DEMONSTRATION EXPERIMENTS AND THEIR PLACE IN THE TEACHING OF CHEMISTRY ARTHURB. Gono, SALEM COLLEGE, SALEM, WESTVIRGINIA
The student w'll learn more chemistry from the indiuidual experiment. The demonstration experiment i s a valuable method which may be used to teachfacts and principles, and to demonstrate manipzdation. For this reason it is a most zlaluable method for use during the beginning weeks of theintroductory course. Of the three types of demonstrations, teacher, student, and student-teacher, thefirst i s considered in regard to its value to the indiwidual and to the class. Some of the objections raised in regard to the use of demonstration work are discussed. Several points of w e in making a demonstration experiment more useful and also some characteristics of a good demonstration are listed.
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When chemistry was first offered as a course in the public schools of this country the experimental work was done by demonstration methods in most cases. There were several reasons for this state of affairs. I n the first place there was no ready source of apparatus such as we have a t present in our many houses specializing in scientific supplies. Then the apparatus that was available was too expensive for the equipping of a laboratory for each school. And, as our present-day facilities of transportation were lacking, many of the schools were rather isolated from the sources of supplies that did exist. As aresult the work that was done in the classes was mostly demonstration work and the simplest apparatus and materials were used. From this state of affairs we have changed to the opposite and almost every school that has a course in chemistry has a laboratory that is equipped for individual student experimentation, and in many cases all, or most, of the experimental work is individual and there are very few demonstrations. We might say that chemistry has inherited this system of laboratory instruction. At this point i t would perhaps be well to say a word in regard to the place of individual experimentation in elementary chemistry. The psychologists tell us that scientific ability is a complex mixture of native physical characteristics, mental and physical habits and reactions, and emotional attitudes. To acquire a very important part of this group, namely, physical habits and reactions, i t is necessary to have a chance to exercise these factors by the use of personal experimentation. If it were not for the skills and habits that are acquired by individual work, we would not have the science of chemistry and the large group of chemists that we have a t present. This is just another way of saying that we would not have many of the important processes and products of chemistry which we all enjoy either directly or indirectly and would certainly miss very keenly. After everything is considered the best way to learn to do a thing is to do it, or to apply this to our case the best way t o train chemists is to have them 297
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work a t chemistry, performing individual experiments. Chemistry certainly is not an "armchair" science. Perhaps the relationship of individual and demonstration experiments may he brought out best by an analogy. We will all admit that it is impossible to teach a person to drive a car by taking him to a busy street corner and having h i watch the cars rush past, or even by having him ride with an experienced driver. He must learn to drive by driving. However, it is true that if the student chauffeur knows how to drive a car under ordinary conditions on the open country road he will be able to learn some of the fundamentals of city driving by observing traffic, either from the sidewalk or by riding with an experienced driver. It is just the same with chemistry: the actual driving technic comes from the experiments we do ourselves, and then we are better able to watch another more skilled person perform a demonstration experiment, and we will learn much more from it due to our own slight knowledge of the manipulation required. It is true that in our schools there are certain students that are more interested in learning about chemistry than they are in learning the principles of chemistry. There are enough such students that some of the larger schools have organized classes especially for them. For this type of student the demonstration experiment is more suitable than for those who wish to learn the principles of chemistry. However, even for this type of student i t is necessary to teach some of the principles of chemistry, and so since we have both types in any high-school class i t is not possible to use one class of experiment exclusively, even if it were desirable. Whether or not transfer of learning is a reality, any student has had a very poor course in a science such as chemistry who finds after he has dropped the science as a formal study that he has nothing that will be of value to him in every-day life. When we stop to think that chemistry as a modern science has developed in the last one hundred fifty years i t is very evident that the subject of chemistry is rapidly increasing in subject matter and in the complexity and number of "every-day" household and industrial applications. As a result i t falls to the lot of the teacher to collect and classify material for consideration, rejecting that which cannot be used for one reason or another, in order that the class will be able to cover the maximum of important material in the time available. While the theory of learning by doing is verymTimportantit-is impossible to do all of the work that is suggested in the-course of a year and so a large amount of it must be omitted, especially if all of the experiments are of the individual type. To help solve this difficulty the demonstration experiment may he used to great advantage by using i t as supplementary experimentation. The term supplementary signifies that we would not cut down the number of individual experiments but would increase the
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number of demonstrations in the classroom and use them to expand the principles taught by the individual work, or to teach new and more difficult principles. This plan would not only make i t possible to cover more ground but it would also make for more thorough treatment of the involved principles, and would give the teacher the best possible chance to correlate theory and data. There are three types of demonstrations, the teacher demonstration, the student demonstration, and the student-teacher demonstration. In general, the same methods of procedure and the same values may be attached to these three types of experimentation as far as the class as a whole is concerned. However, in the student and the student-teacher demonstrations, the students who take part in the actual work will get much more from the experiment than those who just observe it, and they will usually get more from it than they would if they did the same experiment in the laboratory as individual work, for they feel more responsibility and so will study the experiment more thoroughly. This makes the use of demonstrations very valuable as a means of giving the students who are especially interested in scientific work more difficult problems and a t the same time benefiting the entire class. Also the help of students in demonstration work will greatly reduce the time the teacher will have to spend on the demonstration, especially if the student is a good technician and can prepare the apparatus with little or no help. The student help does not 'relieve the teacher of any responsibility, for, regardless of whether or not he takes an active part in the demonstration, he is, in the end, responsible for seeing that the class understands the principles and facts of the experiment. In the following discussion the demonstration is considered as a teacher affair. The individual teacher can easily apply the principles set forth to student and student-teacher work. If the student is to get the greatest amount of benefit from the experiments that are performed as class demonstrations he must be led to think of the principles that are involved, and so i t is necessary to use some method of securing this result. Perhaps the best method to use for this purpose is to have the student write up the demonstration experiment as carefully as if it were individual work. Some teachers have a list of mimeographed questions prepared and depend upon them to bring out the main points of the experiment and drive them home. Others depend upon the questions asked in class to bring out the difficulties and main points of the experiment. Whatever method the teacher employs to start the students thinking along the lines of the experiment the best results will be secured only if the student and teacher both ask questions during the time of experimentation. With this plan of procedure the student should develop good reasoning ability, and he will as a rnle be interested in the work
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since there is a certain fascination in seeing work carried out with actual materials. The use of the purely spectacular experiment as a demonstration has no place in chemistry classes, for i t does not have any point. These experiments may be used for entertainment but not for teaching. The demonstration, to be justified, must have some definite point that will be clearly illustrated. To secure this result there must be some well-defined change that is easily seen from all parts of the room, thus making it easy to follow the course of the reaction and thereby making the experiment more successful as a teaching tool. Many demonstrations fail because the teacher does not see the experiment as i t appears to the people in other parts of the room, and so it is pointless as far as the students back of the front row are concerned. To get the best results it is necessary to use some dramatic principles to secure and hold the interest of the students. It is best, if possible, to have the apparatus set up but not on the lecture table until i t is to be used. In this way the experiment is observed while the first interest of the student, which is the strongest interest, is still in operation. Also an interesting piece of apparatus on the lecture table will attract the attention of the students from the discussion of topics related to the demonstration experiment. During the first part of the year more demonstration work shoul I be used than later in the year. The reason for this is that the student has come into an entirely new situation and as a result he does not have any idea of laboratory technic. If the demonstrations in the classroom show the simple manipulations that the student is first called upon to use in the laboratory the result will be that the student will be able to carry out his experiments with less trouble, and will get more from them than if he were sent into the laboratory and asked to follow printed instructions without any background. At the same time he will be much more apt to form good habits of laboratory technic and will not form so many habits that will have to be reformed. For these reasons it may be justifiable to carry out some parts of the laboratory work for the first day or so in the lecture room as demonstrations, and then have the students repeat them later as individual experiments. But this should not be done after the student has a few basic skills mastered. Throughout the year it is a good idea to demonstrate new and particularly difficult points in technic before the students are required to use them in the laboratory. This may be done by illustrating the difficult point by itself, and does not require the performing of the entire experiment. The use of too many demonstrations may, from the nature of the typical demonstration experiment, lead the student to think that chemical reactions are always more or less spectacular and very evident in their
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changes. Plenty of individual work in the laboratory will guard against this mistaken idea. There are some objections that are frequently raised when demonstration experiments are suggested to a teacher. Perhaps the first one is that the demonstrations require too much of the teacher's time. It is true that it takes time for the teacher to set up the apparatus and test the experiment before it is used. This objection must be answered by the individual teacher. Perhaps there are students in the class that would he only too glad to help the teacher set up the experiment and test it, and so save much time. The student demonstration is another method of saving the teacher's time. Another objection is that the demonstration experiment requires expensive apparatus. I t is true that some of the experiments do require such apparatus, and those that require very complicated, delicate, or expensive apparatus should be performed as demonstrations. However, surprising results can be obtained by the use of the simple apparatus available to all laboratories. The main requirement in overcoming this objection as to expense is that the teacher exercise a little ingenuity in the use of his apparatus. Another objection may be that the demoustration teaches the student to watch and not to think. If this is true it is the fault of the teacher, for it is the teacher's task to keep the student thinking and reasoning all of the time a demonstration is going on. Still another objection is that the demonstration does not teach the student the art of chemistry. This is perfectly true, hut the individual experiment will do this and the demonstration is only supplementary. Also you will hear it stated that too many demonstrations become monotonous. While this is true it is easily remedied. In the first place the demonstrations should be made so interesting that the students will be interested in a large number of them. The demonstration should be used to break the monotony of the lecture period, and should be arranged so that it will show the most possible in the shortest time. There is no typical demonstration experiment, but there are certain points that must he taken into consideration in planning and performing a demonstration so that the student will get the greatest possible benefit from it. I t might be well to list a few of the most important of these points here. 1. The experiment must be as complete and accurate as the time available and the skill of the teacher will permit. 2. The experiment must demonstrate a defmite principle or process which is very evident and is not obscured by some minor points that are more noticeable. 3. More than one principle should not be demonstrated by one ex-
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periment. If the same experiment is used to demonstrate more than one point is should be performed a different time for each point. 4. The experiment must work quickly and thus avoid the loss of valuable class time. 5. The apparatus must be as simple as possible so that i t will be easy to follow the process, and so the apparatus will not attract the attention of the student from the process demonstrated. 6. The action to be studied must be clearly visible from all parts of the room. If the students on the back row cannot see what is taking place they will get very little benefit from the demonstration, and will often distract the attention of those who could observe the reaction and so spoil the experiment for them. 7. Test the experiment just before the demonstration to be sure that the desired result will be obtained. It is poor teaching, and very embarrassing, to explain why an experiment is a failure. 8. Permit the students to examine the apparatus and samples of the materials and products after the class period. The success of the demonstration depends upon the teacher. There are no definite rules that may be laid down and the results guaranteed if the teacher follows them. One teacher may have fine results and another fail utterly with the same demonstration when using the same apparatus and the same general plan of procedure. Therefore the extent to which demonstrations are used and the details of procedure in the experiments depend upon the individual teacher, and he must work out his own policy. In conclusion, remember that the demonstration is a method of teaching and so the student should be held responsible for the principles shown and for the facts. The demonstration teaches principles and facts while the individual experiment adds technic to the list. The demonstration is a means to an end and not an end in itself.
