72 MODERN PAPER-MAKING
The straw may be cut up in a chaff-cutter or packed into the boiler in bundles.
It is best, however, to cut it up, as dirt is then much more easily loosened
and dusted out. It is unnecessary to remove the knots from the straw stems
before boiling, but in order to free it from corn and hard particles of grit, etc.,
it is cut into short lenghts of i to 2 inches and blown through a trunk into a
hollow gauze chamber. The heavier particles remain behind and fall through
the gauze, while the lighter straw passes on and is filled into the digester. After
the digester is full, or while it is being filled, the straw is soaked with water or
with caustic solution in order to pack it down. The digester is then filled up
again with more straw, and the boiling commenced. The pressures employed
vary from 20 to 80 Ib. per square inch, and the caustic soda from 10 to 20 per
cent. The resulting stuff is a pulpy mass which can be run through pipes to
draining tanks, whence the lye is drained away for recovery, and fresh water
is run on to the pulp to complete the washing. After draining, the pulp is dug
out, bleached in potchers, run off on a presse-pate, and is ready for furnishing
to the beater.
Another method, which, however, is very wasteful of small fibres, is to
wash the boiled straw in ordinary breakers with drum washers. The wire
cloth covering of the drums in this case must be of very fine mesh in order to
retain the smaller fibres and cells.
We are indebted to Mr. B. A. Poulie Wilkins, Managing Director of the
Stroostoffabriek 'Phoenix', Veendam, Holland, for the following particulars
of the treatment of straw for making fine writing papers:
'The straw is cut into short pieces about an inch in length, and is then
boiled in rotary boilers with sulphate liquor of about the same constitu-
tion as the liquor used for boiling kraft sulphate pulp. After cooling,
the contents are blown into washing tanks for the separation of the stuff
from the black liquor. The stuff is next run through a refiner into the
bleaching tanks, where it is treated with about I per cent of chlorine. It
is then run off on a pulp-drying machine and is ready for use.
"The black liquor from the washing tanks goes to the soda recovery
department, first to the quadruple-effect evaporators, where it reaches a
strength of 25° to 32° Baume; the rotary fiirnace fully dries the black
mass, and this material is burnt in the smelting furnace to IStaCOa and the
NatSO* is reduced to Na*S; the causticising plant does the rest
'The composition of the straw itself is of vital importance, and also
its state of cleanliness. In this country [Holland], for instance, the examina-
tion of stalks of rye straw has revealed that those grown near the North
Sea—that is, on the land which contains a very high percentage of silicates