This section is from "Scientific American Supplement Volumes 275, 286, 288, 299, 303, 312, 315, 324, 344 and 358". Also available from Amazon: Scientific American Reference Book.
4. The learning of the importance of following directions. Chemistry, especially, is full of those cases where this means everything. Sometimes, not often in experiments performed in school, however, it may mean even life or death.
The time for experiments should be carefully considered. When performed by the teacher they should be taken up during the recitation:
1. If used as a foundation to build upon, at the beginning of the lesson.
2. If used as a summary, at the close.
3. They should be closely connected with the points which they illustrate.
4. When very short, or when so difficult as to demand the whole attention of the teacher, they may be given and afterward discussed. If long or easy, they may be discussed while the work is going on. Changes which take place slowly, as those which are brought about by the gradual action of heat, for instance, are best taken up in this latter way.
5. Exceptions may be necessary, as when experiments which demand special preparation immediately before they are presented are given when the recitation begins, or cases in which experiments are kept until near the close of a recitation, when the teacher finds that attention flags and the lesson seems to have lost its interest to the pupils as soon as the experiments have been given.
When performed by the pupils themselves, experiments should come before the recitation as a part of the preparation for the work of the class room.
Even in those cases in which the teacher performs the work, opportunity should be given, from time to time, for the performing of the experiment by the pupils themselves. This can be done in several ways. During the course in physics here I am in the habit of leaving apparatus on the table in my room for at least one day, often for a longer time, and of giving permission to my class to perform the experiments for themselves when their time permits and the nature of the experiment makes it an advantage to get a nearer view than was possible in the class work. I leave it to them to decide when to perform the experiments, or whether it is to their advantage to take the time to perform them at all. I make no attempt to watch either pupils or apparatus, although I would often assist or explain at intermissions or during the afternoon. The apparatus was largely used, and the effect on recitations was a good one. For advanced pupils, and those who can be fully trusted, the plan is a good one. The only question is the safety of the apparatus; each teacher can decide for himself regarding the advisability of the plan for his own school.
With smaller pupils their own safety may render it best to keep apparatus out of their hands, except under the immediate direction of the teacher. With all pupils that is, doubtless, the best plan where chemicals are concerned.
Another method is to allow pupils to assist the teacher in the preparation of experiments, to call occasionally upon members of the class to come forward and give the experiment in the place of the teacher, and to encourage home work relating to experiments. This latter is often spontaneous on the part of older pupils, and can be brought about with the smaller ones by the use of a little tact; many of the toys of the present day have some scientific principle at bottom; let the teacher find out what toys his young pupils have, and encourage them to use them in a scientific way.
In whatever ways experiments be used, the class should be made to consider the following elements as important in every case:
1. The purpose of the experiment. The same experiment may be performed at one time for one purpose, at another time for another. The purpose intended should be made the prominent thing, all others being subordinated to it. Many chemical reactions, for instance, can be made to yield either one of two or more substances for study or examination, or use, while it may be the purpose of the experiment to close only one of them.
2 The apparatus. All elements should be considered. The necessary should be separated from that which may vary. In cases where the various parts must have some definite relation to the others as regards size or position, all that should be considered with care. In complex apparatus the exact office of each part should be understood.
3. A clear understanding of what happens. To this I have already referred.
4. Why it happens.
5. In what other way it might be made to happen. In chemistry almost every substance can be prepared in several different ways. The common method is in most cases made so by some consideration of convenience, cheapness, or safety. Often only one method is considered in one place in a text book. In a review, however, several methods can be associated together. Tests, uses, etc., will vary, too, and should be studied with that fact in view. In physics phenomena illustrating a given principle can usually be made to take place in several different ways. Often very simple apparatus will do to illustrate some fact for which complex and costly apparatus would be convenient. In such case the study of the experiment with that fact in view becomes important to us who need to simplify apparatus as much as possible.
6. Special precautions which may be necessary. Some experiments always work well, even in the hands of those not used to the work. Others are successful--sometimes safe, even--only when the greatest care is taken. Substances are used constantly in work in chemistry which are deadly poisons, others which are gaseous and will pass through the smallest holes. In physics the experiments usually present fewer difficulties of this sort. But special care is necessary to complete success here.
7. Other things shown by the experiment. While the main object should be kept in most prominent view in all experimental work, the fullest educational value will come only when all that can be learned by the use of an experiment is carefully considered.