JOURNAL OF CHEMICAL EDUCATION
SOME SUGGESTIONS FOR INCREASING INTEREST IN LECTURE DEMONSTRATIONS F. D. MARTIN Purdue University, West Lafayette, Indiana
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continued interest of teachers of chemistry in symposia on lecture demonstrations seems to indicate that Dr. Fbkestraw's introductory remarks before a similar gathering 22 years ago are still applicable ( I ) , "The practice of lecture demonstrations bears the same relationship t o the teaching of elementary chemistry that the experimental method in general bears to the science itself. I can scarcely imagine proceeding without it." It is not my intention to present any startlingly new or difficult experiments. Instead, I hope to use modifications of simple experiments to illustrate various methods for attiacting and holding student interest in lecture demonstrations. From the popularity of certain types of radio and television shows, it is evident that audience interest is secured through audience participation in the show. Although it is not practical to use a group of 200 students as lecture assistauts, it is still possible to invite all to participate in many types of experiments, particularly those involving the measurement of time. For example, consider the classical experiment on spontaneous combustion, making use of filter paper dipped in a solution of yellow phosphorus and carbon disulfide. Added interest may be aroused by predicting
in advance the length of time needed for the paper to burst into flame and asking the students to snap fingers when they have measured this interval with their own watches. Other suitable experiments for this type of mass participation are the similar clock reactions (2, 3). After the initial run, taking about 62 seconds as measured with the help of the students, another run is made with double concentration of one of the reactants. Before mixing the reagents, the students may be asked t o predict the new reaction time and measure it as before with their own watches. The sudden appearance of the blue color, as the students snap their fingers a t the end of 31 seconds, seems to give the audience more of a feeling of personal participation than is possible when the instructor alone measures the time. Borrowing again from the field of amusement, the use of a helper selected from the audience seems to create added interest in lecture demoustrations. Here the author differs with the advice offered by Fowles: "Get promising members of the class to help with the experiment" (4). My own practice is to call on the least promising members of the class. This is not done with the idea of making the weaker student an object of
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ridicule, but because such a student is less likely to of detergents in making "wetter water" can also be anticipate the result of an experiment and hence ex- illustrated by adding lycopodium powder to ordinary hibits, without coaching, the type of genuine astonish- water. The immersion test shows that the powder is ment which delights an audience. For example, an not wet by the water until one of the modern detergents experiment described by Arthur (5) seems to attract is added t o the water. In closing, I should like t o call your attention to more attention and create more discussion when performed as follows. After a discussion of the effect of another method for attracting the interest of an auditemperature on the rate of reaction, the low tempera- ence which seems to be very effective, to judge from ture of liquid air is demonstrated by one of the usual the present craze for auto racing, on and off the highmethods, such as holding a heavy weight on a hook ways. I refer to the chance of failure. Experiments formed from "frozen" rubber tubing. The question seem to attract the interest of students when something is then raised as to how fast a cigarette would burn seems to go wrong with the lecturer's demonstration. after being "frozen" in liquid air. A "volunteer'' is This streak of mental sadism may be turned to useful chosen for the test and is given a cigarette, the outer tip scientific ends if the causes for the failure are discussed of which has been immersed for a few seconds in liquid and the experiment repeated under more favorable air. The results usually surprise the class as much as conditions. For example, the spontaneous combustion the would-be smoker. No personal danger t o the of acetylene in chlorine may be carried out quite suchelper is likely as long as care is taken to choose a cessfully by following the directions of Davison (6) student wearing glasses and the usual sweater or or Fowles (7). But let us try the experiment under T-shirt. water, using a glass tube 3 ft. long, 2 in. in diameter. This last experiment also illustrates the third method The tube is clamped in a vertical position, along with for arousing student interest, namely, "the man bites two inlet tubes running along the outside from a point dog" surprise of an unexpected result. Time does not above water level to the two-hole rubber stopper at the permit elaboration of this point, but I suggest that the bottom of the reaction tube. The inlet tube carrying conditions necessary for the prevention of ordinary a mixture of air and chlorine ends in a small perforated combustion may be more forcefully illustrated by glass bulb above the inside surface of the stopper; the having a timorous student "volunteer" t o extinguish a other inlet tube, connected to a tank of acetylene, is lighted cigarette in a small beaker filled with gasoline in bent in a half-circle after passing through the stopper place of water. For those teachers who may hesitate so that its end is directly above the bubbles coming to present m experiment in which gasoline is used as a from the perforated bulb. With an excess of air fire extinguisher, it is possible to use one of the new practically no reaction occurs at the point where the gas fire retardant paints' t o demonstrate the same prin- bubbles mix. Failure of the reaction under these ciples. The application of a flame from a Bunsen circumstances may be used to create the desirable burner to a piece of wood or cardboard covered with "why" attitude and a call issued for suggestions from such a paint, causes the evolution of a gas which causes the students. Most of the students, after considering the paint t o puff up, forming a thick layer of porous the equation fire-resistant material. CIHl + CI2 2HC1 + 2C It has been said that: seem t o he able t o suggest the use of undiluted chln"A pompous word will stand you instead rine in place of raw chlorine-air mixture. The better For that which will not go into the head." ones recall the activation of chlorine by light in a As an example of pompous words which often "do not previous experiment on the chain reaction between go into the head," consider the use of the terms "hy- chlorine and hydrogen and suggest illumination: But drophobic" and "hydrophilic" in the usual discussion only the very good students recall the relation between of colloid chemistry. The average student is more wave length and energy and propose what gives the likely to have his interest aroused if this topicis intro- most eye-catching results-illumination by ultraviolet duced by a simple experiment involving "dry water." light. By sprinkling a hydrophobic powderZover the surface LITERATURE CITED of water in a large beaker, a film may be built up which N. W., J. CHEM.EDUC.,6,1882(1929). is sufficiently thick to prevent the wetting of a match (1) RAKESTRAW, (2) ARTHUR, PAUL, "Lecture Demonstrations in General Chemor even the hand when dipped under the surface of the istry," McGraw-Hill Book Co., Inc., New York, 1939, pp. water. This is also the type of demonstration which 37-8. attracts many "unbelievers" a t the end of a lecture, (3) MCALPINE,R. K., J. CHEM.EDUC.,22, 387-90 (1945). anxious to try the experiment themselves. The action (4) FOWLES,G., "Lecture Experiments in Chemistry," P.
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'Samples from Albi Manufacturing Co., Inc., 29 Bartholomew Ave.. Hartford 6, Connecticut. PSantocel C (Hydrophobic type) from Monsanto Chemical Co., Organic Chemical Division, St. h u i a 4, Missouri, or hycopodium powder.
Blakiston's Son and Co., Inc., Philadelphia, 1937, p. 7. ( 5 ) ARTHUR, PAUL,op. Cit., p. 232. (6) DAVISON, H. F., "A Collection of Chemical Lecture Experiments," The Chemical Catalog Co., Inc., New York, 1926, p..lll. (7) FOWLES, G., op. eit., p. 124.
