nitrogen in addition, and in many cases sulphur as
well.

227. The Selection of Dyes. When silk and wool, cotton and linen,
are tested in various dye solutions, it is found that the former have,
in general, a great affinity for coloring matter and acquire a
permanent color, but that cotton and linen, on the other hand, have
little affinity for dyestuffs. The color acquired by vegetable fibers
is, therefore, usually faint.

There are, of course, many exceptions to the general statement that
animal fibers dye readily and vegetable fibers poorly, because certain
dyes fail utterly with woolen and silk material and yet are fairly
satisfactory when applied to cotton and linen fabrics. Then, too, a
dye which will color silk may not have any effect on wool in spite of
the fact that wool, like silk, is an animal fiber; and certain
dyestuffs to which cotton responds most beautifully are absolutely
without effect on linen.

The nature of the material to be dyed determines the coloring matter
to be used; in dyeing establishments a careful examination is made of
all textiles received for dyeing, and the particular dyestuffs are
then applied which long experience has shown to be best suited to the
material in question. Where "mixed goods," such as silk and wool, or
cotton and wool, are concerned, the problem is a difficult one, and
the countless varieties of gorgeously colored mixed materials give
evidence of high perfection in the art of dyeing and weaving.

Housewives who wish to do successful home dyeing should therefore not
purchase dyes indiscriminately, but should select the kind best suited
to the material, because the coloring principle which will remake a
silk waist may utterly ruin a woolen skirt or a linen suit. Powders
designed for special purposes may be purchased from druggists.

228. Indirect Dyeing. We have seen that it is practically impossible
to color cotton and linen in a simple manner with any degree of
permanency, because of the lack of chemical action between vegetable
fibers and coloring matter. But the varied uses to which dyed articles
are put make fastness of color absolutely necessary. A shirt, for
example, must not be discolored by perspiration, nor a waist faded by
washing, nor a carpet dulled by sweeping with a dampened broom. In
order to insure permanency of dyes, an indirect method was originated
which consisted of adding to the fibers a chemical capable of acting
upon the dye and forming with i