the line these phases are in equilibrium with each other. The diagram shows
four different phases and five regions. The region below the broken line
denotes a mixture of two phases: ice crystals and fructose?2H 2 O crystals.
The diagram also has two coexistence points (C and D) where three phases
are in equilibrium.
Suppose we have a solution of composition and temperature given by
point A. If we now decrease the temperature, it will at some time reach that
of point A^0. At that moment ice can begin to form. Ice formation does not
begin at 0 8 C, since the fructose causes depression of the freezing point: see
Section 2.2.4, Eq. (2.16). As more ice is formed, the solution becomes more
concentrated and the freezing point will be further depressed. The
composition of the solution and the temperature of ice and solution will
change along the coexistence line until point C is reached. Then the whole
system will freeze, forming ice and sugar crystals. C is called theeutectic
point, characterized by the eutectic temperature Te and the eutectic
compositionce.
FIGURE15.14 Partial phase diagram of the mixture water andD-fructose.Tis
temperature;cis mass fraction of fructose; the subscript e refers to the eutectic
point.