sulphuric
acid.

_Salmon_.--Prepare the dye-bath with 1/4 oz. Fast Acid Violet R,
1/2 oz. Orange G, 10 lb. Glauber's salt, 1 lb. sulphuric acid. Work at
the boil to shade.

The mordant reds are fairly numerous, and include both natural and
artificial red dye-stuffs. The principle or property on which the
application of this group of dye-stuffs to the dyeing of textile
fabrics depends is that they are of an acid character and combine with
metallic oxides, like those of iron, aluminium, or chromium to form
insoluble coloured bodies, or "colour lakes" as they are called. The
shade or tint of these colour lakes depends, firstly, upon the (p. 114)
dye-stuff, and, secondly, upon the metallic oxide. Thus Alizarine with
alumina gives a scarlet, with chrome a dark red, and with iron a dull
violet. Alumina and chrome are the metallic mordants most commonly
used in the dyeing of reds; sometimes tin is used, but never iron.

The coal-tar colour makers have placed at the service of dyers a great
variety of mordant dyes, which may be classified somewhat roughly into
groups, according to their chemical composition. The first group is
called phenolic colours. These contain the group, or radical OH,
hydroxyl, once or oftener. It is to the presence of this group that
they owe their acid character and the property of combination with
metallic oxides. To this group of dye-stuffs belong such dyes as
Alizarine, Alizarine Cyanine, Anthragallol, Gambine, Coerulein, and
some others. The natural red dye-stuffs, Cochineal, Brazil-wood,
madder, etc., probably belong to this class.

None of these are essentially dyes of themselves, and used alone will
not dye any fibre, it is only when they are brought into combination
with the mordant that they will dye the wool fibre.

The next group may be called hydroxy-azo dyes, and are quite of modern
introduction. They are azo dyes, one of whose constituents is a body
like salicylic acid, amido-benzoic acid, dihydroxy-naphthalene-sulpho
acid, which contain the group OH, hydroxyl with carboxyl COOH. The
first group imparts phenolic characters, while the second gives true
acid properties, and both of these acting together cause the dyes to
be able to form colour lakes with metallic oxides. There is one point
of difference between the two groups of dyes, the phenolic dyes are as
a rule not dyes of themselves, some of them are practically free from
colour, and it is only when brought into combination w