2 MODERN PAPER-MAKING
In isolating cellulose from plants, chemical and mechanical processes are
necessary,. differing for the various plants under treatment. These processes
are chiefly directed to the removal of the various' impurities, gums, resins,
starch and other natural products of growth from the plant, leaving the cellulose
more or less pure. Lignin is the life juices (or their resulting gums or resin?) of
the plant, intimately bound up with the cellulose. Being, therefore, cellulose
imperfectly formed, or in process of being formed, it may be removed by
chemical means, which, in some cases, just fall short of the destruction of the
cellulose proper.
Cotton is the purest form of cellulose which nature produces. It requires
practically no preliminary treatment to render it fit for papewnaking.
Each of the celluloses produced from the various raw materials mentioned
is, however, different from the others in the size, length, strength and structure
of its fibres. They have therefore different paper-making properties.
As a simple illustration, these different fibres may be likened to the various
sticks or branches which may be cut from different trees or bushes; for although
all these consist of wood, yet they are far apart in texture, strength and form;
one stick may be hard and brittle, such as elm or beech, another tough and
whippy, such as ash or willow, a third long and straight, such as bamboo or
cane. All these grow in various but definite forms, and each has its use in a
different way.
All fibres are tubular—that is, they have an outside wall and a hollow centre.
The thickness of this outside wall and consequent narrowness of the central
canal or 'lumen', as it is called, varies with the different fibres, and has its effect
on the ultimate properties or quality of the finished paper.
Cotton (Fig. i, No. i).—The cotton fibre is a single slender hair or cell,
which grows out from the end of the cotton seed. It was probably evolved as a
covering or protection for the seed, or an attraction for the insects which transfer
pollen from one plant to another and so fertilize the seeds. The cotton plant
is cultivated principally in India, Egypt and America, from whence the fibre
is exported to such places as Lancashire for spinning and making into cotton
goods. The latter, in the form of rags of all descriptions, is our raw material,
but it is also used in the natural form, when we receive it as the refuse of cotton-
seed oil and cake works, naked with seed husks and dust. This 'recovered' fibre
is called cotton 'linters'.
The cotton fibre is a comparatively long, flat tube, its average length being
about i inch, while its width is abo'ut ^ or —55 part of an inch; in other
words, 1000 or 1200 fibres placed side by side would take up i inch of space.
The central canal of this tube, during the period of growth, contains the
juices which build up the fibre. When growth ceases, these juices dry up and