20 MODERN PAPER-MAKING
hawsers, which entail a lot of heavy work in handling and preliminary treat-
ment. The largest ropes are cut up with felling axes, and then divided into
the smaller component strands, which are in themselves thick ropes; they are
then cut up by means of a mechanical rope chopper, of which there are several
varieties. The simplest form consists of a machine similar to a chaff-cutter,
which shaves off the rope into pieces of suitable length ready for the boiler.
There are not many contraries contained in ropes, but 'shakes' are often
included, and these consist of frayed ends and small rough pieces which contain
dirt or dust.
The boiling, of this material is far more drastic and prolonged than that
of any of the canvas previously referred to. Tarred hemp ropes and coal
sacks are often boiled several times with a high percentage of reducing agent,
and subsequently they are bleached and allowed to drain, and then bleached
again.
This treatment results in the production of a strong, tough, flexible half
stuff of a pure white colour combined with great opacity.
Manilla rope stock is prepared in the same way as hemp, except that the
treatment in the boiler is less drastic, as a white half stuff is not usually desired
nor is it easily obtained. The shive is very difficult to remove, but the half
stuff is very soft, flexible and silky, and capable of producing papers of enormous
strength and toughness—some, in fact, are almost untearable.
Jute cuttings, various strings, jute bagging, etc., are used for the manufacture
of brown wrapping papers, but very little chemical treatment is necessary,
as the papers to be made are very coarse and their colour is of comparatively
little importance. Lime is used in the boiling of such material to remove grease
and other objectionable matter.
Of course these materials may be resolved to a very pure cellulose, if re-
quired, by using caustic soda and employing high pressures, and by using
chlorine gas as the bleaching agent, afterwards removing the chlorination
compounds by washing. The yield, however, is much reduced, and the
strength of the fibre much impaired in the process.