2 DIKECTIONS FOR WORK
Present this preliminary report to an instructor and obtain
his approval before beginning operations.
Manipulation. All references from the procedure to the
general notes on laboratory manipulation (pp. 4-22) should have
been studied before making the preliminary report. Indeed the
instructor will probably make sure by a quiz that this has been
done before he accepts the preliminary report.
Laboratory Record. The working directions, in the section
entitled procedure, are to be kept at hand while carrying out the
manipulations. These directions do not need to be copied in the
laboratory note book; but it is essential, nevertheless, to keep a
laboratory record in which are entered all important observations
and data, such, for example, as appearance of solutions (color,
turbidity); appearance of precipitates or crystals (color, size of
grains, crystalline form); results of all weighings or measure-
ments; number of recrystallizations; results of test for purity
of materials and products, etc.
Questions on the Preparations. The sections under this title give
suggestions for study, which involves laboratory experiments, con-
sultation of reference books, and reasoning.
The answers to the questions should be written in the labora-
tory note book following the entries for the exercise, and this
book should be submitted at the same time as the preparation for
the approval of an instructor.
Use of Time in Laboratory. In preparation work it is fre-
quently necessary to wait for considerable periods of time for
evaporations, crystallizations, etc., to take place. This time may
be utilized for work upon the study questions and experiments,
but even then it is advisable to have usually more than a single
preparation under way. Thus no time need be wasted by the
energetic student who plans his work well. A program of work
should be made out in advance of the laboratory exercise.
Yield of Product. Where possible the methods employed in
these preparations resemble those actually used on an industrial
scale; where this is impossible on the limited scale of the laboratory,
mention is made of the fact, with reasons therefor. On account
of the limitations connected with work on a laboratory scale,
it is of course impossible to get as high percentage yields as could
be obtained on a commercial scale. The weight of each prepara-
tion is to be determined and recorded, but the chief stress is to be