alkali is washed out

=Treatment of Straw.=–As a paper-making material, the employment
of straw is of very early date, a patent for producing paper from
straw having been taken out by Matthias Koops as far back as
1801. The material, however, was used in its unbleached state,
and formed a very ugly paper. White paper was not obtained from
straw until 1841, but no really practical method of treating this
material was devised until about ten years later, in France, when
MM. Coupier and Mellier introduced a process which, with subsequent
modifications, has been extensively adopted. A great advance in
the manufacture of paper from straw has since been effected by the
introduction of various boilers, specially constructed for boiling
the material at high pressures, and for keeping the alkaline
liquors freely circulated amongst the fibre during the progress of
the boiling. These boilers are of different forms–being either
cylindrical or spherical–and are preferably of the revolving type,
which causes the caustic ley employed in the boiling to become
uniformly mixed with the fibre. Sometimes the vomiting boilers
described elsewhere are used by paper-makers in preference to those
referred to.

=Bentley and Jackson’s Boiler.=–This boiler, a representation of
which is shown in Fig. 18, is 7 feet in diameter, 18 feet long on
the cylindrical surface, with hemispherical ends of Martin-Siemens
steel plate 7/16 inch thick in the shell, and ½ inch thick in
the ends. It is double riveted in the longitudinal seams, has
two manholes 3 × 2, forged out of solid steel plate. Inside are
two perforated lifting plates or shelves, each 1 foot wide, ¼
inch thick, the full length of the shell, and secured to the ends
by strong angle-irons; it is supported on two turned cast-iron
trunnions. These boilers are tested by hydraulic pressure to 120
lbs. per square inch.

[Illustration: Fig. 18.]

The varieties of straw generally used for paper-making in this
country are wheat and oats, though rye and barley straws are also
used, but in a lesser degree. The treatment of straw differs
greatly at different mills, some makers using strong liquors
and boiling at a lower pressure, while others prefer to use
less caustic soda and boil at a higher pressure. There can be
little doubt, however, that the high temperatures resulting from
boiling at very high steam pressure must deteriorate the fibre
considerably, causing subsequent loss of fibre in the processes of
washing and bleaching.

=Boiling the Straw.=–The straw is first cut into short lengths
of one or two inches by means of a chaff-cutter, or by a machine
similar to a rag-cutter, and the cut material is then driven by
an air-blast through a wooden tube into a chamber having coarse
wire-gauze sides: a second chamber surrounds this, in which the
dust from the straw collects as it passes through the wire gauze.
The winnowed straw, freed from dust and dirt, is then conveyed in
sacks to the boilers. In charging the boilers, a certain quantity
of ley is first introduced, and steam also, and the cut straw then
added, which soon becomes softened, and sinks to the bottom of the
boiler, when further quantities of the material are added, until
the full charge has been given. The requisite proportion of ley
and water is then run in and the head of the boiler secured in its
place. Steam is now turned on, until a pressure of 20 to 40 lbs.,
or even more, has been reached, when the boiling is kept up for
3½ to 8 hours, according to the pressure used and the strength of
the alkaline liquor, which varies from 9° to 16° Tw. From 10 to 20
lbs. of caustic soda per cwt. of straw are generally required to
boil the material thoroughly. The boiling being complete, steam is
turned off, and when the boiler has somewhat cooled, the material,
which is in the form of a pulp, is discharged by the pipes beneath
into a large tank or strainer, the bottom of which is fitted with
a series of plates having long narrow openings or slits, through
which the liquor drains. The pulp is then washed with water, and
again allowed to drain thoroughly, after which it is dug out and
transferred to the potcher to be again washed and bleached. At
some mills the straw is boiled whole and not subjected to any
preliminary cutting In such cases the boiled straw, not being so
fully pulped as when cut into short lengths, is emptied from the
boiler through the manholes used for charging the material into the
boiler.

[Illustration: Fig. 19.]

=Bertrams’ Edge-runner.=–For the purpose of crushing the knots
of the straw, and other hard particles derived from weeds, etc.,
a machine termed the “koller-gang” or “edge-runner” is sometimes
employed. This machine, which is manufactured by Bertrams, Limited,
and of which an illustration is given in Fig. 19, consists of two
large millstones, made from hard red granite, the surfaces of
which are sometimes grooved with V-shaped equidistant grooves.
These stones are worked by a horizontal spindle, and are caused to
revolve very rapidly in an iron basin, in which the washed pulp
is placed, and by this means the knots and harder portions of the
fibre not fully acted upon by the caustic alkali, become so reduced
as to be more readily accessible to the action of the bleach,
and thus a very superior straw pulp is produced. In using this
machine in the way indicated, the washed pulp is mixed in a chest
provided with agitators, with water, is then pumped into a second
chest above it, from whence it flows into the basin shown in the
engraving, while the stones are revolving.

=M. A. C. Mellier’s Process.=–By this method the straw is first
cut into small lengths as usual; it is then steeped for a few hours
in hot water, and afterwards placed by preference in a jacketed
boiler, the object being to heat the materials without weakening
the ley by the direct introduction of steam into the body of the
material. The boiler is to be heated to a pressure of 70 lbs. to
the square inch, or to a temperature of about 310° F., by which
means, it is said, a considerable saving of alkali is effected,
as also time and fuel, as compared with the ordinary practice of
boiling. The alkaline ley which M. Mellier prefers to use is from
2° to 3° B., or of the specific gravity of from 1·013 to 1·020,
and in the proportion of about 70 gallons of such solution to each
cwt. of straw. The boiler should revolve very slowly, making about
1 or 2 revolutions per minute. The boiling occupies about 3 hours,
at the pressure named, when the steam is turned off and cold water
passed through the jacket of the boiler, which assists in cooling
the pulp, the water thus used being afterwards employed in washing
the pulp. The pulp is then thoroughly washed until the last water
runs off quite clear, when it is next steeped for about an hour
in hot water acidulated with sulphuric acid, in the proportion of
about 2 per cent. of the weight of the fibre. The pulp is then
washed with cold water, when it is ready for bleaching in the usual
way.

=Manilla, Jute, etc.=–Previous to boiling these fibres it is
usual to cut them into short pieces by a machine such as is used
for cutting straw, after which they are cleaned in a willowing and
dusting machine. The boiling is then conducted in the same way as
for esparto. Manilla fibre is not so much used in this country
as in the United States, where its employment forms an important
feature in the manufacture of certain kinds of paper. Some idea of
the extent to which it is used by the paper-makers of America may
be gleaned from the following statement of Mr. Wyatt:–“Another
large and important branch of the American paper trade are the
mills running on news and Manilla paper. Many of these mills turn
out a vast quantity of paper, running up to two hundred tons per
week, besides making their own ground wood pulp. The American news
is composed mainly of ground wood pulp, with an admixture of about
15 to 25 per cent. of sulphite wood or jute fibre, and not much
loading, and the machines are run at high speed. What is termed
Manilla paper is very largely used in the States, and much more so
than with us for common writings, envelopes, and wrapping papers.
The paper is composed of Manilla, jute fibre, old papers, etc., and
is highly finished at the machine. I was told of one mill belonging
to a large company running altogether six mills on news and
Manilla, turning out, with one 96-inch machine and beater capacity
of 1,800 lbs., and one Jordan, 10 to 12 tons of 2,000 lbs., of
Manilla paper per day at an average speed of 200 feet per minute.”

Jute is seldom reduced to the condition of a fine white pulp since
the treatment necessary to obtain that condition would result in
a weak fibre; it is usual, therefore, to only partially reduce
the material, when a strong fibre is obtained, which, lacking
in whiteness, is used for coarse papers. This also applies to
Adamsonia, or Baobab, another description of bast obtained from
the West Coast of Africa. These fibres are chiefly used for papers
which require strength rather than whiteness of colour, such as
wrapping papers, &c.

“Broke” paper is a term applied to paper which has been imperfectly
formed on the paper machine or damaged while passing over the
drying cylinders. Imperfect sheets when they are not sold as
_retree_, and clean waste paper, also come under this designation
and are re-converted into pulp after undergoing the treatment
described below.

=Waste Paper.=–In treating waste paper for conversion into pulp
for paper-making, it is doubtless advisable to separate, as far as
can be done economically, papers which have been written upon with
common ink, as old letters, documents, &c., from printed papers,
since the latter require a more severe treatment than the former.
While simple boiling in water containing a little soda-ash will
discharge ordinary writing ink, printer’s ink can only be extracted
by using rather strong solutions of soda-ash or caustic soda; and
even with this treatment it can only be rendered serviceable for an
inferior paper, owing to the grey colour of the resulting pulp, due
to the carbon of the printer’s ink, upon which the alkali has no
solvent effect.

=Boiling Waste Paper.=–This is sometimes effected in iron vats,
about 8 feet deep and 8 feet in diameter at the bottom, and about
6 inches wider at the top. At the bottom of each vat is a false
bottom, closely perforated with small holes. Steam is introduced
by a pipe below the false bottom, which passes through the
perforations and thus becomes uniformly distributed to all parts
of the vat. To facilitate the emptying of the vats, the false
bottoms have connected to them three or four iron rods, to the
tops of which iron chains are hooked, and by this means the false
bottom, carrying the mass of boiled paper can be raised by a steam
hoisting engine or crane and deposited where desired. When the
boiling is commenced, the vat should first be about one-fourth
filled with a solution of soda-ash, and the steam then turned on.
When the liquor boils, the papers having been previously dusted,
are introduced gradually, and well distributed through the liquor;
if they are thrown into the vat in large quantities at a time, and
especially if they are in a compact state, the portions in contact
may not be reached by the liquor, and an imperfect boiling will be
the result. To ensure a uniform distribution of the boiling liquor
over the surface of the material, an iron pipe extends from the
centre of the false bottom to nearly the top of the vat, and this
pipe is covered with a hood, which causes the soda liquor to be
evenly spread over the whole mass. The vats are either cased with
wood or coated with asbestos to prevent the escape of heat, and
the vessel is covered with a flat iron cover, which is generally
in two halves. The steam enters the tubs at the side, below the
false bottom, and the exhausted liquor is drawn off through a valve
connected to the bottom of the vat. In some mills the liquor is
not drawn off after each boiling, but the boiled paper is hoisted
from the vat as before described, and the liquor strengthened by
the addition of from 10 to 20 lbs. of soda-ash for each 100 lbs.
of the paper to be next boiled. Paper that is thickly coated with
printing ink requires an extra dose of soda-ash. The boiling is
continued for twelve to twenty-four hours according to the nature
and condition of the waste paper under treatment.

Waste papers are frequently boiled, after dusting, in revolving
boilers, in a solution of soda-ash or caustic soda, but it not
unfrequently happens that some portions of the material become so
agglomerated or half pulped during the boiling that the alkali
fails to reach all the ink, and as this cannot be removed by the
after processes of washing and breaking, it remains in the body
of the pulp and necessarily forms a constituent part of the paper
to be produced from it. The mass, when discharged from the boiler
and drained is then conveyed to the washing-engine, in which it
becomes broken and freed from alkali and so much of the ink as may
have been dissolved or loosened, and it is afterwards treated in
the beater and mixed with varying portions of other paper stock,
according to the quality of paper to be produced. In some mills the
boiled waste paper is disintegrated after boiling, by means of the
edge-runner (Fig. 19).

=Ryan’s Process for Treating Waste Paper.=–The following process
for treating waste paper so as to produce a “first-class clean
paper” therefrom, was patented by Mr. J. T. Ryan, of Ohio. The
waste paper is first passed through a duster in the usual way, all
thick old books being previously torn apart to separate the leaves.
The papers are then boiled in a hot alkaline liquor without pulping
them, whereby the alkali acts on the surfaces of the papers, and
dissolves off, carrying away all the ink into the liquor. The
papers, which are still in sheet form, are then drained as free as
convenient from the alkaline liquor, and are next washed in the
washing-engine, which leaves the material perfectly clean. It is
then pulped in the beating-engine; and it is claimed that it can be
formed into first-class paper without the addition of any new or
expensive paper stock. The details of the process are thus given by
the patentee: “Into a bucking-keir put a soda-ash solution having
a density of 5° B., at 160° F., put in the stock, and shower for
eight hours at a temperature of 160° F., without pulping the paper,
then lift and drain, and cleanse well in the washing-engine; then
pulp and form into paper. As the draining will always be imperfect,
each charge removed will carry away some of the soda-ash solution,
and leave the remainder of impaired strength. After each drainage
add water to make up for loss in quantity of the solution, and add
enough soda-ash solution at a density of 13° B., to bring all the
liquor up to 5° B. at 160° F. In about eighteen working days the
liquor will have accumulated considerable ink and other matter.
Then blow one half of the liquor, and restore the quantity for
proper working. None of the soda-ash solution is wasted, except
such as falls to drain and what is blown out as last mentioned.” In
carrying out this process every care must be taken to guard against
pulping before the alkali is washed out.

=Bleaching Operation.=–The half-stuff treated in the
breaking-engine is run into the potcher, and the water it contains
is lifted out as far as practicable by the washer; the spent liquor
from the presses or drainers is then run in in lieu of water, and
as much fresh bleaching liquor as may be required is then measured
in, and in from two to six hours the pulp becomes perfectly
white. “However well managed a mill may be,” says Mr. Arnot, “it
is scarcely possible to avoid having a small residue of unused
chlorine in the liquid which drains from the bleaching stuff.” The
rule, therefore, is to use this liquor in the way above indicated,
by which the unexhausted chlorine, operating upon fresh half-stuff,
becomes available, and is, therefore, not wasted. “That as little
of this residual chlorine as possible may remain in the stuff,”
Mr. Arnot further observes, “when put into the beating-engine,
powerful hydraulic presses are employed to compress the stuff
and squeeze out the liquid. These presses should be large enough
to contain easily the whole contents of a poaching-engine, and
of unexceptional workmanship. The perforated lining especially
should be carefully prepared and properly secured. I have seen
much trouble from negligent workmanship in this respect. Recently
I examined a number of samples of press drainings, and found
the unexhausted chlorine to vary very much–from a few grains of
bleaching powder per gallon to about one ounce.”

Sometimes it is the practice to partly fill the potcher with water,
and the engine being set in motion, the half-stuff is gradually
introduced until the full charge has been given, and the stuff is
then washed for some time, after which the drum-washer is raised,
and the bleaching liquor then run in, care being taken that the
necessary quantity is not exceeded, otherwise the fibre will
suffer injury from the chemical action of the bleaching agent.
When vitriol is employed to liberate the hypochlorous acid, the
vitriol, previously diluted with water, should be placed in a
small lead-lined tank in such a position that the acid liquor may
slowly trickle into the engine at the rate of 1 lb. of sulphuric
acid in twenty minutes. As soon as the bleaching is complete the
stuff is emptied into large stone chests, each of which will hold
the contents of two engines. On the bottom of these chests are
perforated zinc drainers, while a similar drainer runs up the back
of each chest. The bleached stuff is allowed to remain as long as
may be convenient in these chests, after which it is removed to
the beating or refining engines. In some mills the bleaching is
effected in the breaking-engine, while at other mills the operation
is performed in the beating-engine.

In bleaching it is considered to be more advantageous to employ
moderately strong liquors rather than weaker ones, inasmuch as
the object is effected in less time than when weaker liquors are
employed. An extreme in the opposite direction, however, must be
avoided, since a very strong bleach will inevitably cause injury to
the fibre. Sometimes the potchers are fitted with steam-pipes, in
order that the diluted bleaching liquor may be heated, if required,
to facilitate the operation. If the temperature be raised too high,
however, the effect upon the fibre will be at least as injurious
as if too strong a bleach were employed. It must also be borne in
mind that in either case, after the pulp has been bleached and the
liquor allowed to run off, the mass has to remain some time–even
if pressed to remove as much of the liquor as possible–in direct
contact with the products resulting from the decomposition, and
probably some undecomposed hypochlorite also, which will continue
their chemical action upon the fibre until removed by washing, or
neutralised by one or other of the agents employed for the purpose.

=Sour Bleaching.=–When the bleaching liquor, after acting upon
the half-stuff for some time, has become partially exhausted,
dilute sulphuric acid–about one part acid to fifteen parts of
water–is added, which, by liberating hypochlorous acid, hastens
the bleaching considerably, and when the chemical action resulting
from this treatment is nearly complete, the spent liquor is
allowed to drain away, and fresh bleaching liquor is introduced,
the strength being regulated by the progress made in the first
case, which will depend upon the character of the fibre treated.
In the second application of the bleach no acid is used. When
sulphuric acid is added to the bleaching liquor, as above, the
process is termed _sour bleaching_. Sometimes hydrochloric acid is
used for this purpose, but in either case it is necessary to avoid
employing the acid in too concentrated a state, or in too great a
quantity, otherwise free chlorine will be liberated, which, besides
being injurious to the health of the workmen and the surrounding
machinery, also involves loss, while the colour and strength of the
fibre itself will also be impaired. In some mills the bleaching is
effected in the beating-engine, the bleaching liquor being pumped
in while the machine is in motion.

Respecting the time which the bleaching operation should occupy,
there appears to be some difference of opinion, or, at all events,
the practice seems to vary in different mills, but there is, no
doubt, an advantage, so far as ultimate yield is concerned, in
moderately slow bleaching at a moderate temperature, inasmuch as
there is less risk of chemical action upon the cellulose itself
than when strong liquors are used, at a higher temperature, with a
view to hasten the operation and economise the bleaching powder.

[Illustration: Fig. 20.]

=Bleaching with Chloride of Lime= (_Preparation of the Bleaching
Liquor_).–Chloride of lime, or hypochlorite of lime, commonly
called bleaching powder, when well prepared, contains from 32 to
35 per cent. of active chlorine. Being readily decomposed by the
air, and also by heat, this substance should always be stored in a
cool and dry place until required for use. A solution of bleaching
powder is generally prepared in large tanks lined with lead, which
are provided with agitators or stirrers, so that the powder, when
added to the water, may be freely diffused, and its active material
dissolved in the liquid. A machine, or “bleach-mixer,” manufactured
by Messrs. Bryan Donkin and Co., of Bermondsey, is shown in Fig.
20, which is so constructed that the strong bleach liquor does
not destroy it. The device for agitating the contents of the tank
explains the principle of the machine. To prepare the bleaching
liquor, about ½ lb. of chloride of lime to each gallon of water
is used, which yields a liquor at about 6° T. When the required
quantity of bleaching powder and water have been introduced into
the mixer and sufficiently agitated, the vessel is allowed to
rest until the residue, which chiefly consists of free lime and
its carbonate, has subsided, when the clear liquor may be run off
for use. When all the clear liquor has been drawn off the residue
should be washed with water, and after again settling, the washing
water run off, and fresh water added, these washings being repeated
as often as necessary to remove the last traces of the “bleach,” as
it is technically called. The washing waters may be used in lieu
of water in the preparation of fresh bleaching liquors. In some
mills the bleaching powder is mixed with from 2 to 3 times its
weight of water; the mixture is then well agitated and the residue
afterwards allowed to settle, the clear solution being afterwards
drawn off and the residue then washed as before. In either case the
residual matter is afterwards well drained and then cast aside. The
bleaching liquor is stored in large tanks ready for use, from which
it is withdrawn as required by means of a syphon or otherwise.

=Bleaching with Chlorine Gas= (_Glaser’s Process_).–This method of
bleaching is not so much adopted in England as formerly, but has
found much favour in Germany; indeed, within the past few years,
namely, in March 3rd, 1880, a process was introduced by Mr. F. Carl
Glaser for treating straw, in which, after boiling with caustic
soda as usual, the pulp is bleached by the action of chlorine
gas. The straw, after being separated from weeds by a slight or
superficial picking, is cut into pieces of from ⅓ to ⅔ of an inch
in length. The cut straw is then placed in a rotary boiler for
about four hours, at a pressure of about 4 to 4½ atmospheres, in a
solution composed of 29 lbs. of caustic soda at 71°, and 48 lbs.
of calcined soda at 90°, rendered caustic, for every 220 lbs. of
straw. After boiling, the dirty ley is drawn off, and the boiled
straw subjected to two washings with water. It is then conveyed
to the washing-engine, where it is washed for an hour; the drum
of the machine should have a sieve or sifter, the apertures
of which are about 60 to the square inch. The washed straw is
next dried by centrifugal force in a hydro-extractor, until it
contains about 70 per cent. of water, which is necessary for the
action of the chlorine gas. To effect this, so as to obtain not
very solid or close cakes of straw, the holes of the wire of the
hydro-extractor should not be more than 50 to the square inch.
The cakes of straw thus formed are then exposed to the action
of chlorine in leaden chambers of the ordinary kind, in which
they are placed in layers upon hurdles, or upon shelves. If the
chlorine is produced by hydrochloric acid, for every 220 lbs. of
unboiled straw, 51½ lbs. of the acid at 20° B., and a corresponding
quantity of 70 per cent. peroxide of manganese are used. After
the bleaching operation, the acid formed is removed by washing in
a washing-engine. If a complete reduction of the fibres has not
been effected by the bleaching, this may be completed by the aid
of well-known machines, and either before or subsequent to the
after-bleaching there is used for 220 lbs. of straw about 4½ lbs.
of chloride of lime, at 35° [per cent.?] The patentee then gives
the following explanation:–“As pine wood or fir is chemically
freed from its colouring principle and transformed into fibres as
well as cellulose, the object of the intense action of the chlorine
is to destroy the mucilage of the straw, as well as the incrusting
matters which have not been destroyed by the boiling with caustic
soda, and consequently to strip or expose and open the fibres.” It
will be readily seen that this process bears a close resemblance to
Mr. C. Watt’s wood-pulp process.

=Electrolytic Bleaching= (_C. Watt, jun.’s, Process_).–At the
present time, when the means of obtaining the electric current for
practical purposes in the arts have so far exceeded that which
would have been deemed probable some forty years since, we find
that many ingenious processes, which were found to be unpractical
at that time from the want of cheap electrical power, have since
reappeared in the form of patented inventions, which would seem to
possess every merit–but originality.

So long ago as September 25th, 1851, the author’s brother, Mr.
Charles Watt, obtained a patent for, amongst other claims,
decomposing chlorides of sodium and potassium, and of the metals of
the alkaline earths into hypochlorites by electricity. It may be
well to make a few extracts here from his specification in order
that some of the subsequent patents, to which we shall refer, may
be traced to what may, perhaps, be considered their true origin.
In the specification in question, the inventor says:–“The third
part of my invention consists of a mode of converting chlorides of
potassium and sodium, and of the metals of the alkaline earths,
into hypochlorites and chlorates, by means of a succession of
decompositions in the solution of the salt operated upon, when
induced by the agency of electricity…. Electricity first
decomposes the chloride, the chlorine being eliminated at one of
the electrodes, and the alkaline or earthy metallic base at the
other electrode…. The liberated chlorine will, when it is set
free, combine with a portion of alkali or alkaline earth in the
solution, and a hypochlorite will be formed. The hypochlorite thus
formed will, by the continued action of heat, be resolved partly
into a chlorate of the alkali or alkaline earth, and partly into
a chloride of the metallic base, and the chloride will again be
subjected to decomposition, and a hypochlorite formed…. If I
desire to produce a hypochlorite of the alkali or earth, I merely
keep the vessel warm … and continue the process until as much
of the saline matter has been converted into a hypochlorite as
may be required for the purpose to which the solution is to be
applied. This mode of forming a hypochlorite of the alkalies and
alkaline earths may be used for preparing a bath for the purpose of
bleaching various kinds of goods, and the bath may be strengthened
[recuperated] from time to time by the action of the electric
current.”

Thus it will be seen that this specification clearly described a
process by which the chlorides of sodium and potassium, and of the
metals of the alkaline earths (chloride of magnesium, for example),
may be converted into hypochlorites by electrolysis, and the
hypochlorite solution obtained used for the purposes of bleaching.
It would appear difficult to conceive how any subsequent patent for
accomplishing the same thing, and using essentially the same means,
can claim originality in the face of such “prior publication” as
was effected by the usual “Blue-book,” which any person can buy for
eightpence.

=Hermite’s Process.=–The following description of this process
has been furnished by the engineers engaged in connection with
the process to the _Paper Trade Review_:–“Briefly described,
the Hermite process consists in manufacturing a solution of high
bleaching power by electrolysing an aqueous solution of magnesium
chloride. The salt is decomposed by the current at the same time
as the water. The nascent chlorine, liberated from the magnesium
chloride, and the nascent oxygen, liberated from the water, unite
at the positive pole, and produce an unstable oxygen compound of
chlorine of very high bleaching power. The hydrogen and magnesium
go to the negative pole; this last decomposes the water and forms
magnesium oxide, whilst the hydrogen is disengaged. If in this
liquid coloured vegetable fibre is introduced, the oxygen compound
acts on the colouring matter, oxidising it. Chlorine combines with
the hydrogen to form hydrochloric acid, which finding itself in the
presence of magnesium in the liquid combines with it, and forms the
initial chloride of magnesium.”

=Andreoli’s Process.=–This process consists, avowedly, in
bleaching pulps “by means of hypochlorite of sodium, produced
by electrolytical decomposition of a solution of chloride of
sodium.” In carrying out his process, M. Andreoli uses as an
electrolyte “concentrated or non-concentrated sea-water, or a
solution of chloride of sodium, the specific gravity of which
varies according to the quality and nature of the materials to be
treated. Generally the solution to be electrolysed works better
with a density of 8° to 12° B., but although salt is cheap, and the
solution when exhausted may be regenerated by passing an electric
current, I always endeavour to have when possible (_sic_) a weak
solution, and with some kinds of pulp an electrolyte having the
density of sea-water (3° B.) is sufficiently strong to bleach.”

The foregoing are the only electrolytic processes for bleaching
fibres that need recording, and we fancy there will be little
difficulty in tracing the resemblance between the two latter and
the process of Mr. C. Watt.

=Thompson’s Process.=–This process, for which a patent was
obtained on February 3rd, 1883, may be thus briefly described:–In
bleaching linen fabrics the material is boiled for about three
hours in a solution of cyanide of potassium or sodium–about
half an ounce of the salt to each gallon of water–to remove the
resinous matter from the fibre, so that the cellulose may be
exposed to the action of the bleach. The fabric is then washed,
and again boiled for three hours more in a similar solution, and
after being again washed is ready for bleaching. With cotton the
preliminary boiling is not necessary, unless the material is
greasy, in which case a solution of half the strength and two
hours’ boiling is sufficient. In ordinary cases cotton is not
boiled at all, but is simply washed in cold water and squeezed.
In bleaching, all vegetable fibres are treated in the same way,
the only difference being in point of time. The cotton or linen,
after being treated as described, is then piled somewhat loosely
in an air-tight vessel, 9 lbs. of cloth to the cubic foot of space
being considered sufficient. The vessel is then filled with a weak
solution of bleaching liquor, consisting of about one ounce of dry
bleaching powder to each gallon of water. “After the vessel has
been filled, the liquor is immediately run out, and is replaced
by an atmosphere of carbonic acid, which quickly liberates the
chlorine on the fibre, and thus decomposes the water, uniting with
the hydrogen and liberating the oxygen, the result of which, is
to bleach the fibre or fabric. In about an hour the whole of the
bleaching liquor in the fibre will have been thus decomposed, and
this operation must be repeated until the material is of the proper
whiteness to be withdrawn from the action of the chlorine. The
material is then washed and squeezed. Chlorine, however, always
leaves these materials of a yellowish white.” To remove this tint,
the material is passed through a solution of oxalic acid–about 2
oz. to the gallon–squeezed as it passes out of this solution, and
then passed through another solution made by dissolving ¼ grain
of triethyl rose aniline to the gallon of water, or 20 grains
of indigo, as may be preferred. To this solution oxalic acid is
added until it becomes of an opaque but bright turquoise blue. The
material, after washing, is then white.

The patent describes and illustrates the apparatus to be used
in conjunction with certain parts of existing apparatus used in
bleaching.

=Lunge’s Process.=–In this process acetic acid is used in place
of hydrochloric or sulphuric acids, etc., to set free the chlorine
or hypochlorous acid, in the ordinary method of bleaching with
hypochlorite of lime, or bleaching powder, which, the inventor
says, “combines all the advantages of the materials formerly
employed, without any of their drawbacks…. The price is no
impediment, for a minimal quantity is sufficient, the same being
regenerated over and over again. At first acetic acid and chloride
of lime decompose into calcium acetate and free hypochlorous
acid. In the bleaching process the latter yields its oxygen,
hydrochloric acid being formed. The latter instantly acts upon the
calcium acetate; calcium chloride is formed and acetic acid is
regenerated, which decomposes a fresh quantity of chloride of lime,
and so forth. Consequently the smallest quantity of acetic acid
suffices for splitting up any amount of chloride of lime…. The
hydrochloric acid formed is never present in the free state, as it
instantly acts upon the calcium acetate. This is very important,
since hydrochloric acid weakens the fibre by prolonged contact,
whilst acetic acid is quite harmless. Since there are no insoluble
calcium salts present, the operation of ‘souring’ after bleaching
is quite unnecessary; this not merely saves the expense of acid,
and of the subsequent washing of the fabrics, but it also avoids
the danger, especially present in the case of stout fabrics, of
leaving some of the acid in the stuff, which concentrates on drying
and weakens the fibre; it may also prove injurious in subsequent
dyeing operations. But in the new process no free acid is present
except acetic acid, which has no action upon fibre, even in its
concentrated state and at a high temperature.”

The acetic acid may be employed in various ways, including the
following:–A small quantity of the acid may be added from the
first to the bleaching liquor; or the fabric, after being treated
in the ordinary way with a solution of the bleaching powder, may
be steeped, without previous washing, in water containing a little
acetic acid; or the fabric may be steeped in water acidulated with
acetic acid, and bleaching liquor afterwards run in slowly and
gradually, with continuous agitation in the usual way. In the case
of hard water, or of impure bleaching liquors, a good deal of the
acetic acid would be consumed in neutralising the lime; in this
case, some hydrochloric or sulphuric acid may be added, but only
sufficient for the purpose, so that no acid but hypochlorous or
acetic acid exists in the free state. The process is applicable to
the bleaching of vegetable fibres, whether spun or in the unspun
state, and for bleaching paper pulp made from rags, wood, straw,
esparto, etc. Besides acetic acid, any other weak organic acid of
an analogous nature may be used.

=Zinc Bleach Liquor.=–Strong acids are often objectionable for
liberating chlorine from bleaching powder, and especially in
bleaching some classes of paper pulp. If a solution of sulphate
of zinc be added to one of bleaching powder, sulphate of lime is
precipitated, and the zinc hypochlorite formed at once splits up
into zinc oxide and a solution of free hypochlorous acid. Chloride
of zinc acts similarly; for a saturated solution of zinc in
hydrochloric acid decomposes as much bleaching powder as half its
weight of concentrated oil of vitriol.–_Varrentrapp._ Consequently
zinc salts can be employed in place of sulphuric acid, and thus
bleach the paper pulp very quickly. When this mixture is employed
in bleaching pulp, the precipitated sulphate of lime resulting from
the reaction and also the oxide of zinc formed, remain in the pulp,
and serve as loading materials.

=Alum Bleach Liquor.=–Orioli[19] recommended for use, in
paper-mills especially, a bleach liquor made by decomposing
equivalent quantities of a solution of chloride of lime and
sulphate of alumina, formerly known as _Wilson’s Bleach Liquor_.
Sulphate of lime is precipitated, and hypochlorite of aluminium
remains in solution; this being a very unstable salt can be applied
for bleaching without the addition of an acid, splitting up into
aluminium chloride and active oxygen. Consequently the liquid
always remains neutral, and the difficulty caused by the obstinate
retention of free acid in the fibre, by which it is strongly acted
upon in drying, in this case does not exist. The aluminium chloride
also acts as an antiseptic, so that the paper stock may be kept for
many months without undergoing fermentation or other decomposition.
The solution is allowed to act for about ten minutes in the
engine.–_Lunge._

=New Method of Bleaching.=–Young’s Paraffin Oil Company have
recently introduced what they term an “intermediate oil for
paper-making,” to be used with alkali in the boiling of rags and
esparto, for the purpose of increasing the bleaching power of
the powder, and producing a softer pulp, at the same time having
no smell. Several well-known paper-makers have tried, and speak
favourably of it. The quantity of oil to be added to the caustic
varies for different stock, but may be said to average about 1½
gallon per ton.[20]

=Beating.=–One of the most important operations in the manufacture
of first-class paper is that of _beating_, by which the half-stuff
becomes reduced to a fine state of division, and the fibres which,
in the condition of half-stuff, are more or less loosely held
together in a clotted state, become separated, and are thus put
into a condition in which they will intertwine with each other, or
_felt_, as it is termed, when submitted to the vibratory motion
of the wire-cloth of the paper machine. The beating-engine, or
beater, as it is commonly called, much resembles in construction
the washing- and breaking-engine, but since it is required to still
further reduce the pulp to a condition suitable for paper-making,
the knives of this engine are more numerous and are made to revolve
more rapidly. In this engine the half-stuff is cleansed from
bleach, hydrochloric or sulphuric acid–whichever acid may have
been used in the bleaching–chloride of calcium, and the various
products resulting from the decomposition of the chloride of lime.
In this engine, also, the loading, sizing, and colouring materials
are worked up with the pulp, and the stuff fully prepared for its
final transfer direct to the paper-machine. Before describing
the various forms of beating-engines which have been from time
to time introduced, including some of the most recent types, to
which special attention will be drawn, we purpose quoting some
observations of well-known experts in paper manufacture which will
be read with interest, since they fully explain the importance that
attaches to the proper manipulation of the beating-engine for the
production of paper of high quality.

=Mr. Dunbar’s Observations on Beating.=–There is no operation of
the paper-mill that requires more careful attention and experienced
judgment than that of beating, or refining, to bring the pulp to
the finest possible condition for paper-making; in this department,
Mr. Dunbar urges, “none but thoroughly efficient men should be
employed, for it is here that the paper is really made–that is,
the quality of the paper produced at the paper-machine will be
in proportion to the treatment the material has received; and if
the half-stuff sent to the beating-engines is not subjected to
judicious manipulation and careful preparation for the special
paper to be made, all future doctoring will prove unsatisfactory.”

=Mr. Arnot on Beating Engines.=–On this subject Mr. Arnot
says:–“Upon the management of the beating-engine the character of
the paper produced largely depends. What is wanted is not a mincing
or grinding of the fibre, but a drawing out or separation of the
fibres one from another; in fact, the name of the machine indicates
pretty accurately the nature of the action required–beating.
Long, fine fibres can only be produced [obtained] by keeping the
roll slightly up off the bed-plate, and giving it time to do
the work. Sharp action between the roll and the bed-plate will,
no doubt, make speedy work of the fibre, but the result will be
short particles of fibre only, which will not interlace to make a
strong felt. Indeed, the action I refer to will reduce the long,
strong fibre of linen to little better than that of wood or straw.
Practice and careful observation can alone make a good beater-man,
and for the finer classes of paper none but careful, experienced
men should be entrusted with the management of the beating-engine.
Sometimes the operation is conducted in two successive engines,
the first being called the intermediate beater, but I have hitherto
failed to see wherein the advantage of this system lies. The time
usually occupied in beating esparto for printing-paper is about
four hours, while for rags the time may vary from four to twelve
hours, or even more.” This, however, depends upon the nature of the
rags themselves, and the purposes to which they are to be applied.

=Mr. Wyatt on American Refining-Engines.=–Referring to the
engines adopted in America, Mr. Wyatt says:–“There are various
modifications of the original Jordan, the principal ones being
the Marshall, Jeffers, and improved Jordan; but I gathered that
experience proves the Jordan type to be the most practical and
efficient in the end, and is one of the most generally used.
One Jordan is required for each machine, refining all the stuff
supplied to it. The roll, or plug, runs from 350 to 400 revolutions
per minute, the horse-power consumed varying from 25 to 40
horse-power according to the work done, and an engine will do up to
1,000 lbs. of pulp per hour. The time saved in the beating-engine
by the use of the Jordan is just about one-third of what would
otherwise be necessary, that is to say, pulp requiring otherwise
six hours beating only takes four hours if finished in the Jordan.
The half-beaten pulp is emptied into a stuff-chest, and the Jordan
is furnished with a small stuff-pump and service-box, just as at
the paper-machine what the Jordan does not take flows back again
into the chest: the pulp from the Jordan is run into the ordinary
machine stuff-chests. The finished pulp can be taken from the
Jordan at three different levels from the circumference of the
roll, or plug. If the pulp is wanted ‘free,’ it is drawn from the
bottom of the engine; if wanted ‘wet,’ or well greased, it is drawn
from the top; and if medium from the centre.”

=The Beating-Engine.=–The ordinary form of beater consists of a
cast-iron trough 13 feet 6 inches long × 6 feet 6 inches wide, and
the bottom is dish-shaped, so as to prevent the pulp from lodging,
which would inevitably be the case if the bottom were flat, as the
pulp would be apt to lodge in the angles formed by the junction of
the bottom with the vertical walls of the trough. The iron trough
is fitted with a cast-iron roll, 3 feet 6 inches × 3 feet 6 inches,
which is provided with 69 “roll-bars,” or knives, arranged in 23
groups of 3 bars each; this roll is suspended upon a malleable iron
shaft 5 inches in diameter, resting upon side levers; suitable
gearing is attached by which the roll can be lifted or lowered at
will, the action being uniformly equal on both sides, by which the
knives of the roll are kept uniform with those of the bed-plate
beneath. The bed-plate, furnished with 20 steel knives, of the
same length as the roll, is placed immediately beneath the roll.
When the knives of the bed-plate are straight they are fitted into
the plate-box at an angle, but in some cases they are bent at a
slight angle, when they are termed _elbow plates_. There have
been, however, many improvements in the beating-engine introduced
of late years, some of which are of considerable importance, and
to some of these we will now direct attention. Although our own
manufacturers have introduced improvements in beaters which have
been fully recognised by the trade, the American engineers have
not been behindhand in devising modifications which appear to
have some important advantages. The Jordan beater, which has been
extensively adopted in the States, consists of a roll in the form
of a truncated cone, furnished with knives in the usual way; this
revolves in a box of a similar form, fitted with knives in the
direction of its length, but at slightly different angles. In this
engine the stuff enters at the narrow end through a box having an
arrangement which regulates its flow, and the pulp is discharged
by several openings in the cover at the wider end. In an engine
invented by Mr. Kingsland there is a circular chamber furnished
with knives covering its sides; between this is a circular plate,
also fitted with knives, which revolves. The stuff enters through
a pipe in the centre of one of the sides of the chamber, and flows
out through an opening in the opposite side.

[Illustration: Fig. 21.]

=Forbes’ Beating Engine.=–This engine, an illustration of which
is given in Fig. 21, is manufactured by Bertrams, Limited, of
St. Katherine’s Works, Edinburgh. The engine has three chambers,
two rolls, and a mixing wheel; the rolls, only one of which is
uncovered in the engraving, are fixed in the outer channels,
and the mixing wheel is placed in the middle channel. By this
arrangement the pulp flows alternately into the two outer channels,
and after passing through the rolls again it enters the centre
channel at the opposite end.

[Illustration: Fig. 22.]

=Umpherston’s Beating Engine.=–This engine, for which a patent
was granted in 1880, has been successfully adopted at the _Daily
Chronicle_ and other mills, and presents several important
advantages, one of the chief being that it occupies much less
ground space than ordinary beating-engines. Indeed, we have heard
it remarked of this engine that it will do double the amount of
work in the same ground space as the ordinary engine, and this,
in some mills, would be a decided advantage. The construction
of this beater, a drawing of which is shown in Fig. 22, is thus
described by the patentee:–“In the common and almost universal
form of engines used for preparing pulp for paper-making, the
pulp travels horizontally in a trough with semi-circular ends,
and straight sides, partly divided longitudinally by a partition
called the midfeather, around which the pulp flows from the back
of the roll to its front, where it passes under the roll and over
the bottom working-plate, and is again delivered over the back
fall to pass again round the midfeather to the front of the roll.
In the course of these repeated revolutions part of the pulp near
the circumference of the tub has much farther to travel than the
part near the midfeather, and consequently is not so often operated
upon, and the pulp is thus unequally treated. As an improvement
upon this form of tub, I make it so that the pulp passes from the
back of the roll to its front through a longitudinal passage under
the back fall, the pulp thus moving as through an inverted syphon,
the superincumbent weight of the semi-fluid pulp, as delivered
over the back fall of the roll, pressing it along this passage and
upwards, to enter again in front of the roll. The roll A, bottom
plate B, and the form of the back fall C, are similar to those
of ordinary engines, but the trough is formed with the passage D
under the bottom plate B, so that the semi-fluid contents of the
engine, in travelling from the back fall C to the front of the roll
A, pass by means of the passage D under the bottom plate B in the
direction indicated by the arrows, the superincumbent weight of
the semi-fluid pulp, as it is delivered over the back fall C at
the back of the roll A, pressing it along the under passage D and
upwards to the front of the roll A. The position of a drum-washer
is shown at E, and at F is seen a section of the cross shaft for
raising or lowering both ends of the roll A simultaneously; G is
the roll cover, which may be of any usual form. By this invention
the semi-fluid pulp is acted upon in a more effective manner, and
its particles are also more equally treated than has hitherto been
the case.”

[Illustration: Fig. 23.]

[Illustration: Fig. 24.]

The beating-engines are usually driven from a separate engine, but
Messrs. Bertrams have introduced a system of direct driving for
these engines by which, it is said, there is a considerable saving
in power. The accompanying engravings, Figs. 23 and 24, show a
series of eight beaters, each carrying 300 lbs. of pulp, driven by
one of their compound direct-driving steam-engines, and now being
worked at the Forth Paper Mills.

=Operation of Beating.=–Having referred to some of the more
important improvements connected with the beating-engines, we will
proceed to explain the operation of beating as briefly as possible.
The bleached half-stuff is removed from the tray of the press in
caked masses, and in this condition is conveyed in trucks or boxes
to the beating-engine. The first thing to be attended to is the
removal of the last traces of chlorine from the pulp, which, if
not effectually done, would cause injury to the size, and also
corrode the strainer plates and wire-gauze of the paper-machine.
It is possible to wash out the chlorine by an abundant application
of pure water, but this method of removing the chlorine is very
tedious and occupies a long time, while it also involves the use
of enormous quantities of water–a serious consideration in some
mills; to this may be added the still more important fact that
by the method of washing out the chlorine a considerable loss of
fibre takes place. The plan most usually adopted is to neutralise
the chlorine left in the pulp by the application of suitable
chemical agents, whereby the chlorine is rendered inert. These
agents, technically termed “antichlors,” are sometimes objected
to, however, although they are in themselves practically harmless
so far as their action upon cellulose is concerned. Mr. Arnot,
who has considered this subject very thoroughly, says:–“I do not
think there is much in this objection, as those agents that are
soluble pass through the wire of the machine almost completely,
while those that are insoluble are in the finest possible state of
division and pearly white. The chemical agent most largely used is
hyposulphite of soda, but hyposulphite of lime is also employed,
and those agents, known by the name of ‘antichlor,’ are put into
the engine in such a quantity as will ensure the neutralisation
of the whole of the chlorine. The products of the reaction, when
the soda salts are used, are chloride of sodium (common salt) and
sulphate of soda (Glauber’s salt), and, when the lime salt is used,
chloride of calcium and sulphate of lime, the latter identical with
the pearl hardening so well known as a loading agent.” From this
it will be seen that little or no harm can possibly occur either
to the fibre or the metal work of the machine by the employment of
the neutralising agents named, and when it is borne in mind that
the simple washing of the pulp would occupy the beating-engine
for a lengthened period and exhaust a considerable quantity of
water–which, as we have said, would in some mills be a serious
matter–the adoption of the neutralising method would undoubtedly
have the preference.

The engine, being partly filled with water, is set in motion, and
the bleached half-stuff introduced in small quantities at a time,
each portion being allowed to become thoroughly mixed with the
water before the next batch is added. The charging of the beater
with half-stuff is kept up until the mass becomes so thick that it
will only just move in the trough under the action of the revolving
roll. If the beater is of the older type, portions of the pulp
are liable to lodge in corners, to remove which the “beater-man”
uses a wooden paddle, with which tool he also pushes the slowly
moving pulp in the direction of the roll, especially when the stiff
mass appears to move too slowly. At this stage the neutralisation
of the chlorine in the pulp is effected, which is done by adding
a solution of hyposulphite of soda, a little at a time, until
the liquor ceases to redden blue litmus paper, strips of which
should be dipped into the pulp every few minutes until the paper
persistently retains its blue colour. This operation should be
conducted with great care, so as to exactly neutralise the traces
of chlorine without adding an excess of the hyposulphite of soda.
Besides this salt, other substances are used as “antichlors,” as,
for example, hyposulphite of lime, which is prepared by boiling
milk of lime (slacked lime made into a thin mixture with water) and
flour of sulphur in an iron vessel until the latter is dissolved,
when, after cooling and settling, the resulting solution, which
is of an orange-yellow colour, is ready for use. One great
objection to the use of hyposulphite of lime, however, is that when
decomposed by the chloride of lime remaining in the pulp sulphur
is set free, which, mingling with pulp, will impart to it a yellow
tint; besides this, in passing over the drying cylinders of the
machine the sulphur present in the paper may attract oxygen from
the air, converting it into sulphuric acid, which must inevitably
prove injurious to the manufactured paper. Sulphite of soda has
also been used as an antichlor, and is said to be preferable to
hyposulphite of soda,[21] inasmuch as the latter salt is liable to
decompose with the liberation of free acid, which is not the case
with the sulphite of soda.

=Test for Chlorine.=–Instead of relying solely upon the litmus
paper test when applying the antichlor, the following test for
chlorine may also be used with advantage:–Take 2 drachms (120
grains) of white starch, and make it into a paste with a little
cold water; then pour over it about half a pint of boiling water,
stirring briskly; to this add 1 drachm of iodide of potassium,
and stir until dissolved and well incorporated with the starch
solution. The mixture is then to be allowed to cool, when it is
ready for use. A few drops of this mixture dropped upon a small
sample of the pulp will indicate if any chlorine be present by the
spot assuming a blue colour; if such be not the case, the pulp may
be considered free from chlorine.

During the beating, the roll, which should make not less than 220
revolutions per minute, is lowered, a little at a time, so that
the cutting edges of the bars and plate may be brought together
gradually and equally until the pulp is reduced to the desired
condition. The pulp is made long or short according to the quality
of paper to be produced; news papers, which require strength, are
made of long-fibred pulp, while writing paper, or paper of fine
texture, is made of shorter pulp. The stuff should be what is
called “mellowed” in the engine, which is effected by a judicious
working of the roll, not lowering it suddenly but gradually, and
not much at one time, on the plate, until the pulp attains the
fineness required. This is generally arrived at in about three and
a half to four hours, though sometimes the beating of pulp from
rags is continued for more than double that time. It should be
added that if the cutting edges of the roll and plate are brought
together suddenly and too closely, the fibre will be cut, and as a
consequence the paper produced will be tender.

Esparto, which, in the process of boiling becomes reduced to
such a soft condition that the fibres may be readily separated
by the fingers, does not require such excessive beating as rags;
indeed, the perfect disintegration of the fibres of esparto is
practically accomplished in about half the time occupied by rags,
and often much less, but this of course depends upon the nature
of the esparto itself and upon the thoroughness of the boiling.
Wood pulps also require but moderate beating, since the process of
disintegration is generally pretty effectually accomplished by the
processes to which the raw material is subjected in the course of
manufacture into half-stuff, which is the condition in which this
paper material is furnished to the manufacturer.


=Blending.=–To produce papers of the different qualities required
by the trade, a system of blending is adopted, which may be
effected–(1) by mixing the materials in the raw state, or the
rags, previous to boiling; and (2) blending the half-stuff in
the beating-engine. The latter method, however, is generally
preferred. Sometimes, also, pulps of different character are beaten
separately and then mixed in the stuff-chests, where they are mixed
as thoroughly as possible before passing on to the machine, but
this method would be less likely to ensure a perfect mixture of
the respective pulps than would be effected with proper care in
the beater. The proportions of the several materials to be blended
is also a matter of important consideration. In blending esparto
with rag stuff, if the former be in excess it becomes reduced
to the proper condition before the latter is sufficiently fine,
which causes the rag fibre to appear in “knots and threads” in the
manufactured paper. But if the rag stuff be allowed to predominate,
the beating is conducted as though no esparto were present, by
which, while the rag stuff becomes reduced to the proper length of
fibre, the esparto, which is still further reduced, in mingling
with the longer fibre of the rags forms what is called a “close”
paper. Mr. Dunbar, in his useful little work, “The Practical
Paper-maker,” furnishes a series of receipts for blending for
high-class papers, as also the proportions of colouring matter to
be used, which the reader will do well to consult. For news papers,
esparto and straw pulps are generally used, in varying proportions
according to the nature and quality of the esparto; these
proportions have to be regulated according to the judgment of the
paper-maker, and vary greatly at different mills. A large quantity
of sulphite and other wood pulps are also used, those coming from
Scandinavia and Germany being especially suited to the requirements
of the English manufacturer. Mechanical wood pulp is also used in
a moderate degree–sometimes up to 15 per cent., in some English
mills, but it is said that in Germany this paper stock is sometimes
used to the extent of 90 per cent.

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