ughly
taken up from the bath than is the case in dyeing cotton; thus often
with the same amount of dye-stuff in proportion to the material used
the wool will dye rather a deeper shade than will cotton. In some
cases, especially with the blues and violets, the shade is greatly
different on wool from what it is on cotton, being generally redder
and much stronger. (See the chapter on Union Dyeing.) While the shades
are somewhat faster to light on wool than they are on cotton, they are
no faster to soaping and in some cases not so fast. What may be the
function of the salt, or other such added substance, is not very
clear, probably it plays the same part as to similar bodies in dyeing
the basic dye-stuffs. The dye-stuffs which are referred to above are
all derived from coal-tar, and in the recipes which follow many
examples of their use will be found.

There are but few natural dye-stuffs that have any direct affinity for
wool. Turmeric, saffron, anotta, are about the only representatives,
and these are not of much importance in wool dyeing by themselves,
although they are sometimes used in conjunction with other natural
dye-stuffs, when they are applied by a process which is adapted more
especially for the other dye-stuff which is used.

_Second Method_.--The method of wool dyeing now being dealt with does
not differ essentially from that described above, but as it is applied
to quite a different class of dye-stuffs it is thought better to
consider it as a second method. The dye-stuffs made use of in (p. 064)
this method are what are called the basic coal-tar colours, and it may
be remarked in passing that there are no natural colouring matters
having the same properties. These dye-stuffs are derived from a number
of so-called colour bases, such as Rosaniline, Pararosaniline,
Methylrosaniline, Phenyl-rosaniline, and Auramine base. Many of these
are colourless bodies containing the Amidogen group NH_{2}, which
imparts to them basic properties enabling them to combine with solids
to form salts, and these salts have a strong colouring power. They
form the commercial dye-stuffs Magenta, Saffranine, Thioflavine T,
Auramine, Benzoflavine, Brilliant green, Methyl violet, etc., and
these are salts (usually the hydrochloride) of colour bases. All these
basic dye-stuffs have strong affinity for the wool fibre, and will
immediately combine with it, dyeing it in colours which resist
washing, etc., to a considerable extent, alth