8 MODEKN PAPER-MAKING
All the juices contained in the fibre cells are boiled out, leaving spaces
ready to be filled with water. Very exhaustive research work has been done
on wood pulp, so far as its value to the paper-maker is concerned, by the Wood
Pulp Evaluation Committee of the Papermakers' Association of Great Britain
and Ireland, and the results of their work are contained in a report published
by the Technical Section.
Esparto, or Alfa Grass (Fig. i, No. 3).—The botanical name of esparto grass
is Stipa tenadssima, meaning Very strong blade'; Algerian 'Alfa,' Arabic
'Haifa'. This grass grows only in a hot, sunny climate, where the rainfall
does not exceed 24 inches annually, and at a high altitude—between 1000 and
4000 feet above sea level. It is a product of Northern Africa, but a superior
quality, though less quantity, is grown in Southern Spain. The nature of the
soil, altitude and rainfall modify considerably the qualities of esparto. On
siliceous soil, the plant fibres are hard and brittle; on sandy soil, they are finer,
lighter in colour, longer and stronger; salty earths produce thicker but less
tenacious fibres. Iron in the soil accentuates colour. Altitude varies the weight
and size of the leaf blade. The heaviest and longest comes from sandy clay
alluvia, medium from higher strata, and the lightest and smallest from moun-
tainous regions. The medium is the kind most used by the paper-maker. The
longest and heaviest is worked into mats, ropes, etc., and the lightest and finest
is best adapted for basket-work.
Green or partially ripened leaves produce the best paper-making fibres.
Fully ripened leaves contain more silica and absorbed iron, which resist the
action of bleach, and make it difficult to obtain a good white colour. The grass
itself is a long, flat blade, curled by the heat of the sun into almost cylindrical
shape, with innumerable fine hairs or filaments on its surface. These can easily
be felt by drawing a blade slowly through the fingers. When harvested it
is not cut, but plucked, and this accounts for the quantity of roots found amongst
it. If pulled at the proper time (Le. unripe) the grass comes away more easily,
with less roots.
The fibres are distributed through the mass of the blade, together with small
fibrous particles, termed cells. These may be serrated, or pear-shaped and
pointed. They are of little or no value to the paper-maker, most being lost or
washed away in the boiling, washing and bleaching. The pear-shaped cell,
however, is peculiar to esparto and forms a sure indication of that fibre when a
paper is being examined under the microscope.
The fibres themselves are very, fine, cylindrical and smooth, with a
minute central canal. Their average length is 1.5 mm. and their diameter
0.012 mm.
Their shortness prevents them from imparting any great strength to paper,