"To prepare hydrogen gas,
pass a thistle tube and a delivery tube through a cork which fit tightly
in the neck of a bottle," etc., is simple enough. Let a pupil try with a
cork which does not fit tightly and he will never forget that condition.
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.
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