ail to meet with among
those groups which usually furnish our fast colors, e.g., the alizarin
group?

Passing on to the "Congo violets, blues, and purples," we find few
colors worthy of particular notice for fastness. Diamine violet N
appears, perhaps, of medium fastness on wool and silk, while
sulphonazurin, benzo-black blue, and direct gray may claim the same
distinction on silk.

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. Particularly fugitive are the eosins, and yet
some of these, by a slight modification of constitution, e.g., the
introduction of an ethyl group, as in ethyl-eosin, are rendered
distinctly faster.

In the azo group some colors are fugitive, others are moderately fast,
and it is generally recognized that certain classes of the tetrazo
compounds are distinctly faster than the ordinary diazo colors.

By a careful study of the influence of the atomic arrangement upon the
stability of colors, information useful to the color manufacturer may
possibly be gained, but at present my facts are not yet sufficiently
tabulated to enable one to recognize any generally pervading law in
this direction.

It is scarcely necessary to say that the fastness to light of a color
is independent of its commercial value, this being mai