PREFACE. 
The title of this monograph might well have been 
“A Century of Tannin,” as just about one hundred 
years have elapsed since tannin first became recog¬ 
nized as a distinct substance, or class of substances, as 
we now express it. To emphasize this idea of a class 
of substances the present title was selected. 
About twelve years ago the author commenced 
to collect a portion of the literature on the subject, 
especially that referring to the astringent value of 
certain tannin-bearing materials, with the methods 
involved in their estimation. He found, however, the 
task rapidly assuming such formidable proportions 
that only by beginning with the history and system¬ 
atically pursuing the subject through its various phases 
to an ending, with a complete index to the literature, 
could he hope to reduce the many published inconsist¬ 
encies and contradictions to a condition that would be 
available to himself as well as to others. 
The taking of notes and references has been persist¬ 
ently carried on, especially during the past five years, 
until it is now thought best to give to the public the 
work on the general subject, with gallotannic acid, and 
the index to the literature, leaving for a subsequent 
volume the remaining individual tannins, with such 
further additions to the index as it may be found 
possible to collect. 
It has been the constant effort of the author to make 
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