may be performed in a few minutes before a class which has taken an hour
or more of time in its preparation. The pupil fully appreciates its
importance, and is in the best condition to remember it only when he
has had a part of the hard work attending that preparation. Again,
conditions under which an experiment is successfully performed are often
not appreciated when merely stated in words. "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