Further, I wish to give
you an ocular demonstration of the action of light or dyed colors, by
means of these silk, wool, and cotton patterns, portions of which have
been exposed for 34 days and nights on the sea coast near Bombay,
during the month of February of this year.
I may remark that this test has been a very trying one, for I estimate
that it is equal to more than a year's exposure in this country.
During the whole period there was cloudless sunshine, without any
rain, and each evening heavy dew. I have pleasure in acknowledging the
services of Mr. W. Reid, a former student, who superintended the
exposure of the patterns, and from time to time took notes of the rate
at which individual patterns faded.
These diagrams contain, perhaps, the most complete series of both old
and new dyes, on the three fibers, which have been simultaneously
exposed to sunlight, and they form an instructive object lesson.
Let me first direct your attention to the diagram containing the
_natural coloring matters_--those dyestuffs which were in use previous
to 1856. Broadly speaking, they are of two kinds; those which dye
textile materials "direct," and those which give no useful color
without the aid of certain metallic salts, called "mordants.
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