SOSMAN AND MERWIN : LIME: FERRIC OXIDE 533 



cement, we are publishing this preliminary report in order to 

 make these results accessible to those interested. 



It is possible that work on three component systems in which 

 Fe 2 3 and CaO are components, especially on the system Si0 2 — 

 CaO — Fe 2 3 , in which quenchings can be made, will indicate 

 changes that should be made on the accompanying CaO — Fe 2 3 

 diagram, which, however, represents satisfactorily the facts so 

 far obtained. 



Method and materials. For the thermal data we depended 

 almost entirely upon thermal curves (temperature-time curves). 

 The method of quenching in mercury is of little avail in the 

 system CaO — Fe 2 3 , for the reason that the products crystallize 

 so easily and so rapidly that undercooled "glasses" are not 

 obtained as in the case of the silicates, and the primary phase 

 cannot, therefore, be always identified. Heating curves com- 

 bined with optical examinations are, however, sufficient for the 

 working out of the diagram. The optical properties are not as 

 readily determinable as those of the silicates, on account of the 

 deep colors and high indexes of refraction of the compounds, but 

 the use of high refracting immersion glasses makes it possible to 

 identify the phases with certainty. 



Thermal curves and optical examinations were made on vari- 

 ous mixtures of CaO and Fe 2 3 , made up initially from chemically 

 pure CaC0 3 (J. T. Baker, and Baker and Adamson) and Fe 2 3 

 (Baker and Adamson, and Kahlbaum). Charges of from 1.0 to 

 2.5 grams were used, in small platinum crucibles in a platinum- 

 wound furnace. The carbonate-oxide mixtures were first melted 

 down and then ground and re-melted for the determination of 

 the thermal breaks. The mixtures containing less than 50 molec- 

 ular per cent CaO were not heated above 1250°, to avoid, as 

 far as possible, dissociation of the Fe 2 3 . Temperatures were 

 measured by the platinum-platinrhodium thermoelement and 

 potentiometer. 



The composition-temperature diagram. We find only two binary 

 compounds in the system CaO — Fe 2 3 . These are: (1) the 

 1 : 1 compound, CaO . Fe 2 ; (2) the 2 : 1 compound, 2CaO . Fe 2 3 . 

 Both of these appear to be dissociated at their melting points. 



