Leonard W. Fine Housatonic College Bridgeport, Connecticut David N. Harpp McGill Universih, Montreal. Quebec,Canada Earl Krakower' Rochester Institute of Technology Rochester. New York 14623 James P. Snyder University of Copenhagen Copenhagen, Denmark
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Lap-Di~sdveSlides Multiple-use formats for me-laboratory instruction
The attainment of an effective level of laboratory instruction poses many interesting challenges to the instructor in that students need to be evaluated on such diverse matters as manipulative skills, data aquisition, and interpretive abilities. The most important characteristics of any laboratory exercise lie in the student's ability to successfully carry out the procedure while gaining a clear understanding of the theory on which the experimental procedure is based. T o simplify the transition that the chemistry student must make-in putting classroom theory into laboratory practice-pre-laboratory instruction has become an important element of undergraduate chemistry. Pre-laboratory instructional programs tend to vary in their scheduling formats and content emphasis. The direct approach is the traditional short lecture presented a t the start of the laboratory period. Here, theory relevant to the experiment is reviewed-time nermittine. But eenerallv. the emphaiis is placed on disa~ssimof laboratory proredures directly related to the en~eriment.Both time limitations and class size often preclude effective pre-lab demonstrations of the exneriment. A serious disadvantaee of this instructional format is its infringement on scheduled laboratory time. As an alternative, actual course lecture time can be set aside each week for laboratory orientation. However, if discussion of the laboratory exercise coincides with the first class meeting of the week, two or three days may elapse before students carry out the exoeriment in the laboratorv-a considerable disadvantage frim an instructional point of view. While all of these formats are nominally effective, they uniformly suffer from an old idea: in order for a laboratory exercise to become a meaningful educational experience, students must' be made to grope and stumble to a proper conclusion on their own. While there are important lessons to be learned in unaided discoverv. i t is doubtful that facultv members can continue to indulge cn'these same tactics because of increasing demands for classroom efficiency and instructional accountability. We believe that the use of audiovisual technoloev nrovides an excellent means of workine- toward -" . those goals in that a maximum of information can be made available to the student in a minimum of time. The pre-laboratory programs that we have developed during the past six years provide teacher-produced instructional materials for use by students and faculty in coniunction with a variety of media delivery systems. The focus bf the media component for these pre-laboratory programs are sets of highly registered 35mm slides for use with twin slide projectors, alternately activated by a dissolve control unit. This delivery technique, known asLap-Dissolve Projection, has nroven to be a remarkablv effective means of demonstrating chemical concepts through controlled motion for a erowing audience of chemistrv instructors (1-5). We wish to describe the use of ~ a ~ - ~ i s s omaterials lve to prepare self-pacing instructional programs that students may
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* To whom reprint requests should be addressed. Presented at the Fourth Biennial Conference an Chemical Education, Madison, Wisconsin,August, 1976. 72 1
Jownal of Chemical Education C
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Figure 1. Lap-Dissolve sequencing-free radical bromination of toluene experiment. use at any time prior to their scheduled laboratory period. The laboratorv exneriment. includine"the orocedure and related . theory is i r s t butlined in storyboard form, edited, refined, and then transformed into precisely registered sequences of 35mm slides. These sets of slides can then be channeled into a variety of delivery systems for in-class use, either by the instructor or as part of an independent study project for use a t the student's discretion. I t has been our collective experience that effective use of visual materials in this manner represents a significant pedagogical improvement, providing students and faculty with the opportunity to make better use of available laboratory time and space Technical Skllls and Operatlonal Procedures LapDissolve Projection and Related Delivety Systems
Lap-Dissolve Projection uses two 35mm slide projectors, aligned relative to each other so as to project registered, overlapping images on the same area of the screen. However, rather than exneriencine the ex~ectedabruot chanee as slides are advanced, a dissolve-control unit connected in series with each of the projectors blends the image creating the effect of visual continuity between the alternately advancing slides. The use of this techniaue has mown in its acceotabilitv and popularity among academic users because of this ability to animate nhenomena in a user-controlled fashion when the chemicaiproperties of the system exhibit time- or positiondependent change. Molecular motion, reaction sequences, laboratory safet; demonstrations, operation of instrumentation, and virtually any other concept that conveys change are all at the fingertips of the instructor, who can activate the slide projection system by remote control cable a t his or her own discretion
The visual impact of the Lap-Dissolve technique as i t applies to lahoratory-related instruction is illustrated in Figure 1for the case of the hromination of toluene. Each of the frames corresponds to a single slide consisting of two 35mm transparencies "sandwiched" into a pin-registered slide mount. The test-tube reaction is photographed on the right using high speed Ektachrome f h .Color changes enhance the effectiveness of the visual demonstration hut are not reproduced here due to rather prohibitive publication costs. T h e comolete documentation of the theory (Frame 4) is prepared as the original master artwork using L s f e r letteri&. Using Kodalith film. the ohotoaraphir result is at leoct four frames of "white" letterinion a black background. Opaquing material is applied directly to the negative thereby sequencing the chemical reaction (Frames 14).Duplicate Kodalith slides are then made to reverse the image and produce black lettering on a transparent hackground. Exuct superpmitwn allows the student toohserve each slide in relation to its predecessor as a continuous visual overlap. Moreover, the documentation of the chemical theory parallels the actual reaction.
Formats for Media Delivery
Lap-Dissolve Projection demonstrations require careful planning and organization of materials. That in itself is a useful piece of pedagogy, causing both the instrudor, who had to think about and prepare the pre-laboratory Lap-Dissolvt demonstration, and the student for whom it was designed, to sharpen the focus of their attention. However, for pre-lahoratory instruction, once the concepts are formulated and photographed as Lap-Dissolve sequences appropriately related to the laboratory experiment, the result is the production of a self-sustainine unit which may he used in a variety of educational situacons by student i n d instructor. ~ i ~ & 2 e describes the various formats of media delivery that we have used for pre-laboratory instruction. Instructor Use: In the Lap-Dissolve mode, the smooth transition from slide-to-slide commands the viewers primary attention. em~hasiziuethe connection between before and after. h hat is rar less &dent with the usual single projection programs in which one slide is projected onto the screen, its contents discussed, following which, in a visually unrelated way, the next slide literally explodes on the screen. For maximum visual impact, the Lap-Dissolve user's commentary must respond to two significant demands for effective utilization ofthis technique (1) it must succeed in eliciting a heightened audience anticipation of the next slide ~~~
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(2) it must be carefully regulated tc coincide with the programmed number of slides per sequence
Student Use: Duplicate sequences of Lap-Dissolve slides can be edited for sinple'slide presentation. The henefits of animation are lost withuut the dual projection system but this is offqet in part hv sn~dentacc~ssihilityti, the visual materinls. Several ofthe pie-lahoratory programs separate the theory from the actualexperiment. Others incorporate visuals, similar in format to Figure 1. Program content emphasizes the demonstration of laboratory techniques (use of the analytical balance...~ r e.~ a r a t i oofnchromatoaraohic - . columns, titrations. construction of molecular models-to name a few-the table) and illustrates the actual exoeriments. Furthermore, the slide projector and the slides can.he kept in the laboratory for immediate re-use by instructor or student as the need arise. Alternate Delivery Systems
Audiotapes have been prepared that relate the narrative to the visual and automatically advance the slides sequen-
FOR USE BY INSTRUCTOR
FOR USE BY STUDENT
3 . Lap-Disdve
1. S i t e Silde
Projsctlon
Pmlectlan
lhnimatbnl
istaus1 2. S(lds/Acdla Taps
2. Single Slids
Sum - Bmrn/Audlo
Tape
ROieotiM
3.
(Stalk1
4. Filmstrips
