A Relevant Sublimation Experiment The new "solid state" air fresheners (largely p-diehlarobenzene) provide the basis of an interesting sublimation experiment for the first assignment of a non-majors laboratory entitled "Physical Constants." A small amount of the highly aromatic air freshener (1 g) is placed in a 250-ml beaker, and a 100-ml round-bottom flask filled with ice is fitted into its top. The assembly is placed in a 45°C water bath (hot tap water in an aluminum pan). The weight of the beaker is sufficient to keep it in place. Over the course of an hour, long (2 cm)monoclinic needles of the active principle, p-diehlorobenzene, m.p. 5 3 T , form on the bottom of the flask.' In this time the bath is changed twice with fresh hot tap water. At 4 5 T , the solid does not melt, unequivocally demonstrating the solid-vapor equilibrium. Moreover the product is easily removed and a melting point determined. Since little attention is required, the student has available time to pursue the other elements of the two week assignment. Normally we include the identification of a solid unknown (melting point, mixed melting point and soluhility), and a liquid unknown (boiling point and refractive index) in the two periods. Recrystallization of an impure solid is the major task in one week, sublimation in the second. The sublimation hence provides a "leavening" for the laboratory particularly since we include the following quotation on the properties of the active principle of the deodorant in the p r ~ c e d u r e . ~ "Human Toxicity: Continued exposure to vapors for months or years may cause headache, nausea, vomiting, weakness, portal cirrhosis, subacute yellow atrophy of Liver, cataract, pulmonary granulomatosis, anemia, granulocytopenia. Irritation to skin, eyes, throat also may occur." We allow the students to draw their awn conclusions. Note that under the same conditions negligible sublimation is observed with camphor or naphthalene Steeher, D. G. (Editor), "The Merck Index,"8th Ed., Merck and Co. Inc. Rahway, New Jersey, 1968. University of Victoria Victoria, B. C., Canada
R. H. Mitchell W. A. Scott P. R. West
Volume 51. Number 10. October 1974
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