STRAW . 73
—contain as- much as 5 per cent by weight of silicate. Straw grown, on
average soil contains only about 0.5 per cent.
'From this it will be realised that raw materials varying so much in
composition require different treatment. Great difficulty is experienced
in the soda recovery department when dealing with the waste liquors from
straw containing a high percentage of silicates, on account of the formation
of sodium silicate on the melting furnace/
Excellent writing papers may be made from straw pulp manufactured by
the above method, in the furnish of which as much as So per cent of straw is
included.
At present there is a tendency to move out of the old rut in the preparation
of raw materials for making white papers, and to carry out the boiling and
bleaching on more scientific lines, and to take advantage of the advances in
the knowledge now available so far as the chemistry of cellulose is concerned.
Two processes have been largely developed in recent years, mainly for the pro-
duction of bleached pulp from raw materials such as straw, hemp, flax, and other
plants and grasses. The first of these was developed and put on to a commercial
basis by De Vains, who originally applied Ms methods to producing satisfactory
pulp from straw about twenty-five years ago. This process has been further
developed, and now Professor Pomilio has also developed a process on rather
similar lines, which seems to have met with some success in various parts of the
wTorld. Both these processes rely to a great extent on chlorine gas acting upon
the moist pulp and removing the lignin. Satisfactory results have been obtained
by both processes, but there are a certain number of difficulties to be contended
with in each case.