eady forming part of the hat bodies,
and a new layer of pure, unproofed wool or fur is gradually wrought on
to the proofed surface. The hat-forms are then taken out and washed, and
can be dyed with the greatest ease and with excellent results, as will
be seen from the accompanying illustration (see Fig. 15). This
successful invention emphasises the value of the microscope in the
study of processes connected with textile fibres. I would strongly
advise everyone interested in hat manufacturing or similar industries to
make a collection of wool and fur fibres, and mount them on microscope
slides so as to form a kind of index collection for reference.

[Illustration: FIG. 15.

1. Natural wool fibre unproofed.

2. Wool fibre showing proof on surface, filling up the cells
and rendering the same dye-proof.

3. Fur fibre from surface of veneered felt, showing dye
deposited in cells and on the surface, bright and lustrous.

4. Wool fibre as in No. 2, with dye deposited on surface of
proof.

5. Section of proofed and veneered body, showing unproofed
surface.

6. Section of proofed body without "veneer."]

LECTURE VIII

MORDANTS: THEIR NATURE AND USE

The name or word "mordant" indicates the empiricism, or our old friend
"the rule of thumb," of the age in which it was first created and used.
It serves as a landmark of that age, which, by the way, needed
landmarks, for it was an age of something between scientific twilight
and absolute darkness. _Morder_ in French, derived from the Latin
_mordere_, means "to bite," and formerly the users of mordants in dyeing
and printing believed their action to be merely a mechanical action,
that is, that they exerted a biting or corroding influence, serving to
open the pores of the fabrics, and thus to give more ready ingress to
the colour or dye.

Most mordants are salts, or bodies resembling salts, and hence we must
commence our study of mordants by a consideration of the nature of
salts. I have already told you that acids are characterised by what we
term an acid reaction upon certain vegetable and artificial colours,
whilst bases or basic substances in solution, especially alkalis,
restore those colours, or turn them to quite another shade; the acids do
the one thing, and the alkalis and soluble bases do the opposite. The
strongest and most soluble bases are the alkalis--soda, potash, and
ammonia. You all know, probably