FUNCTION OF THE LECTURE DEMONSTRATION IN SCIENCE EDUCATION WILLIAM HERED Calumet Center, Indiana University, East Chicago, Indiana
N o SATISFACTORY substitute for first-hand observation of phenomena has yet been developed in science education, nor is one likely to be found. Science cannot be presented as a living and gro~vingbody of knowledge without constant referral to its highest court, the laboratory. Individual laboratory work, furnishing ideal contact of student with phenomena, is indispensable; situations arise, however, in which lecture-table experiment.ation has the advantage of immediacy and relevance to a topic under discussion. This paper proposes to inquire into possible criteria for selection or design of lecture experiments to serve the modern first-year college course in chemistry. Since the aims of the course itself necessarily shape those of the lecture experiment, consideration may be given to those aims which are least disputed, although considerable difference of opinion exists as to the mauner of achieving them. The principal aim is that of exhibiting the mechanism of the scientific method so effectively that understanding results, not only of its modus operandi, but also of its aspirations and possible limitations. A secondary aim for the majority of students is to furnish groundwork for future specialization. For either objective the amassing of isolated bits of fact,ual information is inappropriate. Although general agreement exists as to the worthiness of the aims stated above, examination of the literature discloses a disappointingly tenuous relationship of lecture experiments to the aims. Instead, the following extraneous aims appear to be implied. 1. To entertain the demonstrator and, possibly, the onlookers. The fluorescent flowers in a gaseous discharge tube presumably perform this function, as do explosions, smokes, and smells. 2. To reduce the expense attendant upon individual laboratory work. 3. To avoid the inefficiency of student manipulation. I t is debatable whether improved efficiency compensates for the loss of opportunity to experience a t first hand the "innate cussedness of matter" which is so essential a component of the scientist's battle. 4. To simplify the understanding of concepts by substituting mechanical models for the concepts themselves. The danger inherent in this kind of simplification is illustrated by the statement of one bemused student: "Hydrogen is a white cube with one hook; oxygen is a blue cube with two hooks. Water can be prepared, therefore, by hooking two white blocks to a blue block."
Also implied in the literature is a far more defensible aim, that of bringing to life the phenomena which are involved in the evolution of a principle or theory. Here the lecture experiment performs its highest instrnctional service, for the phenomena of chemistry are rarely as intuitive a part of human experience as are those of mechanics, for example, and must be presented as part of the logical structure being erected. With the acceptance of this function as the primary aim of lecture experimentation, the criteria for selection or design become clarified considerably. The experiment must adhere to the tenets of scientific inquiry, partaking of the objectivity and rigor of the method to as high a degree as possible. In such adherence the lecture experiment can make a contribution, not obtainable otherwise, to the central theme of instruction. Some of the desiderata may now be examined. In the first place the operations involved should be transparent enough so that very few assumptions need be made. The procedure should require only a minimum of explanation by the lecturer. Apparatus of the push-button variety, in which practically all of the equipment is hidden from view, is to be shunned. Measurements should be direct and involve familiar instruments, meters and gages being omitted in favor of possible cruder but more obvious instruments. Solutions should be prepared in full view of the audience whenever possible. Secondly, the procedure must be such that conclusions can be drawn by the student himself, the lecturer acting merely as moderator. In this way the climate is rendered suitable for original thought. Fruitful discussion concerning sources of error, implicit assumptions, limitations of interpretation, and questions of methodology, is thereby encouraged. Thirdly, the phenomena must be represented honestly. The temptation to simplify or to stretch the facts has led many a demonstrator to "rig" up false situations. One instance involves the well-known ferrithiocyanate equilibrium. That the equilibrium is not among ferric ions, thiocyanate ions, and ferric thiocyanate molecules has long been realized. Yet this discarded interpretation is frequently used because it is "simpler," though it necessitates the exclusion of certain effects which are not explicable on this basis. The experiments described below illustrate how these criteria may be applied to specific situations. Rate of Reaction-The Iodine Clock (1). Solutions of potassium iodate and acidified sodium sulfite are mixed,
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and the time required for the blue starch-iodine color to develop is determined. The sudden appearance of the blue complex is one of the most startling phenomena in chemistry, and yet it might just as well be a sudden ringing of a bell or a deflection of a galvanometer needle for all the relevance it has to measurement of a rate. Only the completion of the first in a series of reactions is indicated; the progress of any one reaction is impossible to follow. Aside from the doubtful value of inferring a rate from data on completion time, this experiment is defective in requiring either an involved explanation of the accepted mechanism or the usual simplified but invalid interpretation. Rate of Reaction by Gas Evolution. The rate of evolution of hydrogen from an acid and active metal under varying conditions is estimated from the expansion of balloons attached to the reaction flasks. Although not well suited to quantitative investigation, this experiment is elegant in that it requires practically no assump tions and permits the progress of a reaction to be followed continuously. Chemical Equilibn'um (2). Lecturer and assistant, working at cross-purposes, dip water from one of two large dishes into the other. Equilibrium is considered to be attained when the water levels in the dishes remain constant. Differing reaction rates are simulated by the use of dippers of differing sizes. In the words of the author, "This experiment enables the student to seewhat, in the ordinary equilibrium reaction, he must imagine or visualize." This statement is difficult to reconcile with the implications of the operations performed. The student observes a model and not its referent; his attendant difficulty in translating from model to actuality is likely to be even greater than visualizing molecular kinetics from blackboard exposition. Moreover, a number of odd interpretations may occur to the student; for instance, that reaction occurs in a discontinuous manner on the macro scale, or that conservation of mass does not apply to systems in equilibrium. Mean Free Path (3). Two flasks, one containing a small amount of crystalline iodine, are joined by a narrow tube. On warming a t ordinary pressures, the sublimate collects fairly evenly on all surfaces. As the system is evacuated, the sublimate concentrates directly opposite the connecting tube in the receiving flasks. The demonstration is direct and to the point; little emlanation is needed for full comnrehension. ~elatioeActivity of Metals. samples of copper and zinc are exhibited, and then dissolved separately in excess acid being neutralized. *fter the operational definition of relative activity has been reviewed, metallic copper is dipped into the solution of zinc ion and metallic zinc is dipped into the copper ion solution. The identity of the deposit is established. A feelinx for the concept "relative activityn and for the operati&al character of some scientific definitions is assisted by this procedure.
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The Gas Laws (4). The apparatus consists of a sidearm flask equipped with a barometer tube, thermometer, air inlet, and separatory funnel, all contained in a large beaker fitted with a second thermometer. The laws of Boyle and Charles are derived from data obtained by suitable manipulation of the apparatus. Although the results reported are quite satisfactory, the complexity of the equipment is unfortunate. Less distraction would result from the use of separate pieces of apparatus, even though precision is lessened. The Law of Conservation of Mass. Two solutions contained in separate open vials are placed in a flask which is then sealed and weighed. After reaction is induced by mixing the two solutions, the Hask is reweighed. The fact that no change in mass is found is hardly surprising, considering the conditions of the experiment. A precise balance would show a change due to water adsorption, etc. When the exactness of a law is the point a t issue, lecture demonstrations of the law are doomed to failure. Instruments of the lecture-table variety are incapable of distinguishing between the "exact laws" and those laws which are merely a fairly precise description of nature. It is fundamentally wrong to give students the impression that "exactness" can be illustrated by approximate methods. Adsorption and Desorption (6). Natural gas is passed through a solution of boric acid in methanol, and then through separate ducts t o two burners. One path is through an adsorbent. The green flame color is observed only for one burner. After saturation of the adsorbent, both flames are green. When pure methanol is substituted for the boric acid-methanol solution, the gas passing through the adsorbent yields a green Hame; the other flame is colorless. The student is quite capable of drawing valid inferences in so simple a situation. A further virtue of the demonstration lies in its use of a control. The literature is replete with excellent suggestions for lecture experiments. Unfortunately, many time-honored demonstrations are seen to be faulty on critical examination. It is hoped that this paper will stimulate further discussion of ways and means of implementing the conviction of most science teachers that experimentation, when used with proper regard for course objectives, is an indispensable ingredient of science education. LITERATURE CITED (1) ARTHUR, P., "Lecture Demonstrations in General Chemistry," McGraw-Hill Book Co., Inc., New York, 1939, pp.
-. -. 27-9.
(2) SORUM, C. H., J. CKEM. EDUC.,25,489 (1948).
(3) Sxrra, H. D., AND C. W. UFFORD, "Matter, Motion, and Electricity," McGraw-Hill Book Co., Inc., Sew York, (4) DEVOR 1939, p. A.31. W. J. CREM.EDUC.,22, 268 (1945). (5) F., mD p. D ~ ibid., 26,~ 105-6 (1949).
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