IMPROVEMENTS IN THE PROCESS OF AND APPARATUS FOR BOILING WOOD AND THE LIKE WITH SULPHITES AND IN THE PREPARATION OF SULPHITES FOR USE THEREIN to be as follows
Year: 1884

page_text: PROVISIONAL SPECIFICATION.
I, ALEXANDER MITSCHERLICH 6 Leopold Street, Friburg, Grand-Duchy of
Baden, German Empiro, Professor of Chemistry and Doctor of Philosophy, do
hereby declare the nature of my said invention for "IMPROVEMENTS IN THE
PROCESS OF AND APPARATUS FOR BOILING WOOD AND THE LIKE WITH SULPHITES
AND IN THE PREPARATION OF SULPHITES FOR USE THEREIN to be as follows:-
"
In the treatment of wood with solutions of sulphurous acid compounds for the
preparation of paper material and bye products it has been found that it is most
advantageous to use such a solution for the boiling operations as is entirely or
almost entirely free from free sulphurous acid, and consequently only contains the
solution of normal bisulphite or a solution containing still less sulphurous acid than
is necessary for the above combination. The quantity of free sulphurous acid must
not materially exceed 1 per cent of the solution. This solution cannot be
commercially produced with advantage by the solution of sulphite of lime in
aqueous sulphurous acid. The main object of this peculiar composition of the
solution consists in the reduction of the pressure during the boiling process which
is produced by the presence of free sulphurous acid, or if less quantities of sulphurous
acid are used, in a saving of the latter.
For the production of the said solution absorption arrangements are advan-
tageously used, in which the method of reversed currents is employed in such
manner that the gases containing most sulphurous acid are brought in contact with
the most concentrated solution, and the gases containing least sulphurous acid
with the weakest solution, or with water.
By this means the complete absorption of sulphurous acid is obtained and a
sufficiently concentrated solution for the manufacture of sulphite cellulose is
produced. The latter is more particularly effected by causing the gaseous current
employed to contain the largest possible quantity of sulphurous acid and to be as
cold as possible.
An excess of free sulphurous acid in the solution to be produced, must, as above
stated, be avoided as much as possible, for a good reaction in the manufacture of
sulphite cellulose.
!

page_text: If it is difficult to avoid an excess of sulphurous acid, owing to the difficult
solubility of the sulphite compound, the solution produced is passed through special
receptacles which contain the original material to be employed, or when a tower is
used the sulphurous acid is not led in at bottom but at a point, higher up, in
order that any free sulphurous acid of the solution may find material for the 5
formation of the sulphurous acid compound. By this means it is always possible
to avoid free sulphurous acid. In addition it is necessary for the production of the
required conceutration of the solution to bring the material to be acted upon as
intimately as possible in contact with the sulphurous acid solution; thus it is
necessary in the production of bisulphite of lime to bring a comparatively large 1
quantity of carbonate of lime offering large surfaces (by preference tufaceous lime
stone) in contact with the descending water and the ascending gas containing the
Bulphurous acid.
For a daily production of about 900 cubic feet of solution, about 10 tons of lime
should be used; a larger quantity can be used without detriment. If the sulphite 1
desired is to be produced from a substance soluble in water this aqueous solution is
caused to pass down the tower like the water in the lime compound, the tower
being charged with a neutral solid porous material instead of with limestone.
In this case also, the above named temperatures should be observed.
In the construction of the absorption apparatus the greatest care inust be taken 2
_that_they are such that-all-the-sulphurous_acid is utilised in the chemical reaction,
in order that none may pass away-into-the-atmosphere.
These conditions are fulfilled if for the preparation of the solutions the absorption
of the sulphurous acid gas is effected in a very high tower.
The high specific gravity of the gases containing the sulphurous acid does not 2
permit of its being led through chambers in which, as is here necessary the gases
have to rise upwards. In order to produce-such upward motion, the apparatus is
by preference so arranged that the hot gases are led through tubes that first ascend-
and then descend in the ascending part of which on account of their greater
expansion by the heat-on-first-entering, they are made to ascend, while by the 3
resulting cooling thereof, they are then made to fall down-in-the-descending pipo.
In the latter, the high specific gravity of the cold gases produces an increased
draught. By this means it is possible to obtain sufficient pressure to force the gases
through apparatus in which counter pressure exists without requiring the use of
fans, injectors and such like appliances.
The higher the arrangement of tubes is with the use of heated gases, the stronger
will be the draught.
This forward motion of the gases which should be regulated by valves and slides,
should be very carefully attended to, as if it be on the one hand too quick, the
gases become too dilute because too much air is drawn into the furnace in which
the pyrites or sulphur is being treated, and thus too dilute solutions are produced,
while if the motion be too slow the combustion in the furnace will be imperfect,
causing free sulphur to pass into the absorption apparatus which may have a
detrimental effect upon the subsequent boiling operations.
In order to readily indicate the presence of free sulphur and thus to allow the
prevention thereof by proper regulation of the draught, the following may be
employed.
A portion of the gases passing from the furnace is caused to circulate continuously
through a small pipe connected to the said large tubes near the inlet from the
furnace and provided with a glass tube. By the cooling action of the glass tube
any free sulphur passing through the same will form a yellow deposit thereon and
consequently, on observing this, the operator can at once regulate the draught, so
as to prevent its occurrence. Furthermore, detrimental sulphur compounds can
pass into the absorption apparatus if the pyrites or sulphur employed contains
impurities, such as substances of organic origin, which, with imperfect combustion
will form other compounds than sulphurous and sulphuric acids, as for instance
sulphuretted hydrogen, These latter sulphur compounds cannot be detected by the
3

page_text: above mentioned glass pipe but they yield in the absorption apparatus compounds
that are very detrimental to the boiling process. Consequently to prevent this
inconvenience, care must be taken that only materials that are free from such
impurities are used in the roasting process. A good regulation of the draught
cannot well be effected with the roasting furnaces as at present constructed and
consequently a suitable concentration of the solution is with difficulty obtained.
In order to carry out the process advantageously the material used in tho
construction of the roasting furnaces is of importance. With the arrangement of
tubes described, a suction is produced which renders the furnaces of ordinary
construction useless, because the air finds its way through the number of small
cracks, as also through the porous material of which the furnace itself is constructed
and thus a proper regulation of the draught is not possible, as although all the
ordinary inlets for air may be closed, sufficient air will still find its way into the
furnace to maintain the combustion.
.
According to my present invention, I therefore construct the furnaces of a
material that is impervious to air; for this purpose, bricks saturated throughout or
at least on their surface with tar may be advantageously used, cemented together
with a tar mortar consisting of a mixture of tar with a finely divided material that
is not attacked by acids.
In order to furthermore ascertain whether the apparatus is acting properly, and
whether the solution contains any of the said sulphur compound impurities, the
following method is employed.
To small quantities of the said solution are added some copper salts in a suitable
vessel and this mixture is boiled until it hardly smells of sulphurous acid. Sufficient
hydrochloric or other similarly acting acid is added to the light colored precipitate
and the sulphurous acid is boiled off. If a dark colored precipitate is produced it
shews, the presence of sulphur compounds that are detrimental to the sulphite
boiling processes, the quantity of the dark deposit indicating also the quantity of
the said sulphur compounds.
An experience of several years has shown that the statement contained in the
Specification to Tilghman's Patent No 385 of 1867, to the effect that liquids
containing sulphurous acid will attack wood at low temperatures, is erroneous; in
consequence hereof, it is advantageous to employ only wood for the apparatus for
the production and storing of such solutions.
In order to obtain a uniform and constantly good sulphite cellulose, it is necessary
to introduce the wood in definite dimensions into the boiling apparatus and careful
experiments have led to the result, that with fir (Picca Abies L. or Picea Excelsa)
discs of about from 0.6in to 1.5in thickness (cut across the grain) or slabs of about
from 0.2in to 0.6in (cut parallel with the fibre) should be used, while with poplar
(Populus italica) scotch fir (Pinus silvestris) and pine wood (Abies alba or Pinus
Picea), discs cut across the grain of from 0.6in to 3in thickness and even more, and
with the grain from 0·2in to 1.5in may be used; with beech (Fagus silvatica)
from 0 Gin to 1.5in and 0:2in to 1.5in; oak (Quercus) from 0.6in to 0.8in
and 0.2 to 0.8 and analogous woods of similar dimensions. It is here to be
particularly observed that for obtaining a uniform and perfect material with
boilings of not excessive length, the dimensions given are of the greatest importance,
and absolutely necessary and that this constitutes an integral part of the improved
process.
Thus if larger dimensions be employed the fact that the internal portions are
with difficulty perfectly treated, is of great detriment to the boiling process which
may thereby become entirely uscless.
If it be endeavoured to perfect the boiling by carrying it out very slowly,
several days would be required for one boiling which would render the process
impracticable.
If, on the other hand, smaller dimensions are employed than those indicated, the
circulation of the liquid will be very much impeded and it would then be necessary
to employ.boilers to which a rotary motion is imparted, or to, obviate this difficulty

page_text: by the use of circulating pipes. Both expedients have however great disadvantages.
Also, if the wood is of very small dimensions, the boilers can only be charged with
small quantities in proportion to their volume, because such small pieces form very
loose heaps. As the use of the above dimensions allows of a free circulation of the
liquid in the boiler, it is possible to use boilers of as large dimensions as can be
manufactured.
This is again of the greatest importance for the sulphite cellulose manufacture,
because in such boilers it is easy to maintain the temperatures prescribed in the
Specification to my previous Patent dated 12th September 1883 N° 4371.
In using wood prepared as above described, there may exist, even if all other
conditions for the production of good cellulose are complied with, bundles of fibre
of a brown color which may result from the originally perfectly white bast fibres of
the wood. This defect renders the cellulose of considerably less value on account
of the paper becoming spotty. By carefully removing these objectionable bast
fibres the said brown bundles of fibre are avoided.
Formerly Scotch fir (Pinus silvestris), larch (Larix) and similar woods were
excluded from use in the manufacture of sulphite fibre, because a portion of these
woods did-not become perfectly-done even aftor several boilings. But by removing
the core thereof which forms the-part-which does not become easily done, these
woods will yield as good cellulose with the above process-as-fir-(Picea Abies or
Picea excelsa).
Materials in a small state of subdivision such as sawdust etc. are also disadvan-
tageous because they cannot be perfectly boiled in large boilers on account of the
-imperfect communicability of the heat, caused by their fine state of subdivision.
This disadvantage is easily-obviated by the following arrangement;-so-that-oven
-the smallest particles of wood can be effectually treated in the largest. boilers.
Between the pieces of wood-of the above indicated dimensions, heaps-of-the-
sawdust or other small material are distributed in-such-manner that the liquid
which can circulate freely between the pieces of wood also passes among the said-
heaps. In consequence hereof they become sufficiently impregnated, if not too
large, so that the smallest wood particles will become done during the usual boiling
process.
This invention also relates to the construction of the boilers. In order to produce
a perfect sulphite cellulose, it is essentially necessary to use boilers of as large
dimensions as possible, as already stated. In order to effect a quick filling and
emptying of the boiler it is provided with manholes at the points indicated on the
accompanying drawing. By the position of these at the underside it is possible to
place workmen on both sides of the manholes in the boiler, whereby it can be
quickly emptied; furthermore, by the position of the manholes with suitable regu-
lation of the steam inlet and outlet taps, the steam can be distributed perfectly
uniformly through the wood in the steaming operation.
Furthermore it has proved to be very advantageous to fix the necessary boiler
fittings on the manhole covers, because by fixing them on the sides of the boiler
dangerous leaks may be produced, while these would cause no great damage on the
manhole covers on account of the greater thickness thereof, particularly as they
may be so fixed that the iron of the cover need not be entirely bored through and
under any circumstances the covers can be easily replaced. The hermetic closing
of the manholes on the top of the boiler has caused great difficulties. Lead appeared
to be the only suitable packing material but with lengthened use great disadvan-
tages appeared, as, for instance, the considerable compression of the lead of the
manholes, whereby it quickly becomes deteriorated etc. The use of a thick paste
of cellulose placed upon the joint to be packed has proved, on account of its
inexpensive nature, to be particularly advantageous in such pulp works and
obviates all inconveniences arising from a bad packing when a substance such as
sulphurous acid is used.
Another improvement consists in employing a constant higher pressure in the
beating pipes, constructed of hard lead, than in the boiler itself. The lead pipes

page_text: which are very difficult to maintain perfectly tight easily become choked when
leakages occur, by the formation of sulphite compounds that dissolve with difficulty,
for instance when using bisulphite of lime in boiling, by the separation of sulphite
of lime. These obstructions can hinder the heating of the liquid and may cause
the spoiling of a charge which generally represents a value of about £50. By
always using a higher pressure in the heating pipes than outside, the liquid can
never pass from the boiler into the pipes when a leak occurs in the latter; but only
steam or water can pass from the latter into the former and thus any such obstruc-
tion of the pipes is avoided. Even with the most careful maintenance of the proper
temperatures and regular progress of the boiling it has occurred that under certain
circumstances the pressure gauge indicates a high pressure that does not correspond
to the temperature, in consequence of which the high pressure oxisting in tho
boiler caused the liquid therein to be forced through the smallest leaks into the
pipes, thus producing the above named evils. It has been found that under
the said circumstances the fault lies in the fact that the boiler was filled with too
much liquid.
Such overfilling is not of much importance with other materials that contain
air, as for instance unsteamed wood, because the clasticity of the air contained in
the wood prevents the attainment of too great a pressure on the expansion
of the liquid on heating. This air has however been completely removed when the
wood has been previously steamed, and in consequence hereof very high pressure
may be produced at comparatively low temperatures which may cause the bursting
of the strongest boilers. In order to avoid this danger with certainty, a very
simple remedy has been found, namely not to fill the boilers beyond th of their
capacity. It has been found convenient in the case of horizontal boilers of about
13ft diamoter, to leave a space of about 1" from the crown froe of liquid.
00
In my before mentioned former Patent No 437183 the sulphite boilers were
described as protected by a peculiar cemented layer of thin sheet lead, and brick-
work.
It has been proved that in lining the iron boilors inside with other descriptions
of lead coverings than that described, for instance by soldering the same, such lead
is attacked by the lye in a short time to such an extent that it requires to bo
frequently renewed. The considerable defects that are caused by this are great
deterioration of the iron boilers, with danger of explosion, and extensive repairs,
combined with long interruptions of the working. If however the lead lining is
further protected by a lining of connected brickwork, neither a chemical nor a
mechanical destruction thereof will take place and it will hardly become deteriorated
at all.
In the manufacture of sulphite cellulose further disadvantages have arisen through
the inconvenienco caused by allowing the large quantities of waste liquor to flow
away into the drains while hot, in which condition it has a very objectionable
smell.
These disadvantages can be very considerable for the manufacturer under certain
circumstances, as the authorities may oppose great difficulties in granting con-
cessions, and these may even be entirely refused on that ground. By the following
method these disadvantages are entirely obviated.
The discharge pipe from the boiler is connected to a large tank sunk in the
ground, having a capacity of at least double that of the liquid discharged at one
operation. The sides of this tank are formed either of brickwork or wood, and it
is closed in with boarding on which is laid a layer of earth, or it may be enclosed
hy brickwork arches. The discharge pipe from the boiler is made to enter this
tank at a point below the middle of its height, and at the middle of its height
a pipe with small bore leads into the drain. All the cold waste liquors arc by
preference also discharged into this tank. The liquid passing from time to time
in large quantities from the boiler into this tank becomes sufficiently cooled
by admixture with the cold liquid contained therein so that no objectionable
vapors will be discharged therefrom into the air as it flows off. If this liquid be

page_text: discharged into a stream of about 1000 times the volume, it will become sufficiently
diluted to be harmless for animals or vegetation. The use of iron pipes more
particularly cast iron, for leading off the liquid is particularly convenient because
a black deposit is formed where the liquid comes in contact, which effectually
protects the iron against the further action of the liquid.
Lastly it is to be particularly observed that a deterioration of the cellulose may
be easily effected by the discoloring thereof during the boiling, this taking place
either in separate bundles of fibre as above mentioned or throughout the mass. By
incans of many experiments it has been proved that this defect is produced by
subjecting the wood to a temperature of above 212° Fahr. without the presence of
the sulphite solution, either before or after the boiling, or by letting the boiled
mass stand for a length of time at about this temperature. This must consequently
be entirely avoided, and the boiled mass should be cooled off at once as soon as the
liquor is discharged.

page_text: COMPLETE SPECIFICATION.
I, ALEXANDER MITSCHERLICH of 6 Leopold Street, Friburg, Grand Duchy
of Baden, German Empire, Professor of Chemistry and Doctor of Philosophy,
do hereby declare the nature of my invention for "IMPROVEMENTS IN THE
PROCESS OF AND APPARATUS FOR BOILING WOOD AND THE LIKE WITH SULPHITES,
AND IN THE PREPARATION OF SULPRITES FOR USE THEREIN 19
and in what inanuer
the same is to be performed to be particularly described and ascertained in and by
the following statement :-
In carrying out the treatment of wood with solutions of sulphurous acid
combinations for the preparation of paper material and bye products, improve-
ments have been made which form the subject of the present invention and which
relate as well to the preparation or treatment of the raw materials as to the boiling
process and the apparatus employed for that purpose.
The production of the sulphurous compounds is effected in the case of bisulphite
of lime (acid sulphite of lime) generally by conducting over moderately sized
pieces of carbonate of lime which are confined in a tower simultaneously from
above water and from below a current of sulphurous acid produced by burning
sulphur or by calcining sulpho metals and sulpho-ores. By this method the result
may be a sulphurous solution containing a great surplus of sulphurous acid and
polythionic acids if the managements and the conducting of the process is not a
very careful one in the conditions prescribed.
The present invention avoids these evils even in the roasting, in which by means
of special appliances a more intensive draught is produced to carry off the gases
better, and the admission of air is lessened and in which gases are produced free of
sulphur, sulphuretted hydrogen and other injurious gases, and these sulphurous
gases can be tested as to the amount of sulphur they contain by the peculiar
application of a sublimation tube and finally the absorption of the sulphurous acids
thus produced takes place in such a way that the presence of sulphurous acid and
of polythionic acids is avoided for certain.
The roasting of the raw material for the production of sulphurous acid, is done,
as is well known, in kilns in which the sulphur or sulpho-metals are burnt.
In these kilns it is of particular importance that the material of which they are
built does not allow the air to penetrate.
If common material is used for the purpose, the requisite exact regulation of the
draught, as will be mentioned farther on, is rendered impossible, for so much air
finds its way into the kiln through the numerous little crevices, which are always
to be found in common masonry, and even through the porous bricks themselves
that the material to be roasted would mostly keep on roasting after the proper
aperture for the admission of air has been closed. It is therefore necessary in the
construction of these kilns that at least one layer of the masonry be of a material,
that prevents air from penetrating.

page_text: This airtight material is produced in various ways, one of which is to steep the
heated bricks in tar and to connect them firmly when building up the kiln by
means of a thickish mortar which must be of such a nature that it hardens
gradually, shews little or no porosity and is not at all affected in temperatures
prevalent in the kiln either by sulphuric or sulphurous acida. A mixture of tar
and of any fine grained substance unaffected by acids, such as fine quartz sand
'sieved coal, ashes, pulverised slag etc., is well adapted for the cementing material.
The burning in the kiln and the flowing off of the gases that arise must be
conducted in such a manner that the latter acquire a certain velocity only, for in
case of too quick a motion the gases, when pyrites are roasted or sulphur burnt,
easily get too thin, owing to too much air entering the kiln and the result of this
is, that during the later occuring absorption too greatly diluted solutions are
formed. If the motion of the gases is too slow, the burning in the kilns will be
incomplete, free sulphur will get into the absorption appliance and be the cause of
polythionic acid being formed, which has a very injurious influence on the solution:
just produced.
The creation and regulation of draught for avoiding the evil mentioned is
effected by the application of an ascending and descending U-shaped bent
tube UU-as represented in fig.-1-of-the accompanying drawing. In this case
the motion of the gas is produced by the hot gases from-the roasting kiln passage
having first to-ascend in this U shaped bent tube, which-is.effected by the heat
due to their original great development.
Owing to their cooling in their passage through this tube they will descend on
reaching the bent part-of-the-tube-U and the high specific weight of the cold gases
will produce-an.augmentation of draught.
By means of the cooling appliance described it is easy with-a-proportionally
strong pressure-to-make the gases go further and pass through the tower from
the bottom upwards (even if there-is-a-strong counter pressure acting-against__
them) without its being necessary to use any further appliances, such as fans,
injectors, etc.
The force of the draught depends on the height chosen for the tube system, and
it can be regulated even still more by using slides and dampers at u.
Owing to the cooling of the gases caused by this arrangement, they are reduced
to a temperature below 86° Fahr., which is of particular importance in the
subsequent absorption process for the practical chemical effect and the complete
utilisation of the gases. Should the gases not be sufficiently cooled by the above
process which however will seldom be the case, a further cooling can be very
conveniently effected by encasing the downward part of the tube with boards at a
small distance therefrom.
The atmospheric air will be warmed in the intervening space by the tube and
consequently be forced in strongly from below, escaping at the top. By means of
the strong current of air thus produced a sufficient cooling of the tube will be
attained.
The gases issuing from the roasting kiln may also contain, if the draught be too
weak, sulphur vapors, the penetration of which into the tower would be very
injurious for the solution formed owing to the formation of polythionic acids.
In order to be able to ascertain easily the presence of free sulphur in these gases
flowing out of the roasting-kila and in order to prevent the formation of free
sulphur by adequate regulation of the draught a so-called sublimation tube, S
is fitted into the tube system which takes up the gases flowing out of the roasting
kiln, as close as possible to the point of outflow in the kiln in the ascending part of
the cooling-tube, as may be seen in fig. 1 in combination with the other parts of
the apparatus, and in fig. 2 designed on a larger scale. A glass tube S is fitted in
a vertical direction into the two elbow tubo picces E and E¹, so as to rest upon a
projection of the tube piece E and made removeable through the opening P of the
tube piece E'. When in operation the connections K K' and O are made air tight

page_text: with clay. Through this apparatus pass constantly in the direction of the arrows,
small quantities of the gases escaping from the kiln.
The free sulphur that may be present is precipitated at once by the cooling on
the sides of the glass tube S and will be seen there as a yellowish coating, and in
such a case the precautionary measures in the regulation of the draught already
mentioned against this formation can be taken immediately. If a covoring of
sulphur is formed in the glass tube, the latter is removed and replaced by a
clean one.
The gasos which pass out of the cooling tube U and have a certain velocity aro
allowed to enter the absorption tower in which the lime is, and over which water
is conducted from above in a fine spray. It must be borne in mind here that
particularly in the production of bisulphite of lime a very great quantity of car-
bonate of lime is requisite which exposes largo surfaces to the sulphurous acid
passing through (tufaceous limestone is most practical) and experience has shown
that with a daily production of 880 cubic feet (25 cm) of solution, about
22,000 lbs (10,000 kg) of lime must be used, a greater quantity of lime being by no
means injurious. In order to prevent, in the solution thus forming, the development
of free sulphurous acid in the tower itself, the gases are not allowed to enter the
latter quite at the bottom but flow in at a certain height above it. As may bo
seen in fig. 1 of the drawing the current of gas discharges below the grate R. In
the space underneath this grate is a layer A of limestone into which the solution
forming in the tower enters. By this the free sulphurous acid that may still be
present in the solution is taken up so that the solution flowing out through the
communicating tube B into suitable reservoirs contains only the smallest quantity
of free sulphurous acid.
Instead of using the appliances described above, the solution produced may be
allowed to pass into particular vessels which contain the original material to be
employed (that is to say for bisulphite the carbonate of lime) in such a manner
that the fluid comes as much as possible in contact with the material for instanco in
such a way that the fluid flows into the vessel below and flows out at the top.
For these vessels both the reservoirs for the ready solution and also intermediate
vessels can be used. If desired, both arrangements can be used combined. If the
sulphurous acid compound is to be made of a substance soluble in water then this
watery solution is allowed, just as the water in the description given above of the
lime combination, to pass through the tower which latter is filled in this case,
instead of with limestone, with a porous and firm material unaffected by this
process, as for instance with coke, stovebricks etc. The temperature stated is like-
wise in this case imperative. In the arrangement described and especially when a
high tower is used & complete utilisation of the sulphurous acid produced in the
roasting kiln will be effected in the chemical reaction so that all chance of its
escaping into the open air is avoided and at the same time a sulphurous acid solu-
tion is formed, which is either completely free or at least almost completely free of
free sulphurous acid.
.
In order to obtain a uniform and constantly good sulphite cellulose it is necessary
to introduce the wood in definite dimensions into the boiling apparatus, and
careful experiments have led to the result that with fir (Picea Abies L. or Picea
Excelsa) discs of about from 0.6ims to 1.5ins thickness (cut across the grain) or slabs.
of about from 0.2 ins. to 0.6ins (cut parallel with the fibre) should be used; while
with poplar (Populus italica) scotch fir, (Pinus silvestris) and pine wood (Abies
alba or Pinus Picea) discs, cut across the grain, of from 0.6 ins. to 3ins thickness and
even more, and with the grain from 0.2ins to 1.5ins may be used, with beech (fagus
silvatica from 0.6ins to 1.5in³ and 0.2ins to 1.5ins oak (Quercus) from 0.6ias to 0.8ing
and 0.2ins to 0.8ins and analogous woods of similar dimensions.
It is here to be particularly understood that for obtaining a uniform and perfect
material with boilings of not excessive length, the dimensions given are of the
greatest importance and absolutely necessary and that this constitutes an integratę
part of the improved process.

page_text: Thus, if larger dimensions be employed the fact that the internal portions are
with difficulty perfectly treated is of great detriment to the boiling process which
may thereby become entirely useless.
If it be endeavored to perfect the boiling by carrying it out very slowly, several
days would be required for once boiling which would render the process impractic-
able. If on the other hand smaller dimensions are employed than those indicated,
the circulation of the liquid will be very much impeded and it would then be
necessary to employ boilers to which a rotary motion is imparted or to obviato
this difficulty by the use of circulating pipes. Both expedients have however great
disadvantages. Also if the wood is of very small dimensions, the boilers can only
be charged with small quantities in proportion to their volume because such small
pieces form very loose heaps. As the above dimensions allow of a free circulation
of the liquid in the boiler, it is possible to use boilers of as large dimensions as can
be manufactured. This is again of the greatest importance for the sulphite cellulose
manufacture because in such boilers, it is easy to maintain the temperatures
prescribed in the Specification to my previous Patent dated 12th Sept, 1883
N° 4371.
In using wood prepared as above described there may exist, even if all other
-conditions for the production of good cellulose are complied with, bundles of fibre
of a brown color which may-result from the originally perfectly white bast-fibres
of the wood. This defect renders the cellulose-of-considerably less-value_on
account of the paper becoming spotty. By carefully removing these objectionable
bast fibres the said brown bundles of fibre are avoided.
Formerly scotch fir (Pinus silvestris) larch (larix) and similar woods were
excluded from use in the manufacture of sulphite fibre because a portion of these
woods did not become perfectly reduced even after several boilings. But by
removing the core thereof which forms the part which does not become easily-
reduced, these woods_will_yield as good cellulose with the above process_as fir
(Picea Abies or Picea excelsa). Materials in a small state of subdivision, such as
saw-dust etc, are also disadvantageous because they cannot be perfectly boiled in
large boilers on account of the imperfect conduction of the heat, caused by their fine
state of subdivision. This disadvantage is easily obviated by the following
arrangement so that even the smallest particles of wood can be effectually treated
in the largest boilers.
Between the pieces of wood of the above indicated dimensions heaps of the saw-
dust or other small material are distributed in such manner that the liquid which
can circulate freely between the pieces of wood also passes among the said heaps.
In consequence hereof they become sufficiently impregnated if not too large, so
that the smallest wood particles will become reduced during the usual boiling
process.
This invention also relates to the construction of the pulp boilers. In order to
produce a perfect sulphite cellulose, it is essentially necessary to use boilers of as
large dimensions as possible, as already stated. In order to effect a quick filling
and emptying of the boiler, it is provided with manholes at the points indicated
on the drawing. By the position of these at the underside, it is possible to place
workmen on both sides of the manholes in the boiler whereby it can be quickly
emptied; furthermore by the position of the manholes with suitable regulation of
the steam inlet and outlet taps, the steam can be distributed perfectly uniformly
through the wood in the steaming operation.
Furthermore, it has proved to be very advantageous to fix the necessary boiler
fittings on the manhole covers because by fixing them on the sides of the boiler
dangerous leakages inay be produced, while there would be caused no great damage
on the manhole covers on account of the greater thickness thereof, particularly as
they may be so fixed that the iron of the cover need not be entirely bored through
and under any circumstances the covers can be easily replaced. The hermetic
closing of the manholes in the top of the boiler has caused great difficulties. Lead
appeared to be the only suitable packing material, but with lengthened use great

page_text: disadvantages appeared as for instance the considerable compression of the lead of
the manholes, whereby it quickly becomes deteriorated etc., The use of a thick
paste of cellulose placed upon the joint to be packed has proved on account of its
inexpensive nature to be particularly advantageous in such pulp works and it
obviates all inconveniences arising from a bad packing, when a substance such as
sulphurous acid is used.
Another improvement consists in employing a constant higher pressure in the
heating pipes constructed of hard lead than in the boiler itself. The lead pipes
which are very difficult to maintain perfectly tight easily become choked when
leakages occur by the formation of sulphite compounds that dissolve with
difficulty; for instanco when using bisulphite of lime in boiling by the separation
of sulphito of lime.
These obstructions can hinder the heating of the liquid and may cause the
spoiling of a charge which generally represents a value of about £50. By always
using a higher pressure in the heating pipes than outside the liquid can never
pass from the boiler into the pipes when a leak occurs in the latter, but only
steam or water can pass from the latter into the former and thus any such
obstruction of the pipes is avoided. Even with the most careful maintenance of
the proper temperatures and regular progress of the boiling it has occurred that
under certain circumstances, the pressure gauge indicates a high pressure that does
not correspond to the temperature in consequence of which the high pressure
existing in the boiler caused the liquid therein to be forced through the smallest
leaks into the pipes, thus producing the above named evils. It has been found
that under the said circumstances the fault lies in the fact that the boiler was
filled with too much liquid.
Such overfilling is not of much importance with other materials that contain air,
as for instance unsteamed wood, because the elasticity of the air contained in the
wood prevents the attainment of too great a pressure on the expansion of the liquid
on heating.
This air has however been completely removed when the wood has been
previously steamed, and in consequence hereof very high pressure may be produced
at comparatively low temperatures which may cause the bursting of the strongest
boilers. In order to avoid this danger with certainty a very simple remedy has
been found, namely not to fill the boilers beyondths of their capacity. It has
been found convenient in the case of horizontal boilers of about 13 ft. diameter to
leave a space of about 1 ft. from the crown free of liquid.
In my before mentioned former Patent No 4371 of 1883 the sulphite the sulphite
boilers were described as protected by a peculiar cemented layer of thin sheet lead
and brick work.
It has been proved that in lining the iron boilers inside with other descriptions
of lead coverings than that described, for instance by soldering the same, such lead
is attacked by the lye in a short time to such an extent that it requires to be
frequently renewed. The considerable defects that are caused by this are great
deterioration of the iron boilers, with danger of explosion, and extensive repairs,
combined with long interruptions of the working. If however, the lead lining is
further protected by a lining of cemented brick work neither a chemical nor a
mechanical destruction thereof will take place and it will hardly becomo deteriorated
at all.
In the manufacture of sulphite cellulose further disadvantages have arisen
through the inconvenience caused by allowing the large quantities of waste liquor
to flow away into the drains while hot, in which condition it has a very
objectionable smell.
These disadvantages can be very considerable for the manufacture under certain
circumstances as the authorities may oppose great difficulties in granting concessions,
and these may even be entirely refused on that ground. By the following method
these disadvantages are entirely obviated.

page_text: 7, In the construction of pulp boilers, the use of manholes arranged as described
with reference to the drawing for the purpose of rapidly emptying the same and
the arrangement of the boiler fittings on the manhole covers, also the application
of cellulose pulp is a luting for the upper manhole covers, substantially as herein
described.
8, In pulp boilers the employment of steam at a higher pressure within the
heating pipes than in the body of the boiler in order to prevent deposits in the
pipes and filling the boiler only to the extent of the of its capacity when
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the wood under treatment has been previously boiled in order to avoid excessive
pressure substantially as herein described.
9, Providing lead lined boilers with an inner lining of cemented brickwork,
substantially as and for the purposes described.
10, The method of preventing the waste waters from sulphite boilings from
being obnoxious by discharging the same through iron pipes into collecting tanks
containing cold liquid and then causing the same to mix with about 1000 times
their volume of water, substantially as herein described.
11, The method of preventing the discoloration of the cellulose in sulphite
boilings by keeping the temperature of the material at or below about 212° Fahr.,
both before and after the chemical reaction without sulphite solution substantially
as herein described.