States of uniform composition in mixed crystals

Considerations essentially similar to those above apply also to states of uniform composition in a continuous series of mixed crystals. Equation (21.52 ) can be applied not only to a liquid solution but also to mixed crystals, so that instead of (28.25), we have at all points of uniform composition  

Azeotropes formed between ethanol B.P. 78.3 °C) and various halogen compounds 

The applicability of (28.27) is illustrated by fig. 28.3 which refers to a series of binary alloys. Again the indices 1 and 2 have been chosen so that X2jx- is less than 

Fe + V Ni + Pd agree well with the formula, while Au+Cu, Ni +V and Cu + Mn are in poor agreement presumably because one of the phases (probably the solid) cannot be regarded as a regular solution. 

From the position of the state of uniform composition, we can calculate a -using (28.28). Thus for Co + Mn we find a value of 1070 cal. /mole. This is very large and indicates that the departure from ideality, measured by the magnitude of a, is very much greater in the solid state than in liquids. 

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