and these agents have no influence in any way
on the material, but it is soluble in some special solvents that will be
noted later on.

ACTION OF ALKALIES.

The action of alkalies on cellulose or cotton is one of great importance
in view of the universal use of alkaline liquors made from soda or
caustic soda in the scouring, bleaching and dyeing of cotton, while
great interest attaches to the use of caustic soda in the "mercerising"
of cotton.

Dilute solutions of the caustic alkalies, caustic soda or caustic
potash, of from 2 to 7 per cent. strength, have no action on cellulose
or cotton, in the cold, even when a prolonged digestion of the fibre
with the alkaline solution takes place. Caustic alkali solutions of from
1 to 2 per cent. strength have little or no action even when used at
high temperatures and under considerable pressure--a fact of very great
importance from a bleacher's point of view, as it enables him to subject
cotton to a boil in kiers, with such alkaline solutions at high
pressures, for the purpose of scouring the cotton, without damaging the
fibre itself.

[Illustration: FIG. 2.--Mercerised Cotton Fibre.]
[Illustration: FIG. 2A.]

Solutions of caustic soda of greater strength than 3 per cent. tend,
when boiled under pressure, to convert the cellulose into soluble
bodies, and as much as 20 per cent. of the fibre may become dissolved
under such treatment. The action of strong solutions of caustic soda or
caustic potash upon cellulose or cotton is somewhat different. Mercer
found that solutions containing 10 per cent. of alkali had a very
considerable effect upon the fibre, causing it to swell up and become
gelatinous and transparent in its structure, each individual cotton
fibre losing its ribbon-like appearance, and assuming a rod-like form,
the central canal being more or less obliterated. This is shown in Fig.
2 and 2A, where the fibre is shown as a rod and the cross section in
Fig. 2A has no central canal. The action which takes place is as
follows: The cellulose enters into a combination with the alkali and
there is formed a sodium cellulose, which has the formula
C{6}H{10}O{5}2NaOH. This alkali cellulose, however, is not a stable
body; by washing with water the alkali is removed, and hydrated
cellulose is obtained, which has the formula C{6}H{10}O{5}H{2}O.
Water removes the whole of the alkali, but alcohol only removes one
half. It has been observed that during the process of washing wi