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 The project extended over a period of two weeks and phase rule is ordinarily difficult because the highly consisted of preparing the space analogs of the six important ternary systems require the use of three- typical concentration-temperature diagrams of Rankin dimensional models. Thus, a great portion of the time and Wright,' a choice dictated by the fact that the allotted to class discussion of such systems must be students concerned were majoring in ceramic or geo- given to the purely geometrical problem of passing from logical engineering. The work was carried on in pairs, a conventional, plan-view, triangular figure to the and large half cakes of Ivory soap were used. The completed equilibrium surface in space. This limits accompanying photograph shows a typical set of models. the opportunity for dealing with the significant, and Acquiring a general familiarity with the space rela- often complicated, aspects of their physical and chemi- tion of ternary diagrams is ordinarily difficult. In this cal behavior. This is a problem which should not be work, after lettering his models, the student clearly treated too lightly, for the student must be able to make perceives their connection with the binary cases. such transitions with sureness and ease in order to ap- In a manner far more effective than by mere discus- ply his previous knowledge of binary systems. The sion, he is aided in comprehending the differences be- author has felt that the models now on the market do tween alteration lines and eutectic lines, hesitation not sufficiently stimulate the powers of visualization, points and quintuple points, etc. Further, the models

PHASE MODEIS CARVED IN S O A P

and has required students to carve phase models out of can he saved from year to year, and the student can soap, working only from printed, two-dimensional dia- turn to them for review when he must apply his knowl- mams. The experiment has been so successful that we edce of these systems. Lave adopted i t as a regular assignment in one of our ,RANKIN AND wmGBT, G 1 ~ h e ternary C ~ O - A ~ G - courses of physical chemistry. SiOt." Am. J. Sci., 39. 18 (1915).