ROBERT C. PLUMB
chemical principles exemplified
Worcester Polytehnic tnrtitut. 01609 Worr.st.r, Mm~~orhuutfr
Footnote to the Drinking Duck Exemplum The drinking duck, described in this column in March of 1973 and by D. L. Frank in the same issue of this Journal, has been used by many chemistry teachers to illustrate principles of phase equilibria and thermodynamics. Some effective variations in the use of this thought-provoking device are described below. Contribution by Judson B. Cross Physical Science Group 38 Cunninghan Street Boston University Boston, Massachusetts I t is simple to make the duck a teetotaler and yet still bob up and down. All you do is put a little masking tape around the base of his stem just above the bottom bulh, sDrav . .the bottom hulb with lacouer and then roll i t around in some carbon hlack (or powdered charcoal). Then paint his head and beak (the red flock art). also his neck down to the carbon black, with white enamel paint. I added another touch. I painted his hat white, hut the top and brim with "silver" model paint. I t is best to remove his tail before blackening his bottom, unless you wish him to have a hlack tail. Now he will run very well in the sunlight without henefit of any water. Actually, when I had him propped u p on a piece of wood, he would dip and dip into the top of a "miniature" of gin. I had, of course, removed the gin and filled the bottle ahout two-thirds full of water. When he dips, his bill is too big to get into the neck and to reach the "gin" level below. So he keeps trying and trying and trying!!! Maybe I should have referred to him as a confirmed alcoholic desperately trying to get a drink, rather than a teetotaler. His bottom can also he irradiated with the radiation from a light bulb or anelectric heater so he will run in bad weather. Contribution by Robert G. Keil University of Dayton Dayton, Ohio 45469 Far too often students compartmentalize topics which they have learned and as a result lack the ability to inte-
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grate their knowledge in an effort to solve a problem. The duck's value to us is that i t presents a phenomena which requires simultaneous application of knowledge regarding gases, liquids, and solutions as well as equilibrium considerations. We have utilized the duck in both general chemistry and physical chemistry courses to test a student's ability to coordinate the use of various topics. In our classes the duck is set in motion and is apparently drinking water. The students are asked to form a hypothesis and subsequently to prove the hypothesis. In our case two interesting things which have yet to be mentioned occurred. First, someone suggested that if the atmosphere around the duck could he isolated the duck should slow its drinking rate as the vapor became saturated with water. This hypothesis was tested with the aid of a hell jar. The duck's motion stopped within several minutes. The vaporization of the liquid from the cloth is an integral part of the reasons why the bird works. Another student suggested that suhstitution of a more volatile "drinking" liquid should cause the duck to oscillate more rapidly. This point was confirmed and in fact a bonus obtained. After several oscillations our duck tips over backward, much like a person a t the bar who has over indulged.
