n fibre.
(8) Dyeing by impregnating the cotton with the dye-stuff,
followed by oxidation or steaming.

It is of course not easy to elaborate a simple scheme of grouping the
processes that shall definitely include all processes, but the above
grouping will be found as successful as any, and each will be considered
as fully as is deemed necessary.

(1) DIRECT DYEING.

Nothing in the history of cotton dyeing caused such a revolution in the
methods of working as did the introduction some fifteen years ago of the
forerunners (Congo red, Benzo purpurine, Chrysamine, Azo blue) of the
now numerous group of direct dyes, followed as they were by the Benzo,
Congo, Diamine, Titan, Chicago and Zambesi members of the group. Prior
to their introduction cotton dyeing was always more or less complicated
and mordanting methods had to be employed.

With the introduction of the direct dyes cotton dyeing has become even
more simple than wool or silk dyeing, and now all that is necessary is
to prepare a dye liquor containing the necessary amount of dye-stuff and
Glauber's salt, or common salt or soda, or some similar body, or a
combination thereof. The method of working is to place the cotton in a
lukewarm or even in a hot bath, raise to the boil, allow the goods to
remain in the boiling bath for half an hour to an hour, then take them
out, wring, wash and dry. This method is simple and will answer for all
the dyes of this group. There are some that do not require the working
to be done boiling; it is simply needful to enter the cotton into a
boiling bath and work without steam until the bath has cooled down.
Furious boiling is not needed--a gentle simmer gives the best results.
Uneven dyeing seems to be an impossibility in this group of dyes, unless
the cotton is dirty; no matter how the operations are carried on, level
dyeing is the rule not the exception. An enormous variety of shades and
tints can be obtained from these dyes, and they can be combined together
in every conceivable manner and proportions.

No satisfactory explanation has yet been given as to what feature in the
chemical composition of these dye-stuffs give them such an affinity for
the cotton fibre as to enable them to dye in so simple a manner such
fast shades as they do; it is a fact there is such an affinity and there
the matter must rest.

It has been found in practice that the efficiency of the dyeing
operation depends, primarily of course, on the particular