Construction of Models Which Demonstrate Planes Models demonstrating planes of interest (for example, a mirror plane in a meso form) can be easily eonstrueted from framework molecular models and polyester casting resin. The resin, along with colored solutions for tinting it, can be bought at stores carrying arts-andcrafts supplies. When cast upon saturated aqueous sodium chloride in a large container, the resin sets to a rigid transparent disc about 4 mm thick. About two or three merization times the manufacturer's promoter is required recommended in orderamount to obtain of satispoly-
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factory hardening of the resin under these conditions. The framework model is placed in a plastic dishpan and is oriented so that the plane to be shown is horizon": tal. To get some models into the correct orientation, parts of them can be embedded in pieces of modeling clay wrapped around metal slugs. Saturated salt solution is added until the surface of the solution is just below the plane one wishes to depict. The casting resin mixed with polymerization promoter and, if desired, coloring is then poured onto the surface. The resin separates into floating heads, but these can be made to coalesce by breaking their edges with the blade of a knife. The resin begins to set in ahout 15 minutes and is hardened after about a day. Surface tackiness can be cured by exposure of the completed model to bright sunlight for several hours. The surfaces of the plastic "plane" are somewhat rumpled, and there is a slight curl to the edges; these defects do not impair the usefulness of the models. The cast resin assumes a circular shape, presumably because of surface effects, hut if parts of the framework model protrude through the body of the cast near its edges, the perimeter of the finished plane is irregular. The photograph shows a model constructed using this technique. The model demonstrates the plane which bisects each of the earbon-carbon bonds of a chair form of cydohexane. The plastic "plane" is approximately hexagonal, and the distance between opposite vertices is about 25 cm.
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Thomas J. Clark Humboldt S t a t e University Arcata, California 95521
628 / Journal of Chemical Education
