572 JAMES ASTON 
two other jogs in the curve, at 880° and 780°, denoting changes in the 
solid state. These represent the transition points of the three allo- 
tropic modifications of pure iron, and are designated as the a, 8, and ¥ 
states. These allotropic states represent changes in the properties 
of the iron without change of composition, and are analogous to 
some cases of pleomorphism in minerals; for example: 
orthorhombic pseudo-isometric | 
Sulphur to 96° ~=— Leucite « to 500° 
monoclinic ] isometric | 
FREEZING-POINT CURVES 
In the investigation of alloys, we consider three general types of 
solubility relations; with complete miscibility in the molten state 
it may after solidification be complete, partial, or nil. 
COMPLETE SOLUBILITY | 
7 y 
y NN 
< 
< NS 
& Wy 
Wy Q 
S S 
Ry RN 
TIME A COMPOSITION 8 
FIG. 2 
Referring to Fig. 2, we have represented the type of complete 
solubility before and after solidification. On the left is the cooling- 
curve for a single mixture. We note two breaks, at /’, that due to 
commencement of solidification, and at Ff, a change of direction due 
