaO 







Fig. 1. Composition-temperature diagram of the system CaO-Fe 2 3 . Circles 

 represent observed thermal breaks. 



forms relatively large, rounded, clear grains, which dissolve as 

 the temperature is raised, until they disappear completely at the 

 temperature of the liquidus curve. 



The corn-pound 2CaO . Fe 2 3 crystallizes well, giving black crys- 

 tals which are of a yellowish brown color by transmitted light 

 under the microscope. The liquid can be undercooled to 1385° 



2 This Journal, 3: 31.5-318. 1913. 



3 Rankin and Wright. Am. Journ. Sci., 39: 3. 1915. 



