PHASE MODELS FOR TERNARY SYSTEMS PAULPORTER SUTTON .Vorth Carolina State College of 4gricultsre and Engineeringof the Univerrityof ,Vorth Cmrolino, Raleigh. Vorth Carolina
THE teaching of heterogeneous equilibria and the phase rule is ordinarily difficult because the highly important ternary systems require the use of threedimensional models. Thus, a great portion of the time allotted to class discussion of such systems must be given to the purely geometrical problem of passing from a conventional, plan-view, triangular figure to the completed equilibrium surface in space. This limits the opportunity for dealing with the significant, and often complicated, aspects of their physical and chemical behavior. This is a problem which should not be treated too lightly, for the student must be able to make such transitions with sureness and ease in order to apply his previous knowledge of binary systems. The author has felt that the models now on the market do not sufficiently stimulate the powers of visualization,
The project extended over a period of two weeks and consisted of preparing the space analogs of the six typical concentration-temperature diagrams of Rankin and Wright,' a choice dictated by the fact that the students concerned were majoring in ceramic or geological engineering. The work was carried on in pairs, and large half cakes of Ivory soap were used. The accompanyingphotograph shows a typical set of models. Acquiring a general familiarity with the space relation of ternary diagrams is ordinarily difficult. In this work, after lettering his models, the student clearly perceives their connection with the binary cases. In a manner far more effective than by mere discussion, he is aided in comprehending the differences between alteration lines and eutectic lines, hesitation points and quintuple points, etc. Further, the models
PHASE MODEISCARVED IN S O A P
and has required students to carve phase models out of soap, working only from printed, two-dimensional diamams. The experiment has been so successful that we Lave adopted i t as a regular assignment in one of our courses of physical chemistry.
can he saved from year to year, and the student can turn to them for review when he must apply his knowledce of these systems.
,RANKIN AND wmGBT, G 1 ~ hternary e
SiOt." Am. J. Sci.,39. 18 (1915).
C~O-A~G-
