or acid vapours which might
be given off from the former might damage the latter.

When thoroughly dry the yarn is ready for the next operation.

2. _Developing._ The developing bath is made in the following manner:
1-1/2 lb. paranitroaniline is mixed with 1-1/2 gallons of boiling water,
and 1-3/4 quarts of hydrochloric acid at 30 deg. to 32 deg. Tw. Stir well until
the paranitroaniline is completely dissolved, add 3-1/2 gallons of cold
water, which will cause a precipitation of the hydrochlorate of
paranitroaniline as a yellow powder. Let the mixture thoroughly cool
off, best by allowing to stand all night; 1-1/4 lb. of nitrite of soda
is dissolved in 4 quarts of cold water, and this solution is added to
the paranitroaniline solution slowly and with constant stirring; in
about fifteen to twenty minutes the diazotisation will be complete. At
this and following stages the temperature of working should be kept as
low as possible. Some dyers use ice in preparing their diazo solutions,
and certainly the best results are attained thereby, but with
paranitroaniline the ice can be dispensed with. After the end of the
time sufficient cold water is added to bring the volume of the liquor up
to 10 gallons. This diazo liquor will keep for some days, but it
decomposes in time, so that it should not be kept too long.

Another liquor is made by dissolving 4 lb. acetate of soda in 11 quarts
of water.

The developing bath is made by taking 4 gallons of the diazo liquor and
1 gallon of the acetate liquor and mixing together, and in this bath the
prepared yarn, 2 lb. at a time, is worked. The colour develops
immediately. The yarn when dyed is lifted out, wrung, and then it is
well washed with water, soaped in a bath at 120 deg. F., with a liquor
containing 1/2 oz. soap per gallon, then dried. As the cotton yarn is
being passed through the developing bath, the latter is freshened up
from time to time by suitable additions of the diazo and acetate liquors
in the proportions given above.

Some dyers use a special form of dye vat for dyeing paranitroaniline red
on yarn, whose construction can be seen from Fig. 27.

[Illustration: FIG. 27.--Dye-tub for Paranitroaniline Red.]

The beta-naphthol bath does not keep well and in time tends to grow
brown, and when this occurs stains are invariably produced on the
cotton. When the yarn or cloth has been prepared with the beta-naphthol,
and dried, the developing should be immediately proceeded