IMPROVEMENTS IN BLEACHING FIBRES FOR PAPER MAKING PURPOSES
Year: 1883

page_text: PROVISIONAL SPECIFICATION left by George Mackay at the Office of the
Commissioners of Patents on the 24th October 1883.
GEORGE MACKAY of Edinburgh in the County of Mid-Lothian, North Britain,
"IMPROVEMENTS IN BLEACHING FIBRES FOR PAPER MAKING PURPOSES,"
"
•
This Invention relates to improvements in bleaching esparto and other grass,
straw, wood, rags, Jute, Jute butts and other fibres for paper making purposes.
As presently practised these materials are first boiled with caustic soda or lime
and soda ash and after being broken into a pulp they are bleached in the " potching"
engine with bleaching powder dissolved in water, the quantity required to bleach
white eight hundredweights of material being about 200 (two hundred) gallons of
the bleaching liquor.
This liquor is ordinarily run into the engine from a cistern and thoroughly mixed
with the pulp after which the pulp is usually heated with steam to about 95 degrees
and kept bleaching for about an hour but it is sometimes also bleached without
being beated.
The bleach liquor is next thoroughly washed out of the pulp which
is then let down into the stuff chest and thereafter further treated by the usual
process for the manufacture of paper.
Under this Invention the materials are boiled in the same way but by the
improved process instead of using about 200 (two hundred) gallons of bleach liquor
about 133 (One hundred and thirty three) gallons only are used and whilst the
said liquor is running into the "potching" engine I add crystal soda to it.
The crystal soda may be dissolved either in hot or cold water but when added to
the bleach liquor the solution of soda must be cold.
The Crystal Soda may be used in various proportions but I have obtained good
results with from 5 (five) to 20 (twenty) pounds for each eight hundredweights of
pulp according to the material being treated.
After the Crystal Soda is added the potching engine is started and the bleach
liquor and soda is thoroughly mixed with the pulp for say 15 (fifteen) minutes and
the pulp is then heated up to about 95 (Ninety-five) degrees and kept at that heat
for one hour or until the stuff comes white or the bleaching may be effected
without the use of heat.

page_text: After the bleaching has been effected the bleach and soda liquor is thoroughly
washed out of the pulp which is then let down into the stuff chest and treated in
the usual way.
Under another method soda ash or recovered soda may be used instead of the
Crystal Soda.
Under another method the weight of bleaching powder may be added in the dry
state to the "potching" engine and the Crystal Soda is then dissolved and poured
into the engine.
Under another method Soda Ash or recovered Soda may be used in place of
Crystal Soda, but these latter methods are not preferred as the dry bleaching
powder and the Soda Ash might attack the machine wires or felts and the dry
bleaching powder might be gritty or dirty.
In the treatment of Jute butts the material, after being boiled, is bleached with
After so bleaching it
bleaching liquor and Crystal Soda as hereinbefore described.
the bleach and Soda liquor is washed out and subsequent to such washing if the
material is desired of a white colour I again add a small quantity of bleach liquor
and a small quantity of dissolved Crystal Soda, Soda ash or recovered soda and
gradually heat up the engine again for about 15 (fifteen) minutes after which the
bleach and soda liquor is again washed out and the pulp treated in the usual way.