b. Katigen olive G, 50 lb. salt, 10 lb.
soda, and 6 lb. sulphide of sodium, working at the boil for one hour,
then lift, wash and dry. By chroming a darker and faster olive is got.

_Brown._--Dye with 20 lb. Katigen dark brown, 50 lb. salt, 10 lb. soda
and 6 lb. sulphide of sodium at the boil for one hour, then treat in a
fresh bath with 2 lb. bichromate of potash, 2 lb. sulphate of copper and
2 lb. acetic acid for half an hour at the boil, then wash well.

_Pale Brown._--Dye with 8 lb. Immedial bronze A, 2 lb. soda, 2 lb.
sulphide of sodium and 10 lb. Glauber's salt at the boil for one hour,
then lift, rinse and pass into a fresh bath containing 1 lb. bichromate
of potash and 2 lb. acetic-acid at 150 deg. F. for half an hour, then lift,
wash and dry.

_Dark Brown._--Dye with 12 lb. Immedial brown B, 5 lb. sulphide of
sodium, 5 lb. soda and 20 lb. salt at the boil for one hour, then lift
and treat in a fresh bath with 2 lb. bichromate of potash, 2 lb.
sulphate of copper and 2 lb. acetic acid.

The Immedial blacks, blue, bronze and brown dye very fast shades,
standing soaping, acids and light. They may be combined together to
produce a great range of shades of blue, brown, green, grey, etc.

These examples will perhaps suffice to show how this new but important
class of sulphyl colours are applied to the dyeing of cotton. They may
be topped with aniline black, indigo, basic dyes, or combined with such
direct dyes as produce shades fast to chroming to form a very great
range of shades which have the merit of fastness.

(3) DIRECT DYEING FOLLOWED BY FIXATION WITH DEVELOPERS.

A large number of the dyes prepared from coal tar are called azo
colours, such for instance are the Biebrich and Croceine scarlets and
oranges, Naphthol black, Congo red, etc., just to name a few. The
preparation of these is about the simplest operation of colour
chemistry, and consists in taking as the base an amido compound as the
chemist calls such. These amido compounds, of which aniline, toluidine,
benzidine, naphthylamine are familiar examples, are characterised by
containing the molecular group NH{2}, which radicle is built up of the
two elements nitrogen and hydrogen. All compounds which contain this
group are basic in character and combine with acids to form well-defined
salts. When these amido bodies are treated with sodium nitrite and
hydrochloric acid they undergo a chemical change, the feature of which
is that the nitrogen atoms