In the small group of colors which are produced directly upon the
fiber, none seems to call for special notice, except aniline black,
which, notwithstanding its direct derivation from aniline, is probably
the fastest color we have upon any fiber.
Now, in classifying the whole range of coal tar coloring matters into
"mordant dyes" and "direct dyes," and the latter into acid, basic,
Congo colors, etc., I have looked at them from the point of view of
the dyer and arranged them according to color and mode of application.
The chemist, however, classifies them quite differently, viz.,
according to their chemical constitution, i.e., the arrangement of the
atoms of which they are composed, and thus we have nitro colors,
phthaleins, azines, and so on.
In studying the action of light on the coal tar colors from this point
of view, we find that whereas the members of some groups are for the
most part fugitive, the members of other groups are nearly all fast,
and it becomes at once apparent that the chemical constitution of a
coloring matter exercises a profound influence upon its behavior
toward light. Members of the rosaniline group are all similarly
fugitive, while those of the alizarin group possess generally the
quality of fastness.
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