indigo and 7-1/2 lb.
indophenol is used. Good blue shades of considerable fastness can thus
be got.

_Aniline Black._--This black is produced direct upon the cotton fibre by
various processes which entail the oxidation of aniline. The chemical
composition and constitution of aniline black has not yet been worked
out. It is not by any means an easy colour to dye, but still with
careful attention to carrying out the various operations in detail
excellent results can be attained.

Aniline black is the fastest black which is known, it resists when well
dyed exposure to air and light, is quite fast to washing and soaping.
Its disadvantages are that there is, with some methods of working, a
tendency to tender the cotton fibre, making it tear easily; secondly, on
exposure to air it tends to turn green, this however only happens when
the black has not been dyed properly.

At the present day it is perhaps without doubt the most used of all
blacks. The methods for producing it are many and varied, the following
recipes show how some of the finest aniline blacks can be dyed:--

Ungreenable black is formed when the aniline is by the action of the
oxidising agents converted into a substance named nigraniline. This
compound when formed will not turn green on the fibre under the
influence of acids.

1. The most usual oxidising agent employed for dyeing aniline black is
bichromate of soda, which salt will be found much better for all
purposes than bichromate of potash. Two separate solutions are prepared:
(1) 61 lb. aniline, 9 lb. hydrochloric acid and 10 gallons of water; and
(2) 12 lb. bichromate of soda and 20 gallons of water. After cooling,
equal quantities of these solutions are mixed and the cotton worked
rapidly through the mixture, in a few minutes it assumes a bronze black.
The material is then wrung out and steamed for twenty minutes at 3-1/2
lb. pressure, which process renders it jet black and also ungreenable.

2. Another aniline black: For 100 lb. cotton use 11 lb. aniline oil, 15
lb. bichromate of soda, 40 lb. hydrochloric acid and 160 gallons water
or 12 lb. sulphuric acid. The dye-bath is filled with the water and the
cold solution of aniline oil and a part of the hydrochloric acid in
water is first added, afterwards the bichromate is dissolved in a small
quantity of water, working cold at first and gradually rising to the
boil.

3. Another method is the following and gives a black that is fast and
ungreenable