t the boil.
If the bath contained only the dye-stuffs there would be a liability
for the dyeing to be uneven, to prevent which a saline compound, such
as salt, is added. Taking it all round, salt is the best body to add
as it suits all colours very well indeed. Then come Glauber's salts;
borax and phosphate of soda can also be used, but, owing to their
slight alkaline properties, they are not so good as the neutral salts,
like the two first named. When these colouring matters are dyed on
cotton some of them dye best in a bath containing potash or soda, but
these bodies, for reasons previously pointed out, are not available in
wool dyeing, and should never be used. Wool dyes best in a slightly
acid bath, and this may be taken advantage of in dyeing the yellows
and blues of this group by adding a small quantity of acetic acid. The
reds, as a rule, are affected by acids, and, therefore, it is not
possible to use an acid bath with Benzopurpurine, Congo red, with the
possible exception of the Titan reds and scarlets, Diamine scarlet,
Benzo fast scarlet, Purpuramine, which are faster to acetic acid than
the other reds of this class of dye-stuffs.

Probably the best plan of dyeing these colours is to first heat the
bath to about 160 deg. F., then enter the goods, and turn over two or
three times to ensure that they are thoroughly impregnated with
dye-liquor. The bath is now raised to the boil, and, steam being
turned off, the goods are handled without further steam until the
desired shade is obtained. Another plan is to enter the goods when the
bath is at about 150 deg. F., and, after raising to the boil, to work for
half to one hour at that heat; but the plan first described gives
rather better results, and is far preferable. The dye-baths, as a
rule, are not completely exhausted, except when very pale shades are
being dyed; in no case is it necessary to throw the dye-bath away, but
simply to add the required amount of dye-stuff for a new batch; (p. 063)
with those colouring matters which are not entirely exhausted from the
bath a smaller amount, generally about three-fourths only, is required
to be added, with about one-third the quantity of salt which was added
to the first bath. Of course it is not advisable to keep the same bath
or liquor in work always, but after about twenty or thirty batches of
goods are dyed to throw it away and start a fresh liquor.

As a rule it will be found that these dye-stuffs are more thoro