Demonstrations vs. Chemistrv Laboratorv J

for Freshman Engineers SAUL B. ARENSON University of Cincinnati, Cincinnati, Ohio

T THE University of Cincinnati there are five A elementary courses in general chemistry given to students in: (a) liberal arts; (b) evening col-

lege; (c) business administration; (d) chemical en- gineering, and (e) all other fields of engineering. The subject of this paper is the course (e) given to freshman non-chemical engineers, and has nothing to do with any of the others.

Up to three years ago, that course was a conven- tional orthodox course, consisting of four to five lectures, a three-hour laboratory period and a one-hour quiz section per week. At present the lecture and quiz section hours are still unchanged but the three-hour laboratory period has been changed into one-hour demonstrations late in the afternoon on two days a week.

These demonstrations are not the simple ones per formed by the teacher during the regular class hour- those are still part of the lecture routine. Nor are they necessarily the same experiments which the student would perform in the laboratory. The easiest way to explain them is to give a few examples.

An experiment found in practically every labora- tory manual involves heating KClOa and MnOz, and testing the O2 thus made. That is practically a repe- tition of what students have seen their lecturer do, during lecture hour. But one of our experiments on OX to the engineers consists in a demonstration-usually spread out over two or three periodsshowing the use of O2 in the determination of the calorific value of a coal sample. During that demonstration everything is done except the firing of the sample. The bomb is loaded, the apparatus assembled and explained, and typical time-temperature data are given. Th$stndents, having inspected the apparatus, having looked through the telescope a t the mercury level in the Beckmann ther- mometer, then draw a timetemperature ignition curve during the demonstration period. Finally, they cal- culate the calorific value of the coal in B.t.u./lb. and cal./g., making, of course, all necessary corrections. Not only that, but they are given data on another coal sample and are required to find out which sample gave more B.t.u./dollar.

Likewise the calorific value of a gas is demonstrated. These experiments should give to non-chemical engi- neers a better appreaation of the work of the chemist and chemical engineer.

The usual experiment performed by students on glass bending involves making a wash bottle and getting it approved. For our demonstration on glass working, a graduate student or faculty member who is an expert glass manipulator demonstrates the simple thinm about

how to make T-tubes, how to put side arms on flasks, how to work pyrex glass, why hard glass cannot be sealed on to soft glass, how metal wires are inserted in glass, etc.

"So you expect the student to be able to duplicate that expertness, having seen it done?" asked someone during a discussion of this plan. In the h t place, the students seeing this demonstration are never going to do any glass bending unless these non-chemical engineers get a job making neon lamps-which is quite unlikely. In the second place, even if they had per- formed the simple experiments themselves, they couldn't classify themselves as experts. What these students are learning, among other things, is an ap- preciation of what has to be done to glass by the glass worker-what can be done and what cannot. Cer- tainly those students who are going on with chemistry need the experience of glass bending, preliminary to their courses in organic and physical chemistry. But why do these non-chemical engineering freshmen need to burn their fingers making glass bends?

Some more examples: To illustrate specific gravity, the student is shown various pieces of apparatus, ranging from simple apparatus to that used in physical chemistry research. He gets acquainted with specific gravity spindles, hydrometers, pycnometers, Westphal balances, and other instruments, and recognizes their accuracy and usefulness. . .

To emphasize viscosity, various viscosimeters, from a pipet on up, are brought into the demonstration room. Samples of oil are run on a "Saybolt" under varying conditions of temperature. That certainly should emphasize the principles of viscosity needed by an engineer.

Many of the experiments are quantitative in nature and most of them, with preliminary preparation by the instructor, can be performed in twenty minutes, leaving a half hour for discussion, calculating results, and evaluating the data.

To get the students to appreciate the work of the analytical chemist, and to teach them the principles of normal solutions a t the same time, the following are demonstrated : (a) Per cent NaOH in lye ( b ) Per cent NarC08 in soda ash (two ways) (6) Per cent Fe in iron ore (d) Per cent 1% in tincture of iodine (6) Per cent Cu in ore (an indirect determination) (fl Per cent N in a fertilizer (Kjeldahl) To emphasize the principle of fractional precipita-

tion, a titration is run determining the per cent of NaCl by the Mohr method.

Not only are some of the nicest ex~eriments of auan- glass bending. Then in the rest of the period he shows titative analysis run as demonstrations, but the cream

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of the physical chemistry experiments is likewise stolen. Usually the experiments are first performed with rela- tively simple apparatus, such as freshmen themselves could handle. The errors involved in the use of the crude apparatus are discussed, then the real physical chemistry apparatus is introduced to show the refine- ments. The principle is put across by the simple experiment, so that the students will not lose sight of the fundamentals involved because of the multitude of complicating details in the daborate apparatus.

An experiment in photography can be performed, in a semidarkened room, doing everything except the development of panchromatic film. Intensifying, re- duction, making of blue prints-all of those are proc- esses of interest to the average freshman engineer.

There are many reasons for this sort of change from laboratory to demonstrations. Many teachers believe that, per hour of teaching, laboratory instrnc- tion is a very inefficient method. No matter how you try to influence students to ask questions of the labo- ratory assistants, they always get a great deal of their . information from their neighbors. In our demonstra- tions, the faculty lecturers answer the many questions. The trouble of checking in and out of laboratory is eliminated. The lessened number of students taking laboratory avoids congestion a t the stockroom window. Even the saving of chemicals is no small item. But the main purpose, let me repeat, is better instruction in the way that it will do this type of student the most good.