Many precautions are
required both in the mordanting and dyeing processes in order to
obtain trustworthy results; and though the trials with bichromate of
potash give the most reliable information of any single test, they
should be supplemented by the subsidiary tests already alluded to, and
also by a chemical examination, in order to obtain a knowledge, not
merely of the wood strength, but also of the general nature of the
extract. An adulteration with molasses or glucose can be best
determined by fermentation in comparison with a pure sample. Mineral
adulterants may, of course, be detected by an estimation and analysis
of the ash, after making due allowances for variations due to
differences in different kinds of the same dyewoods. The estimation of
the individual coloring matters in these extracts by means of a
chemical analysis is under all circumstances a task requiring much
experience, especially as the coloring principles are associated in
different qualities of each class of dyewood with different
proportions of other constituents which often give much trouble to the
unpracticed experimenter. Extracts made from logwood roots are now
largely manufactured and often substituted or mixed with the extracts
of real logwood, and have in some instances been palmed of as logwood
extracts of high quality. The correct determination of such
admixtures, like the fixing of anything like the exact commercial
value of dyewood extracts, requires nothing less than a complete
chemical investigation coupled with numerous dyeing trials in
comparison with standard preparations, and should be left to an
expert.
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