Liquefaction continued compositions

Conversely, if a solid solution of the composition and at the temperature x is heated, liquefaction will begin at the temperature yielding a liquid of the composition d. On continuing to add heat, the temperature of the mass will rise, more of the solid will melt, and the composition of the two phases will change as represented by the curves da and cb. When the temperature has risen to a, complete liquefaction will have occurred. The process of solidification or of liquefaction is therefore extended over a temperature interval ac. 

In this case, as in the case of those systems where the pure components are deposited, a minimum freezing-point is obtained. In the latter case, however, there are two freezing-point curves which intersect at a eutectic point in the case where mixed crystals are formed there is only one continuous curve. On one side of the minimum point the liquid phase contains relatively more, on the other side relatively less, of the one component than does the solid phase while at the minimum point the composition of the two phases is the same. At this point, therefore, complete solidification and complete liquefaction will occur without change of temperature, and the solid solution will accordingly exhibit a definite melting-point. ... 

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