Passage V

When a mixture is at equilibrium, no net phase changes occur. Figure 1 shows the phases of the metals gold (Au )and thallium (TI) present in various Au-TI mixtures at different temperatures and at equilibrium. The Au-TI mixtures contain only Au and Tl, so an Au-TI mixture that contains 60% Au will contain 40% Tl, and 100 g of this mixture will contain 60 g of Au and 40 g of Tl.

Figure 1 adapted from the National Research Council, International Critical Tables of Numerical Data, Physics, Chemistry and Technology; Volume II. @1927 by the McGraw-Hill Book Company, Inc.

A cooling curve shows how the phases of the metals in the mixture change as it cools over time. Figure 2 shows a cooling curve for an Au-TI mixture containing 58% Au. Figure 2 also explains how Figure 1 is related to Figure 2.