BIRTH AND APFINITIES, OF CRYSTALS 127 
with mixtures of two salicylates, salol and betol, choosing these 
substances merely because they melt at convenient temperatures, 
and we have succeeded in tracing for them the complete curves 
like those shown in fig. 2. By means of the refractive index 
we have traced the changes in each solution as it cools, and 
have always obtained curves resembling abf of fig. 1. We 
22) 
TEM pCrature 
Xx B 
Percentage of B 100 
oD 
Fig. 2. 
have also found that, as is clear from the figure, any mixture 
has no less than four possible freezing points—namely, two 
temperatures, a and c, at which A and B crystallise respectively 
by inoculation, and two others, 6 and ad, at which A and B 
crystallise spontaneously. 
The same general principles must hold for mixtures of more 
than two components; we have already traced the super- 
solubility curves for mixed solutions of sodium nitrate and lead 
