IV PREFACE TO FIFTH EDITIONlaboratory facilities. Indeed, except that he must not forget that
class room quizzes and examinations are based on the posted
preparations, the better student may be allowed to substitute
others for posted ones.
All students entering the Massachusetts Institute of Tech-
nology should have met an entrance requirement in chemistry.
It is very discouraging to such students to be set at once to re-
viewing what they have already had, however much they may
need the review. The nature, and the considerable freedom in
the choice, of laboratory work solves this situation in a very
satisfactory manner. A review of preparatory school work is of
course necessary, but by bringing this in incidentally the sting
of it is removed.
The chapters of the book are divided into two parts, part
one containing the directions for laboratory work, and part two
the discussion of principles, review of previous work, and problems.
Except for Chapters I and III the first part contains the directions
for preparations involving the elements with which the chapter is
concerned. Part two of these chapters contains directions for
short experiments, many of which will be familiar from secondary
school work or will have been shown in the lecture; the facts ob-
served in the experiments, however, are stated, and the significance
of the facts is discussed in the text. The student is privileged
to perform as many of these experiments as he elects, but he is not
required to perform any. He is required, however, to study and
understand the experiments. In this way the necessary review is
achieved while at the same time adding considerably to the
student's previous knowledge and comprehension. These chapters
end "with a set of general questions which require a good deal of
thinking and looking up of data. Written discussions of these
questions are to be handed in by all students.
Chapter I is devoted to the quantitative measurements of
chemistry — combining ratios, densities, and so forth. Part one
may be actually performed in the laboratory or it may be handled
with part two entirely in the class room; the laboratory work
may start with the preparations of Chapters II and IV. Chapter
III deals with the ionic theory. The preparation work is inter-
rupted after about the fifth week and the short experiments in
ionization are performed in the laboratory. Part two of Chapter
III is simultaneously handled in the class room.