12 MODERN PAPER-MAKING
textile factory. The rags may then be dusted, and boiled to remove any
starch or loading which may have been added during the 'finishing' process.
If the rags are really good, they may be furnished straight into the breaker
or beater.
If after washing and breaking they are of a sufficiently white colour for the
paper required to be made from them, they are ready for the beater. If not,
they are bleached with bleaching solution until the required degree of whiteness
is reached.
New White Cotton Cuttings are almost as valuable material for the manu-
facture of the best papers as the new white linens, except that they do not
give quite such a strong or firm handling paper, and in consequence they are
cheaper. The method of preparation of half stuff is generally the same as for
linen, though less drastic.
New Unbleached Linen.—Tim material consists of linen which has been
freed from a good deal of the undesirable shive or bark with which it was
associated when in the form of flax plant. It comes to the paper-maker in
the form of new linen threads, linen canvas cuttings and brown linen cuttings.
These are capable of producing papers of great strength, but in order to obtain
papers of a good white colour, drastic and prolonged chemical treatment is
necessary, and for this reason they are much cheaper than the white cuttings.
The threads or cuttings are first overlooked and, if necessary, cut up by
hand; they are then cut and dusted prior to boiling. If they are examined
before boiling, they will be found to be of a dark grey or brownish colour,
and, on close examination, large quantities of shiny brown or yellow shive or
lignocellulose will be seen, closely interwoven with the linen threads.
It is necessary for these impurities to be destroyed before the linen fibres
are ready to be made into paper. This is effected by boiling the rags, under
pressure, with a high percentage of caustic soda for as long as 10 to 12 hours.
The percentage of caustic soda required is sometimes as high as 20 per cent,
and die pressure may be from 15 to as much as 45 Ib. per square inch.
When the rags are removed from the boiler, they will be found to be very
much softened, to have lost a good deal of their grey or brown colour, and
the particles of shive will be seen to be softer, and lighter in colour.
The rags are now washed with water and bleached with a bleaching solu-
tion. If, when the bulk of the fibres has turned almost white, a handful is
removed from the breaker, it will be seen that the shive is still present, although
paler in colour: In order to destroy it further, dilute hydrochloric or sulphuric
acid may be added in small quantities. This causes the formation of hypo-
chlorous acid, which attacks and destroys the brown or yellow colour of the
shive. This shive or lignocellulose may also be destroyed by subjecting the