Finally, and perhaps this is the most important cause of all, many of the fugitive coal tar colors are gifted, I will not say with fatal beauty, but with a facility of application, and such comparative cheapness in consequence of their intense coloring power, that the dyer, tempted by competition, applies them not unfrequently to materials for which, because of their ultimate uses, they are altogether unsuited; and so it comes about that we find the most fugitive colors applied indiscriminately and without due discretion.

As we look upon these multitudinous colors, one other thought cannot fail to cross our minds.  Is there not surely an overproduction of these fugitive coal tar colors?  Is not the dyer bewildered with an embarras de richesses, so that he knows not where to choose?

There is indeed much truth in this.  With rare skill and ingenuity an army of chemists is busy elaborating these wonderful dyes; but in such quick succession are they introduced into the dye house that the busy dyer has no time sufficiently to prove them, and it is not surprising therefore that he is liable to commit errors in their application.

But if there is an over-production of fugitive colors, there is also at work, as in the organic world around us, the counteracting influence of the law of the survival of the fittest.  Sooner or later, the fugitive colors must give way to those which are more permanent, and already the number of coal tar colors which have been discarded, for one reason or another, is considerable.

Not unfrequently one is asked the question, Is there no method whereby these fugitive colors can be made fast?  Knowing the efficacy of mordants with certain coloring matters, is there no mordant which we can generally apply with this desirable object in view?  The discovery of such a universal mordant I believe to be somewhat chimerical, and yet, curiously enough, a number of experiments have been recorded in recent years, which almost seem to point in the direction of selecting for such a purpose ordinary sulphate of copper.

Some of these diagrams before you this evening show clearly the fastness to light generally of the lakes formed with copper mordant.  This peculiarity of the copper compounds has not escaped the notice of other observers.  Dr. Schunck, for example, during the progress of his research on chlorophyl, noticed the very permanent green dye which this otherwise fugitive coloring matter gives in combination with copper.

Then there is the assertion of practical dyers, that the use of copper sulphate in dyeing catechu brown on cotton assists materially in rendering this color fast to light.

The use of copper mordant with phenolic coloring matters is perfectly natural.  Some time ago, however, it was successfully applied, for the purpose of rendering more permanent, to certain of the Congo colors on cotton, e.g., benzo-azurine, etc., in the application of which, metallic salts had not hitherto been deemed necessary.