ough there are great
differences between the various members of the group in this respect.
It has been shown that what takes place in dying wool with these
colouring matters is that the colour base combines with the fibre the
acid of the dye-stuff remaining in the dye-liquor.

Although it is possible to dye wool with the basic dyes from a plain
bath containing water only, yet the results are not satisfactory,
especially when working on a large scale; and for dyeing pale shades
especially, the affinity of the dye-stuff for the fibre is so great
that the first portions of the goods which are entered into the
dye-bath have a great tendency to absorb all the dye-stuff, or the
larger proportion of it, so that uneven dyeing is the result, one end
of the piece of cloth being darker than the other end. This defect is
particularly accentuated when pale tints are being dyed, the colouring
matter being completely absorbed before all the goods are entered into
the bath, but it may be remedied by adding the dye-stuff to the bath
in small quantities at intervals during the process of dyeing. The (p. 065)
best and most satisfactory method, however, is to add to the bath 10
per cent. of the weight of the wool of Glauber's salt, or some other
neutral alkaline salt, which addition almost entirely prevents any
defect of uneven dyeing. How these assistant mordants act is somewhat
uncertain, the explanation generally given is that they exert a
slightly solvent action on the dye-stuff, and so prevent it from going
upon the fibre too readily. This is scarcely an adequate explanation,
but in want of a better it will have to stand.

The affinity of the basic dyes for wool increases with increase of
temperature. This is a property that has an important bearing on the
method of dyeing, and to any person who pays some attention to theory
in its practical applications it indicates the most rational method of
working, which is to enter the goods into the bath cold, or, at the
most, at a hand heat, then, after working a short time to get the
goods thoroughly impregnated with the dye-stuff, to gradually raise
the temperature to the boil and work for from half an hour to an hour
longer, even if before this time the dye-bath be exhausted. The reason
for giving a fair length of time in the bath is to get the colour
properly fixed on the fibre. The combination of the dye-stuff and the
fibre is a chemical one, and, as stated above, the dye-stuff has to be