SOLIDIFICATION OF ALLOYS AND MAGMAS 575 
Of this type are the Sb-Pb, Pb-Sn, Cd-Zn alloys. 
A third type of freezing-point curve is that of partial-solubility 
solid, as shown in Fig. 4. This condition is really a combination of 
--the two types previously described. For mixtures between JF and 
GK, freezing will be of the type of complete solubility. Between 
F and G, the freezing will be selective, as in the complete insolubility 
type, except that, since there is partial-solubility solid, the excess 
metal to separate out will be saturated with the other element; and 
PARTIAL SOLUBILITY 
TEMPE RATURE 
COMPOSITION 
FIG. 4 
the eutectic will be a composite of A saturated with JF per cent. of 
B and B saturated with GK per cent. of A. 
With this type of freezing, therefore, we. have freezing with com- 
plete solubility at the two ends of the series, and under the microscope 
we should find a homogeneous structure. For the intermediate 
mixtures there will be selective freezing and under the microscope 
we should expect a heterogeneous structure of an excess substance 
either A saturated with B or B saturated with A, depending upon 
