them will dye vegetable fibres like cotton and linen directly. Almost
all substantive colours may, however, be fixed on cotton and linen by
first preparing or mordanting those vegetable fibres. Silk, wool, fur,
etc., act like fibre and mordant together, for they absorb and fix the
substantive colours firmly. In our experiments we saw that turmeric is
one of the few substantive colours fixing itself on both cotton and
wool, without any aid from a mordant or fixing agent. Magenta was also a
substantive colour, but Alizarin was certainly not one of this class.

_Adjective Dyestuffs._--Some of these substances are definitely coloured
bodies, but in some of them the colour is of no consequence or value,
and is quite different and distinct from the colour eventually formed on
the fibre, which colour only appears in conjunction with a special
mordant; but, again, some of them are not coloured, and would not colour
the fibre directly at all, only in conjunction with some mordant. All
the polygenetic colours are, of course, comprised in this class, for
example Alizarin and logwood (Hæmatein), whilst such monogenetic colours
as annatto and turmeric are substantive, for they will fix themselves
without a mordant on cotton and wool. The adjective colours can be
conveniently subdivided into--(_a_) those existing in nature, as logwood
(Hæmatein) and Cochineal; (_b_) those artificially formed from coal-tar
products, as Alizarin (madder), Gallein, etc.

_Mineral and Pigment Dyestuffs._--These colours are insoluble in water
and alcohol. They are either fixed on the fibre by mechanical means or
by precipitation. For example, you use blacklead or plumbago to colour
or darken your hats, and you work on this pigment colour by mechanical
means. I will show you by experiment how to fix a coloured insoluble
pigment in the fibre. I take a solution of acetate of lead (sugar of
lead), and to it I add some solution of bichrome (potassium bichromate).