PREFACE TO SECOND EDITION. 
In the six years which have elapsed since the appearance of 
the first edition, the great majority of American Chemists have 
come to regard the microscope as a necessary adjunct to the 
chemical laboratory. The Great War brought us face to face 
with a multitude of intricate industrial and economic problems, 
in the solution of which the chemist was not slow to appreciate 
the importance and the value of industrial chemical microscopy. 
It is probable that a greater number of new applications of micro¬ 
scopic methods were made in our industries during the war than 
in the entire preceding quarter of a century. Since, however, 
this progress has been rather in applying existing methods to 
the solution of new problems, it has been thought best to pre¬ 
serve in this new edition the same view-point as in the old. 
This book is intended to serve as an introduction to the micro¬ 
scope and its accessories as tools for the chemist to work with 
and even though practical applications are referred to, the author 
has made no effort, and has no desire, to have the book take 
the form of a manual of industrial microscopy. 
The changes made have been chiefly in the rearrangement 
of the Chapters, in the elaboration of the data presented and 
in the rewriting of obscure passages. Comparatively little new 
apparatus has been described or new methods introduced. 
Illustrations of the characteristic crystals constituting a satis¬ 
factory test for the elements and compounds discussed in Chapter 
XIV have been omitted as in the previous edition for two reasons, 
(i) The book is essentially a text and not a reference book. 
It came into being because of the necessity of providing a text 
for use by students in Cornell University. In this course, 
training in accurate observation is emphasized; it has been 
ill 
