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Title: A Text-book of Paper-making

Author: C. F. Cross
        E. J. Bevan

Release date: March 4, 2018 [eBook #56679]
                Most recently updated: June 25, 2020

Language: English

Credits: Produced by Chris Curnow, RichardW, and the Online
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*** START OF THE PROJECT GUTENBERG EBOOK A TEXT-BOOK OF PAPER-MAKING ***




Produced by Chris Curnow, RichardW, and the Online
Distributed Proofreading Team at http://www.pgdp.net (This
file was produced from images generously made available
by The Internet Archive)









 A TEXT-BOOK OF PAPER-MAKING;
 BY C. F. CROSS AND E. J. BEVAN (1888)




 [Illustration:

 COTTON. × 50.

 LINEN. × 50.

 ESPARTO. × 50.

 MECHANICAL WOOD-PULP. × 50.

 CHEMICAL WOOD-PULP. × 50.]




 A
 TEXT-BOOK OF
 PAPER-MAKING.

 BY
 C. F. CROSS AND E. J. BEVAN.

 [Illustration]

 E. & F. N. SPON, 125, STRAND, LONDON.
 NEW YORK: 35, MURRAY STREET.
 1888.




PREFACE.


The practical portion of the present work has in part already appeared
as an article, by one of the authors, in ‘Spons’ Encyclopædia of the
Industrial Arts.’ Since its publication, however, many and important
improvements have been introduced in this, as in other branches of
the art of paper-making, which necessitated considerable additions to
the original article. It has at the same time been to a great extent
re-written, and, as the authors hope, improved.

Our object in writing this book has been to bring before students and
others the principles upon which scientific paper-making should be
conducted, a concise exposition of which has not, we believe, been
hitherto attempted.

Considerable prominence has been given to this aspect of the subject,
possibly at the expense of what some may consider more essential
details.

A belief in the importance of a thorough scientific training for
paper-makers has dictated the style and purpose of the book.

We have not thought it necessary to enter into minute details
respecting the construction of machinery, &c. for these the reader
is referred to such works as Hofmann’s Treatise on the Manufacture of
Paper.

Much of the scientific portion is here published for the first time.
Part of it has already appeared in the form of papers read before
various societies.

The chapter relating to the Treatment of Wood formed the subject of an
essay, which obtained the prize offered by the Scottish Paper-makers’
Association, in connection with the Edinburgh Forestry Exhibition, 1884.

We would here express our obligations to Messrs. G. and W. Bertram,
Messrs. Masson, Scott, and Bertram, Messrs. Rœckner and Co., and
others, for their courtesy in furnishing us with the drawings from
which the illustrations were prepared; to Dr. C. R. A. Wright, F.R.S.,
who kindly communicated the substance of the chapter on the Action of
Cuprammonium on Cellulose; to Mr. Carl Christensen, for drawings and
information regarding the manufacture of mechanical wood-pulp; also
to the following friends, among others, who have, in various ways,
rendered us important assistance:—Messrs. R. C. Menzies, C. M. King, G.
E. Davis, A. Beckwith, and C. Beadle.

Finally, we would tender our thanks to Mr. C. G. Warnford Lock for the
care he has bestowed on the editing of the book. The indexing and the
Chapter on Statistics are entirely his production.

  C. F. CROSS and E. J. BEVAN.

  4, NEW COURT, LINCOLN’S-INN, W.C.



  CONTENTS.


  INTRODUCTORY NOTE . . . 1


  CHAPTER I.

  CELLULOSE—THE CHEMICAL PROPERTIES OF TYPICAL MEMBERS OF
     THE CELLULOSE GROUP, WITH REFERENCE TO THEIR NATURAL
     HISTORY . . . 4


  CHAPTER II.

  PHYSICAL STRUCTURE OF FIBRES—MICROSCOPICAL EXAMINATION
     . . . 30


  CHAPTER III.

  CHEMICAL ANALYSIS OF PLANT SUBSTANCES . . . 42


  CHAPTER IV.

  AN ACCOUNT OF THE CHEMICAL AND PHYSICAL CHARACTERISTICS
     OF THE PRINCIPAL RAW MATERIALS . . . 46


  CHAPTER V.

  PROCESSES FOR ISOLATING CELLULOSE FROM PLANT SUBSTANCES
     . . . 62


  CHAPTER VI.

  SPECIAL TREATMENT OF VARIOUS FIBRES—BOILERS, BOILING
     PROCESSES, &C. . . . 79


  CHAPTER VII.

  BLEACHING . . . 110


  CHAPTER VIII.

  BEATING . . . 117


  CHAPTER IX.

  LOADING, SIZING, COLOURING, &C. . . . 127


  CHAPTER X.

  PAPER MACHINES, HAND-MADE PAPER . . . 144


  CHAPTER XI.

  CALENDERING, CUTTING, &C. . . . 167


  CHAPTER XII.

  CAUSTIC SODA, RECOVERED SODA, &C. . . . 177


  CHAPTER XIII.

  THE TESTING OF PAPER, MECHANICAL, CHEMICAL, AND
     MICROSCOPICAL . . . 193


  CHAPTER XIV.

  GENERAL CHEMICAL ANALYSIS FOR PAPER-MAKERS . . . 205


  CHAPTER XV.

  SITE FOR PAPER-MILL—WATER PURIFICATION . . . 210


  CHAPTER XVI.

  ACTION OF CUPRAMMONIUM ON CELLULOSE—WILLESDEN PAPER
     . . . 217


  CHAPTER XVII.

  STATISTICS . . . 221


  CHAPTER XVIII.

  BIBLIOGRAPHY . . . 229


  CHAPTER XIX.

  ADDENDA . . . 231


  INDEX . . . 233

{1}




PAPER-MAKING.

INTRODUCTORY NOTE.


The raw materials of the paper-maker are primarily the vegetable
fibrous substances; in addition to these there are various articles
which are employed as auxiliaries, either in the preparatory or
finishing processes to which these fibrous materials, or the web of
paper are subjected. The latter class are of subsidiary importance,
more especially from our present point of view.

In insisting upon the recognition of first principles, we cannot
overrate the importance of a thorough grasp of the constitution of the
plant fibres, as the necessary foundation for the intelligent conduct
of paper-making, and to this subject we will at once proceed.

Careful study of a mature plant will show that it is made up of
structural elements of two kinds, viz. fibres and cells, which, to use
a rough parallel, we may liken in function to the bricks and mortar
of a house. It is the former which admit of the many extended uses,
with which we are familiar, in the arts of spinning and weaving, and
which constitute the fabrics which are the most indispensable to our
civilised life. For the most part, as we know, fibres and cells are
aggregated together into compound tissues, and a process of separation
is therefore a necessary preliminary to the utilisation of the former.
The cotton fibre is the only important exception to this general
condition of distribution. Here we have the seed envelope or perisperm,
converted into a mass {2} of fibres, and these by a spontaneous
process accompanying the ripening, so isolated as to be immediately
available. Next in order in point of simplicity of isolation, are those
fibrous masses, or tissues, which, although components of complex
structures, exhibit a greater cohesion of their constituent fibres than
adhesion to the contiguous cellular tissues with which they go to build
up the plant. Into such a tissue the “bast,” or inner bark layer of
shrubs and trees, more especially those of tropical and sub-tropical
regions, frequently develops, and it is, in fact, this bast tissue,
graduating in respect of cohesion of its constituent fibres, from a
close network such as we have spoken of, to a collection of individual
fibres or fibre-bundles disposed in parallel series, which supplies
the greater part of the more valuable of the textile and paper-making
fibres; we may instance flax, hemp, and jute, each of which is the
basis of an enormous industry. According to the degree of adhesion of
the bast to the contiguous tissues, or, in another aspect, according to
its lesser aggregate development, so is the difficulty of isolation and
the necessity of using processes auxiliary to the mechanical separation
of the tissue.

It is worthy of note here that the Japanese paper with which we
are in these times so familiar, is prepared by the most primitive
means from the bast of a mulberry (_Broussonetia papyrifera_); the
isolated tissue, consisting of a close network of fibres, is simply
cut and hammered to produce a surface of the requisite evenness, and
the production of a web of paper is complete. In isolating the bast
fibres employed in the textile industries, a preliminary partial
disintegration of the plant stem is brought about by the process of
steeping or retting, by which the separation of fibre from flesh or
cellular tissue is much facilitated.

Last in order of simplicity of distribution, we have the fibres
known to the botanist as the fibro-vascular bundles of leaves and
monocotyledonous stems, these bundles being irregularly distributed
through the main cellular mass, and consequently, by reason of adhesion
thereto, much more {3} difficult of isolation. For this and other
reasons, more or less in correlation with natural function, we shall
find this class of raw material lowest in value to the paper-maker.

It is necessary at this stage to point out that the work of the
paper-maker and that of the textile manufacturer are complementary one
to the other, and the supply of fibrous raw material is correspondingly
divided: it may be said, indeed, that the paper industry subsists
upon the rejecta of the textile manufactures. The working up of
discontinuous fibre elements into thread, which is the purpose of the
complicated operations of the spinner, is conditioned by the length
and strength of these ultimate fibres. Paper-making, on the other
hand, requires that the raw material shall be previously reduced to
the condition of minute subdivision of the constituent fibres, and
therefore can avail itself of fibrous raw material altogether valueless
to the spinner, and of textile materials which from any cause have
become of no value as such. To the raw materials of the paper-maker,
which we have briefly outlined above, we must therefore add, as a
supplementary class, textiles of all kinds, such as rags, rope, and
thread.

Having thus acquired a general idea of the sources of our raw
materials, we must study more closely the substances themselves, and
first of all we must investigate them as we should any other chemical
substance, i.e. we must get to understand the nature and properties
of the matter of which the vegetable fibres are composed. While these
exhibit certain variations, which are considerable, the substances
present a sufficient chemical uniformity to warrant their being
designated under a class name: this name is cellulose. The prototype of
the celluloses is the cotton fibre.

{4}




CHAPTER I.

CELLULOSE: THE CHEMICAL PROPERTIES OF TYPICAL MEMBERS OF THE CELLULOSE
GROUP, WITH REFERENCE TO THEIR NATURAL HISTORY.


Plants are so far built up of cellulose that it may be called the
material basis of the vegetable world. Plant tissues, however, seldom,
if ever, consist of pure cellulose, but contain besides, other products
of growth either chemically combined with the cellulose or mechanically
bound up with the tissue, which are, according to the nature of their
union, removable either by means of fundamental chemical resolution
or by the application of simple solvents. A general method for the
isolation of cellulose consists in exposing the moist tissue to
the action of chlorine gas or of bromine water in the cold, and
subsequently boiling in dilute ammonia; repeating this treatment until
the alkaline solution no longer dissolves anything from the tissue or
fibre. The cellulose is then washed with water, alcohol, and ether,
and dried. Obtained in this way, or in the form of bleached cotton, or
of Swedish filter paper, it is a white substance, more or less opaque,
retaining the microscopic features of the tissue or fibre from which it
has been isolated. Its sp. gr. is 1·25–1·45. Its elementary composition
is expressed by the percentage numbers (Schulze)

  C      44·0      44·2
  H       6·3       6·4
  O      49·7      49·4

or by the corresponding empirical formula, viz. C_{6}H_{10}O_{5}.

These numbers represent the composition of the ash-free cellulose.
Nearly all celluloses contain a certain proportion, {5} however small,
of mineral constituents, and the union of these with the organic
portion of the fibre or tissue is of such a nature that the ash left on
ignition preserves the form of the original. It is only in the growing
point of certain young shoots that the cellulose tissue is free from
mineral constituents. (Hofmeister.)

As already indicated, cellulose is insoluble in all simple solvents;
it is, however, dissolved by certain reagents, but only by virtue of a
preceding chemical modification. An exception to this is to be found,
perhaps, in the ammoniacal solution of cupric oxide (Schweitzer’s
reagent), in which it dissolves without essential modification, being
recovered by precipitation, in a form which is chemically identical
with the original, though differing, of course, in being structureless,
or amorphous. This reagent may be employed in a variety of forms, but
the following method of using it is to be recommended as the most
certain in its results. The substance to be operated upon is intimately
mixed with copper turnings in a tube which is narrowed below and
provided with a stopcock. Strong ammonia is poured upon the contents of
the tube and, after being allowed to stand for some minutes, is drawn
off and returned to the tube; the operation is several times repeated
until the solution of the substance is effected. In order to facilitate
the oxidation of the copper by the atmospheric oxygen, a current of
air may be aspirated through the apparatus. The solution of the oxide
prepared in this way is more effective in its action on cellulose
than that obtained by dissolving the precipitated hydrate in ammonia.
Cellulosic tissues in contact with this reagent are seen to undergo
a disaggregation of their fibres, which swell up, become gelatinous,
and disappear in solution. On adding an acid to the viscous solution,
a precipitate of the amorphous cellulose is obtained in the form of a
jelly resembling hydrated alumina; after washing and drying, it forms
a brownish, brittle, horny mass. The cellulose is also precipitated
upon simply diluting the viscous solution with water and allowing it
to stand {6} 8–10 days in a closed vessel. From this observation it
was inferred by Erdmann that the cellulose could not be considered
as dissolved in the strict sense of the word, but the experiments
of Cramer upon the osmotic properties of the solution proved this
inference to be unfounded, and that cellulose is actually dissolved by
the ammoniacal solution of copper oxide.

On treating the ammonio-cupric solution of cellulose with metallic
zinc, this metal precipitates the copper, replacing it in the solution,
and producing the corresponding ammonio-zincic solution of cellulose,
which is colourless. Some of these solutions are lævo-gyrate.

Cellulose, in those forms to which the application of the term has
been hitherto restricted, is a comparatively inert substance, and its
reactions are consequently few. One of these is available for the
identification of cellulose, and is chiefly used in the microscopical
examinations of tissues: this is its reaction with iodine. Cellulose
is not coloured blue by a solution of iodine excepting under the
simultaneous influence of hydriodic acid, potassium iodide, sulphuric
acid, phosphoric acid, or zinc iodide or chloride. The solution is
prepared in the following way: zinc is dissolved to saturation in
hydrochloric acid, and the solution is evaporated to sp. gr. 2·0; to
90 parts of this solution are added 6 parts potassium iodide dissolved
in 10 parts of water; and in this solution iodine is dissolved to
saturation. By this solution cellulose is coloured instantly a
deep-blue or violet. For the identification of cellulose in the gross,
mere inspection is usually sufficient; confirmatory evidence is
afforded by an observation of the action of the ammonio-copper reagent,
and of the absence of reaction with chlorine water. (See p. 18.)

Cellulose in its earlier stages of elaboration has no action upon
light; but with age it acquires the property of double refraction, not,
as has been shown by experiment, by virtue of its state of aggregation,
but of its molecular constitution (Sachs). {7}

_Animal Cellulose._—The mantles of many of the mollusca, e.g. the
_Pyrosomidæ_, _Salpidæ_, and _Phallusia mammillaris_, contain a
resistant substance which, after isolation by chemical treatment,
has been found to be identical both in composition and properties
with vegetable cellulose. Cellulose has also been stated to occur in
degenerated human spleen and in certain parts of the brain.

_Compounds of Cellulose._—The chemical inertness of cellulose is a
matter of everyday experience in the laboratory, where it fulfils
the important function of a filtering medium in the greater number
of separations of solids from liquids. Its combinations with acids
and with basic oxides are, as might be expected, few and of little
stability. It has been shown by Mills that cellulose (cotton) in
common with certain other organic fibrous substances, when immersed in
dilute solutions of the acids or basic oxides, condenses these bodies
within itself at the expense of the surrounding solution, which is
proportionately weakened. This effect of concentration is sufficiently
uniform and constant to lead us to assign it to a chemical cause, and
the view is strengthened by a consideration of the relative effects
upon the various acids and bases which have been investigated, and
brought to the following numerical expression:—Weight of cotton 3
grm. (with 6·9 per cent. H_{2}O and 0·05 per cent. ash)—i.e. 2·893
anhydrous fibre. Strength of solution about 0·5 grm. of the reagent in
250 cc.

                      Temp.          Time.      Weight absorbed.
  H_{2}SO_{4}      4° C. (39° F.)    3 min         0·00495
  HCl                    „            „           0·00733
  NaOH                   „            „           0·02020

The molecular ratio of the absorption, in the two latter, is
3 HCl : 10 NaOH, and it is noteworthy that the same ratio was observed
for silk.

Cellulose removes barium hydrate from its solution in wafer to form
with it an insoluble compound. On adding lead acetate to the solution
of cellulose in the ammonio-copper reagent, so prepared as to contain
no carbonate, a {8} precipitate is obtained consisting of a compound of
cellulose with lead oxide, but in variable proportions. The compound
C_{6}H_{10}O_{5}PbO is formed by the action of finely-divided lead
oxide upon the above solution. Quite recently it has been shown
(O’Shea, _Chem. News_, May 28th, 1886) that when dilute solutions of
lead are passed through ordinary filter paper, a certain amount is
retained which cannot be removed by washing.

Cellulose does not combine with metallic salts, a fact which has been
established incidentally to researches upon the mode of action of
mordants.

The combinations of cellulose with acid radicles (ethereal salts) are
both definite and stable.

_Triacetyl Cellulose_ [C_{6}H_{7} (C_{2}H_{3}O)_{3} O_{5}] is formed
by treating cellulose with six times its weight of acetic anhydride at
180° C. (356° F.). The product of the reaction is a syrupy solution
from which the compound in question separates on dilution with water as
a white flocculent precipitate.

Triacetyl cellulose is insoluble in alcohol and in ether, but soluble
in glacial acetic acid. It is easily saponified by boiling with a
solution of potassium hydrate, the cellulose being regenerated. No
derivative containing more than three acetyl groups has been obtained;
but a mixture of the mono-and di-acetyl cellulose is formed in treating
cellulose with only twice its weight of acetic anhydride, the formation
of these bodies being unattended by their solution.

Whenever cellulose, in any form, is brought into contact with strong
nitric acid at a low temperature, a nitro product, or a nitrate, is
formed. The extent of the nitration depends upon the concentration of
the acid, on the time of contact of the cellulose with it, and on the
state of the physical division of the cellulose itself.

Knop, and also Kamarsch, and Heeren, found that a mixture of sulphuric
acid and nitric acid also formed nitrates of cellulose; and still later
(1847), Millon and Gaudin employed a mixture of sulphuric acid and
nitrates of soda or potash, which they found to have the same effect.
{9}

Several well characterised nitrates have been formed, but it is a very
difficult matter to prepare any one in a state of purity, and without
admixture of a higher or lower nitrated body.

The following are known:—

Hexa-nitrate, C_{12}H_{14}O_{4}(NO_{3})_{6},[1] gun cotton. In the
formation of this body, nitric acid of sp. gr. 1·5, and sulphuric acid
of sp. gr. 1·84 are mixed, in varying proportions, about 3 of nitric to
1 of sulphuric (sometimes this proportion is reversed), and cotton is
immersed in this at a temperature not exceeding 10° C. (50° F.) for 24
hours: 100 parts of cellulose yield about 175 of cellulose nitrate. The
hexa-nitrate so prepared is insoluble in alcohol, ether, or mixtures of
both, in glacial acetic acid or in methyl alcohol. Acetone dissolves
it very slowly. This is the most explosive gun-cotton. It ignites at
160°–170° C. (320°–338° F.). According to Eder the mixtures of nitre
and sulphuric acid do not give this nitrate. Ordinary gun cotton may
contain as much as 12 per cent. of nitrates soluble in ether-alcohol.
The hexa-nitrate seems to be the only one quite insoluble in
ether-alcohol.

     [Footnote 1: To represent the series of cellulose nitrates so as
     to avoid fractional proportions, the ordinary empirical formula
     is doubled and the nomenclature has reference to this double
     molecule.]

Penta-nitrate, C_{12}H_{15}O_{5}(NO_{3})_{5}. This composition
has been very commonly ascribed to gun-cotton. It is difficult,
if not impossible, to prepare it in a state of purity by the
direct action of the acid on cellulose. The best method is the one
devised by Eder, making use of the property discovered by de Vrij,
that gun-cotton (hexa-nitrate) dissolves in nitric acid at about
80°–90° C. (176°–194° F.) and is precipitated, as the pentanitrate,
by concentrated sulphuric acid after cooling to 0° C. (32° F.); after
mixing with a larger volume of water, and washing the precipitate with
water and then with alcohol, it is dissolved in ether-alcohol, and
again precipitated with water, when it is obtained pure.

This nitrate is insoluble in alcohol, but dissolves readily
{10} in ether-alcohol, and slightly in acetic acid. Strong
potash solution converts this nitrate into the di-nitrate,
C_{12}H_{18}O_{8} (NO_{3})_{2}.

The tetra- and tri-nitrates (collodion pyroxyline) are generally
formed together when cellulose is treated with a more dilute nitric
acid, and at a higher temperature, and for a much shorter time (13
to 20 minutes), than in the formation of the hexa-nitrate. It is not
possible to separate them, as they are soluble to the same extent in
ether-alcohol, acetic ether, acetic acid or wood spirit.

On treatment with concentrated nitric and sulphuric acids, both
the tri-and tetra-nitrates are converted into penta-nitrate and
hexa-nitrate. Potash and ammonia convert them into di-nitrate.

Cellulose di-nitrate, C_{18}H_{13}O_{8} (NO_{3})_{2} always results as
the final product of the action of alkalis on the other nitrates, and
also from the action of hot, somewhat dilute, nitric acid on cellulose.
The di-nitrate is very soluble in ether-alcohol, acetic ether, and in
absolute alcohol. Further action of alkalis on the di-nitrate results
in a complete decomposition of the molecule, some organic acids and
tarry matters being formed. The reactions and resolution products of
this body have, however, been but slightly studied, and apparently not
at all with the view to elucidate anything respecting the constitution
of cellulose itself.

_Cellulose and Chlorine._—Dry chlorine gas has no action upon
cellulose, but the presence of water determines an indirect oxidising
action. This oxidising action results from the decomposition of water
by chlorine with formation of hydrochloric acid and liberation of
oxygen. The reaction, however, can only take place in the presence of
light.

_Cellulose and Oxygen._—When cotton is exposed for some time to the
action of a solution of bleaching powder, in the cold, and with access
of air, e.g. when a piece of white calico is moistened with the
solution, squeezed out and exposed to the air, it is found to undergo
gradual disintegration accompanied by a change in composition, and an
elementary {11} analysis of the product shows it to contain less carbon
and more oxygen than the original cellulose. The following percentage
numbers indicate the composition of these oxidised derivatives of
cellulose, and the progress of the oxidation:—

        12 hours’ exposure.  24 hours’ exposure.
  C      43·78  43·47           43·00  42·90
  H       5·85   6·13            6·28   6·18
  O      50·37  50·40           50·72  50·92

Other oxidising agents produce similar results; even by exposure to
air and light, cellulose is slowly converted into these oxidised
derivatives.[2] From their mode of formation, they have been termed
oxycelluloses, and to distinguish them from a series of more
highly oxidised derivatives, produced by the action of nitric acid
upon cellulose, which they nevertheless resemble in many of their
characteristics, the prefix α is employed. The following are the
distinguishing features of the α oxycelluloses as represented by the
more extreme of the above mentioned products. It reduces Fehling’s
solution at the boiling temperature, and the cuprous oxide is deposited
upon the fibre in a state of intimate union, producing the effect of
an orange dye. It attracts the basic colouring matters from their
solutions and is dyed to a full shade, the depth of colour being
proportionate to the amount of oxidation to which the cellulose has
been subjected. See also p. 43. Treated with a warm solution of
phenylhydrazine salts in water, it is coloured a bright lemon-yellow.
Its most remarkable property is its attraction for the vanadium
compounds, which is so powerful that combination may be proved to
take place when this element in the form of chloride is presented to
the oxycellulose in an aqueous solution containing not more than 1 in
1,000,000,000,000 parts.

     [Footnote 2: Witz. Bull. Soc. Ind. Rouen, _X._ 416, and _XI._ 189.]

The β oxycellulose resulting, as already indicated, from the
action of dilute nitric acid upon cellulose, will be subsequently
considered, under the head of the decompositions of cellulose, to
which the reaction which we have been considering may be regarded as
transitional. {12}

_Decomposition of Cellulose._—_Acids._—Of the decomposition of
cellulose by artificial means, i.e. by the action of reagents, the
most important are those which disclose the relationship which it
bears to the group of so-called carbo-hydrates. Cellulose is, indeed,
a highly _elaborated_ carbo-hydrate, differing from dextrin and
starch, not so much in its essential constitution as in the molecular
arrangement which has been impressed upon it in and through the life of
the plant. There are numerous observations in biological science which
demonstrate the close connection, and in many cases the physiological
equivalence of the members of this natural group, which includes the
sugars, dextrin, starches, and cellulose. The following facts show the
constitutional or chemical ties which underlie their interdependence.

_Amyloid._—When cotton is treated with 30 times its weight of sulphuric
acid somewhat diluted (1 part H_{2}O, 4 parts H_{2}SO_{4}) it quickly
dissolves, the solution being at first gelatinous, becoming afterwards
syrupy. On pouring this solution into water, a white flocculent
precipitate is formed, consisting of a substance closely resembling the
cellulose from which it is derived, differing, indeed, only in being
amorphous, and in being coloured blue by iodine. This substance, from
its resemblance to starch, has been called _amyloid_. When sufficiently
dehydrated it constitutes a swollen starchy mass, which dries to a
brittle transparent solid. This transformation appears to consist in a
simple hydration of the cellulose molecule, thus:—

    Cellulose.                      Amyloid.
  2 (C_{6}H_{10}O_{5}) + H_{2}O = C_{12}H_{22}O_{11}.

The modification of cellulose, which occurs on the conversion of
unsized paper into the so-called parchment paper, by exposure for a
short time to the action of strong sulphuric acid, and subsequent
washing and drying, consists doubtless in a superficial conversion of
the cellulose into _amyloid_, or a body closely resembling it.

_Hydracellulose._—Closely related in composition to the above {13}
described amyloid, is the substance called hydracellulose, into which
cellulose is converted by exposure for some time to the action of
moderately strong sulphuric, or hydrochloric acids (sp. gr. 1·35).
This substance is also formed by the action of very weak acids, if the
exposure of the cellulose be sufficiently prolonged. Its formation is
accompanied by the complete disintegration of the cellulose. If the
action of strong sulphuric acid be prolonged, a further modification
ensues, dextrin or sugar being formed. These products have not been
sufficiently studied to have established their exact identity with
any of the substances known under these group-names. The dextrin has
a close resemblance to the dextrin obtained from starch; the sugar
is susceptible of fermentation; but beyond this nothing specific is
known of these bodies. Their general properties, however, and mode of
formation, sufficiently establish the fact that cellulose itself is
constituted of similar molecules.

The action of zinc chloride solution upon cellulose is similar to that
of sulphuric acid.

Cellulose in contact with iron, and in presence of air and moisture, is
converted into a sugar and a gummy substance, which latter is converted
into a sugar on boiling with dilute acids. Oxidised by potassium
permanganate or bichromate in presence of acetic acid, it is converted
into glucose, dextrin, and formic acid.

_Cellulose and nitric acid: β Oxycellulose._[3]—On digesting cellulose
with nitric acid (sp. gr. 1·3) at 100° C. (212° F.), a considerable
quantity of oxalic acid is formed; but after prolonged digestion, a
residue remains, which yields but very slowly to the action of the
acid. This substance, which is white and flocculent, when thrown upon
a filter and washed with water, combines with the latter to form a
gelatinous hydrate. It dissolves in dilute alkalis, but without forming
a stable compound with the base. It usually amounts to about 30 per
cent. of the cellulose acted upon. Its elementary composition is
expressed by the formula {14} C_{18}H_{26}O_{16} (C = 43·4, H = 5·3
per cent.). Treated with a mixture of concentrated sulphuric and nitric
acids, it dissolves, and, on pouring the solution into water, the
compound C_{18}H_{23}O_{13}(NO_{3})_{3} separates as a white flocculent
precipitate. In its essential properties therefore β oxycellulose
exhibits a close resemblance to cellulose itself. This oxycellulose is
distinguished from the members of the cellulose group by dissolving
in concentrated sulphuric acid with development of a pink colour. It
appears to stand in very close relationship to the group of pectic
substances, which are oxidised derivatives of cellulose.

     [Footnote 3: Cross and Bevan, Chem. Soc. Journ., xliii. p. 23.]

_Alkalis._—Concentrated solutions of the caustic alkalis in the cold
attack and disintegrate cellulose but slowly. The action is in many
cases merely superficial. Dilute solutions of the alkalis are without
action upon cellulose even at the boiling temperature, unless the
condition of oxidation is super-added; in this case, acid bodies are
found. The extreme product of the oxidation of cellulose in presence of
the caustic alkalis is oxalic acid; this acid has indeed been prepared
on the commercial scale by the “fusion” of cellulosic substances,
with mixture of sodium and potassium hydrates. Malic acid has been
obtained as an intermediate product of this decomposition. By potassium
permanganate in presence of potassium hydrate, both in solution,
finely divided cellulose is oxidised to a syrupy mixture of acids
resembling in composition and properties Frémy’s meta-pectic acid. A
similar decomposition is effected by concentrated solutions of the
hypochlorites, employed cold.

_Water at High Temperature._—Cellulose itself is only slightly affected
by exposure to a temperature of 200° C. (392° F.) but in contact with
water at this temperature, in sealed glass[4] most part into dark
brown insoluble products, a portion, however, passing into solution in
the water, imparting to it a deep yellow colour. A large quantity of
carbonic acid is {15} formed, and the solution contains in addition to
formic acid an appreciable quantity of pyrocatechol. The formation of
this aromatic substance from cellulose is, perhaps, the most noticeable
feature of the decomposition.

     [Footnote 4: The action of alkaline substances dissolved from the
     glass must be taken into account in this decomposition.]

_Decomposition by means of ferments, &c._—The soluble ferment of the
foxglove has been found to convert cellulose into glucose and dextrin.
The fluid from the vermiform appendix of the rabbit has also been found
to digest cellulose with liberation of marsh gas and formation of a
soluble compound which reduces cupric oxide in alkaline solution.

_Humus._—In the natural decay of cellulosic structures a large quantity
of marsh gas is formed, and solid products are formed, which are
usually known as humic or ulmic substances. These bodies are amorphous,
are largely dissolved by alkaline solutions, and are attacked by
chlorine gas in presence of moisture, yielding yellow coloured
chlorinated derivatives whose composition has a general resemblance to
the chlorinated compounds obtained from the compound celluloses, to be
hereafter described.

The most important part which ulmic substances play in the economy of
nature, is in the composition of soils. It is doubtful whether they
act directly as fertilisers, but by their action upon the mineral
constituents of soils they contribute to the supply of these necessary
elements of growth to the plant.

_Synthesis of Cellulose._—A transformation of certain soluble
carbo-hydrates into cellulose, which may be regarded as a proximate
synthesis of cellulose, has recently been brought to light. This is
set up spontaneously in beet-juice, and results in the formation of
a hard white substance, insoluble in boiling dilute potash, soluble
in the ammonio-copper reagent, converted by sulphuric acid into
dextrin and sugar, and by nitric acid into oxalic acid. On adding
some of these cellulose lumps to a solution of pure cane-sugar, a
further transformation of the saccharose into the same substance is
brought about. At the same time there is simultaneously produced a
gummy substance, which is precipitated by {16} alcohol as a white
amorphous caoutchouc-like mass, of the same composition as cellulose,
but swelling up with water, and otherwise differing in its physical
properties from cellulose. This latter substance is also formed by the
action of diastaste upon a solution of saccharose.

The process of cellulosic fermentation may be represented by the
equation:

  n. (C_{12}H_{22}O_{11}) = n. (C_{6}H_{10}O_{5}) + n. (C_{6}H_{12}O_{6})
        Saccharose.               Cellulose.               Glucose.

A similar transformation takes place under the influence of certain
fatty seeds, e. g. those of rape and colza; and it is probable that
the formation of cellulose in living plants may take place at the
expense of saccharose and under the influence of ferments. In support
of this it has been established that in the sugar-cane, the formation
of wood—i.e. cellulose—is accompanied _pari passu_ by a decrease
in saccharose. More recently, A. Brown (_Chem. Soc. Journ._, 432,
1886) has investigated the formation of cellulose by the “vinegar
plant” growing in solutions of the carbo-hydrates, e. g. dextrose in
yeast-water. The cells elaborate an extra-cellular fibrin, which acts
as a “cell-collecting medium,” and they possess therefore a two-sided
activity, i.e. the property above mentioned, in addition to their
strictly fermentative activity. The cellulose film in question was
found to contain 50 to 60 per cent. of pure cellulose. It is noteworthy
that in a solution of levulose the growth of the “plant” is unattended
by fermentative action, 33 per cent. of the substance being, on the
other hand, transformed into cellulose.

_Modifications of Cellulose in the Plant. Compound Celluloses._—It has
been already stated that cellulose occurs in nature for the most part
in a form different from that in which we have hitherto considered it,
viz. either combined or mixed with other substances which are of such
a nature that they may be removed by a chemical process, more or less
simple. One of the most characteristic of these modified celluloses
constitutes the jute fibre, the isolated bast of an Indian plant,
{17} which has an enormous industrial application for the coarser
textile purposes. The chemistry of jute throws light on the course of
lignification, the process by which cellulose is modified into wood,
and in studying it in preference to wood we have the advantage of
studying a simple tissue.

Like cellulose, jute dissolves in cuprammonia, and is similarly acted
upon by the concentrated acids. By nitric acids it is converted into
nitric ethers, which are yellow coloured, but in other respects closely
resemble the pyroxylins. They are entirely soluble in acetone.

Jute differs from cellulose in the following respects: its percentage
composition (excluding ash) is

  C      47·0      48·0 per cent.
  H       5·9       5·7    „
  O      47·1      46·3    „

It is harsher to the touch, and its colour varies from grey to brown;
it combines directly with the greater number of the organic colouring
matters, removing them from solution, i.e., becoming dyed with them;
it is coloured deep yellow by immersion in a solution of aniline
sulphate; moistened with a solution of phloroglucol and afterwards
with hydrochloric acid, it gives a deep red coloration; with pyrrol
also in presence of hydrochloric acid it gives a deep carmine colour;
it is attacked and partially converted into soluble products by a
number of reagents which have no action, under similar conditions, upon
cellulose. Certain of these we must consider more in detail.

_Iodine._—Jute absorbs iodine from its solution in potassium iodide.
This action is characteristic of all lignified tissues, the quantity of
iodine taken up being proportional to the amount of lignification. If
the physical conditions remain the same, the amounts of iodine absorbed
will be found to be constant for each particular fibre. This constancy
points to the formation of a definite chemical compound, probably
resembling the blue compound of starch and iodine. This property may
be made available for the estimation of the {18} amount of mechanical
wood-pulp in papers; it will be more fully considered elsewhere.

_Bromine._—Jute, exposed to the action of bromine water in the cold,
combines with the halogen, being oxidised at the same time, and the
products may be dissolved by boiling the modified fibre in weak
alkaline solutions. On repeating this treatment four or five times, a
residue of cellulose is ultimately obtained, amounting to 72 or 73 per
cent. of the original fibre: the cellulose is obtained in the form of
the disintegrated fibre elements. On allowing the halogen to act in
presence of an alkali, _i.e._, as hypobromite, not only is its action
intensified and accelerated, but its _modus operandi_ more clearly
revealed. The chief products are in this case, carbonic acid, bromoform
CHBr_{3} (which may be isolated by distillation), and cellulose. At
the same time the yield of cellulose is considerably less than by the
former method, the cellulose itself being attacked by the hypobromite.

_Chlorine._—Dry chlorine gas has no action upon jute even when the
temperature is raised to 140° C. (284° F.), but the presence of
moisture determines rapid combination, at ordinary temperature,
accompanied by evolution of heat. The colour of the jute changes to
a bright yellow, which, on treatment of the fibre with a solution
of sodium sulphite, gives place to a pure magenta. This reaction is
characteristic of all lignified tissues, and is a valuable aid in the
micro-chemical examination of plant structures. For this purpose, the
reagent may be employed in the form of chlorine water; the sections or
small fragments to be examined are allowed to remain in this solution
a short time, and then mounted for observation in a dilute solution of
sodium sulphite. By combination with chlorine the fibre substance or
_ligno-cellulose_ is partially resolved. Alcohol dissolves away from
the chlorinated fibre, a bright yellow substance, which is precipitated
in yellow flocks on pouring the solution into water. This chlorinated
derivative has the composition C_{19}H{18}Cl_{4}O_{9}. By this formula,
as well as by its colour reactions, and by its yielding protocatechuic
acid on fusion with potash, it is {19} shown to be related to the
trihydric phenols, and to the tannins which are derivatives of these.

After dissolving away this compound by exhaustive treatment with
alcohol, the fibre still gives a brilliant reaction with sodium
sulphite, showing that a portion is still held back in combination
with the cellulose, or cellulose residue. On treating the residual
fibre with boiling nitric acid, a considerable quantity of chloropicrin
CCl_{3}NO_{2} is formed, and it is probable that the union of the
molecule C_{19}H_{18}Cl_{4}O_{9} with the cellulose may be effected
by the aldehyde[5] molecule CCl_{3}COH; each group being contained
in the original lignocellulose, the action of the chlorine tending
to disturb the atomic equilibrium and to rearrange the atoms into
groups, which in their modified form have less mutual coherence. If the
chlorinated fibre be directly boiled with the sodium sulphite solution,
its resolution into cellulose and soluble non-cellulose derivatives
is complete: and this treatment constitutes the most simple and rapid
method of estimating the cellulose in lignified tissues. It is only
necessary finally to wash the cellulose with hot water containing a
little acetic acid (when placed in a funnel it acts as its own filter),
and then with, alcohol, when it may be dried and weighed. In order to
ensure the resolution of the fibre by a single chlorination (in the
case of jute, and the like), it must, previously to exposure to the
gas, be boiled in a dilute (1 per cent.) solution of potassic hydrate.
In the case of wood and other more resistant structures, it will be
necessary to repeat the chlorination.

     [Footnote 5: Furfural may also be isolated from the chlorinated
     jute; the survival of this aldehyde is noteworthy.]

The percentage of cellulose yielded by this method is, in the case
of jute, usually 2–3 per cent. higher than by the bromine method.
Moreover, if the temperature be maintained at 0° C. (32° F.), by
placing the fibre, which is to be exposed to the action of the gas,
in contact with pounded ice, the percentage may be still further
increased, amounting {20} in some cases to 80–82. Corresponding to
this increased yield, the cellulose is obtained in long filaments.
It will be seen, therefore, that the cellulose isolated by chemical
treatment from a _compound cellulose_ is affected both in character
and quantity by the process employed, and it is affected in a much
greater degree than the cellulose itself exposed to the same treatment,
_after isolation_. The composition of the cellulose obtained in this
way differs from that of celluloses, such as cotton, which exist in
the plant in an isolated and more fully formed condition; it contains
43 per cent. C and 6 per cent. H, corresponding to the formula n
[3 C_{6}H_{10}O_{5}H_{2}O.] The composition of this cellulose will
be seen to be identical with that of certain of the oxycelluloses
previously described; and its properties are, moreover, those of an
oxycellulose. These facts go to show that the jute fibre substance,
and the substances allied to it, are compounds of cellulose with
other molecules, _i.e._ they are _compound celluloses_. They may be
conveniently grouped under the term _ligno-cellulose_.

_Dilute Mineral Acids._—Under the action of dilute sulphuric or
hydrochloric acid (5–10 per cent.) at 60°–80° C. (140°–176° F.), a
considerable portion of the fibre substance is dissolved. The action
of either reagent is of course purely hydrolytic; and the hydrolysis
is of the simplest character, since the substance dissolved as well as
the residual fibre are found to have the same percentage composition.
Moreover, the residual fibre, though having undergone a profound
structural modification, and having been converted into a disintegrated
mass of brittle fragments, still preserves the chemical characteristics
of the original, unaltered. Thus it is converted by the action of
chlorine into a similar complex of derivatives, yielding on resolution
by sodium sulphite solution 75 per cent. of cellulose; also when acted
upon by alkaline hypobromite it yields bromoform. Under the action of
these hydrolytic reagents, therefore, the fibre shows itself to be
essentially a chemical whole. At the boiling temperature, these acids
resolve as well as dissolve the fibre substance, and the volatile
products are acetic acid and the peculiar aldehyde {21} _furfural_
C_{4}H_{3}O.COH. The yield of this aldehyde may be raised with suitable
precautions to 15–20 per cent. of the raw fibre. The action of dilute
nitric acid upon the fibre differs from that of the above-mentioned
acids, in effecting its resolution into soluble derivatives and
insoluble cellulose; the yield of the latter when the reaction is
conducted at 60° C. (140° F.), with 5 parts HNO_{3} is 60 per cent.
only, showing that in the process of isolation some of the cellulose
itself is attacked and converted into soluble products.

Schulze’s method of isolating cellulose from wood, and from the
ligno-celluloses generally, consisted in macerating them for 12 to
14 days with 8⁠/⁠10 their weight of potassium chlorate dissolved in
12 parts by weight of nitric acid (sp. gr. 1·10), and completing
the resolution by afterwards boiling with dilute ammonia. By the
action of a more concentrated acid, 50 per cent. HNO_{3}, at 80° C.
(176° F.), a soluble derivative is obtained which has the composition
(C_{25}H_{40}NO_{25}). It is a syrupy, highly acid body, dyeing animal
fibres a deep yellow shade, and giving with the earthy bases salts
of the formula (C_{25}H_{32}NO_{25}M_{4}), which are precipitated by
alcohol from their aqueous solution in the form of bright yellow flocks
that dry to a yellow powder.

_Dilute Alkalis._—The action of boiling dilute solutions of the caustic
alkalis upon the ligno-celluloses is similar to that of the dilute
acids, viz., purely hydrolytic, causing no essential change in the
composition of the fibre substance.

_Water at High Temperatures._—The ligno-celluloses undergo a profound
modification when heated with water at elevated temperatures. They
are to a great extent converted into soluble products, of which
a large proportion are the volatile bodies, acetic and formic
acids and furfural. The residual fibre is found to be more or less
disintegrated, and of a dark-brown colour, but preserving many of
the chemical features of the original. A similar disintegration
is caused by exposing the ligno-celluloses in a dry state to an
atmosphere of superheated steam, the effect being much increased if
the ligno-cellulose be previously bleached by any of the ordinary {22}
processes, i.e., under oxidising conditions. In these decompositions
oxidation, as well as hydration, plays an important part. It is found
that the presence of small quantities of reducing agents, e.g.,
sulphites, exerts a remarkable effect in retarding and often entirely
preventing these changes. It is probable that they act in obviating an
initial change, which, with a cumulative reaction on the fibre, effects
the profound resolutions above described. (See p. 71.)

_Concentrated Hydrochloric Acid._—When exposed to the concentrated
aqueous acid at ordinary temperatures, ligno-cellulose undergoes a
profound structural modification, and is largely converted into soluble
bodies. The disintegrated residue reacts with chlorine similarly to the
original jute, but the quantity of cellulose isolated by subsequent
treatment with alkaline solutions is only 50 per cent. of the original.
Since jute cellulose, after isolation, exhibits under similar treatment
a much smaller conversion into soluble products, 10 per cent. as
compared with 33, we have here further evidence that the cellulose is
present in the fibre in a condition chemically different from that of
the isolated cellulose.

_Sulphuric Acid._—On triturating the fibre with the concentrated acid,
it dissolves to a brownish-purple solution; on pouring this solution
into water, a substance is precipitated in dark-brown flocks; when
dried it has the following composition:

  C      64·4
  H       4·4
  O      31·2

The solution yields on distillation furfural and acetic acid.

_Nitric and Sulphuric Acids._—(1 : 2 by vol.)—By the action of these
acids ligno-cellulose is converted into yellow-coloured explosive
compounds, preserving all the external features of the original fibre,
and showing a close resemblance to the pyroxylins.

The increase in weight resulting from the fixation of the {23} nitric
acid residue is approximately equal to that of cotton “nitrated” under
the same conditions.

They are freely soluble in acetone. On examination they prove to be
homogeneous. If the fibre be warmed with the mixture after the first
reaction is completed, it dissolves. The solution is found to contain
oxalic, succinic, and suberic acids, but no aromatic nitro-derivatives,
whereas if ligno-cellulose contain a benzene nucleus, as has been
supposed, such derivatives could not fail to be formed under these
conditions.

_Animal Digestion of Ligno-cellulose._—It has long been known
that the urine of herbivorous animals contains hippuric acid, or
benzoyl glycocine, as a normal constituent, and it has been shown
that the benzoyl radicle necessary to form this body by reacting
with the glycocine of the liver, is a product of the digestion
of ligno-cellulose. On the other hand, it has been shown that
ligno-cellulose contains no benzene compounds as such. We have
therefore, in this fact additional evidence that a portion of the
complex ligno-cellulose molecule is in what we may term a potentially
aromatic condition.

_Distribution of Ligno-celluloses._—As already indicated, the
distribution of the ligno-celluloses is extremely wide; they are met
with in every variety of vegetable tissue, and their presence is
readily ascertained by the reaction of chlorination already described.
Of these ligno-celluloses most closely allied to jute, we may mention
the stony concretions of pears (glycodrupose) and the main tissue of
fir wood (glycolignose).

_Decay of Ligno-cellulose._—When a mass of ligno-cellulose (jute)
is allowed to lie for a long period in a damp state, it undergoes
resolution accompanied by structural disintegration. The soluble
products of this change are acid bodies of the pectic class, and
astringent substances closely resembling the tannins. In this
decomposition also we have evidence of the plastic condition of the
ligno-cellulose molecule, of the variety of its modes of resolution,
according to the various directions in which it is attacked.

_Decomposition by Heat._—The celluloses burn in the air with {24} a
quiet luminous flame. When heated out of contact with the air, they
are completely resolved into gaseous and volatile products on the
one hand, and a residual black mass, which, although containing a
high percentage of carbon, and approximating in its properties to the
element itself, nevertheless contains hydrogen and oxygen in essential
chemical union with the carbon, in consequence of which it is expedient
to apply the term pseudo-carbon to this as to all similar substances.
The volatile products of the destructive distillation of pure cellulose
have not been studied, but those of certain of the ligno-celluloses
(woods) have been exhaustively investigated, and have moreover, a very
considerable commercial importance. They divide themselves into two
groups (_a_) soluble in water, and containing, besides water, acetic
acid, methyl alcohol, methylic acetate and acetone; (_b_) insoluble in
water, or wood tar, containing tolyene, xylene, cymene, naphthalene,
chrysene, anthracene, retene, pittacal, cedriret solid paraffins, &c.
The quantity of the pseudo-carbon (charcoal) obtained is, in the case
of the hard woods, about 25 per cent. of their weight. The liquid
portion of the products amount to some 50 per cent., and contains
about one-fifth of the carbon of the original wood; the remainder of
the carbon is eliminated in the gaseous form (CO, CO_{2}, &c.). The
proportion of acetic acid is 3–4 per cent., the tar amounting to 7–8
per cent.

The coals themselves may be regarded as pseudo-carbon derivatives of
celluloses, formed by a process of molecular condensation, the true
nature of which remains a matter of speculation. In this view, the
whole of our vast series of aromatic or benzene compounds, derived as
they are from the products of the destructive distillation of coals,
may be traced back to a cellulose origin.

Pseudo-carbons are obtained as products of the action of various
reagents upon the celluloses, and other of the so-called
carbo-hydrates. These reagents, such as sulphuric acid, act in virtue
of their dehydrating power; and the recognition of this fact, together
with the supposed “carbonaceous” {25} character of the product,
led to the erroneous conclusion that the carbohydrates are in such
decompositions simply resolved into carbon and water; a conclusion
which seems to derive additional warrant from the peculiar numerical
relationship which exists between the C, H, O atoms of all the members
of the group. Their relation is expressed in the general formula C_{n}
H_{2(n−m)} O_{(n−m)}, and in the somewhat misleading term carbohydrate,
which is applied to the whole group. We now know that the removal of
water from these bodies by the action of dehydrating agents—including
heat—follows the ascertained laws of chemical dehydration, involving
molecular condensations and rearrangement, and that the pseudo-carbons
are the extreme terms of a series of such condensations or cumulative
resolutions. The matter, however, is not as yet sufficiently
investigated to enable us to state with any preciseness the mechanism
of these changes. Still this general statement will enable us to avoid
many of the erroneous views which have existed on the subject, and in a
measure to anticipate the results of future investigation.[6]

     [Footnote 6: It is worthy of mention that by the action of
     chlorine in presence of water, and by the action of concentrated
     nitric acid upon the cannel coals, substitution derivatives are
     formed resembling those obtained by the action of these reagents
     respectively upon the ligno-celluloses.]

_General conclusions._—The aldehydic character of the group of
ligno-celluloses is typical of the constituents of plant tissues
generally, and is, there can be no doubt, extended to the celluloses.
Indeed the evidence of biological observation goes to show that the
ligno-celluloses are formed, by a process of chemical modification,
from some more purely cellulosic tissue, which preceded it, and
with this modification there is, nevertheless, a retention of the
general features of the original cellulose. In the domain of animal
chemistry, recent investigation has also shown that the development
of proteid tissues finds its chemical expression in their aldehydic
characteristics, or as it has been put, the immediate physical cause
of life is to be found in the _chemical tension_ of aldehydes. The
meaning of this expression will be readily grasped on {26} reference
to the properties of the aldehydes as a group; their power of combining
with oxygen; of uniting by their own molecules, to polymerise; of
uniting by way of dehydration; of combining with the aromatic alcohols;
a consensus of properties which shows them to possess an activity
surpassing that of any other group of compounds. The evidence of
biology, added to our knowledge of the properties of these substances,
would lead us therefore to define cellulose as a condensed aldehyde
allied to the sugars, and likewise containing alcoholic OH groups; and
ligno-cellulose a compound cellulose, containing a cellulose nucleus or
residue so combined with certain groups which may be included in the
term _non-cellulose_, that it yields, under the action of reagents,
products belonging either to the aromatic, the furfural, or the fatty
group.

_Adipo-cellulose._—Cork or Cuticular Tissue.—From the mode of formation
of cork and cuticular tissues, it has been concluded that they are also
modified celluloses. The aggregate ultimate composition of cork is
represented by the following percentage numbers:

  C      65·7
  H       8·3
  O      24·5
  N       1·5

Cork, however, unlike the jute fibre, is by no means chemically simple,
but can be resolved by the action of mere solvents into a number of
proximate constituents, such as acids, a variety of fatty bodies,
nitrogeneous bodies, &c.

Cuticular tissues, such as constitute the covering of fruits, are more
simple in composition; the cuticle of the apple after purification, has
the following percentage composition:

  C      73·66
  H      11·37
  O      14·97

The cuticular substance of cotton, straw, esparto, &c., are doubtless
similar bodies. These numbers point to a {27} remarkable similarity
in composition to the fats, and, indeed, from the results of his
study of this tissue, Frémy concluded that it was a fat in everything
but its physical properties, of which we may mention insolubility in
alcohol and in ether, and infusibility. This tissue, however, as also
cork, contains a cellulose residue, which may be isolated by any of
the methods of treatment given for ligno-cellulose. Under the action
of boiling nitric acid these tissues are resolved into cellulose
on the one hand, and a series of fatty acids or products of their
decomposition, suberic and adipic acids, &c., on the other; the latter
amounting in the case of cork to 40 per cent. of the weight of the
substance treated. The cellulose obtained by this treatment is but 2–3
per cent.; this number, however, represents only the amount which has
survived a treatment which we know to be destructive to cellulose. If,
on the other hand, cork be resolved by treatment with sodium sulphite
solution at 100lb. pressure, or 166° C. (331° F.), a soft mass is
obtained, preserving the structural features of the original cork,
until subjected to slight pressure, when it falls to a cellular mass.
From this, cellulose is isolated by any of the less drastic processes
above described, and is found to amount to 9–10% of the original cork.
As in ligno-cellulose, we have evidence of a transition from cellulose
to the tannins, so in cork and cuticular tissue we have evidence of
the metamorphosis of cellulose into fats, a fact indicated in the term
_adipo-cellulose_, which we have applied to the compound celluloses
constituting these protective plant tissues. This metamorphosis is
doubtless a very complex process, and would appear to involve the
formation of tannins also, at least as a subsidiary result. Still,
the essential feature of the change is the production of the peculiar
fat-like substances which have been described; and with due regard
to the limitation pointed out, the views here advanced represent the
results of the investigations of the subject as far as they have
proceeded.

It may be observed that the general characteristics of the {28}
adipo-celluloses as of the ligno-celluloses are those of a complex
aldehyde.

_Pecto-Cellulose._—The compound cellulose described under the names
adipo-cellulose and ligno-cellulose have this feature in common, that
they are richer in carbon than cellulose. On the other hand there is
a large number of cellulosic tissues which contain in the aggregate
less carbon, i.e., in which the cellulose is combined or mixed with
substances of lower carbon percentage than itself. Such tissues, or
rather the substances which compose them, are resolved by simple
treatment with dilute alkaline solutions into insoluble cellulose,
and soluble bodies of the pectic class. Thus the purified bast of the
Russian flax, i.e., the raw flax, is found to contain—

  43·7 per cent. C.
   5·9    „      H.

On boiling with an alkali it loses in weight about 20 per cent.,
the substance dissolved being identical in properties with Frémy’s
pectic acid, a substance containing 42 per cent. C and 4.8 per cent.
H = C_{16}H_{22}O_{15}. Many other bast fibres, as well as cellulose
tissues, exhibit similar properties, and although this branch of the
subject has been but little investigated, there is sufficient evidence
for constituting a special class of compound celluloses under this
term, pecto-cellulose, having properties indicated in the type selected
above.

In addition to pectic acid there exists in, or can readily be obtained
from certain plants, a series of bodies of a similar nature, such
as pectose, pectin, parapectic acid and metapectic acid. The most
important of these are pectic acid and metapectic acid.

Pectic acid, though it rarely exists ready-formed in the plant, can
readily be obtained from it by the action of weak alkalis. It is best
procured by boiling the pulp of turnips with a 10 per cent. solution
of sodium carbonate for about half an hour. If an acid be added to
the filtered liquid, pectic acid is precipitated as a transparent
colourless jelly, which {29} dries up to a transparent horny mass. By
the prolonged action of alkalis or acids, pectic acid is converted into
metapectic acid (C_{8}H_{14}O_{9}), which may be obtained as a syrupy,
strongly acid liquid.

From what we know of the properties of the members of the pectic group,
and therefore of the pecto-celluloses, it will be readily seen that
the latter are very liable under the action of alkalis to undergo
conversion into soluble derivatives.

Conversely, a study of the action of alkalis upon plant substances,
enables us to determine to what extent the latter partake of the nature
of the pecto-cellulose, the importance of which to the practical paper
maker we need hardly point out. For a further development of this idea
(see p. 43).

{30}




CHAPTER II.

PHYSICAL STRUCTURE OF FIBRES.


We now have to treat of the fibrous raw materials from the point of
view of form or structure, which is, of course, a very important
factor in determining the quality of the paper or other fabric into
which they are manufactured. It is sufficiently evident that the
strength of paper is primarily due to the cohesion of its constituent
fibres. When paper is torn, the edges present a fibrous appearance,
and observation teaches us that, other things being equal, the greater
the manifestation of fibrous structure the stronger will be the paper.
If a paper be thoroughly wetted, its tensile strength is reduced to a
minimum, and if subjected to a slight strain we get, not a tearing, but
a pulling asunder of the fibres. If this be performed under a lens, the
structure of the paper is more clearly seen, and it will be appreciated
to what extent the qualities of a paper are the aggregate of the
qualities of its constituent fibres. A more careful dissection of the
paper shows that these fibres, which are the _ultimate fibres_ of the
plant, as distinguished from the bundles of these, or _filaments_,
which the spinner employs, are interlaced in all directions. To produce
this effect of interweaving, and to insure that uniformity which is an
essential feature of good paper, we have among others the following
contributory causes: (1) the deposition of the fibres from suspension
in water; (2) the composition of the pulp with regard to the reduction
of the fibrous bundles, and the isolation of the individual fibres; and
(3) the _structure_ of these ultimate fibres. It is with the last that
we are chiefly concerned at present.

To convey a general notion of the influence of the structure {31}
of fibres upon fabrics, we shall with advantage travel outside
our immediate province to consider briefly the woollen and silk
manufactures in relation to this point. Wool is, as we know, a
discontinuous fibre, and its structure is that represented in Fig.
1, the most conspicuous feature being its broken surface, consisting
apparently of imbricated scales.

[Illustration: FIG. 1.]

The silk fibre, on the other hand, is a dual cylinder, spun by the
worm in a continuous length, and with a perfectly smooth surface.
Now, it would not be to our purpose to point out that in starting
from a discontinuous simple fibre, to produce a continuous, therefore
necessarily compound one, a very different treatment or process of
spinning is required from that which the opposite condition renders
practicable. We will rather consider the influence of structure upon
materials manufactured from these fibres. It is obvious that the wool
fibres, brought into contact with one another, tend to interlock;
whereas silk fibres if rubbed or pressed together, simply slide
over one another; the result in the fabric is by multiplication of
the effect, a shrinking or contracting in length and breadth. This
interaction of the fibres, and the phenomena to which it gives rise,
is known as the _felting_ of wool and woollen goods; this tendency,
for the contrary reason, is not seen in silk fabrics. The production
of paper from a disintegrated fibrous mass or pulp introduces
similar considerations. That paper will be the stronger in which the
constituent fibres are the better felted, and the degree in which
felting takes place will depend to a great extent upon the form or
microscopic peculiarities of the fibres. This is only one of the
more obvious inferences to be drawn from the structure of fibres to
the qualities of the papers which they compose. Other {32} equally
important practical bearings will be seen to attach to the microscopic
study of our fibrous raw materials, and to the consideration of this
branch of the subject, we now ask the careful attention of the student.


MICROSCOPICAL EXAMINATION.—Under the head of “Microscopic Features”
we must include everything which has to do with the structure of the
vegetable fibres, as well as their organisation and distribution
in the plant. In the analysis of “organised” structures we employ
the two methods. (1) of _dissection_; (2) _examination_ by means
of the microscope; in other words, we first isolate the part under
investigation by a mechanical process and then proceed to the optical
resolution or analysis of the part. Having by analysis acquired a
knowledge of the _parts_, we study their mutual relations in the
structure they compose—we integrate our knowledge, so to speak—by means
of sections of the structure, cut so as to preserve the cohesion of
the parts in section, and yet in so fine a film as to appear under
the microscope to be virtually a plane surface. These points are
illustrated in the drawings given.

It is impossible for us to deal specially with the subject of the
microscope and its manipulation. The microscope, as a revealer of
natural wonders is one thing; as an instrument of scientific discovery,
quite another. For the latter, the student must train himself by
systematic work, and should especially concentrate his attention upon
some _one_ branch of natural history, however restricted.

We shall assume, in our treatment of the subject, a knowledge of
the microscope as an instrument of research, such as can be easily
acquired in a few weeks of work under the guidance of a teacher or
of one of the excellent manuals which now abound. We also assume a
certain acquaintance with the elements of vegetable physiology, which
it will be seen is necessary for a full grasp of the subject. Such an
acquaintance, also, may be easily acquired, under direction, in a few
weeks of work.

[Illustration: FIG. 2.]

[Illustration: FIG. 3.]

We have before alluded to the differences presented by {33} mono and
dicotyledonous stems in regard to the distribution of their fibrous
constituents. In illustration of this, we may cite Figs. 2, 3, which
represent, (2) a section of the aloe, (3) a section of the jute plant.
The available fibres are in (2) the fibro-vascular bundles (_f_),
which are irregularly distributed throughout the main mass of cellular
tissue, and {34} in (3) the bast fibres (_f_), which constitute a
definite and separate tissue. We have already alluded to the practical
consequences of this typical difference of distribution, in regard to
processes of separating these fibres on the large scale.

This process we have explained is necessarily simpler in the case of a
fibrous _tissue_, definitely localised; and this may be demonstrated
by a superficial examination of a young branch of an exogen. As we
know, the bark tissues are easily stripped from the underlying wood.
If now we work up the former in a mortar, with a little water, we soon
perceive the separation of the compound tissue into cellular matter
on the one hand and _fibres_, the latter being more or less long
and silky, according to the plant from which isolated. They vary in
length from one millimetre to several centimetres, and are aggregated
together in the plant in such a way as to constitute bundles, often
of very considerable length; the general arrangement being comparable
with that of the tiles in the roof of a house. It is important to
distinguish the fibre-bundles from the elementary or normal _fibres_,
and to this end they are designated by the term _filament_. Bast
_fibres_ are flexible and fusiform, terminating gradually in a point
at either end, as represented in Fig. 4; bast _filaments_, built up of
these fibres, containing often as many as twelve in the bundle, are
usually cylindrical, but exhibit the widest differences in regard to
the aggregation, in degree as well as number of their constituents. It
is obvious that while the spinner has to do with these _filaments_, the
paper maker works up the ultimate fibre constituents or _fibres_. It is
also an obvious corollary from this distinction that a fibrous material
which from “weakness” is unavailable for textile application, may yet
be perfectly “strong” from the paper maker’s point of view; in other
words, the individual fibres may be strong, but have little cohesion
in the filaments. As we proceed, the student will see more and more
the practical bearings of this branch of the study, and will perceive
the inferences to be drawn from the investigation of {35} minute
relationships to manufacturing processes and their products.

[Illustration: FIG. 4.]

We shall say but little as to the necessary equipment. (1) A dissecting
microscope, for dissecting under a lens, magnifying the object to 40
or 50 diameters. (2) An ordinary student’s microscope with lenses for
magnifying to 100 and 300 diameters. This is adequate to the work,
though of course, it may be an advantage in certain cases, to be
provided with higher powers. (3) A glass slide, carrying an engraved
scale of centimetres and millimetres for measuring the lengths of
objects, and a micrometer, divided into 1⁠/⁠10 mm. for measuring
diameters. It is also important to be able to determine the degree of
enlargement under any particular combination of lenses, and for this
purpose to possess a micrometer eye-piece, with a millimetre scale
divided into hundredths. (4) An effective microtome and the usual
mounting accessories.

A very important feature in the diagnosis of fibres, more especially
in regard to the composition of the fibre substances, is the effect
produced by treatment with various reagents. Certain of these reactions
we have already {36} indicated. We shall now give the details of
composition of the several solutions which will be required.

_Neutral Mounting Solutions._—It is advantageous in mounting
transparent objects to employ a solution of the same refractive power
as the substance itself. For this purpose, pure glycerin or a syrupy
solution of calcium chloride may be employed; it is expedient to mix
with either reagent a small proportion of acetic acid. The designation
“neutral” has reference to the fact that these reagents are without
sensible action on the fibres.


_Iodine Solution._—We have previously described the preparation of
a solution, giving the characteristic blue reaction with cellulose
directly. It is, however, often preferable to bring about this
colouration in another way, and the following are the solutions
employed:—1 gramme of potassium iodide is dissolved in 100 cc. water,
and the solution is saturated with iodine; it is preserved in stoppered
bottles, containing a few fragments of the element, so as to keep up
the saturation of the solution.

The accessory solution, dilute sulphuric acid, which is employed
to determine the reaction between the cellulose and the iodine, is
prepared as follows:—2 volumes of concentrated glycerin are mixed with
1 volume water, and to the mixture an equal volume of oil of vitriol
(1·78 sp. gr.), is slowly added, so as to prevent as far as possible a
rise of temperature. The effect of the glycerin is very remarkable in
preventing the distortion of the objects under the action of the acid,
which in other respects remains uninfluenced.

By way of verification of this iodine test, which is somewhat
capricious, it is advisable to test the reagents with a standard
substance. The best for the purpose is a linen yarn which has been
_partially_ bleached. Under the action of the reagents the fibres
composing this yarn, which must, of course, be suitably “teazed out”
for mounting, are coloured a light blue, the centre, however, showing
a yellow line, {37} marking the distribution in the interior canal of
a non-cellulose fibre constituent. Should these effects not appear,
it may be concluded that the acid requires to be strengthened. On the
other hand, too great a concentration is equally to be avoided; it is
evidenced by causing a _distortion_ of the fibre, easily recognised by
comparison with the fibre mounted in a neutral medium.


_Chlorine Water._—One of the most characteristic reactions of lignose,
or lignified cellulose, is that of combining with chlorine. The
reaction of the chlorinated derivatives with sodium sulphite solution,
is an important feature in the microscopic diagnosis of lignified
fibres and cells. The reagent is prepared by dissolving chlorine to
saturation in water. The sodium sulphite solution is prepared by
dissolving the crystallised salt in 20 parts distilled water.


_Aniline Sulphate Solution._—With this reagent lignose gives a
characteristic deep yellow colouration. A convenient strength is a 2
per cent. solution of the salt. The colour is more quickly developed
if the reagent is acidified; a few drops of sulphuric acid should
therefore be added.


_Solutions of the Aniline Colours._—Some of these are of importance
in enabling the microscopist to differentiate plant tissues. The
“affinities” of the fibre substances for these are very various in kind
and intensity. The phenomena of staining cannot be adequately treated
in our histological scheme, which is necessarily very restricted. We,
therefore, merely mention the more important colours which are used in
staining, viz., magenta, methylene blue, eosine, diphenylamine blue. A
convenient strength is a solution of 1 in 2000. (See also p. 43.)

The employment of the aniline sulphate solution, as well as of the
solutions of the aniline colours, presents no difficulties, and
therefore needs no detailed description. The former strikes a more or
less deep yellow with lignose; the aniline colours stain or dye the
tissue or fibre more or less deeply, according to its composition, and,
as it is a reciprocal action, {38} according also to the composition
of the colouring matter. In following up this subject, the student will
require to consult works on vegetable histology.


_Preparation of the objects._—The necessary preliminary to the
examination of the fibres themselves is their isolation. This is
accomplished either by means of the dissecting microscope, or more
roughly, according to circumstances. Having obtained the filaments,
they are boiled in a 10 per cent. solution of sodium carbonate until
sufficiently softened to yield easily to the “teazing” needles. In
certain cases the boiling must be supplemented by trituration in a
mortar; this, or some similar operation, is especially necessary when
the fibres are embedded in a mass of cellular tissue (parenchyma) e. g.
in the fibro-vascular bundles of monocotyledons.

Sections of the filaments are prepared by cutting in a microtome, the
filaments being previously agglutinated into a stiff bundle by means of
any of the usual stiffening solutions, and after drying, embedded in
wax in the usual way. Sections of fresh stems and tissues are cut with
a “section” razor.

Having prepared the objects, their examination under the microscope
necessarily divides itself into:—(1) the determination of external
features; (2) the diagnosis of chemical composition. The fibres
themselves will be individually considered in regard to microscopic
features.

There is one aspect of these structural features, however, which admits
of more general treatment, and in respect to this we may anticipate
with advantage, viz., the dimensions or simple elements of form. The
importance of the determination of the length and diameter of both
filaments and fibres will be readily appreciated by an inspection of
the following table, in which the numbers are given for several of the
more important.

A careful study of this table in relation to the application of these
several fibres, will show that the correlation of the latter with these
ultimate dimensions is close and essential. {39}

         TABLE OF LENGTHS OF RAW FIBRES (FILAMENTS) AND DIMENSIONS OF
                       CONSTITUENT CELLS AND FIBRES.

  ---------------------------------------------+-------------+-----------+---------------------
                                               |             |           |  Diameter of Cells.
                                               |  Length of  | Length of +-----------+---------
                                               |  Filament.  |  Fibres.  |  Extreme. | Normal.
  ---------------------------------------------+-------------+-----------+-----------+---------
                                               |     cm.     |    cm.    |  1⁠/⁠100mm. | 1⁠/⁠100mm.
  A. _Seed hairs._ Filaments composed          |             |           |           |
     of individual cells.                      |             |           |           |
                                               |             |           |           |
        _Cottons._                             |             |           |           |
           _Gossypium barbadense_ (Sea Island) |    4·05     |   4·05    | 1·92–2·79 |  2·52
           _Gossypium acuminatum_              |    2·84     |   2·84    | 2·01–2·99 |  2·94
           _Gossypium arboreum_                |    2·50     |   2·50    | 2·00–3·78 |  2·99
                                               |             |           |           |
        _Bombax heptaphyllum_                  |    2–3      |   2–3     | 1·9–2·9   |   ..
                                               |             |           |           |
  B. _Bast fibres._ Filaments or fibre         |             |           |           |
     bundles, made up of individual            |             |           |           |
     fibre-cells aggregated together.          |             |           |           |
                                               |             |           |           |
        _Flax._ Linum usitatissimum            |   20·140    | 2·0–4·0   | 1·2–2·5   |  1·6
                                               |             |           |           |
        _Hemp._ Cannabis sativa                |  100–300    |    ..     | 1·5–2·8   |  1·8
                                               |             |           |           |
        _China Grass._ Boehmeria nivea         |     ..      |  22·0     | 4·0–8·0   |  5·0
                                               |             |           |           |
        _Ramie._ Boehmeria tenacissima         |     ..      |   8·0     | 1·6       |  ..
                                               |             |           |           |
        _Jute._                                |             |           |           |
           Corchorus capsularis                |  150–300    |    ·8     | 1·0–2·0   |  1·6
           Corchorus olitorius                 |  150–300    |    ·8     | 1·6–3·2   |  2·0
                                               |             |           |           |
        _Paper mulberry._ Broussonetia         |             |           |           |
           papyrifera                          |     ..      |  ·7–2·1   |    ..     |  3·6
                                               |             |           |           |
        _Linden bast._ Tilia grandifolia       |     ..      | 1·1–2·6   |    ..     |  1·5
                                               |             |           |           |
  C. Fibro-vascular bundles                    |             |           |           |
                                               |             |           |           |
        _New Zealand Flax._ Phormium tenax     |    80–110   | 2·5–5·6   |  ·8–1·9   |  1·3
                                               |             |           |           |
        _Aloe._ Aloe perfoliata                |    40–50    | 1·3–3·7   | 1·5–2·4   |   ..
                                               |             |           |           |
        _Esparto._ Stipa tenacissima           |    10–40    | 0·5–1·9   |  ·9–1·5   |   ..
  ---------------------------------------------+-------------+-----------+-----------+---------

A very important point in the diagnosis of a raw material, and next in
order of treatment, is the degree of purity of the substance, in so
far as this is related to structure. The fibres may be associated with
cellular tissue, or with cellular debris, if they have undergone the
retting process or other treatment for separation; or with “encrusting
and intercellular substances” in various proportions. In the latter
case the association with the fibres is usually much more intimate;
they are in fact essential constituents of the fibre _bundles_ {40}
(bast-fibres, fibro-vascular bundles), whereas the former we may
regard as “foreign matter.” We may, however, distinguish between the
normal incrustation of the fibre-cells, and such an incrustation of
the filaments as would be described as a loose adhesion of non-fibrous
matter. The latter is seen in such tissues as the bast of the
adansonia, and the fibro-vascular bundles of the aloes. These are
points with which observation alone can familiarise the student; as
experience grows he will find it increasingly easy to follow _general_
distinctions, and in proportion as he uses his own faculties, so he
will be able to generalise for himself. He will find this equally
true of the second section of the microscopic examination, i.e., the
micro-chemical diagnosis of fibres. Under this head is included the
observation of the behaviour of fibres towards the various reagents
above described. In addition to their microscopical employment it is
useful to note their effect on fibres in the gross, both in their
natural state and after treatment with bleaching agents.

In applying the iodine reaction, attention must be paid to the
following details of manipulation. Place the object (dry) upon the
glass slide, moisten with a few drops of the iodine solution, cover
with a glass slip and examine under the microscope. Note the effects,
which are those of the iodine alone. Then remove the iodine solution
by means of blotting paper, and introduce the sulphuric acid by the
method of “irrigation.” The colouration of the cellulose (blue-violet)
is immediate; it has the effect moreover, of bringing out more clearly
a number of the structural details of the fibre.

We have already treated of the resolution of the raw fibres into
cellulose and non-cellulose constituents by processes which convert
the latter into soluble derivatives. The student will derive much
instruction from following up the attendant structural disintegration
with the aid of the microscope. The chemical dissection of lignified
fibres by the alternate action of bromine water and alkalis, should
be studied by mounting specimens of the fibre at all stages and {41}
carefully noting all the changes which occur. The more drastic action
of chlorine should also be studied by mounting the chlorinated fibre
(in water) and then irrigating with the alkaline solvent (caustic
alkali or sulphite) and noting the stages in the completion of the
disintegration.

{42}




CHAPTER III.

SCHEME FOR THE DIAGNOSIS AND CHEMICAL ANALYSIS OF PLANT SUBSTANCES.


It will be convenient at this point to present to the reader a general
scheme for the chemical analysis of fibrous raw material.

We have already discussed (p. 4) the methods for the determination of
cellulose in fibrous substances. This is to the paper-maker the most
important constituent, and is that upon which his calculations of the
value of a raw material are based. Not only, however, is it of the
greatest importance for him to be able accurately to determine the
_amount_ of cellulose, but it is necessary to be able to form some
idea of the _nature_ of the cellulose and also the ease with which it
can be obtained from the fibre. This latter point can only be properly
established by direct trial of the fibre under the conditions existing
in the factory. It should also be borne in mind that these conditions
influence to a considerable degree the amount of cellulose, actually
obtained in practice, and that therefore the percentage shown by a
careful determination in the laboratory should only be taken as an
indication of the amount likely to be realized. The student will be
able, from what has been said before of the properties of the different
celluloses, to apply his knowledge to a determination of any particular
specimen. In order to supplement this knowledge, it may be well at this
particular point to cite the chief results of an investigation bearing
upon this point by Webster (Chem. Soc. Journ., 1883, p. 23).

His method of investigation consisted in (1) estimating {43} the
cellulose; (2) determining the loss sustained by the fibre when boiled
for 5 minutes, and also for 60 minutes, with an alkaline solution
(caustic soda 1 per cent. Na_{2}O), the former being taken to represent
the purely solvent action, the difference between the two amounts being
an indication of the _degrading_ action of the soda; (3) determining
the ultimate composition (C H and O) of the fibre substance. It should
be observed that the specimens were carefully averaged and purified by
boiling in glacial acetic acid and in alcohol. On carefully considering
the following table it will be seen that the chief points brought
out by Webster’s investigation are (1) the association of a low
carbon percentage with pectous properties and considerable degrading
action on long boiling in alkali. The bearing of this will be better
understood in connection with a discussion of the properties of pectic
acid (p. 28) and the oxycelluloses (p. 13). (2.) The influence of the
composition of the original fibre on the isolated cellulose.

The solutions of aniline sulphate and of the aniline colours give
valuable aid in a diagnosis of plant substances. Webster observed, as
was to be expected, that the yellow colour produced could be taken as
an indication of the amount of lignification, those fibres which were
of a pectous nature showing little or no colour. On the other hand,
when the fibres were treated with a neutral solution of the so-called
alkali-blue it was found that the converse took place, highly pectous
fibres being dyed much more deeply than those which were lignified.
(Compare the action of aniline colours on oxycellulose, p. 11.)

If the student require more precise knowledge of the nature of
a fibrous material than that afforded by a determination of the
cellulose, the following method of analysis will prove of service.

{44}

  FIBRO-VASCULAR BUNDLES OF MONOCOTYLEDONOUS PLANTS.
     ----------------------+------------+------------+--------------+--------------+--------------+
                           |            |            |   Ananassa   |     Musa     |   Phormium   |
                           |   Agave    |   Yucca    |    sativa    |  paradisiaca |    tenax     |
                           | Americana. |  gloriosa. |(Pine Apple.) |  (Manilla).  | (New Zealand |
                           |            |            |              |              |    Flax).    |
     ----------------------+------------+------------+--------------+--------------+--------------+
     1. Yield of cellulose |   81·2     |   80·8     |   76·3       |   62·8       |   86·3       |
        by chlorine method |            |            |              |              |              |
                           |            |            |              |              |              |
     2. Character of       |Fibres free.|Fibres free.| Fibres       |Fibres        | Fibres       |
        isolated cellulose |            |            | agglutinated.|agglutinated. | partially    |
                           |            |            |              |              | agglutinated.|
                           |            |            |              |              |              |
     3. Loss in boiling 1  |    9·9     |   14·5     |   9·6        |   18·6       |   5·8        |
        per cent. caustic  |            |            |              |              |              |
        soda (5 minutes)   |            |            |              |              |              |
                           |            |            |              |              |              |
     4. Ditto (60 minutes) |   14·6     |   16·5     |   19·0       |   31·7       |   9·9        |
                           |            |            |              |              |              |
     5. Ash                |    1·0     |   1·3      |   1·0        |   1·6        |   0·9        |
                           |            |            |              |              |              |
     6. Elementary     C.  |   45·9     |   ..       |   42·5       |   42·6       |   44·4       |
        composition    H.  |    6·1     |   ..       |   5·6        |   5·6        |   5·9        |
                           |            |            |              |              |              |
     7. Lignified or       |Lignified.  |Lignified.  |Lignified.    |Lignified.    |Lignified.    |
        otherwise. Aniline |            |            |              |              |              |
        sulphate reaction  |            |            |              |              |              |
     ----------------------+------------+------------+--------------+--------------+--------------+

  BAST FIBRES OF DICOTYLEDONOUS PLANTS.
     ----------------------+---------------+------------+------------+--------------+-------------+------------
                           |               |   Urtica   | Crotolaria |              |    Linum    |  Corchorus
                           |   Boehmeria   |heterophylla|   juncea   |   Hibiscus   |usitatissimum| capsularis
                           |     Puya.     | (Nilgherry |   (Sunn).  |  strictus.   |   (Flax).   |   (Jute).
                           |               |  Nettle).  |            |              |             |
     ----------------------+---------------+------------+------------+--------------+-------------+------------
     1. Yield of cellulose |     83·8      |   95·0     |   76·9     |   63·0       |   82·0      |   75·0
        by chlorine method |               |            |            |              |             |
                           |               |            |            |              |             |
     2. Character of       |Fibres         |Fibres free.|Fibres free.| Fibres       |Fibres free. |Fibres free.
        isolated cellulose |partially      |            |            | partially    |             |
                           |agglutinated.  |            |            | agglutinated.|             |
                           |               |            |            |              |             |
     3. Loss in boiling 1  |     15·6      |   2·6      |   5·3      |   13·7       |   7·8       |   17·2
        per cent. caustic  |               |            |            |              |             |
        soda (5 minutes)   |               |            |            |              |             |
                           |               |            |            |              |             |
     4. Ditto (60 minutes) |     24·1      |   7·3      |   10·7     |   25·5       |   16·6      |   18·6
                           |               |            |            |              |             |
     5. Ash                |      3·7      |   1·0      |   0·9      |   2·0        |   1·7       |   1·1
                           |               |            |            |              |             |
     6. Elementary     C.  |     41·8      |   42·9     |   ..       |   ..         |   43·7      |   47·1
        composition    H.  |      6·0      |   5·9      |   ..       |   ..         |   5·9       |   5·9
                           |               |            |            |              |             |
     7. Lignified or       |      Not      |   Not      | Lignified. | Lignified.   |   Not       |Lignified.
        otherwise. Aniline |  lignified.   | lignified. |            |              | lignified.  |
        sulphate reaction  |               |            |            |              |             |
     ----------------------+---------------+------------+------------+--------------+-------------+------------

About two grms. are taken and dried at 110–115° C. until the weight
remains constant: the loss represents water. The fibre is then treated
with a hot mixture of benzene and alcohol, dried as before and weighed:
the loss is fat, wax, {45} &c. The residue from this treatment is then
repeatedly exhausted with boiling water and again dried at 110–115° C.
and weighed: the loss is put down as aqueous extract. The exhausted
fibre is then treated for cellulose by either of the methods given on
p. 19. The ash is determined in a separate portion.

{46}




CHAPTER IV.

AN ACCOUNT OF THE CHEMICAL AND PHYSICAL CHARACTERISTICS OF THE
PRINCIPAL RAW MATERIALS.


This chapter contains the results obtained from an investigation of the
different plant fibres by the methods indicated in the two previous
chapters.

In the following table the fibres are classified according to the
reactions which they give with iodine solution.


     CLASSIFICATION OF PLANT FIBRES ACCORDING TO THEIR COLOUR
          REACTION WITH IODINE SOLUTION (VÉTILLART).

                    A.              B.                  C.
                Seed Hairs.   Dicotyledonous     Monocotyledonous
                               Bast Fibres.    Fibres corresponding
                                                 to Bast Fibres.

  Blue reaction
                  Cotton.      Linen.              Straw.
                               Hemp.               Esparto.
                               China grass.        Pine apple.
                               Paper mulberry
                               Sunn.
  Yellow reaction
                               Jute.               New Zealand flax.
                                                   Yucca.
                               Hibiscus.           Aloe.
                                                   Manilla hemp.


Class A. COTTON.—Genus, _Gossypium_. Order, _Malvaceæ_. Seed hairs,
consisting of ultimate fibres. Length, 2·0–4·0 c.m., diameter,
0·012–0·037 mm. Mean ratio, 1250. Illustrated in Fig. 5: _a_, sections;
_b_, longitudinal views; _c_, ends; mag. 300.

Microscopic features.—Fibres simple, opaque, flattened, always more or
less twisted upon itself, side wall membranous, showing striæ. {47}

Sections.—Simple, oval, irregular, central cavity often containing
granules.

Micro-chemical reaction.—Blue with iodine solution.

[Illustration: FIG. 5.]

General chemical characteristic.—Pure cellulose basis with slight
admixture of colouring matters, &c.

            COMPOSITION OF RAW FIBRE.

                                       Church.   Müller.
  Cellulose                             91·15     91·35
  Fat                                    0·51      0·40
  Aqueous extract (containing
      nitrogeneous substances)           0·67      0·50
  Water                                  7·56      7·00
  Ash                                    0·11      0·12
  Cuticular substance (by difference)     ..       0·63

E. Schunck in his investigation of cotton bleaching (Chem. News, 17,
p. 11) finds that in boiling with sodium carbonate solution the fibre
loses 5 per cent. in weight. Some portion of the dissolved substances
is precipitated on acidifying and is found to contain a wax, brown
resinous and colouring matters, and pectic acid. {48}

Forms in which employed.—Fibrous refuse from the decortication of the
seeds; spinning waste, threads, rags, new and old.


Class B. FLAX.—Genus, _Linum_. Order, _Linaceæ_, Bast fibres and
filaments. Length of fibres, 25–30 mm.; diameter, 0·02 mm., ratio,
1200. Illustrated in Fig. 6: _a_, sections of the fibres, isolated
and in groups; _b_, the fibres viewed longitudinally, one showing the
creases produced by repeated bending; _c_, ends; _a′_, sections of
fibres situated near the butt of the plant; mag. 300.

[Illustration: FIG. 6.]

Microscopic features.—Fibres transparent, regular, with tapered ends,
side walls thick, consequently central canal small, smooth externally,
sometimes slightly striated. Filaments easily split up into fibres.

Sections.—Polygonal, regular, angles more or less acute, lumen
represented by point; slight indications of concentric arrangement of
fibre substance.

Micro-chemical reaction.—Blue with iodine solution.

General chemical characteristic.—Pecto-cellulose.

Composition of raw fibre.—This varies with the different species, and
is doubtless also influenced by variations in the {49} processes of
retting. The following are the analyses of two samples of Belgian flax
(heckled):—

                         Müller.
  Cellulose          81·99   70·55
  Fat and wax         2·37    2·34
  Aqueous extract     3·62    5·94
  Pectous substances  2·72    9·29
  Water               8·60   10·56
  Ash                  ·70    1·32

The chemistry of the flax fibre has been investigated by Kolb.

Forms in which employed.—Scutching refuse, spinning waste, threads,
rags, new and old.


HEMP.—_Cannabis sativa._ Order, _Cannabinacæ_. Bast fibres: length,
22 mm.; diameter, 0·022 mm.; ratio, 1000. Illustrated in Fig. 7:
_a_, _a′_, sections of groups of fibres of the first and second zone
respectively; _b_, fibres seen longitudinally; _c_, ends; mag. 300.

[Illustration: FIG. 7.]

Microscopic features.—Compact bundles. Fibres show striæ and fissures,
and often fibrillæ, detached or adherent. The central canal almost
obliterated, ends of fibres large and flattened. The bundles show fine
transverse markings. {50}

Section.—Well marked concentric zones of fibre substance, irregular in
outline.

Micro-chemical reaction.—Blue and yellow reaction with iodine solution,
the joint result showing green colouration.

General chemical characteristic.—Pecto-cellulose.

  COMPOSITION OF RAW FIBRE (ITALIAN HEMP).

                    Müller.
  Cellulose          77·13
  Fat and wax          ·55
  Aqueous extract     3·45
  Pectous substances  9·25
  Water               8·80
  Ash                 0·82

Forms in which employed.—Scutching refuse, spinning waste, threads,
cuttings and rope ends.


SUNDA or SUNN HEMP.—Genus, _Crotalaria_. Order, _Papilionaceæ_. Bast
filaments: length, 7–8 mm.; diameter, 0·03; ratio, 200 : 1.

Microscopic features.—Generally similar to those of hemp.

Micro-chemical reactions.—With iodine various, from blue to yellow.
With aniline sulphate, slight yellow.

General chemical characteristics.—Pecto-cellulose (with some
ligno-cellulose).

The following are the results of analysis of the raw fibre (H. Müller):—

  Cellulose           80·01
  Fat and wax           ·55
  Aqueous extract      2·82
  Pectous substances   6·41
  Water                9·60
  Ash                  0·61

This fibre, exported from India and the Sunda Islands, has found
employment in Spain and Portugal, but up to the present has not been
adopted to any extent in other parts of Europe.


CHINA GRASS, RHEA, RAMIE.—Genus, _Bōhmeria_. Order, _Urticaceæ_.
Bast filaments: length, 120 mm.; diameter, 0·05; ratio, 2400 : 1.
Illustrated in Fig. 8: _a_, section of a {51} bundle of fibres; _b_, a
fibre seen longitudinally; _c_, ends; mag. 300.

[Illustration: FIG. 8.]

Microscopic characteristics.—Irregular in form and length; often
conspicuous in respect of latter (see Table, p. 39); fibre sometimes
cylindrical, either smooth or striated, sometimes flattened; central
canal well developed, often containing granules; extremities of fibres
rounded, spatulated or lance-shaped. Sections marked by numerous
concentric layers, often showing radiating striæ.

Micro-chemical reaction.—Blue to violet, with iodine solution.

General chemical characteristics.—Pecto-cellulose.

  Composition of raw fibre (H. Müller):—

  Cellulose            75·83   62·50
  Fat and wax            ·20    0·56
  Aqueous extract       6·29    9·76
  Pectous substances    6·07   12·00
  Water                 8·74    9·55
  Ash                   2·87    5·63

Forms in which employed.—Up to the present the price has been
prohibitive. Has been the subject of successful {52} experiments;
imparts great tensile strength to paper. The portions available will be
as in flax.


COMMON NETTLE.—_Urtica dioica._ Order, _Urticaceæ_. Bast filaments:
length, 27 mm.; diameter, 0·05; ratio, 550. Microscopic characteristics
similar to the above.

The fibres of this plant were, in the olden times, separated in the
same way as flax, and worked up into cloth. At present it has no
practical interest to the paper-maker, but deserves attention at the
hand of the student, as the most easily accessible for the purpose of
study. It is, moreover, possible that, under cultivation, it may yet
become a source of raw material for paper-making.


JUTE.—_Corchorus._ Order, _Tiliaceæ_. Bast: length, 2 mm.; diameter,
0·022; ratio, 90. Illustrated in Fig. 9: _a_, section of bundles of
fibres; _b_, fibres seen longitudinally; _c_, ends; mag. 300.

[Illustration: FIG. 9.]

Microscopic features.—Compact bundles; fibres smooth.

Micro-chemical reactions.—Yellow brown, with iodine; yellow, with
aniline sulphate; bright yellow, with chlorine water; changed to
carmine by treatment with sodium sulphite solution. {53}

General chemical characteristic.—Ligno-cellulose. The chemistry of jute
as the type of ligno-cellulose has been treated on p. 17.

  Composition of raw fibre (Müller):—

                                      Cuttings or Butts.
                         1st Quality.     (Root ends).
  Cellulose                  63·76           60·89
  Fat and wax                 0·38             ·44
  Aqueous extract             1·00            3·89
  Non-cellulose, or lignin   24·32           20·98
  Water                       9·86           12·40
  Ash                          ·68            1·40

Forms in which employed.—Threads, butts, bagging.


BAST TISSUES.—We have alluded, in our opening remarks, to the broad
division of the bast of exogen or dicotyledonous plants into coherent
and non-coherent tissues. We have now considered the more important
of the latter, and we find that they are obtained from the stems of
annuals. We find also that while they constitute a tissue, in the sense
of being definitely localised, the constituent fibres are disposed in
parallel series of independent bundles or filaments, which are isolated
by a mechanical operation after the whole stem has undergone the
preparatory retting process. In exogens of longer and larger growth,
the bast, as might be expected, becomes a coherent compound tissue,
which is, in many cases, easily detached from the underlying wood. We
shall mention three of these as receiving very important applications;
though only one has been applied to any extent by the papermakers of
this country. This, which we shall consider first, is the bast of
the _Adansonia digitata_, or baobab, a tree which flourishes in the
tropical regions of the West Coast of Africa. It is exported chiefly
from Loanga, in the form of fibrous lumps of a brown colour. These
are seen to be composed of a network of bast bundles, which are but
slightly coloured, intersected by medullary rays of a dark brown
colour. The microscopic features of the fibre are those which are
generally characteristic of the bast of exogens; we do not know that we
could cite any whereby it could be identified with certainty. {54}

The fibres give a yellow colouration with aniline sulphate, but they
contain only a small proportion of lignose. The following are the
results of analyses of this bast:—

  Cellulose               49·35     58·82[7]
  Fat and wax              0·94      0·41
  Aqueous extract         13·57      7·08
  Pectous substances      19·05     15·19
  Water                   10·90     13·18
  Ash                      6·19      4·72

     [Footnote 7: Made up of 13·75 cellulose from medullary tissue,
     45·07 cellulose of fibres.]


_Linden Bast_ (_Tilia Europæa_) is the raw material employed in the
manufacture in Russia of the mats so largely used in this country for
wrapping furniture and heavy goods, and also by gardeners for a variety
of purposes. One of the features of this bast is the strong cohesion
of the fibres in the bundles or filaments. They are resolved, but with
difficulty, on long boiling, with a solution of carbonate of soda, the
soluble products being of a mucilaginous nature. This bast has not been
applied to any extent by the paper-makers of this country.


_Bast of the Paper Mulberry_ (_Broussonetia papyrifera_).—This
product deserves mention, not from its importance to the European
papermaker, but because of its application to the manufacture of the
peculiar papers of the Chinese and Japanese. The special features
of this, and the other basts which are similarly employed in these
countries—_Edgworthia papyrifera_, _Broussonetia kaempferia_, are (1),
the ease with which the coherent fibrous tissue is separated from
the parenchymatous tissue which accompanies it; (2), its comparative
freedom from medullary rays; (3), the great length and fineness of the
fibres. These properties conduce to its ready conversion into a well
felted paper, of great tensile strength and remarkable softness.


Class C.—These are whole stems of monocotyledonous annuals. The
isolation of fibres for paper-making from these plants depends upon a
chemical process of resolution; the {55} pulp obtained is, therefore,
a complex of the various orders of cell-fibres contained in the plant.
While the pulp consists for the most part of the vessels of the
fibro-vascular bundles, it contains in addition the serrated cuticular
cells which are so characteristic of this group. They therefore present
a general similarity in microscopic features; there are, however,
certain individual characteristics, such as the form and dimensions of
particular cells, which serve for the identification of the various
pulps. Where such occur they will be indicated.

[Illustration: FIG. 10.]


ESPARTO.—_Stipa tenacissima_ and _Lygeum Spartum_.

Order, _Gramineæ_. Bast fibres of fibro-vascular bundles. Length,
1·5 mm.; diameter, 0·012 mm.; ratio, 125. Illustrated in Figs. 10,
11. In Fig. 10, the fibro-vascular {56} bundles _f_ are seen spread
throughout the interior of the leaf, but the intervals, instead of
being occupied by parenchyma, with large cells and thin walls, are
filled with a compact mass of fine solid fibres _f′_; _e_, external
epidermis; _e′_, internal epidermis; mag. 100. In Fig. 11, _a_ is a
section of a group of fibres; _b_, fibres seen longitudinally; _c_,
ends; mag. 300.

[Illustration: FIG. 11.]

Microscopic features.—Short, smooth, cylindrical, uniform in diameter,
central canal very small, extremities rounded, truncated and bifurcated.

Section.—Minute, generally oval, sometimes polygonal; central cavity
represented by a point.

Micro-chemical reaction.—Both blue and yellow with iodine solution.

In examining a paper containing esparto under the microscope, the
pulp will be found to contain, in addition to the fibres of the
fibro-vascular bundles, a certain number of the cuticular cells (see
Fig. 12), together with some of the fine hairs which are seen in the
section (Fig. 10). These are very characteristic.

General chemical characteristics.—Pecto-cellulose mixed with some
ligno-cellulose. {57}

  Composition (Hugo Müller):—

                             Spanish.  African.
  Cellulose                    48·25    45·80
  Fat and wax                   2·07     2·62
  Aqueous extract              10·19     9·81
  Pectous substances, &c.      26·39    29·30
  Water                         9·38     8·80
  Ash                           3·72     3·67


STRAW.—Order, _Gramineæ_.

Microscopic features.—Generally similar to those of esparto. There are,
however, differences of shape and dimensions of the serrated cuticular
cells, which differentiate the various kinds of straw from each other
and from esparto.

[Illustration: FIG. 12.]

In Fig. 12 are shown these cells, from maize-straw (_a_ and _b_); from
rye-straw (_c_) and from esparto (_d_). The {58} following table gives
the dimensions of the cells from different kinds of straw:—

                Length.            Breadth.
  Barley     0·103–0·224 mm.    0·012–0·014 mm.
  Rye        0·086–0·345  „     0·012–0·016  „
  Wheat      0·152–0·449  „     0·018–0·024  „
  Oats       0·186–0·448  „     0·012–0·017  „

Another distinctive feature of straw-fibre is the presence in it of a
number of oval cells, derived from the pithy matter attached to the
inside of the stem. These are clearly shown at _b_ (Fig. 13), which
represents the general appearance of straw pulp.

[Illustration: FIG. 13.]

General chemical characteristics.—Both ligno-cellulose and
pecto-cellulose.

The following are the results of analyses of straws (Hugo Müller):—
{59}

                           Winter Wheat.   Winter Rye.
  Cellulose                    46·60         47·69
  Fat and wax                   1·49          1·93
  Aqueous extract               8·07          0·05
  Non-cellulose or lignin      28·49         26·75
  Water                         9·85         11·38
  Ash                           5·50          3·20


BAMBOO AND SUGAR CANE.—Order, _Gramineæ_.

From the close botanical relationship of these products to the stems
of the gramineæ of our own climate, their microscopic features are, as
might be expected, similar to those of straw. The similarity is further
shown by the chemical composition (Hugo Müller):—

                                   Air-dried
  Cellulose                          50·13
  Fat and wax                          ·78
  Aqueous extract                    10·56
  Lignin and pectous substances      24·84
  Water                               8·56
  Ash                                 5·13


NEW ZEALAND FLAX.—_Phormium tenax._ Order, _Lineaceæ_. Fibro-vascular
bundles of the leaves.

Microscopic characteristics.—Length of fibres, 9 mm., diameter 0·016
mm., ratio, 560. Fibres are fine, regular and smooth; the walls are
uniform, central canal small, extremities vesicular. The fibres have
little cohesion in the bundle. Sections round or polygonal. Illustrated
in Fig. 4, p. 35.

Micro-chemical reaction.—Yellow, with iodine solution. Characteristic
deep red colouration with concentrated nitric acid (Müller).

General chemical characteristic.—Ligno-cellulose. It contains 86·3 per
cent. of cellulose.


MANILLA HEMP.—_Musa textilis_, Abacá. Order, _Musaceæ_. Fibro-vascular
bundles of leaves.

Microscopic characteristics.—Length of fibres, 6 mm.; diameter, ·024
mm.; ratio, 250. Fibres, white lustrous; the walls are uniform; central
cavity large and very apparent. Fibres easily detached. {60}

Sections round or polygonal. Illustrated in Fig. 14: _a_, section of
bundle of fibres; _b_, fibres seen longitudinally; _c_, ends; mag. 300.

[Illustration: FIG. 14.]

Micro-chemical reaction.—Yellow with iodine solution.

  Composition (Hugo Müller):—

  Cellulose                          64·07
  Fat and wax                          ·62
  Aqueous extract                      ·96
  Lignin and pectous substances      21·60
  Water                              11·73
  Ash                                 1·02


WOOD.—Nearly, if not the whole of the chemical wood pulp used in this
country is obtained from trees belonging to the order _Coniferæ_
(Gymnospermæ), more particularly from the genera _Abies_ and _Pinus_.

In America, however, poplar and other woods are largely employed. The
coniferæ yield a larger proportion of pulp than most other woods, the
individual fibres, moreover, are longer, and for these reasons it is
generally preferred. On the other hand, however, poplar is more readily
acted upon by reagents. Fig. 15 gives the microscopic appearance of
{61} the fibre of the common white fir. It is characterised by the
presence of numerous pitted vessels (Fig. _a_).

[Illustration: FIG. 15.]

Pine wood consists essentially of a compound cellulose, resembling in
most of its properties the jute fibre (see p. 16). With iodine solution
it gives a deep yellow colour. The chemical composition of some of the
more important woods will be seen from the following analyses. (Müller.)

  ----------------+------+------+-----+-----+-------
                  |Birch.|Beech.|Lime.|Pine.|Poplar.
                  +------+------+-----+-----+-------
  Cellulose[8]    | 55·52| 45·47|53·09|56·99| 62·77
  Resin           |  1·14|  0·41| 3·93| 0·97|  1·37
  Aqueous extract |  2·65|  2·41| 3·56| 1·26|  2·88
  Water           | 12·48| 12·57|10·10|13·87| 12·10
  Lignin          | 28·21| 39·14|29·32|26·91| 20·88
  ----------------+------+------+-----+-----+-------

     [Footnote 8: For the amounts of cellulose actually obtained in
     practice see p. 77.]

The above results are calculated on the ash-free wood. The ash varies
from about 0·3 to 0·7 per cent.

{62}




CHAPTER V.

PROCESSES FOR ISOLATING CELLULOSE FROM PLANT SUBSTANCES.


We are now in a position to discuss generally the various methods
by which the paper-maker obtains cellulose from the different raw
materials. The special treatments necessary for each of the more
important of these will be given more fully subsequently. These
methods, though they vary considerably with the different materials
to be treated, may be roughly divided into two groups—the alkaline
and the acid processes. The former, which we will call _a_, comprises
all processes in which caustic soda, carbonate of soda and lime, or
mixtures of these are employed; the latter, _b_, the various processes
which have been introduced of late years, involving the use of
sulphurous acid, either alone or in combination with a base, such as
lime or magnesia.

The processes in group _a_ may be applied to the treatment of every
known fibrous vegetable material; those in group _b_ are at the present
time applied exclusively to the preparation of pulp from wood.

Group _a_ may be conveniently subdivided according to the nature of the
materials operated upon.

It is obvious that those materials, such as bleached cotton and linen
threads and rags, which have already undergone treatment by the textile
manufacturer, and are therefore more or less already in the state of
pure cellulose, require but little chemical treatment at the hands of
the paper-maker, whose attention is therefore chiefly directed to the
removal of such adventitious matters as size, grease, &c. This can
generally be effected by the employment of weak solutions of caustic
soda, or even of lime at a low pressure. {63}

We now have to consider the treatment of those materials which consist
of the compound celluloses.

All methods for the isolation of cellulose from the compound celluloses
depend upon a hydrolytic resolution of their constituents, i.e. a
splitting up by combination with water into cellulose on the one hand,
and a series of soluble derivatives on the other. This, as will be
shown, may to a certain extent be accomplished by the action of water
itself at a high temperature. As, however, the products of such an
action are acid bodies, which, if allowed to remain in contact with the
cellulose, would injuriously affect it, and would induce the production
of complicated bodies, the removal of which from the cellulose would
become increasingly difficult, it is necessary to have present a body
such as caustic soda, which by combining with these acid bodies,
removes them as such from the sphere of action.

In certain raw materials, such as straw and esparto, we have, in
addition to the compound celluloses which form, so to speak, the
groundwork, a certain proportion of fatty and resinous bodies, whose
removal is brought about by the action of the caustic soda converting
them into soaps.

The compound celluloses may be divided, as we have seen, into three
classes—pecto-celluloses, ligno-celluloses, and adipo-celluloses. The
last-named being present in only a few paper-making materials, and then
only in very small proportion, is without any practical interest. We
are concerned therefore with the two former only.

(1) _Pecto-celluloses._—From what we have seen of the nature of the
pecto-celluloses, it follows that for their resolution a tolerably
simple treatment with soda will be sufficient.

The chief members of this group in which the paper-maker is interested,
are esparto and straw. The former being but very slightly lignified,
its resolution can be effected at a very low pressure; in fact it is
even possible by using tolerably strong solutions to do it by boiling
in open vessels.

Straw, on the other hand, though it possesses certain features in
common with esparto, is more lignified, and in {64} consequence,
necessitates a much more energetic action to complete its resolution.
It is therefore usual to boil it at somewhat high pressures (40–70
lb.), and with larger quantities of soda than are demanded in the case
of esparto. It is, moreover, essential, so to regulate the treatment,
that even the most resistent portions of the straw, such, for example,
as the knots, shall be completely resolved, otherwise unbleached
portions are liable to find their way into the finished paper. By
increasing the quantity of soda, it is possible to boil under reduced
pressure, and _vice versâ_; this may be taken as a general principle
applicable in all other cases.

We now come to the second class of celluloses, that is to say, the
ligno-celluloses. Of these, perhaps the most important are jute,
manilla, and wood.

For their _complete_ resolution, it is imperative to employ very strong
solutions at very high temperatures and pressures; thus in the case
of wood it is necessary to boil at temperatures corresponding to a
pressure of 100–120 lb. per square inch.

The use of strong caustic soda solutions at high temperatures is
attended with very serious objections, apart from the question of
cost. Among these may be mentioned the destructive action of the soda
upon the cellulose itself, involving a considerable loss of pulp;
the de-hydration, condensation, and oxidation of the non-cellulose
portion of the fibre (which, as we have seen (p. 25) is of the nature
of an aldehyde, and therefore peculiarly susceptible of such changes),
and the formation of dark coloured products which remain intimately
combined with the residual cellulose; the inconvenience of working at
very high temperatures and pressures.

With a view to removing the difficulties attending the use of soda,
various processes have from time to time been proposed, in which the
hydrolytic agent is a solution of sulphurous acid in water, either
alone or in combination with a base. These processes are comprised
under group B. {65} Several of them have lately acquired great
commercial and industrial importance, and a clear understanding of them
is therefore essential to the student of paper-making.

Though applicable to lignified fibres generally, they have only been
applied up to the present time to wood, and it is in this connection,
therefore, that we propose to consider them.

In order to bring out more clearly the fundamental differences
underlying the two classes of processes, it will be well to consider,
somewhat in detail, these processes, which, although they have now
a merely historical interest, will assist the student in thoroughly
grasping the rationale of the modern and improved methods.


Water Process.—Wood is to a certain extent resolved by treatment with
water at a high temperature, the degree of disintegration being,
within certain limits, proportional to the temperature at which it is
digested. The volatile products of the resolution are chiefly acids
of the acetic series, furfurol and terpenes. The non-volatile soluble
products are for the most part acids. This process was studied by
Fry, who, in 1866, made it the subject of a patent. He found that
under the most favourable conditions of treatment, the yield of brown
pulp amounted to 70 per cent. of the wood employed. The objections
to the process were sufficiently obvious: the pulp produced was of
low quality, and the soluble products acted powerfully on the iron
digesters employed. The chemical causes of its failure lie in the
prominence of the conditions which determine re-combinations of
the products of resolution with one another, viz. oxidation, high
temperature, and the presence of acids. It is worthy of note that in
one experiment the amount of acids produced from 100 parts wood were
equivalent to 3·4 parts of soda (Na_{2}O). This was by far the most
serious defect in the process, and it eventually caused its abandonment
in favour of the older method of treatment with caustic alkali.[9]

     [Footnote 9: See Journ. Soc. of Arts., February 1883, p. 223.]


Alkali Processes.—The first to develop the alkali process {66} were
Watt and Burgess, in America (1853–1857), and Houghton in this country.
To follow up the several modifications introduced is unnecessary; they
differ from one another in the economical balance which they strike
between temperature and quantity of chemicals: thus Watt and Burgess
employed a lye of 12° Baumé, and digested at 60 lb. pressure (equal
to 152° C.), whereas Houghton used a lye of 4° B., at 100–180 lb. One
great defect of these processes was the gradual neutralisation of the
alkali, necessitating as a compensating condition the employment of a
very high temperature towards the end of the operation. To overcome
this objection, Ungerer devised a process which aimed at securing a
properly graduated action of the lye. This process, being based on
an eminently rational view of the action of the alkali, is worthy of
a more extended notice, especially as the principle on which it is
founded is capable of wide application. A system of nine vertical
digesters, connected together in series by means of pipes and cocks, so
that the liquid contents can be transferred from one to the other in
succession, is the main feature of the method employed. In connection
with this system there is a double service of pipes, by which the
hot soda lye at 90 lb. pressure, and cold water, may be respectively
introduced. The operation is so conducted that in five of the digesters
wood is being treated at a high temperature, in three the pulp is being
washed, while the remaining one is being charged with fresh wood.

The whole round of operations may be described thus, numbering the
digesters according to their position in the series:—Nos. 1, 2, and 3,
Washing the finished pulp; 4, Final treatment with lye at the extreme
pressure of 90 lb.; 5, Digesting at lower pressure with lye previously
employed in 4; 6, Treatment at still lower pressure with lye which has
already done duty in 4 and 5; and so on to 8, where the liquor, having
passed through the series, is employed at 15–20 lb. pressure on a fresh
charge of wood. The washings are conducted in such a way that the water
which is introduced into 1 displaces the solution in each digester
without {67} the last being allowed to escape. The introduction of the
fresh liquor at 4 is similarly accomplished, 1, 2, and 3 being cut off
by closing the cocks which control the ingress and egress of liquid.

The pulp produced by this method is of a sufficiently pale colour to
be capable of application for many purposes without bleaching. It is
converted into a perfectly white pulp by treatment in the ordinary way
with from 3 to 4 per cent. of bleaching powder, calculated in the dry
pulp.

As far as it goes the method is practically perfect, and it appears
to have given sound results, at least as regards the main product.
The principal disadvantages were the complications attending such an
elaborate system of working which would doubtless make it costly.

We have next to consider a class of processes which are based primarily
upon the action of an alkali, but which introduce the simultaneous
action of a soluble sulphide, generally that of sodium. As far back as
1855 Jullion patented in this country a process of this nature, which,
however, does not appear to have been applied to wood. The results
obtained with such materials as straw and esparto appear to have been
very unsatisfactory, and to have led to the early abandonment of the
method.

Recently the increased attention which has been given to wood as a
raw material has led to a revival of these sulphide processes for its
treatment. We believe that at least two processes of this class are
being worked on the continent, viz. those of Dahl and Blitz.

That of the former consists in heating wood, at pressures varying
from 60–120 lb. per square inch, with a solution of the following
composition:—

  Sodium sulphate    37
  Sodium carbonate    8
  Sodium hydrate     24
  Sodium sulphide    28
  Various compounds   3
                    ───
                    100

{68}

This solution is obtained only after the process has been some time at
work, and it then remains tolerably constant.

The wood, to commence with, is boiled with a solution containing a
large quantity of sodium sulphate, with a small quantity of sodium
hydrate, obtained by boiling sodium sulphate with lime. The liquor from
this operation is then evaporated and calcined, the result being a
fused mass which, when dissolved in water, yields a liquor containing
the above-mentioned ingredients. The loss of chemicals is made up by
the addition of fresh quantities of sodium sulphate.

From experiments which the authors have made with this process, it
appears, that while it is perfectly true that pulp can be obtained,
it is necessary to employ either very strong solution or very high
pressures. This is equivalent to saying that either the hydrolytic
action is weak, or the tendencies to reversal of the hydrolysis are
strong, and indeed both are to be predicted from the nature of the
solution. One great objection to the process is that during the boiling
a quantity of very foully-smelling compounds are produced.

The process of Blitz consists in heating wood to from 50–60 lb.
pressure, with a solution of sodium sulphide, containing an
infinitesimal proportion of vanadate of ammonia.

It is difficult to see what influence the presence of the costly
vanadate of ammonia can have on the result. Actual experiment on this
point has failed to convince us of its efficacy.

Although in these sulphide processes a strongly reducing agent is
present, its effect in preventing oxidation is more than outweighed by
the weakening of the hydrolytic action of the soda, both directly by
its combination with sulphur, and indirectly by the complication which
it induces by combination with the soluble bye-products. Further, as
regards the final product, they offer no advantage over the caustic
alkali processes. There is, however, a considerable advantage in point
of economy, which should lead to their adoption in districts where the
production of malodorous gases is permitted. {69}


Acid Processes.—We now come to consider the processes which are
based upon the hydrolytic action of acids as a primary condition.
We have seen that in the water process this condition obtains as a
secondary result, and that while it aids in resolving the wood, it also
determines the limit of the action, in consequence of its promoting
secondary combination amongst the soluble products. The use of powerful
oxidising acids, such as nitric and nitro-hydrochloric, induces an
action which is sufficiently drastic to cause a complete resolution
of the non-cellulose constituents of the wood with the formation of
soluble products. The use of these acids has been made the subject of
numerous patents.

The process of Barre and Blondel consisted in digesting the wood in
the cold for twenty-four hours in 50 per cent. nitric acid, by which
it was converted into a soft fibrous mass. This was boiled for some
hours in water, afterwards in a solution of sodium carbonate, and
finally bleached in the ordinary way. Many other patents have been
taken out in this direction, but none have met with practical success,
owing doubtless, to the high cost of nitric acid, and the difficulty
of recovery. A process has lately been patented by Young and Pettigrew
(No. 14,988, 1884) in which they claim the use of either nitric or
nitrous acids; the acid fumes which are evolved being condensed and
reconverted into nitric acid. The process has not yet, however, been
tried on a practical scale.

The resolution of wood by the hydrolytic action of non-oxidising acids,
is for reasons already stated, very imperfect. An important feature,
however, of this action is the production of glucose as a bye-product,
and a process having the double object of producing this, together
with a brown pulp, was patented by Bachet and Machard in 1864, and
worked for some time in Switzerland. The process consisted in boiling
the wood for twelve hours in dilute hydrochloric acid; the solution,
which contained glucose to the amount of 20 per cent. of the weight
of the wood, was drawn off, neutralised with chalk, and fermented by
the addition of {70} yeast. Alcohol was separated from the fermented
liquor in the usual way. The residual pulp, after being ground with
stones, was made into coarse packing paper. The process failed
commercially.

The next processes in the order of the development of our subject,
but not chronologically, are those involving the use of reducing
acids, i.e. those which combine with their hydrolytic function a
de-oxidising or anti-oxidising action. Of these the only one which
has been practically investigated is sulphurous acid. A full account
of the earlier discoveries in regard to the use of this reagent, for
the special purpose under consideration, will be found in the _Papier
Zeitung_, 1884, No. 51, p. 1927; this should be consulted by those who
are interested in the history of a subject which has now grown to be of
the first importance.

The first patented process claiming the use of sulphurous acid, in the
form of its aqueous solution, for the purpose of disintegrating wood,
was that of Tilghmann (1866). So far as is known, however, the results
obtained by the inventor with the acid alone were such as to lead him
to abandon it for solutions containing a certain proportion of base.
The reasons, doubtless, were the greater facility of preparation and
simplicity of application of such solutions.

More recently Professor Pictet, of Geneva, on the basis of the
experience acquired by him in the preparation and employment of
sulphurous acid in his patent freezing processes, has revived and
perfected a process which in other hands had proved impracticable.

The method and apparatus employed will be found fully described in the
author’s specification. The process consists in digesting the wood in
closed vessels with an aqueous solution of the acid (10–12 per cent.
SO_{2}) at 176°–194° F. (80°–90° C.), and under the corresponding
pressure (60–75 lb. per square inch). A complete disintegration of
pine wood is effected in about twenty-four hours’ treatment. The
yield of pulp is, we are informed, from 40–50 per cent. of the wood
(_Pinus sylvestris_); it is also stated to be readily bleached {71}
with a moderate amount of bleaching powder, and to yield a pulp of
the highest quality. Further, the recovery of the sulphurous acid, for
which special apparatus is provided, is practically complete (95–98 per
cent.). In view of the probable utilisation of the bye-products, it is
interesting to observe that they are obtained in a form in which they
can very readily be treated.

The process being as yet undeveloped on a large scale, we cannot do
more than recommend it to the consideration of paper-makers. At the
same time we would draw attention to the features of interest which
it possesses in regard to the general aspect of our subject. The
resolution which it effects is obviously one of simple hydrolysis, and
it affords an indirect proof of the chemical complications which attend
all other processes for disintegrating wood which employ temperature
much above the boiling-point of water. The soluble bye-products are
obtained in the simplest form, and may be isolated by mere evaporation.
As regards the chemical features of the pulp, they will presumably be
different from those of any other, whether on the side of advantage or
not it remains to decide. Provided the process fulfils the condition
of economical working, we have no hesitation in predicting for it a
considerable development.

The difficulties attending the employment of a gaseous acid have
doubtless operated in deterring many, in addition to the originator,
from a complete investigation of its action, and have led them to adopt
in preference one of its several compounds with bases, the employment
of which defines a group of processes to which we now desire to call
attention. There is a variety of processes agreeing in the essential
feature of employing a bisulphite as the disintegrating reagent, and
differing from one another only in the less essential details of method.

The general principle of these processes will be readily understood
from what has gone before. The chief agency is the hydrolytic action
of sulphurous acid, aided by the conditions of high temperature and
pressure: and the subsidiary {72} agencies are—(1) The prevention of
oxidation; (2) The removal from the sphere of action of the soluble
products of resolution in combination with the sulphite as a true
double compound. This mode of union is well known to be peculiarly
characteristic of all aldehydes, to which class we have shown that the
non-cellulose constituents of wood belong. The combination is expressed
by the general equation—


  M.CHO     +  SO_{3}HNa    = M.CH(OH/SO_{3})Na.

  Aldehyde.     Sodium       Double compound.
             bi-sulphite.

(3) The removal of a portion of the constituents in combination with
the base, i.e. with expulsion of sulphurous acid.

The verification of these views has been afforded in the course of an
investigation of the bye-products from the Ekman process, undertaken by
the authors for Messrs. Thomson, Bonar & Co., the proprietors of the
patent.

As the various bisulphite processes differ chiefly in their working
details, the essential feature of the employment of a solution of
sulphurous acid, combined with a certain amount of base, being common
to them all, it will not be necessary to do more than examine one or
two typical cases. We shall select those of Ekman and Partington, the
latter being based upon Francke’s patent, with certain modifications
and additions.


(1) The Chemicals employed.—In both cases sulphur is used as the source
of the sulphurous acid. The Ekman process starts from magnesite, a
native carbonate of magnesia. This is converted by calcination into
magnesia, and in this state is introduced into lead-lined towers,
through which is passed sulphurous acid gas, obtained by burning
sulphur in suitable furnaces, while a stream of water trickles down
from the top. The supply of the gas being properly adjusted, a
continuous production of a solution of magnesium bisulphite of uniform
strength is obtained. To secure this uniformity, constant attention
is necessary, and further, the loss of sulphurous acid by oxidation
to sulphuric acid, and by diffusion, is, in consequence of its
distribution over so large a surface, {73} and with free exposure to
the air, necessarily very large. It is unnecessary, however, to point
out that the preparation of the magnesium bisulphite is capable of
very considerable modification; in fact, we understand that numerous
improvements in this direction have already been introduced by the
proprietors of the process.

Partington’s method, in addition to the advantage of starting
from lime, the cheapest of all basic substances, is free from the
disadvantages referred to as attending the use of a tower. It consists
in passing the sulphurous acid gas through a series of three vessels
connected together with pipes. Into these vessels a charge of milk of
lime is introduced, and the two first being closed air-tight, the gas
is passed in. The third remains open to the air, and from it escapes
a continuous stream of nitrogen, resulting from the removal of the
oxygen by the burning sulphur, from the stream of air which is blown
through the sulphur retort at a pressure of 5 lb. to the square inch.
The expenditure for chemicals is under 1_l._ per ton, whereas, by the
Ekman process, it has been variously estimated at from 2_l._ to 3_l._
10_s._ per ton. Provided therefore, that as good pulp can be obtained
by Partington as by Ekman, the former offers considerable advantages
both from point of view of simplicity and economy. Doubtless the cost
of chemicals could be somewhat reduced in both systems by the adoption
of a cheaper form of sulphur, such as pyrites.


Preparation of the Wood.—Although the acid sulphite processes can,
by suitable modifications, be made available for the preparation of
cellulose from almost all kinds of wood, yet it is necessary, in
order to insure uniformity of result, not only to take care that the
wood is carefully selected, but that it is freed from bark and roots,
which, if allowed to remain, would be imperfectly pulped, and would
be exceedingly difficult to bleach. The most suitable kind of wood is
_Pinus sylvestris_.

After the bark has been carefully removed the logs are sawn into boards
of ordinary sizes. This treatment {74} exposes the knots, which are
then removed either by boring or cutting out with an axe. The pieces
are then passed through a machine, which cuts them or rather breaks
them into fragments about an inch long. In order that the acid sulphite
may as quickly as possible enter into the wood, these fragments must be
crushed and opened out by passing through heavy rollers: moreover, the
wood is cut _across_ the grain, by which means it is more or less split
up into laminæ. A machine for this purpose has been patented by Fry,
Ransome, and Wilkie (No. 11,389, 1884).


The Boiling Process.—Ekman uses a lead-lined, jacketed cylindrical
boiler, suspended on trunnions, so that it can be turned upside down
for discharging. The pressure in the outer jacket is 70 lb. per square
inch, while inside the boiler it is 90 lb., the difference being due
to the tension of the sulphurous acid gas. The duration of boiling
is from ten to twelve hours. Partington, on the other hand, boils
with live steam, and therefore is enabled to use a boiler of simpler
construction. His boilers are spherical, lead-lined and rotary. The
pressure employed does not exceed 60 lb. per square inch, the time of
boiling being about sixteen hours.

Various other sulphite processes have been from time to time devised,
which differ but little either in principle or in working detail from
those described, and therefore a brief mention of them will suffice.
Mitscherlich employs a bisulphite of lime in somewhat weaker solution
than that employed by Francke or Partington, and in order to produce
the same result he is obliged to extend the time of boiling to from 40
to 60 hours.

Graham, after treating the wood with a mono-sulphite, injects into
the boiler either a solution of a bisulphite or gaseous or liquid
sulphurous acid.

Flodgvist uses a solution prepared by dissolving bones in sulphurous
acid solution.

The cellulosic products of the various processes present certain slight
differences, but so far as has been investigated, not such as to
constitute a distinct advantage for one or {75} another. One feature
of these processes, to which but little attention has hitherto been
paid, is that of the utilisation of their bye-products. These bodies
are, as already indicated, obtained in a condition not materially
different from that of the parent substance, the non-cellulose
constituents of the wood. One important property of these bodies, and
one capable of considerable application, has been made the basis of
a patent by the authors. When a solution of gelatin is added to the
liquors in which wood has been treated by any of the bisulphite or
sulphurous acid processes, a body is precipitated in the form of a
caoutchouc-like mass which can be dissolved in neutral sodium sulphite
solution, or in weakly alkaline solutions, and can be reprecipitated on
addition of alum to the solution. The substance consists of a compound
of the gelatin with the non-cellulose constituents resembling, but
not identical with, as has been supposed, the precipitate obtained
by adding tannic acid to a solution of gelatin. The solution of this
substance in sodium sulphite can be applied to many of the purposes to
which gelatin itself is ordinarily applied.

A serious objection to all processes involving the use of sulphurous
acid or acid sulphite, and one which has to some extent deterred
paper-makers from adopting them, is the necessity of using a boiler
lined with lead. In addition to the fact that such boilers are heavy
and costly, they are objectionable on account of the difficulty and
expense of keeping them in thorough repair. This difficulty arises from
the fact that, owing to the different co-efficients of expansion of
lead and iron, the lead lining originally placed in contact with the
iron or steel shell of the boiler, becoming detached on heating, swells
out in various places, which are thus rendered weaker and liable to
fracture. This is especially the case if, in the course of lining the
boiler, any air has been allowed to remain between the two linings.
Various expedients have been proposed to obviate these defects but with
only partial success. Graham (Eng. Pat. No. 5367, 1883) coats the plate
of his boiler by pouring molten lead upon the perfectly clean surface
which has been {76} previously prepared with zinc chloride. Sometimes
minute holes are drilled in the iron plate to allow the escape of air.

Notwithstanding all the attempts that have been made, the use of a
lead-lined boiler is a serious objection, and any process which will
fulfil the conditions on which the bi-sulphite processes depend, and
which at the same time admits of the use of the ordinary iron boilers,
is an obvious desideratum. Such a process is that patented by one of
the authors (Cross, No. 4984, 1880), claiming the use of solutions
of the neutral sulphites with or without the further addition of an
alkali. This process is very suitable for the treatment of fibres such
as straw, jute, &c., but not economically applicable to the preparation
of wood pulp on account of the cost of chemicals. The preservative
effect of the sulphite is shown by the largely increased yield of pulp.

The chief advantages of the various bi-sulphite processes for the
preparation of wood pulp over the old soda processes are, (1) the
increased yield of fibre; (2) the preservation of its original
strength, and (3), the economy in chemicals.

It is well known that cellulose, even in its most stable forms, is
attacked more or less by hot solutions of the caustic alkalis, and
is more or less profoundly modified according to the strength of the
solution and the temperature at which it is employed; while on the
other hand the solutions of the bisulphites affect it but little. Thus,
the authors have exposed jute cellulose, which is of the same nature
as that obtained from wood, to the action of magnesium bisulphite
under the conditions which obtain in the Ekman process, without its
undergoing sensible loss of weight, and further, they have determined
the amount of cellulose in freshly cut grasses, in which it is but
imperfectly elaborated, and therefore very susceptible of modification,
both before and after treatment by the process, and in each case the
percentage obtained was the same.

There is therefore no doubt that in the bisulphite processes, even
the structurally delicate forms of cellulose are conserved. As before
indicated, the influence of this upon the yield of cellulose is of
course very marked; the yield from white pine, {77} by the soda
process, being approximately 33 per cent., whereas by the Ekman process
it is from 45–50 per cent. It is important to remember that this
increased yield of cellulose cannot fail to affect the quality, and
therefore the paper-making properties of the pulp. Papers made entirely
by the bisulphite processes have a strongly marked individuality, being
distinguished by their hardness and transparency. In regard to the
bleaching of the pulp, it will be found that some practical experience
is required for the control of the operation, so as to produce uniform
results.

Although the pulp produced by these processes is of a very light-grey
colour, so light indeed that they may be used for certain low classes
of white paper without further treatment, yet to obtain a pure white
colour almost as much bleaching powder is required as in the case of
soda pulps, although the latter are much darker in colour. The chief
points to be observed are (1) the complete removal of the sulphites
from the pulp before the addition of bleaching liquor, which would
otherwise be ineffectively consumed; (2) the avoidance, in washing, of
waters containing iron, which would combine with certain constituents
of the pulp to form dark-coloured bodies.

The following Table, compiled from Dr. Hugo Müller’s ‘Pflanzenfaser,’
is of interest, as indicating the probable yield of pulp from different
woods, compared with the amounts obtained in actual practice by the
Watt and Burgess (soda) process:—

  ----------+--------+----------+--------+---------+------------+------------
            |        |  Water   |        | Lignin, |            | Pulp—Watt
            | Water. | Extract. | Resin. |   &c.   | Cellulose. |and Burgess
            |        |          |        |         |            |  Process.
            +--------+----------+--------+---------+------------+------------
  Birch     | 12·48  |    2·65  |  1·14  |  28·21  |    55·52   |   40·00
  Pine      | 12·87  |    4·05  |  1·63  |  28·18  |    53·27   |   34·70
  Oak       | 13·12  |   12·20  |  0·91  |  34·30  |    39·47   |   20·60
  Chestnut  | 12·03  |    5·41  |  1·10  |  28·82  |    52·64   |   25·10
  ----------+--------+----------+--------+---------+------------+------------

The following Table, which gives a concise account of the various
typical processes that have been employed for the preparation of wood
pulp, will be readily understood in connection with the theoretical
considerations previously discussed:— {78}

                          VIEW OF THE CHEMICAL PROCESSES FOR DISINTEGRATING WOOD.
        _Aqueous Alkalis._         |            _Water._                 |         _Aqueous Acids._
                                   |                                     |
  Hydrolysis, aided by alkali      | Hydrolysis, aided by acids          | (_a_) Oxidising and hydrolytic—
   directly, also indirectly by    |  formed from the wood. (Fry,        |
   combination with products of    |  1867)                              |    Nitric acid. (Coupier and
   resolution. (Watt and Burgess,  |                                     |     Mellier, 1852. Barre and
   1853. Houghton, 1857.)          | Limit of action determined by       |     Blondel, 1861.)
                                   |  reversal of hydrolysis, i.e.       |
                                   |  dehydration aided by oxidation.    |    Nitro-hydrochloric. (Orioli,
                                   |                                     |     1865.)
                                   |                                     |
                                   |                                     | (_b_) Simply hydrolytic—
                                   |                                     |
                                   |                                     |    Hydrochloric acid. (Bachet and
                                   |                                     |     Machard, 1864.)
                                   |                                     |
                                   |                                     | (_c_) Reducing and hydrolytic—
                                   |                                     |
                                   |                                     |    Sulphurous acid. (Tilghmann,
                                   |                                     |     1866. Pictet, 1882.)
                                   |                                     |
      _Solutions of Alkaline       |                                     |          _Bisulphites._
           Sulphides._             |                                     |
                                   |                                     | Hydrolysis, aided primarily
  Hydrolysis, aided by alkaline    |                                     |  by sulphurous acid, and
   bases directly and indirectly   |                                     |  secondarily by combination of
   by combination with products.   |                                     |  products with bisulphites, also
                                   |                                     |  by prevention of oxidation.
  Reversal of hydrolysis lessened  | _Water, together with neutral       |  (Tilghmann, 1866. Mitscherlich,
   by presence of reducing agent.  |  Sulphites._                        |  1874. Ekman, 1881. Francke,
                                   |                                     |  1881. Graham, 1882.)
      (Both categories: Jullion,   | Simple hydrolysis—                  |
      1855. Blitz, 1883. Dahl,     |                                     |
      1884.)                       |   Products removed from sphere of   |
                                   |    action by combination with base  |
                                   |    and sulphite. (Cross, 1880.)     |
                                   |                                     |
                                   |   Oxidation prevented by presence   |
                                   |    of sulphite.                     |

{79}




CHAPTER VI.

SPECIAL TREATMENT OF VARIOUS FIBRES; BOILERS, BOILING PROCESSES, ETC.


We have already, in Chapter V., discussed in a general way the
principles upon which the treatment of the various fibres should be
based; we now proceed to consider each fibre in detail, giving at the
same time such information as is necessary regarding the preliminary
treatment of the various fibres and describing the forms of apparatus
in which these operations are conducted. We shall consider the fibres
in the order of their simplicity of treatment.


_Rags_ (Linen and Cotton).—The treatment necessary for rags differs
largely with the quality and, of course, with the kind of paper
for which they are intended. These different qualities are known
in the trade by different names and marks, such for example as the
following:—New linen pieces, new cotton pieces, superfines, dark fines,
grey linen, sailcloth, seconds, thirds, &c., &c.

The two former consist of the cuttings produced in the manufacture of
various garments, &c. not having been worn, they are usually free
from dirt, and are, in fact, if bleached, nearly pure cellulose,
containing only the starch and other sizing material which has been
added in the process of finishing the goods. They may, of course,
contain considerable quantities of china clay or other loading
material. In purchasing rags, therefore, regard should be had to the
probable presence of these bodies. Such rags require only a very slight
treatment; in fact, for certain classes of paper they might be used
without any preparation. If, as is sometimes the case, the rags are
unbleached, a rather more severe boiling is necessary. {80}

[Illustration: FIG. 16.]

The greater part of the rags used in paper-making, however, consist of
the residual portions of garments, household linen, &c., which vary in
quality from clean, almost unused portions, to the very foulest sorts;
the latter require a very drastic treatment. The first thing to be done
with the rags is to “sort” and cut them into convenient pieces. This
is usually done by women, who stand at tables furnished with broad
knives firmly fixed into them, with the backs towards the worker, and
inclined at a slight angle. Near to the women are placed a number of
boxes, corresponding with the number of qualities of rags, lined at
the bottom with coarse wire gauze, into which the different sorts are
put. The distinctions made are purely arbitrary, but as a general rule
the rags are sorted with special reference to their colour and the
material of which they are composed. The coloured rags may be allowed
to accumulate, and then made into a coloured paper. During the process
of cutting, all hard substances, {81} such as buttons, pieces of iron,
&c., are carefully removed. The rags are cut into pieces of from two to
five inches square. In some mills machines are used for cutting.

Fig. 16 shows the construction of a machine that may be used either
for rags or rope. The material is passed into the machine along the
table A, where it passes between the stationary knife C and the knives
B, fixed in the revolving drum D. The cut rags fall into a receptacle
placed underneath the drum.

Notwithstanding the extra expense of cutting by hand, it is
nevertheless preferred by many, especially for the finer grades of
paper. One reason for this is to be found in the fact that more perfect
sorting and removal of impurities can be effected. It is moreover said
that less waste of fibre occurs in the subsequent operations.

[Illustration: FIG. 17.]

The next process which the rags undergo is that of removing all loose
extraneous matter. This may be done in a machine such as is shown
in Fig. 17. The rags are fed continuously by the endless travelling
platform A into the willow. This consists of two wrought-iron drums, B
B, furnished with wrought-iron teeth C, which when the drums revolve
pass rapidly near to the stationary teeth fixed into the cast-iron
framework of the willow. The sides are covered in with cast-iron doors,
and the top is covered over {82} with sheet iron. Underneath the drums
is a grating for the escape of dust.

The rags, having been thoroughly beaten by the teeth of the drums, pass
into the duster D, consisting of a kind of hollow cylinder E, made of
strong iron bars securely fastened to the circular ends F, the bars
being covered with wire cloth or perforated zinc. It is made to revolve
almost horizontally, a slight dip being given to it in order that the
rags may be carried forward to the lower end. The bars or skeleton of
the cylinder are furnished with a number of teeth securely bolted on.
The whole is enclosed in a strong wooden box in which it revolves, and
which serves to collect the dust passing through the wire cloth. The
cylinder E is driven by the gearing G. This combined willow and duster
may be used for dusting and cleaning not only rags, but almost any
other kind of fibre. The willow and duster sometimes form two separate
machines.

The cleaned and dusted rags are now ready to be boiled, although it
is the practice in some mills to give them a preliminary washing with
water.

The boiling may be conducted either in spherical or cylindrical
boilers, or in the ordinary vomiting boilers described under Esparto.
(See p. 92.) In Fig. 18 is shown, part in section and part in
elevation, a spherical rag-boiler, as manufactured by Messrs. G. & W.
Bertram.

This boiler, of from 8 to 9 feet diameter, is supported by means of the
hollow journals A on the standards B, and is made to revolve by means
of the gearing C.

Steam enters by the pipe D, which is fitted with a safety-valve E, and
vacuum valve F. The steam on entering the boiler is distributed by
means of the “baffle-plate” G. Lye enters by the pipe H. The boiler is
fitted with two doors I, wherewith to fill and empty; the waste lye is
run off by the cock J. L is a small blow-through cock. The false bottom
K prevents the rags from choking up the cock and also serves to drain
off the waste liquor.

[Illustration: FIG. 18.]

The alkali employed may be either caustic lime, caustic {83} soda,
sodium carbonate, or a mixture of the latter and lime, which is of
course equivalent to using caustic soda. The proportion of alkali
depends upon so many considerations that it is quite impossible to
give exact information on this point. In the case of caustic soda, a
quantity equal to from 5–10 per cent. on the rags may be taken to be
a fair average. If lime be used it should be slaked with water, made
into a thin milk and carefully filtered through fine wire cloth to keep
back the particles of sand, coal, &c., which lime is always liable to
contain. From 5–10 per cent. may be used. The amount of lime actually
dissolved in the water is relatively small (1·3 grms. per litre);
the portion in solution however, rapidly combines with the grease,
dirt, and colouring matter of the rags and forms with them insoluble
compounds, a fresh portion of lime being at the same time dissolved.
This formation of insoluble compounds constitutes an important
objection to the use of lime, as they are liable {84} to remain to
some extent fixed in the rags and are with great difficulty removed
by washing. For this reason, therefore, the more soluble alkali is to
be preferred. Moreover, the lime sometimes tends to exert a hardening
effect upon the cellulose. Notwithstanding these objections, lime is
used by some paper-makers in preference to soda. In making choice of
the chemical for boiling, much depends on the quality of the rags
and the nature of the paper for which they are intended, so that no
definite rules can be given.

The time of boiling varies from 2 to 6 hours, according to the quality
of rags, the chemical employed, and the pressure. The use of very high
pressures should be avoided as far as possible, as there is a danger,
owing to the correspondingly high temperature, of _fixing_ the dirt and
colouring matters instead of dissolving them.

The quantity of water should be kept as low as may be, in order to have
as strong a solution of alkali as possible; this effects a saving both
in the time of boiling, and in the alkali. This is of great importance
where it is necessary to evaporate the whole of the waste liquors. It
should also be remembered that a certain amount of water is always
formed by condensation in all boilers in which live steam is used. On
the other hand, if too little water be added, the rags are liable to
become “burned” and the fibre therefore weakened. During the operation
the boiler should be made to revolve slowly, in order to produce
thorough circulation of the liquor.

The boiling being completed, the pressure is allowed to fall, either
by cooling or by blowing off from a cock usually provided for that
purpose, and the liquor allowed to collect at the bottom of the boiler.
It is then run off by the cock J (Fig. 18), and the rags drained as
much as possible. Water is then run in to give the rags a preliminary
washing. If time permits the steam may be turned in and the operation
assisted. After again draining, the rags are withdrawn from the
boiler into any suitable receptacle. A convenient form is that of a
rectangular iron box on wheels, which can be readily transferred from
one part of the mill to another. {85}

The next process is that of washing. This is usually performed in a
washer or breaker, the construction of which is shown in Fig. 19.

[Illustration: FIG. 19.]

It consists essentially of a rectangular vessel with rounded ends,
in the centre of which, but not extending the whole {86} way, is
a partition B, known as the “mid-feather.” The roll A, which is
furnished with a number of steel knives G, and driven from the wheel H,
revolves in one of the compartments formed by the mid-feather. In this
compartment the floor is inclined in such a way as to bring the pulp
well under the roll, as shown by the dotted line D. Immediately under
the roll is what is called the “bed-plate,” the end of which is seen
at I, extending up to the mid-feather, and fitted with knives similar
to those in the roll A. The arrangement of the knives, both in the
bed-plate and the roll, is similar to that given in Figs. 33 and 34.
The distance between the roll and the bed-plate can be varied at will
by means of the handle E, which is so arranged as to raise both ends of
the roll simultaneously. In those breakers of an older pattern, one end
only of the roll was raised, and thus the knives became worn unequally.

After passing between the roll and the bed-plate, the pulp flows down
the “back-fall” D′, and finds its way round to the other side of the
mid-feather. On the inclined part of the floor, and immediately in
front of the bed-plate I, a small depression is made, covered with
an iron grating, for the purpose of catching buttons, small pieces
of stone, and other heavy substances that may have found their way
into the rags. There is generally a similar grating with rather
finer openings on the other side of the mid-feather. The engine is
constructed of iron, generally made in one casting.

The dirty water from the rags is removed by the “drum-washer” C. It is
divided into compartments by the partitions shown by the dotted line
_c_. The centre of the drum is formed of a conical tube, the narrow end
of which is towards the mid-feather. The ends of the drum are generally
made of mahogany, as this is found to stand the action of alkali better
than any other wood. The periphery is covered with fine copper or
brass wire-cloth, laid on to a backing of a much coarser material. An
improved form of backing has been introduced lately, which is much more
durable than wire. It is formed of brass cut into the form shown in
{87} Fig. 20. The drum can be raised or lowered by the small wheel F,
and it is driven by a belt on the shaft that bears the roll.

[Illustration: FIG. 20.]

The wash-water passes through the wire cloth into the compartments
formed by the partitions _c_, and finding its way down to the narrow
end of the inner conical tube, flows out through the side of the drum
into a trough which is placed across the washer to receive it. Or it
may, as shown in the drawing, be conducted through the mid-feather
itself, which is made hollow at this part for the purpose.

Another form of drum-washer, called the siphon-washer, is sometimes
used. Its construction will be understood by reference to Figs. 21 and
22.

The drum is simply a hollow cylinder of wire cloth, the ends of which
are formed of wood. Inside the cylinder is the siphon tube A, into
which the water passing through the wire cloth flows. The continuation
of the siphon tube B (Fig. 22) is made of flexible tubing. The action
of the siphon is commenced by filling it with water through the cock
C (Fig. 22). The water then flows in the direction indicated by the
arrows. The tube A is fixed, and passes through a hollow journal fitted
on to the end of the drum. {88} The other end is connected with the
rod E, on which the driving pulley D is placed.

[Illustration: FIG. 21.]

[Illustration: FIG. 22.]

The water passing through the wire cloth on the drum carries with it
a certain amount of fibre which, unless special precautions are taken
(see “Save-all,” p. 154) is lost. The amount is considerable in the
case of weak rags, and care should therefore be taken that the washing
is not prolonged more than is consistent with proper cleansing, and
that the pulp should not be too much broken up at this stage.

The washed and broken pulp goes by the name of “half-stuff.” {89}

The following is the usual plan of treating rags in the washer:—It
is first half-filled with water, and the rags from the boiler put in
gradually until nearly filled. Water is now allowed to flow in at the
opposite end to where the drum-washer is placed. This, by the action of
the roll, mixes thoroughly with the pulp and extracts all the soluble
matter, and also carries with it fine insoluble impurities.

The action of the knives in the roll on the rags passing between it
and the knives in the bed-plate serves to break them up and thoroughly
disintegrate them. The dirty water then passes away through the
drum-washer, the stream of pure water being regulated so as to keep the
level constant. This is continued until only pure water passes away.
The supply is then stopped, the washer still being kept in action. As
the level falls the drum is lowered by means of the handle F. When
sufficiently drained the pulp is discharged through a valve in the
bottom of the engine. It is now ready to be bleached. This may be done
in separate engines called “potchers,” somewhat resembling the breaker
or washer already described, or it may be done in the breaker itself.
The process of bleaching will be described in Chapter VII.

Occasionally, the bleaching process is conducted in the “beater”
itself, but this is not to be recommended.


_Esparto._—This fibre, on account of its high percentage of
non-cellulose constituents, requires a large amount of soda to resolve
it; on the other hand, being of the nature of a pecto-cellulose, the
process of disintegration may be conducted at a low pressure; in
fact, it is the practice at some mills to boil in open vessels, in
which case, however, a larger amount of soda is required. As has been
already stated, it may be taken as a general rule for all fibres, that
within certain limits the higher the pressure employed the less soda
is required. The quantity necessary also varies with the district
from which the grass comes. Caustic soda is the chemical invariably
employed; lime, on account of its forming insoluble compounds with
the {90} non-cellulose portion of the grass, is inapplicable. Not
only does the amount of soda depend upon the pressure, but it also
depends to a considerable extent on the form of boiler employed. The
use of rotary boilers is objectionable, as the esparto tends to collect
together into compact masses, which are with difficulty penetrated by
the liquor. It is therefore the almost universal practice to employ
stationary boilers.

[Illustration: FIG. 23.]

The first treatment that the esparto undergoes is that of “picking.”
The bands of the bales in which esparto is packed, generally by
hydraulic pressure, are cut, and the grass is spread out on tables by
women, who carefully remove such impurities as weeds, root-ends, &c.,
which from their nature are with great difficulty boiled and bleached,
and which if not removed would be liable to appear in the finished
paper as dark-coloured specks, technically known as “sheave.” This
treatment is called “dry-picking,” in contradistinction to a subsequent
process, known as “wet-picking.” A portion of the table is covered
with coarse wire gauze, through which when the grass is spread over it
loose particles of sand, dirt, &c., escape. The cleaning of esparto
can be much better accomplished by means of machinery. Fig. 23 is an
elevation of a machine manufactured for the purpose by Messrs. Masson,
Scott and Bertram. The grass, which may be in the form of sheaves, as
taken from the bales, is put in by the hopper A. It passes thence to
a conical {91} drum made of steel bars placed very close together,
driven rapidly by the shaft B. It is provided with five rows of teeth.
Fixed to the sides of the willow there is also a row of stationary
teeth. The grass is thoroughly broken up and dusted by the action of
the teeth, and is transferred to the wide end of the willow at C, where
it is carried forward on the travelling tables D. During its passage
along the tables it can be examined and picked by women standing on the
platforms E. The dust and dirt passing through the steel bars of the
drum are drawn away by a fan through the pipe F.

This machine is also adapted so as to carry the cleaned grass to the
boiler-house. It is taken forward by means of travelling rakes over
the tops of a series of boilers, any one of which can be furnished by
simply opening a door corresponding in position with the lid of the
boiler.

Boiling.—The ordinary form of boiler is shown in Fig. 24. It is
known as a vomiting boiler. The grass is put in by the door E, which
is hinged, and is counterbalanced by the weights L. It is securely
fastened down by the screws F. Steam enters by the inner pipe A, which
dips a little below the perforated false bottom B. Surrounding the
steam-pipe is a wider pipe C, open at the top, which is made slightly
trumpet-shaped; also open at the bottom, where it ends in a kind of
shoulder, on which the false bottom rests. The lower part has two or
more openings G cut away, through which the liquor can freely pass.

In order to get as large a charge into the boiler as possible, steam is
turned on while furnishing, and a quantity of caustic soda lye is also
run in, which has the effect of softening the grass and making it more
compact. This is continued until the boiler is well filled.

The action of the boiler is as follows:—The steam passing through the
pipe A heats the liquor that has drained from the grass through the
perforations in the false bottom, and forcing it up the wide pipe C,
causes it to strike against the dome or bonnet D, and distribute itself
again over the grass. {92} This is technically known as “vomiting.” In
this way a constant circulation of liquor is kept up.

[Illustration: FIG. 24.]

The boiler is emptied by the door H and the liquor is run off by
the cock I. The boilers are usually supplied with a safety valve E,
and also with a pipe for letting off the steam when the boiling is
finished. The boiling generally takes from four to six hours. The
quantity of soda necessary depends upon the nature of the grass,
Spanish requiring less than African. {93}

Routledge, to whom the introduction of esparto as a paper-making
material is due, gives 10 per cent. as the proper quantity.

The pressures employed vary from 5 lb. to 45 lb. There has been a
growing tendency of late to employ the higher pressures for reasons
already stated.

[Illustration: FIG. 25.]

Of late years great improvements in the form of the boiler have been
introduced. Fig. 25 is an illustration of Roeckner’s Patent Boiler. The
vomit pipe is outside the boiler. Steam entering by the cock D, forces
the liquor up the vertical vomit pipe and distributes it over the
grass. The pipe K is used for heating the liquor at the commencement of
the operation by means of waste steam. F F are gauges for indicating
the height of the liquor. The grass is put in by the opening G. The
pipes A B and C are for the supply of {94} steam, strong lye and
water. The boiled grass is discharged by the circular door E.

The boiler holds three tons of grass and the boiling is completed in
about 2 1⁠/⁠2 hours, the pressure being about 35–40 lb. per square
inch. It is claimed that by its use a saving both of time and soda is
effected.

[Illustration: FIG. 26.]

Sinclair’s Patent Boiler is shown in Fig. 26. The vomit pipes, of which
there are two, are made of thin steel plates {95} riveted to opposite
sides of the boiler. The liquor drains through the perforated false
bottom, and is then forced up the vomit pipes above the perforated
plates through which it is distributed over the grass in a number of
fine jets. The boiler is charged by the door _e_ and emptied by _j_.
The small cock _a_ is used as a blow-through cock; the opening _b_ is
used for blowing-off steam when emptying the boiler; _c_ for letting in
caustic soda lye; _d_ for water. Steam enters by the small branch of
the T pipe at the bottom of the boiler, the other, _g_ being used for
running off the waste liquor. A boiler holds from two to three tons of
grass, and a boiling is completed in about two hours at a pressure of
40–50 lb. per square inch.

The two forms of boiler above described possess the obvious advantage
of having the whole or nearly the whole of the interior available for
holding grass; the boilers can therefore be made to hold more, and the
boiling is moreover much more evenly accomplished.

Washing.—The boiling being completed, the steam is allowed to escape
and the liquor to collect at the bottom of the boiler where it is run
away by the pipes placed at the bottom for the purpose. Water is then
run in and steam turned on for a short time; this is also run off,
and the grass drained as completely as possible. The boiled grass is
then emptied into trucks and taken away to the washing engines. These
resemble those already described under rags.

During the process of washing, a certain amount of the shorter fibres
find their way through the meshes of the wire-cloth. In addition
to this a large proportion of the cellular tissue surrounding the
fibro-vascular bundles (see Fig. 12, p. 57) is carried away. If the
wash-water be examined under the microscope, it will be seen to consist
largely of this cellular matter. Though this entails a certain loss
of cellulose, its removal is in other respects advantageous, as it
is possessed of hardly any “felting” properties, and it is moreover
exceedingly difficult to bleach.

The amount of fibre actually obtained in practice is but little below
that contained in the grass. A certain loss is {96} inevitable, but
this probably does not exceed 1 or 2 per cent.

The percentage of cellulose in esparto is given on p. 57. The
following numbers obtained by the authors are somewhat higher. They
are calculated on the absolutely dry fibre; those mentioned are on the
_air-dry_ samples:—

               Cellulose per cent.

  Spanish             58·0
  Tripoli             46·3
  Arzew               52·0
  Oran                49·6

There is no doubt that considerable differences occur even between
different specimens of the same kind of grass.

It is the practice in some mills to wash the grass in a series of tanks
connected together in the same way as the lixiviating tanks of an
alkali works. They are so arranged that pure water flows in at one end,
passes through fresh lots of grass in succession, and issues at the
further end highly charged with the soluble products of the grass. By
such an arrangement the grass can be washed without any loss of fibre,
and with a minimum quantity of water. This latter feature is of great
importance in mills where it is necessary to evaporate the whole of the
waste liquors from the esparto, as they are then obtained in a very
concentrated form. Even with such an arrangement it is advisable to
give the grass a short final treatment in the washing engine.

The washing having been completed, and the esparto having been broken
up into “half-stuff,” it is now ready to be bleached (see Chap. VII.).

The presse-pâte system, originally adopted for the treatment of straw,
has of late years been extensively applied to esparto.

The presse-pâte consists of the wet end of a paper machine, and is
furnished with sand-tables and strainers. The pulp is allowed to flow
on to the wire cloth, so as to form a thick web of pulp. The bulk of
the water passes away through the wire cloth; a further quantity is
removed by the {97} vacuum-boxes and couch-rolls. The pulp, containing
from 50 to 60 per cent. of water, is wound round an iron rod until a
sufficiently large roll is formed.

The advantages of the presse-pâte system are the possibility of the
removal of dirt and unboiled portions by means of the sand-tables and
strainers, and the very complete washing and removal of the products of
the action of bleaching powder.

It also enables manufacturers to dispense with the somewhat costly
methods of dry and wet picking.

The presse-pâte system can also be applied to the unbleached pulp.

It may be interesting at this point to say something about the
substances which are removed from the esparto by the caustic soda. On
referring to p. 57 it will be seen that the original grass contains
nearly half its weight of extractive matter, the removal of which has
to be effected. Only a small proportion of this is extractive matter
in the ordinary sense of the term, i.e. that can be extracted by
the usual solvents; the remainder is intimately combined with the
cellulose. The action of the caustic soda is to resolve these bodies,
the cellulose remaining behind, and the other constituents being
dissolved as resinous bodies by the soda. A certain proportion of the
mineral constituents, notably the silica, dissolves in the lye, the
latter forming silicate of soda.

On neutralizing the liquor with an acid, the bulk of the dissolved
constituents is thrown down as a dark brown resinous mass. If this
crude product be purified, it is found to consist of a definite body
having the formula C_{21}H_{24}O_{8}. By the action of chlorine on
this resin a bright yellow chlorine compound is formed, resembling the
compound from jute described on p. 18. If the resin be treated with
concentrated nitric acid, a bright yellow body is formed, which forms
definite compounds with bases, and which has the property of dyeing
animal fibres a bright orange colour. In addition to this body, a
yellowish-white wax can be isolated. It sometimes happens that this wax
is but imperfectly dissolved in the caustic lye; if the waste liquor
be allowed {98} to stand, the wax is occasionally found to collect in
small quantities on the surface.

Various attempts have been made from time to time to remove from the
waste liquors the soluble matter derived from the esparto by the
addition of lime. This throws it down as a very voluminous precipitate,
exceeding difficult of filtration. The filtrate contains only caustic
soda. The difficulties of removal of the precipitate, however, are
almost insurmountable. The usual method of disposing of the liquor
is to evaporate it to dryness and ignite it, as will be subsequently
described under the head of “Soda Recovery,” Chapter XII.


_Straw._—Straw very closely resembles esparto in its chemical
constitution; it is, however, more highly lignified, and for this
reason (see p. 63) requires a more drastic treatment for its
resolution. It is therefore usual to treat straw with rather larger
quantities of caustic, and generally at high pressures. It is possible,
however, to resolve it at 5–10 lbs. pressure, but the resulting
pulp is more difficult to bleach, and can only be used for inferior
kinds of paper. In treating straw for use in high-class paper, it is
necessary to boil under such conditions that even the knots, which are
much less readily attacked, shall be so far disintegrated that they
may be bleached with a moderate quantity of bleaching powder. Such a
treatment, on the other hand, involves a diminished yield of pulp, and
at the same time a somewhat weakened fibre.

The kinds of straw in general use are wheat, oat, rye, and barley; the
two first constituting the bulk of the raw material, at least in this
country. Some idea of the composition of straw may be gathered from the
analyses given on p. 59.

It will be seen that the amount of cellulose is quite as high as in
esparto, but for the reasons above given and from the fact that a
large proportion of the cellulose consists of cellular tissue (see
Figs. 12 and 13), which is easily attacked by soda and readily passes
through the meshes of the {99} drum-washers and the wire-cloth of the
presse-pâte and paper machine, the yield obtained in practice falls
considerably below that from esparto.

In addition to the numbers already quoted on p. 59, the following
results of analyses made from time to time by the authors, may be
interesting. The percentages are calculated on the absolutely dry
material.

                         Cellulose
                         per cent.
  Oat Straw                52·0
  Oat Straw                53·5
  Wheat Straw              49·6
  Rye Straw (Foreign)      53·0
  Oat Straw (Foreign)      46·5
  Wheat Straw (Foreign)    50·2

The yield of pulp is greatly influenced by the conditions under which
it is obtained; high pressures and temperatures exerting considerable
influence on the result. This is probably the case with straw more than
any other fibre, on account of the physical and chemical nature of
the cellulose. It is doubtful whether much more than 35 per cent. is
actually obtained in practice.

Straw is usually boiled in cylindrical rotary boilers. Some
paper-makers, however, prefer to use one or other of the different
forms of vomiting boilers already described.

The use of a rotary boiler is open to certain objections. In the
first place, it is doubtful if they are as economical of soda as the
vomiting boilers, especially the more recent patterns; and, secondly,
the rotation of the boiler so disintegrates the pulp, that a certain
proportion of the cellulose, especially those fibres which are short,
is liable to be lost during the subsequent treatment. It seems probable
that the best results would be obtained if the rotation of the boiler
were reduced to a minimum, in fact, sufficient only to produce thorough
circulation of the liquor.

The proportion of soda necessary to boil straw thoroughly is, for
reasons already stated, greater than is the case with esparto. The
amount varies from 10 to 20 per cent. on the raw material. {100}

The different processes to which straw is subjected vary greatly. The
following may be taken as a general indication of the methods employed.
The straw is usually cut into short pieces of about 1–2 in. in length
by means of an ordinary chaff-cutter. The cut straw is carried by means
of a blast of air along a wooden tube or shaft into a chamber, the
sides of which are made of coarse iron gauze. This chamber is itself
inclosed in another chamber, in which the dust and dirt accompanying
the straw collect. The clean straw is then placed in sacks and conveyed
to the boiler-house.

Owing to the bulky nature of straw, it is difficult to get a large
charge into a boiler at one operation; it is therefore usual, after
having filled it as completely as possible, to run in a portion of the
lye required, and to turn on the steam for a few minutes. This has the
effect of so far softening the straw as to make it lie closely at the
bottom of the boiler and to allow of a further quantity being put in.
This having been accomplished, the remainder of the lye required is run
in, together with the requisite quantity of water, and the steam turned
on. The pressure may vary from 10 to 50, or even 80 lbs. per sq. in.,
and the time from 4–8 hours.

When the boiler has sufficiently cooled, the charge is run out by
a cock in the bottom. Owing to the rotary action of the boiler the
straw is in the state of fine pulp, having been almost completely
disintegrated; so fine, in fact, that it flows readily through a 3-in.
pipe. It is run into large tanks with perforated tile bottoms, where
the excess of liquor is allowed to drain away and the pulp washed by
the addition of water. It is then dug out and taken to be bleached.
Before this is done, however, it may be necessary to give it a further
washing. This may be done in the potcher itself. Instead of washing
the straw in tanks, it may be washed in an ordinary washing engine,
such as has been already described. Owing to the finely divided state
of the pulp, however, this method, unless the meshes of the wire-cloth
covering the drum washer are very fine, entails {101} a considerable
loss of fibre. It is more suitable in cases in which the straw has
been boiled in stationary boilers, and in which therefore it is
less disintegrated. When stationary boilers are employed, it is not
necessary to cut the straw very fine; in fact, it is sometimes put
into the boiler whole. The cutting has this advantage, that it loosens
the adhering dirt. In cases where the action of the soda has not been
carried far, or when the straw has been put into the boiler whole, the
pulp will not be disintegrated to the same extent, and it would not
flow through a narrow pipe. It is necessary therefore to discharge the
boiler through the doors used for filling.

A novel form of washer especially adapted for straw, whereby the
washing is effected with the minimum quantity of water, has been used
on the Continent to a considerable extent, and to some extent in this
country. The pulp is caused to pass along a series of revolving cones
covered with wire-cloth, through which the liquor escapes. As it
reaches the end of each cone, the pulp is emptied into a small tank
containing water from the cones further on in the series. It is carried
forward by means of hollow bent arms connected with the inside of the
next cone, which then discharges it at the other end, to be again
carried forward.

As already stated, the presse-pâte system is largely adopted for straw
pulp; it has been described under Esparto. It may sometimes be employed
with advantage before bleaching, though it is generally used after.

A method of treating straw is sometimes adopted which produces a pulp
of higher quality than is obtainable by the ordinary method. The washed
pulp is mixed in a chest provided with stirrers, with a large quantity
of water, and is then pumped into another chest placed at a higher
level, from which it flows between a pair of hard granite millstones,
the surfaces of which are cut into radial grooves. The stones are fixed
horizontally, and are made to revolve at a very rapid rate. During the
passage of the pulp through the stones, the knots, weeds, and other
hard portions of the {102} straw which may have resisted the action
of the alkali are reduced to a fine state of division, and are thus
more readily acted upon in the subsequent operation of bleaching. The
degree of fineness to which the pulp is reduced can be determined by
regulating its flow and the distance between the stones. Pulp produced
in this way is of a very even character, and is comparatively free from
unbleached particles.

Within the last few years a process of treating straw has been
introduced which, on account of the high quality of the pulp produced,
has attracted considerable attention from paper-makers. It consists
in exposing pulp obtained in the usual way by the action of caustic
soda to the action of chlorine gas. The method was patented in England
on March 3rd, 1880 (No. 938), by Friedrich Carl Glaser. The amount of
soda in the preliminary boiling is reduced much below that necessary
for perfect pulping, the result being that the cellulose is much less
liable to be destroyed, and thus a greater yield is obtained. The pulp
is thoroughly washed and partially freed from moisture in a centrifugal
machine until only about 70 per cent. remains. The partially dried
pulp is then exposed in leaden or stone chambers for some hours in an
atmosphere of chlorine, produced by the action of hydrochloric acid
upon manganese dioxide. By the action of the chlorine, those portions
of the straw which have been but imperfectly acted upon by the caustic
soda in the boiling process are completely disintegrated, or, rather,
are rendered more susceptible to the action of the bleaching liquor
employed subsequently. The consequence is that when bleaching liquor
is added, the whole of the straw is rapidly reduced to the state of
pure cellulose, and the finished product is remarkably free from
anything like unbleached portions. Owing to the fact that the action
of the caustic is minimised, a considerable proportion of the more
easily degraded cellulose survives, and the yield of pulp is thereby
increased. The process is, however, necessarily expensive. The action
of the chlorine will be readily understood by a reference to p. 19.
{103}

Owing to the fact that a considerable proportion of the pulp obtained
from straw consists of cellular tissue (see Fig. 13, p. 58), which,
although cellulose, is devoid of fibrous structure, paper made from
straw only is found to be much weaker than that made from fibres such
as esparto. On the other hand, being a cheap material, and one capable
of yielding a very white pulp with a moderate quantity of bleach, it
is held in considerable repute by many paper-makers, especially as a
material for mixing with esparto. It is sometimes mixed with cotton and
linen rags, even in the finest qualities of paper.


_Jute, Manilla, Adansonia, &c._—The boiling processes already described
under Esparto and Straw are, with certain slight modifications, equally
applicable to fibres of this class. For convenience in manipulation
they are usually cut into small pieces by a machine such as is shown
in Fig. 16, and are then cleaned and dusted in a willowing machine.
The boiling process calls for no special notice beyond what has been
already said with regard to other fibres.

A cheaper method, and one which is largely adopted in mills where only
a coarse dark-coloured paper is required, consists in boiling the jute
or other fibre in lime. Such a treatment is, however, not so effective
as one in which caustic soda is used, and the fibre produced is harder
and coarser in every way. The yield of pulp, however, owing to the fact
that the fibre is imperfectly resolved, is greater. In many cases, from
questions of economy, lime may be advantageously employed.

Jute can only be employed successfully when it is imperfectly resolved,
that is to say, when it is not reduced to the state of pure cellulose.
In such a state it forms a comparatively weak fibre, owing to the fact
that it is resolved into its individual fibres. If the filaments are
not completely resolved, then a strong fibre is the result, but in
this case, the pulp cannot be obtained in a pure white state. Owing to
this fact, jute has had up to the present only a limited consumption,
except for the manufacture of coarse papers. {104} Jute and Adansonia
are largely used for papers where strength is of more importance than
appearance, such, for example, as paper for telegram forms, strong
wrapping paper, &c.


_Wood._—The processes for treating wood have already been described in
Chapter V.

When an alkaline treatment is adopted, the alkali employed is, at
least in this country, caustic soda. In Germany the sulphide of
sodium processes have been very largely adopted. The alkali method
is, however, being superseded by the more perfect and more economical
method of treatment with sulphurous acid or acid sulphites.


_“Broke” Paper._—Under this head may be included all the partially
formed paper which is always obtained in greater or less degree when
a paper-machine is started, or such portions as are occasionally
unavoidably damaged in its passage over the drying cylinders, together
with the imperfect or rejected portions. It may also include used or
waste paper, a large proportion of which, if not too dirty, is re-made
into paper. The cleaner portions, especially if they have not been
dried, are frequently returned direct to the beaters, and mixed with
other pulp. That which has been actually made into paper requires to be
softened by boiling in water and {105} gentle breaking in an engine.
It may be necessary to heat it for a short time in a weak solution of
caustic soda. This may be done either in a breaker or in special tanks
provided for the purpose. Paper which has been printed upon requires
a rather more drastic treatment, and it must of course be used for an
inferior quality of paper, as it is impossible to get it to as good
a colour as the original pulp from which it was made—at least not
economically. “Broke” paper may be advantageously disintegrated by
means of an edge-runner. It consists of a pair of stones arranged in
the same way as an ordinary mortar-mill (Fig. 27).

[Illustration: FIG. 27.]


_Mechanical Wood Pulp._—A very large quantity of pulp is used in the
commoner kinds of paper, such as cheap news, &c., which is obtained
by disintegrating wood by mechanical means alone, no chemicals being
employed. The idea of making paper in this way dates back about 100
years, but owing to the want of suitable machinery it is only lately
that a good product has been obtained. The following are, in a general
way, the details of the process employed:—

The wood is first cut up into blocks, the size of which is determined
by the width of the stones used for grinding; any knots present are
cut out with an axe. The stones are made of sandstone, and are covered
over three quadrants with an iron casing, the remaining quadrant being
exposed. The surfaces of the stones are made rough by the pressure
of a steel roll studded with points, and which is pressed against it
while revolving. In addition to this, channels about 1⁠/⁠4 in. deep are
cut into the stone at distances of 2–3 in. They are made in two sets,
crossing each other in the centre of the stone, and serve to carry off
the pulp to the sides of the stone, in addition to giving increased
grinding-surface. The pressure of the blocks of wood against the stones
is steadily maintained by screws worked by suitable gearing; this is
necessary in order to obtain a pulp of uniform character. A stream
of water is kept constantly playing on the stone; by this means, the
pulp as fast as it is formed can be conveniently carried away. It is
first passed {106} through a rake, which retains small pieces of wood
that have escaped grinding. The stream of pulp then passes through
the sorters, the object of which is to keep back such portions of
the wood as have not been sufficiently disintegrated. These consist
of cylinders about 3 ft. long and 2 ft. in diameter, covered with a
coarse wire-cloth. The fibres that are retained by this wire fall into
the refiners, which consist of a couple of horizontal cylinders of
sandstone, the upper one only of which revolves. Here they are further
{107} disintegrated, and are again passed through the wire-cloth; this
is repeated until all the fibres have passed through. The pulp, after
passing through the first sorter, may be conducted through a series
of gradually increasing fineness, and, by this means, be separated
into different qualities. Though pulp so prepared cannot compete with
chemically-prepared stuff, as the fibres are extremely short, and have
comparatively little felting-power, it may be used with advantage as a
sort of filling-material.

[Illustration: FIG. 28.]

Various modifications of the foregoing process have from time to time
been proposed; among others, that of softening the wood by previous
soaking in water, or steaming, seems to be valuable, as by so doing,
it is highly probable that a longer fibre could be obtained, the soft
wood being more readily torn away by the stones. Some inventors have
proposed to replace the sandstone by an artificial stone containing a
large quantity of emery.

An improved method of preparing mechanical wood pulp, lately patented
by Mr. A. L. Thune, of Christiania, has been communicated to us by Mr.
Carl Christensen.

[Illustration: FIG. 29.]

[Illustration: FIG. 30.]

The apparatus employed is shown in Figs. 28, 29, and 30. Fig. 28
illustrates an arrangement of grinding apparatus fixed direct on to a
turbine. The stone is fastened on to the shaft S worked by the turbine
T. The wood in the form of small blocks is kept in contact with the
stone by a number of hydraulic presses P. {108}

A somewhat similar arrangement, but placed horizontally, is shown
in front and side elevation in Figs. 29 and 30. The same letters
correspond.

[Illustration: FIG. 31.]

The ground and sorted pulp is made into thick sheets by means of the
board machine shown in Fig. 31. The pulp mixed with water passes down
the shoot D into the vat B in which the cylinder K revolves. This
cylinder is covered with wire-cloth, and as it revolves it takes with
it a certain quantity of pulp in the form of a continuous sheet. This
sheet is taken on to the endless travelling felt F by the small couch
roll E. When it reaches the rolls C it is wound round the upper one,
from which it is removed when a sufficient thickness is obtained.
Obtained in this form the pulp is readily transported.

The woods commonly employed are white pine and aspen. The latter yields
a pulp of a better colour, but of inferior strength than the former.

Paper containing mechanical wood pulp is very liable to become
discoloured by the action of air and light, the ligno-celluloses
being much more readily acted upon than the celluloses isolated from
them. Such fibre is, moreover, devoid of much felting power; it has,
in fact, little to recommend it but its comparative cheapness. It is
nevertheless used in large quantities, some cheap papers being made
entirely from it. {109}

  TABLE OF STRENGTH OF CAUSTIC SODA SOLUTIONS (15° C. = 59° F.)
                           (TÜNNERMAN).

  ----------+-------------+-----------+-----------------------
            |             |           | Equivalent Percentage
   Specific | Degrees     | Per cent. |    of 60 per cent.
   Gravity. |Twaddle.[10] | Na_{2}O.  |     Caustic Soda.
  ----------+-------------+-----------+-----------------------
    1·0040  |     0·80    |   0·302   |         0·503
    1·0081  |     1·62    |   0·601   |         1·001
    1·0163  |     3·26    |   1·209   |         2·015
    1·0246  |     4·92    |   1·813   |         3·021
    1·0330  |     6·60    |   2·418   |         4·030
    1·0414  |     8·28    |   3·022   |         5·037
    1·0500  |    10·00    |   3·626   |         6·043
    1·0587  |    11·74    |   4·231   |         7·051
    1·0675  |    13·50    |   4·835   |         8·059
    1·0764  |    15·28    |   5·440   |         9·067
    1·0855  |    17·10    |   6·044   |        10·073
    1·0948  |    18·96    |   6·648   |        11·080
    1·1042  |    20·84    |   7·253   |        12·090
    1·1137  |    22·74    |   7·857   |        13·095
    1·1233  |    24·66    |   8·462   |        14·103
    1·1330  |    26·60    |   9·066   |        15·110
    1·1428  |    28·56    |   9·670   |        16·117
    1·1528  |    30·56    |  10·275   |        17·125
    1·1630  |    32·60    |  10·879   |        18·131
    1·1734  |    34·68    |  11·484   |        19·140
    1·1841  |    36·82    |  12·088   |        20·147
    1·1948  |    38·96    |  12·692   |        21·153
    1·2058  |    41·16    |  13·297   |        22·161
    1·2178  |    43·56    |  13·901   |        23·170
    1·2280  |    45·60    |  14·506   |        24·177
    1·2392  |    47·84    |  15·110   |        25·170
  ----------+-------------+-----------+-----------------------

NOTE.—It must be borne in mind that the above numbers refer only
to solutions of pure caustic soda. With liquors containing sodium
chloride, sulphate, &c., the specific gravity will give an erroneous
view of the amount of alkali present, as these salts of course raise
the gravity. For example, a liquor prepared by causticising a solution
of recovered soda has a specific gravity of 1·05 (10° Tw.). According
to the above table this corresponds to 6·043 per cent. of 60 per cent.
caustic. Tested by means of standard acid it showed 4·520 per cent. Too
much reliance should therefore not be placed upon determinations of
specific gravity, but in important cases the actual amount of alkali
should be determined by titration with standard acid.

     [Footnote 10: To convert degrees Twaddle into specific gravity,
     multiply by 5, add 1000 and divide by 1000: thus 7° Tw.,

          7 × 5 = 35
                1000
                ────
          1000) 1035 (1·035 sp. gr.
                1000
                ────
                  3500
                  3000
                  ────
                   5000
                   5000
                   ━━━━]

{110}




CHAPTER VII.

BLEACHING.


The methods of bleaching being essentially the same for all pulps, it
will only be necessary to describe one in detail.

The process depends upon the use of a solution of calcium hypochlorite,
prepared by dissolving bleaching powder in water. This solution is
best prepared in a vessel provided with stirrers or agitators, whereby
a thorough mixture of the bleaching powder and water is obtained.
Bleaching powder always contains a certain amount of free lime and
calcium carbonate, which remain undissolved in the water. This should
be allowed to settle to the bottom of the vessel, and the clear liquor
run off. The residue may then be again treated with water, or with weak
liquor obtained by washing the residue. If the washings are too weak to
be conveniently used for bleaching, they may be stored in a separate
tank and used for dissolving fresh powder. In this way a strong stock
solution can be readily prepared, the powder at the same time being
thoroughly exhausted. The washing should be repeated as frequently
as possible, after which the residue may be allowed to drain. This
operation is best conducted on a filter bed provided with an air-pump
similar to that described in Chapter XII. The residue is obtained in
this way as a hard cake, containing about 60 per cent. of water. If the
above operations have been properly conducted, it should not contain
more than about 0·25 per cent. of chlorine.

The original powder should contain from 33·0 to 35·0 per cent. of
“available chlorine,” that is, chlorine which is effective in the
bleaching process. {111}

Owing to the ease with which it decomposes it should be kept cool and
not exposed to the air.

If possible, one or more large store tanks should be provided for
the strong bleach liquor, so that time may be given for the complete
separation of the insoluble portions. The liquor can be drawn off with
a “siphon” pipe without disturbing the residue.

It is of the utmost importance that only clear liquor be used, as a
milky solution of calcium hypochlorite is much more sluggish in its
action than one which is perfectly clear and bright.

A convenient strength for the stock solution is 6° Twaddle: this
corresponds to about half a pound of bleaching powder to the gallon.

The method of testing the powder and its solution will be described in
Chapter XIV.

The washed and broken pulp is placed in the “potcher” together with
the necessary quantity of bleaching liquor and as much water as is
required to produce complete circulation of the mass. In many mills the
breaker itself answers the purpose of a potcher also. The quantity of
water should be kept as low as possible, as it is found that by the use
of strong solutions less bleaching powder is required than with weak
solutions; moreover, less time is required to produce the effect. On
the other hand, with very strong solutions, the pulp is liable to be
injuriously affected.

Straw and esparto pulps are sometimes bleached in large potchers made
of brick covered with cement. The circulation of the pulp is produced
by the action of paddles made of wood or, preferably, of iron.

Many “potchers” are provided with steam pipes, whereby the mass of pulp
and liquor is heated. This should be done with great care, so as to
avoid superheating in any part, as this is certain to cause destruction
of the fibre. The better plan, where it can be adopted, is to uniformly
heat the pulp before running in the bleach.

In certain cases the action of the calcium hypochlorite is {112}
assisted and accelerated by the addition of either sulphuric
or hydrochloric acids; these combine with the lime and liberate
hypochlorous acid, which has a more rapid action than its calcium salt.
If the acid be added in too large quantity, or of too great a strength,
it sometimes happens that instead of hypochlorous acid, chlorine gas
is given off, part of which escapes into the air, thus causing loss.
Moreover, the chlorine is liable to enter into combination with the
fibre substance forming the yellow chlorination products described on
p. 18.

This liability is greater in the case of highly lignified fibres, such
as wood or jute: in these cases, therefore, the use of acids should be
avoided. When used the acid should be largely diluted with water and
added gradually. The best plan is to allow the action of the bleach
to continue for some time, only adding the acid when it is nearly
exhausted. In this way risk of damage to the pulp is avoided.

The diluted acid should be conveyed by a leaden pipe passing down to
the floor of the potcher, and perforated at its lower extremity.

Other means of accelerating the action of the bleaching powder have
been suggested, such, for example, as the use of bicarbonate of soda,
which by double decomposition forms with the bleaching powder carbonate
of lime and free hypochlorous acid. It is, however, much too expensive
an agent.

The amount of bleaching powder necessary to produce a good white colour
differs materially with the fibre to be bleached, and of course with
the degree of resolution of the fibre substance in the preliminary
treatment with caustic soda.

The following numbers may be taken to be approximations of the amount
necessary to bleach well-boiled pulps:—

                    Per cent. Powder
                     calculated on
                    Unboiled Fibre.

  Esparto              10 to 15
  Straw                 7 to 10
  Wood                 15 to 20

{113}

A well-boiled pulp should contain from 90 to 95 per cent. of cellulose.

Very excellent results are sometimes obtained by substituting sodium
hypochlorite for the calcium compound. This is done by decomposing a
solution of bleaching powder with an equivalent quantity of either
sodium sulphate or sodium carbonate. The precipitate of calcium
sulphate or carbonate is allowed to settle and the clear liquor run
off. Such a solution is more sluggish in its action than one of calcium
hypochlorite, but it is more easily controlled, and is less liable to
injure any material treated with it.

The time necessary to produce a perfect bleach depends on the nature
and condition of the pulp, on the degree of concentration of the
liquor, and on the temperature at which the operation is conducted.
Some paper-makers prefer to extend the bleaching over a considerable
period of time, but this involves the employment of a larger system of
“potchers,” which in many instances is an objection. If this method
is adopted, especially in the case of straw or esparto, the action of
the paddles or roll should be stopped, as otherwise the fibres are
liable to felt together in the form of small grains, which sometimes
escape the action of the beating roll, and occasionally find their way
into the paper, causing an unevenness of surface. By giving longer
time to the bleaching there is less risk of damage to the fibre, and
consequently a greater yield of bleached pulp.

The action of the bleaching solution should, as far as possible, be
confined to the non-cellulose portions of the fibre. A certain action
on the cellulose itself invariably takes place, but it should be
reduced to a minimum. The action of bleach upon cellulose has been
indicated in Chapter I., p. 10. For further information on this subject
the reader is referred to the ‘Journal of the Society of Chemical
Industry,’ 1884, April 29 and May 29.

A very good method of bleaching consists in a preliminary treatment in
the ordinary way in the potcher, followed by a prolonged steeping in
tanks. {114}

In the case of pulps which are very difficult to bleach, the action
can be greatly assisted by washing out the products of the bleaching
action, treating the pulp for a short time with a weak alkaline
solution, again washing, and then repeating the bleaching process.
In this way very refractory pulps can easily be bleached. Even an
intermediate washing with water is useful.

In most cases, where a fairly good colour has been obtained by the use
of bleaching powder alone, the colour is greatly improved by a souring
or treatment with weak hydrochloric acid, or, better still, with
solution of sulphurous acid.

Or the bleaching may be conducted in two or more operations with
intermediate treatments with acid.

All these modifications, however, are more or less troublesome, and
should only be resorted to when the ordinary method fails.

After bleaching, a certain quantity of calcium hypochlorite always
remains in the pulp. It may be removed in the potcher itself, or when
the pulp reaches the beater. In any case, the methods adopted are the
same. (See p. 127.)

In some mills it is the practice to free the bleached pulp from the
products of the decomposition of the bleach by pressing the pulp in
hydraulic presses, or by draining in vats provided with perforated
bottoms. Or the pulp may be made to pass through a pulp-saver (see Fig.
52, p. 155.)

Chlorine gas as a bleaching agent has been almost entirely superseded
by the more manageable calcium hypochlorite. Its employment is open
to the serious objection indicated before, viz. the liability to form
difficultly removable chlorine compounds. Its use as a disintegrating
agent has already been alluded to (see p. 102).

A process has lately been invented (English patent, No. 11,333, 1884),
by Prof. Lunge, which involves the use of acetic acid. The quantity
required is, however, very small, as during the process of bleaching
it becomes regenerated. The free lime in the bleaching powder solution
should first be {115} nearly neutralised with a cheaper acid, such as
hydrochloric or sulphuric, followed then by the addition of the acetic
acid. This process, we are informed, gives excellent results with
high-class material, such as the best cotton and linen rags; it is,
however, not to be recommended for such materials as straw or esparto.

For the bleaching of rags the process invented by Thompson (English
patent, No. 595, 1883) has proved very effective. The method consists
in saturating the material with a weak solution of bleaching powder,
and then exposing them to the action of carbonic acid gas. In this way
the bleaching action is made very rapid and effective.


_Electrolytic Bleaching._—Various attempts have from time to time been
made to bleach by means of electricity—that is to say, by means of the
products of the electrolysis of solutions of alkaline chlorides and
the chlorides of the alkaline earths. The only process which has been
to any extent developed is that of M. Hermite. This process is based
upon the electrolysis of a solution of magnesium chloride, this salt
having been found to give the most economical results. The solution,
at a strength of about 2·5 per cent. of the anhydrous salt (MgCl_{2}),
is electrolysed until it contains the equivalent of about 3·0 grms.
chlorine per litre. This solution is then run into the “poacher”
containing the pulp to be bleached; a continuous stream is then kept
up, the excess being removed by means of a drum-washer. This excess,
which after being in contact with the pulp in the engine is more or
less deprived of its bleaching properties, is then returned to the
electrolysing vat, where it is again brought up to the normal strength.

The electrolysing vat consists of a rectangular vessel of slate or
other suitable material. The negative electrode may be constructed of
zinc; for the positive it is necessary to employ platinum.

The electrolysed solution has been found to possess very remarkable
properties, which have considerable bearing upon the economy of the
process. If a solution be taken of equal {116} oxidising efficiency
with one of calcium hypochlorite, as indicated by the arsenious acid
test (see p. 206), it is found that the former possesses greater
_bleaching_ efficiency than the latter in the proportion of 5 to 3.
Moreover, the bleaching is much more rapid, and the loss of weight
which the substances undergo is less, for equal degrees of whiteness
obtained.

It has been shown that by the electrolytic method the bleaching of
paper pulp can be effected at nearly one-half the cost of bleaching
powder. The process is now being industrially carried out. Those
interested in the subject are referred to a paper by the authors in the
‘Journal of the Society of Chemical Industry’ for April 1887.

{117}




CHAPTER VIII.

BEATING.


The bleached pulp is now ready for the final treatment. If it were
attempted to make paper from the pulp in the state in which it leaves
the “potchers” or “steeping” chests, it would be found to be wanting in
evenness of texture and uniformity of surface. This result can only be
secured by an elaborate process of comminution or disintegration. This
is in effect the result produced by the action of the “beaters.”

They resemble in general appearance the breaking engines previously
described; the roll, however, carries more knives, and it is usually
let down much nearer to the bed-plate. In the case of fibrous
substances, whose ultimate fibres are relatively short (see table,
p. 39), it is only necessary to split up the filaments into their
constituent fibres: esparto, straw, and wood are of this class. In the
case of straw, the disintegration is for the most part accomplished
in the boiling and bleaching processes, and therefore but little work
devolves upon the beater. Esparto and wood require a certain amount of
beating, but this should be regulated to the drawing asunder of the
individual fibres, any cutting of the fibres being carefully avoided.
This is accomplished by adjusting the distance of the roll from the
bed-plate, so that by the friction of the fibres upon themselves, when
passing over the plate, a kind of rubbing or “brushing” is produced.
If a carefully-made paper of esparto or wood be examined by the
microscope, it will be found that the majority of the fibres preserve
the pointed or slightly rounded ends {118} characteristic of bast
cells. On the other hand, it is obvious that cotton, whose ultimate
fibres have a length of 20 to 40 mm., and flax (25–30 mm.), with other
similar fibres, will require to be broken up into short fragments in
order to develop to the fullest the felting property of the pulp. Not
only are the fibres reduced to the most favourable dimensions, but
in cotton and linen a further contributory advantage accrues; for on
account of the internal structure of the ultimate fibres they tend to
split up at the point of rupture into a number of fibrillæ, which, in
the case of cotton, take the form of a network; and in case of linen,
are seen as a bundle of distinct fibres parallel to and continuous
with the fibre. This gives to ends of the fragments a ragged contour,
which has considerable influence on the felting power of the pulp, and
therefore on the strength of the paper into which it is made.

With these fibres, therefore, the “cutting” as distinguished from the
“breaking” action should be avoided as much as possible, otherwise the
effect described above will not be produced, and the fibres will show
instead a clean cut. The appearance shown by cotton and linen pulp,
when thoroughly “beaten” and ready to be made into paper, is given in
the frontispiece, which is taken from the author’s micro-photographs.

The “half-stuff” is furnished to the “beater,” or “beating” engine as
it is sometimes called, previously partially filled with water. The
furnishing is done in successive portions, the first being allowed to
mix thoroughly with the water before another lot is added. This is
continued until the mass is so thick that it will only just turn round
in the beater under the action of the “roll.” Owing to the construction
of the beater it frequently happens that a portion of the pulp lodges
in the corners, from which the beaterman removes it by means of a
wooden paddle, which also serves to push forward the pulp to the roll
in case the motion is inclined to be sluggish. The proportion of
water to pulp should not be too high, otherwise the beating is not so
effective; at the same time, {119} if the mass is allowed to get too
thick, imperfect circulation results.

The operation of “beating” occupies a considerable time, and consumes a
large amount of power. Cotton and linen rags naturally take longer—in
some cases as much as ten hours is given to the operation.

Esparto, on the other hand, can be sufficiently disintegrated in from
two to four hours.

Wood pulp requires very gentle beating; it is therefore necessary to
prolong the time to about six hours.

These differences in the duration and method of beating should be borne
in mind when pulps of different natures are mixed together in the same
beater, as is frequently the case. It is better, with very dissimilar
fibres, to “beat” each separately, and only to mix them in the
stuff-chests. This, however, is open to the objection that the pulps
may be insufficiently mixed.

The length of fibre to which pulps should be reduced depends to some
extent upon the kind of paper to which it is to be applied. The authors
have examined a number of papers by well-known makers, and find the
dimensions in millimetres of various pulps to be as follows:—

  Fibre.          Maximum.  Minimum.  Mean.

  Cotton            1·32      0·23    0·75
  Linen             1·20      0·20    0·76
  Esparto           1·40      0·40    1·00
  Straw             1·50      0·50    0·88
  Wood              2·60      1·00    2·00

Wood and straw pulp, when imported in the form of dry sheets, may,
before being beaten, be conveniently disintegrated and thoroughly mixed
with water by means of the edge-runner described under “Broke Paper,”
p. 104, Fig. 28.

In making the finer kinds of paper, the roller bars or knives, instead
of being made of steel are made of bronze, thus any contamination with
oxide of iron is avoided. This is especially liable to take place in
case of steel knives when the beater has been allowed to stand for some
time. {120}

The inside of the heater itself is often lined with lead, a material
which is not liable to oxidize, and which can very readily be cleaned.

When a beater has been running for some time the knives of the roll and
the bed-plate become worn and so far reduced that they must be taken
out and re-cut. The bed-plate is removed, firmly fixed in the bed of a
planing machine, and the edges trimmed by means of a chisel, so as to
cut the knives at the proper angle.

The roll and bed-plate are shown in section in Fig. 32. Fig. 33 is a
plan of a bed-plate, and Fig. 34 illustrates the manner in which the
knives are fixed.

[Illustration: FIG. 32.]

It will be seen that the knives in the bed-plate are placed so that
they do not lie parallel with those of the roll. This arrangement
imitates to some extent the action of a pair of scissors. Occasionally
the knives are slightly bent, so as to form a very obtuse angle.
Bed-plates so fitted are called {121} “knee-plates.” They are largely
used in America, but not much in this country.

[Illustration: FIG. 33.]

[Illustration: FIG. 34.]

To obviate the necessity of removing the roll, a small machine has been
devised whereby the knives can be cut _in situ_. This machine, which
can be firmly fixed between the mid-feather and the side of the beater,
consists of a small steam-engine which actuates a movable cutter, which
is made to pass to and fro horizontally along the edge of each knife
in succession. The engine is supplied with steam by a piece of strong
flexible rubber tubing.

The ordinary form of beater contains only one roll, though some have
been constructed containing two or even four rolls. In America, beaters
of a totally different construction are much in vogue. The most
important of these are the Jordan and Kingsland beaters, so called
from the names of the inventors. The former consists essentially of a
roll in the shape of a truncated cone, fitted with knives in the usual
way, revolving in an iron box of corresponding shape, furnished with
knives placed in the direction of its length, but at slightly different
angles. The half-stuff enters the beater at the narrow end through a
box provided with an {122} arrangement for regulating the flow, and is
discharged by two or more openings in the cover at the wider end.

The Kingsland engine consists of a circular chamber, the sides of which
are covered with knives, and between which a circular plate, also
furnished with knives, revolves. The pulp 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.

Another form of beater is that invented by S. L. Gould. The only
essential difference between it and the Kingsland beater is that,
instead of having a plate which revolves vertically against two
stationary ones, the plate, which is placed horizontally, is furnished
with knives on one side only, and revolves upon but one fixed plate,
much in the same way as a pair of millstones.

The half-stuff supplied to these forms of beater is generally
disintegrated to a greater extent in the breaker than is the case with
those of the ordinary construction, as it is necessary to make it flow
easily through them, and this could not be done if the fibres were kept
long. A single passage of the pulp through the beater is sufficient to
beat it up ready for making into paper. The chief advantages claimed
for them is that they are more economical, both of time and power; also
that the pulp is more regularly beaten.

Certain new forms of beaters have lately been introduced in this
country, and are rapidly gaining in favour, chiefly on account of
the saving of driving power, and the space occupied, compared with
the amount of “stuff” they are capable of beating. Fig. 35 shows the
construction of Forbes’ patent engine, as manufactured by Messrs. G. &
W. Bertram, of Edinburgh. This beater is divided into three channels.
The rolls, one of which is shown uncovered, are placed in the outer
channels, while in the centre one the mixing and circulating wheel a is
placed, the peculiar construction of which enables it to throw the pulp
alternately into the two outer channels, from whence, after passing
under the rolls again, it enters the central channel at the other end
of the beater. {123}

In Umpherston’s patent engine great economy of space is effected by
causing the pulp to travel over and under the backfall (_a_, Fig. 36).
Another advantage is that the stuff circulates freely with less water
than in the ordinary forms, thus increasing its output. It is also
claimed that the pulp is beaten with less power, and as it is less
liable to lodge in corners it is more evenly beaten.

[Illustration: FIG. 35.]

The construction of the engine will be readily understood by reference
to Fig. 36. The direction which the stuff takes is indicated by the
arrows.

Cooke and Hibbert’s beater, as manufactured by Messrs. Masson, Scott
and Bertram, resembles, to a certain extent, Gould’s engine, previously
described; it differs from it, however, in that the discs are placed
vertically, instead of horizontally. Moreover, the general construction
of the beater more nearly resembles those in ordinary use. Fig. 37,
which shows it in plan and in section at the line D E, illustrates its
construction.

[Illustration: FIG. 36.]

[Illustration: FIG. 37.]

The shaded portions A represent the stationary disc. It is furnished
for about two-thirds of its circumference with steel bars or knives,
placed tangentially. B represents the {125} revolving disc on which
similar knives are placed radially round the whole circumference. The
direction that the pulp takes is indicated by the arrows. After passing
between the plates it is thrown violently into the trough at G, the
result being that it is very thoroughly mixed. The distance between the
plates can be regulated by means of the gearing H. The engine is driven
by the pulley C fixed on the shaft F. It is claimed that by means of
this form of beater a great saving in time and power is effected, and
that moreover the pulp is obtained in a more even condition.

[Illustration: FIG. 38.]

[Illustration: FIG. 39.]

The quality of the water used to furnish the engine is a matter of very
great importance, especially in the manufacture of high-class papers.
Above all it should be free from suspended matter, and from dissolved
iron; the former finds its way directly into the paper, and the latter
is liable to become precipitated in the pulp as oxide, thus injuriously
affecting its colour. Careful settling and filtration are sufficient to
eliminate insoluble matter; soluble impurities are more difficult of
removal; therefore the water should, if possible, be free from them.
In most mills settling ponds are provided, for the purpose of removing
suspended matter, and in addition it is usual to employ woollen
filter-bags {126} fastened to the nozzle of the pipe that supplies the
beaters with water.

For methods of purifying water see p. 211.

The beaters are generally driven from a separate engine, and are
connected with it by a system of spur-wheels, pinions, and belts.
Messrs. G. and W. Bertram have lately introduced a system of direct
driving of beaters, whereby a great saving in power is effected. It is
illustrated in plan and elevation in Figs. 38 and 39. The crank-shaft
of the engine is coupled direct on to the main driving-shaft. Large
pulleys are keyed on to this shaft, from which the power is taken
directly on to the pulleys connected with the rolls.

{127}




CHAPTER IX.

LOADING, SIZING, COLOURING, ETC.


The bleached half-stuff as it leaves the steeping chests usually
contains an excess of bleaching liquor, which can be removed in two
ways, viz. by washing or by decomposition with an “antichlor.” The
first method has the advantage of not only removing the bleach, but
of also eliminating the chloride of calcium, partly existing ready
formed, and also that resulting from the decomposition of the calcium
hypochlorite originally present in the bleach. On the other hand, this
method takes some time, and consumes a large amount of water, which in
some mills is a matter of considerable importance. For this purpose,
many beaters are provided with one or more drum washers (see Fig. 36).
An additional objection to this method lies in the fact that a certain
quantity of fibre passes through the meshes of the wire-cloth covering
the washers, and is thus lost.

The more usual plan is to remove the bleach by decomposing it with
an “antichlor.” The substance generally employed for this purpose is
sodium hyposulphite, or thiosulphate as it is now called, which, in
presence of calcium hypochlorite, is oxidized to sodium sulphate, the
latter being reduced to calcium chloride. Double decomposition then
takes place between these salts, with the formation of calcium sulphate
and sodium chloride. The reactions which take place may be expressed by
the following equation:—

  2 (Ca(ClO)_{2}) + Na_{2}S_{2}O_{3} + H_{2}O = 2 CaSO_{4} + 2 HCl  +    2 NaCl.
     Calcium             Sodium       Water.    Calcium  Hydrochloric  Sodium
   hypochlorite.      thiosulphate.            sulphate.    acid.      chloride.

{128}

The above decomposition does not accurately represent the action of
bleach upon sodium thiosulphate. If the solutions employed are very
dilute, the decomposition may take place in another direction, viz.:—

  Ca(ClO)_{2} + 4 Na_{2}S_{2}O_{3} + H_{2}O = 2 Na_{2}S_{4}O_{6} + 2 NaCl
    Calcium            Sodium        Water.          Sodium        Sodium
  hypochlorite.     thiosulphate.                tetrathionate.   chloride.

                        + 2 NaOH +  CaO.
                     Caustic soda.  Lime.

At the particular degree of dilution which occurs in a beater, the
bleach is decomposed almost entirely according to the first of the
equations; from which, on calculating, it will be seen that 158
parts of sodium thiosulphate are equivalent to 286 parts of calcium
hypochlorite. As commercial sodium thiosulphate contains 36·3 per cent.
of water, and bleaching powder 70 per cent. of calcium hypochlorite, on
the basis of 35 per cent. available chlorine it follows that 248 parts
of the former are required to neutralize 409 parts of the latter.

Within the last few years other forms of “antichlor” have been
introduced, such, for example, as the various sulphites. The most
important of these is sodium sulphite, which has been manufactured by
a patent process at a cheap rate, by Gaskell, Deacon, & Co., Widnes.
Their product contained as much as 75 per cent. of Na_{2}SO_{3},
ordinary crystallized sodium sulphite containing only 50 per cent.

Sulphites are converted by the action of bleach into sulphates, thus:—

  Ca(OCl)_{2} + 2 Na_{2}SO_{3} = CaSO_{4} + 2 Na_{2}SO_{4} + 2 NaCl
    Calcium          Sodium      Calcium        Sodium        Sodium
  hypochlorite.     sulphite.    sulphate.     sulphate.     chloride.

From this equation, it will be seen that 252 parts of sodium sulphite
will neutralize 143 parts of calcium hypochlorite, or 204·3 parts of
bleaching powder. Assuming that crystallized sodium sulphite contains
50 per cent. Na_{2}SO_{3}, the same amount of bleach would require 504
parts. As Messrs. Gaskell, Deacon & Co.’s sulphite contains 75 per
cent. Na_{2}SO_{3}, only 336 parts are needed. Comparing these numbers
with {129} those given above for sodium hyposulphite, it will be seen
that 204·5 parts of bleach require for neutralisation 129 parts of
sodium thiosulphate and 504 parts of crystallised sodium sulphite, or
336 parts of the stronger product.

Sodium sulphite is preferred to sodium thiosulphate by some paper
makers, notwithstanding the fact that even in its most concentrated
form, nearly three times as much is required to produce a certain
result. It is said that when it is used the wire cloth of the machine
is preserved for a longer time than if sodium thiosulphate is employed.
This may be due to the fact that with the latter a certain amount of
free acid is always formed, which of course would act injuriously
on the wire; whereas, when sodium sulphite is used, the products of
decomposition are neutral salts without any action upon metals. (See
the above equations.)

A very cheap “antichlor” may be prepared by boiling together lime and
sulphur. One hundred and sixty-eight parts of lime, made into a milk
with water, are heated to boiling in an iron vessel. Three hundred and
eighty-four parts of flour of sulphur or ground sulphur are then added
in small quantities at a time, and the boiling continued until the
whole is dissolved. The liquid which is now of a deep yellow colour,
is allowed to settle and cool and is then ready for use. It contains a
mixture of calcium thiosulphate and calcium pentasulphide, the latter
compound giving to it its deep yellow colour. The following equation
represents the action which takes place between the lime and the
sulphur:—

  3 CaO   +   12 S    =   CaS_{2}O_{3}   +   2 CaS_{5}
  Lime.     Sulphur.        Calcium            Calcium
                          thiosulphate.     pentasulphide.

The decomposition which takes place when the mixture is acted upon by
calcium hypochlorite may be represented as follows:—

  2 (CaS_{2}O_{3} + 2 CaS_{5}) + 9 (Ca(OCl)_{2}) = 6 CaSO_{4}  +
      Calcium        Calcium         Calcium       Calcium
   thiosulphate.  pentasulphide.  hypochlorite.    sulphate.

   18 S +   9 CaCl_{2}
  Sulphur.  Calcium
            chloride.

{130}

From this it is seen that a large quantity of free sulphur is formed,
which is precipitated as a fine yellowish powder in the fibre. This not
only affects the colour of the pulp, but is objectionable on account of
its liability, in contact with the hot cylinders of the paper machine,
or by the action of moisture over a long period of time to become
oxidised to sulphuric acid, which undoubtedly, even if present only in
very small quantities, has an injurious effect upon the finished paper.
(See hydracellulose.) This property of sulphur and its action upon
cellulose may be shown by the following experiment. Take a piece of
water-leaf paper, rub into it a mixture of flour of sulphur and water.
If the paper thus treated be rapidly dried, it will be found to be
weakened or even slightly charred in those portions which have been in
contact with the sulphur. (See also Chem. Soc. Journ., p. 249, 1879.)

Whichever variety of “antichlor” is used an excess should be carefully
avoided, as all act more or less upon the size and colouring matter
added to the pulp subsequently. The proper method is to run in small
quantities of a solution of the antichlor at a time, testing the
pulps, after allowing a few minutes for complete admixture after each
addition. The test is made by immersing a piece of iodide of potassium
and starch paper, which will be turned blue so long as any calcium
hypochlorite is present. These papers are made as follows:—

Three grms. of starch are ground up with a small quantity of water and
poured into 700 cc. of boiling water, and to the solution 1 grm. of
iodide of potassium and 0·5 grm. carbonate of soda are added. Sheets of
white paper, water-leaf in preference, are now soaked in the solution
and dried. In presence of calcium hypochlorite, iodine is liberated
from the potassium iodide, and acting upon the starch forms with it a
characteristic blue colour.


_Loading._—It is usual, except in the case of papers of the very
highest quality, to add to the pulp a quantity of some cheap loading
material, such as china clay, or for the better {131} qualities of
paper, “pearl-hardening,” or sulphate of lime. The addition of clay in
moderate quantity can hardly be looked upon as an adulteration, since
it serves to fill up the pores of the paper, and enables it to take a
good surface in the subsequent operations of calendering. Moreover, it
enables the manufacturer to meet the demand for cheap papers with some
chance of remuneration to himself. If added largely, it of course tends
to weaken the paper.

China clay or kaolin is sold in the form of large lumps of a white or
yellowish-white colour. It is formed by the gradual disintegration
of felspar by means of the action of air and water, and consists
essentially of a silicate of aluminium. Its quality depends upon its
whiteness and its freedom from coarse micaceous particles. It is
usually prepared for admixture with the pulp by making it into a fine
cream with water in a vessel provided with stirrers; it is then passed
through a fine sieve in order to remove any impurities it may contain,
and is then run into the beater. The clay or other filling material
is usually run into the beater as soon as the latter is charged with
pulp, so that by the time the beating operation is concluded, a perfect
admixture of pulp and clay is effected.

Sulphate of lime, or “pearl-hardening,” is usually sufficiently pure
to put direct into the engine. It is made by decomposing a solution of
calcium chloride, with sulphate of soda, and is precipitated as a fine
brilliantly white powder, consisting of CaSO_{4} + 2 H_{2}O.

Two distinct forms of precipitated calcium sulphate are met with in
commerce, differing from each other by their microscopical features,
the one consisting of flat tabular crystals (Fig. 41), the other of
fine needles (Fig. 42). Another form, erroneously called precipitated
pearl-hardening, is also sold: it consists of the finely ground native
mineral.

[Illustration: FIG. 40.]

[Illustration: FIG. 41.]

Some of the finer qualities of paper are made without addition of
any loading material whatever, though such papers are of course the
exception. The proportion of clay or {132} other material that can be
put into a fibre depends to a certain extent upon the nature of the
fibre, and upon the degree of fineness to which it is reduced in the
beater. The amount added by different makers varies considerably, from
{133} two or three per cent. to twenty, and even in rare cases to
thirty per cent.

[Illustration: FIG. 42.]

[Illustration: FIG. 43.]

A new loading material called “agalite” has been lately introduced,
possessing certain advantages over china clay, {134} or calcium
sulphate. Agalite is a mineral of the nature and chemical properties
of asbestos: it consists of nearly pure magnesium silicate. Its
structure is more or less fibrous, like that of asbestos, which,
as is well known, can be spun and woven and even made into paper,
and it therefore, when added to a paper, forms a part of the fabric
itself. It is even claimed that it assists in keeping back some of
the finer fibres that invariably find their way through the meshes of
the wire cloth, and it is said that 90 per cent. of the amount added
to the engine is found in the paper. In the case of china clay it is
well known that only from 40 to 60 per cent. is actually “carried”
by the pulp. Figs. 40, 41, 42, and 43 show the appearance of china
clay, pearl-hardening, and agalite when viewed under the microscope,
magnified 200 times. The nature of agalite is such that it assists the
paper in taking a high finish. This is probably due to its “soapy”
nature, a feature which is characteristic of asbestos, French chalk,
“soap-stone,” and other magnesium silicates.

[Illustration: FIG. 44.]

When papers contain such excessive quantities as 15 or 20 per cent.
of clay, it cannot be to the advantage of the consumer, and should be
looked upon as an adulteration. It is a matter of some importance to be
able to determine rapidly and accurately the amount of mineral matter
in a paper. The usual method is to ignite a weighed quantity of the
paper in a platinum crucible until the ash so obtained is either white
or a very pale grey. From the weight of the ash, the percentage of
mineral matter is easily calculated. The following is a very convenient
plan in cases where a platinum crucible or dish is not obtainable:—Take
a weighed piece of the paper to be examined, from 2 to 4 in. square,
according to the thickness, roll it into a narrow hollow cylinder.
Round this wind a weighed piece of platinum wire about 1⁠/⁠50 in.
thick, as in Fig. 44. Hold this by means of a pair of crucible tongs
in the flame of a Bunsen burner until it is completely burned. If the
wire is carefully wound round, and especially if the roll of paper is
made conical, the ash will be securely held in {135} position. Those
who do not possess a chemical balance of the ordinary form will find
a convenient substitute, which will answer the purpose of weighing
the paper and ash with sufficient accuracy, in the spiral balance
invented by Prof. Jolly[11] illustrated in Fig. 44. It consists of a
spiral of hard wire A, which is suspended in front of a mirror B, upon
which millimetre divisions are marked. A small float D, dipping under
the surface of the water in the vessel E, is provided for the purpose
of steadying the spiral and allowing it to come quickly to rest. The
balance is provided with a light pan made of a thin plate of mica,
and suspended by very thin platinum wires. For the present purpose,
however, the pan is not necessary, and it can be replaced by the roll
of paper and platinum coil as shown in the drawing.

     [Footnote 11: This balance can be obtained from Nalder Bros. &
     Co., Westminster.]

The method of using is exceedingly simple, as the increase in the
length of the spiral is in direct ratio to the increment of weight. The
position of the spiral is ascertained by placing the eye in a direct
line with the small glass bead C and its image in the mirror, and
noting the corresponding division on the scale. The position of the
bead can be altered so as to bring it to any desired point on the scale
by raising or lowering the upright rod F, which is kept in position
by the screw G. The balance stands on a foot provided with levelling
screws.

It is evident that where _proportional_ weights only are required it
is not necessary to know the value of the spiral, but if the balance
is to be used to ascertain _actual_ weights, the coefficient of the
spiral must first be determined. This is done by noting the increase in
length after the addition of a one gram weight. The spirals are made
of different thicknesses of wire, which of course give varying degrees
{136} of sensibility: the most useful is one which gives with one gram
an extension of 100 millimetres: one mm. being therefore equivalent to
one mgrm.

The following experiment will illustrate the method of using the
balance and of calculating the results of a determination of the amount
of mineral matter in a paper:—

  Position of bead on scale                               100 mm.
  Position of bead after attaching platinum wire          151  „
  Position of bead with wire and roll of paper attached   200  „
  Weight of paper expressed as millimetres 200−151    =    49  „
  Position of bead with wire and ash attached           156·5  „
  Weight of ash expressed as millimetres  156·5−151   =   5·5  „

  Weight of paper           Weight of ash  Percentage of
    expressed in            expressed in      ash in
    millimetres.            millimetres.      paper.
        49    :    100    ::    5·5      :   11·224

In order to ascertain the percentage of mineral matter _actually added_
to a paper it is necessary to deduct from the amount of ash obtained a
certain quantity due to the mineral matter in the fibre of which the
paper is composed. This amount varies with each particular fibre, and
with the method by which it has been prepared. The following table
gives the percentage of ash yielded by the various pulps in a perfectly
bleached state. In all cases the fibres were previously treated with a
dilute solution of hydrochloric acid, in order to remove any carbonate
of lime or other bodies which might have been introduced in the boiling
and bleaching processes: the percentages are calculated on the dry
substances:—

  Pulp from linen rags                  ·25 ash per cent.
  Pulp from cotton rags                 ·10  „     „
  Pulp from esparto                     ·50  „     „
  Pulp from straw (soda process)       4·80  „     „
  Pulp from straw (Leunig process)     1·36  „     „
  Pulp from wood (soda process)         ·50  „     „
  Pulp from wood (bisulphite process)   ·06  „     „
  Pulp from wood (mechanical)           ·40  „     „

If the paper contains calcium sulphate the ash obtained may consist
partly of calcium sulphide, due to the reducing action of the carbon
found on ignition, and the amount will {137} therefore not represent
the true amount added. The ash should be moistened with a few drops
of sulphuric acid, and again ignited, in order to reconvert it into
calcium sulphate. It should also be borne in mind that the sulphate
of lime as present in the paper is combined with two atoms of water
CaSO_{4} + 2 H_{2}O, and therefore that every part of calcium sulphate
obtained represents 1·26 parts of “pearl-hardening” actually added.


_Sizing._—Papers that are intended to be written upon with ink, and
also most printing papers, require to have the interstices of the
fibres filled up with some material which will to a greater or less
extent resist the action of water, and thus prevent the ink or other
liquid applied to them from “running.” This may be accomplished in
two ways, viz., by “engine-sizing” and “tub-sizing”; the former is so
called because it is performed in the beating engine itself, the latter
being done on the finished paper, as will be subsequently described.
Engine-sizing consists in precipitating a compound called resinate
of alumina in the pulp. This compound when dried has the property of
being with difficulty wetted with water. In order to obtain a thorough
mixture of this compound with the fibre it is formed in the engine by
adding an aqueous solution of rosin-soap to the pulp, and when this is
intimately mixed with it, running in a solution of alum.

Rosin (colophony) consists of a mixture of pinic and sylvic acids,
which, when heated with a solution of carbonate of soda, combine with
the alkali to form a soap, carbonic acid being evolved. The soap is
prepared in the following manner:—

Ordinary rosin, the quality depending upon the quality of paper,
is boiled in a jacketed pan for from two to three hours with a
solution of carbonate of soda, until a sample of the soap formed
is completely soluble in water. The quantity of carbonate of soda
(Na_{2}CO_{3} 10 H_{2}O) required is about 30 per cent. of the weight
of the rosin. It is usual to employ crystallised carbonate of soda
(soda-crystals), but {138} soda-ash of good quality, or even caustic
soda, might very well be employed, in which case of course the
proportion would be different.

A very convenient form of carbonate of soda has lately been introduced
by Messrs. Gaskell, Deacon & Co., which goes by the name of “Crystal
Carbonate.” It is obtained in the form of minute crystals of the
mono-hydrate, Na_{2}CO_{3} + H_{2}O. It contains 50 per cent. of
alkali (Na_{2}O), and possesses this advantage over soda-ash, that
is dissolves readily in water without forming a hard cake. It is
much cheaper in proportion than soda crystals, as the expense of
crystallisation and carriage is saved. The latter contain only 21·68
per cent. Na_{2}O, 62·93 per cent. of their weight consisting of water
of crystallisation. One hundred parts of soda crystals are equivalent
to 43·36 parts of the “Crystal Carbonate.”

An excess of soda should be carefully avoided, as it consumes an
equivalent quantity of alum (see below): on the other hand, it is very
essential that the rosin should be completely dissolved, otherwise
small particles are sure to find their way into the pulp, and would
form clear transparent specks in the finished paper.

The boiling being completed, the charge is run off into iron tanks
and allowed to settle; the soap forms a semi-solid mass, while a
dark-coloured liquor, containing the impurities of the rosin, rises
to the surface, and can thus be removed. The soap so purified is next
dissolved in hot water containing a small quantity of carbonate of
soda, in case complete solubility has not been attained, and is then
mixed with a quantity of starch paste prepared in a separate vessel
by dissolving starch in boiling water. The mixture is then carefully
sieved and is ready for use.

The proportion of starch to rosin differs in nearly every mill, and
also the quantity of size to be added to the beater varies according as
the paper is required to be soft or hard-sized. About 3 parts of starch
to 1 of rosin, and between 3 or 4 lbs. of the mixture to 100 lbs. of
pulp may be considered an average quantity. Some manufacturers prefer
to add the {139} starch and rosin size to the engine separately;
others again do not dissolve the starch in water, but merely make it up
to a thin paste, in which state it is added to the pulp. This method is
employed by makers of very fine papers, as it is said to give a certain
feel to the paper which cannot be obtained in any other way. The method
is costly, as only a small proportion of the starch added is actually
found in the paper.

Some papers, which are not intended to be sized, such as blotting and
filter-papers, are made with the addition of starch only, this being
used to bind the fibres together to some extent. The presence of the
starch does not prevent the paper from being absorbent. Papers which
are intended to be tub-sized only are usually made up with a small
quantity of starch, and are sometimes sized to a small extent with
rosin also. The addition of a certain amount of ordinary soap to the
rosin soap is said to give good results; it enables the paper to take a
higher finish when calendered. Sizing with animal size (gelatine), or
Tub-sizing as it is called, will be described in Chapter X.

The mixture of size and starch may be added directly to the engine, or
it may be previously dissolved in water; the latter method is perhaps
preferable. After allowing it to mix thoroughly with the pulp, a
solution of alum is run in. It is made up with boiling water in either
lead or copper tanks. Iron or zinc vessels must be avoided, as the
solution acts rapidly on these metals.

Alum consists of a double sulphate of aluminium and potassium or
ammonium, Al_{2}3 SO_{4}, K_{2}SO_{4} + 24 H_{2}O; its function being
to form with the rosin acids insoluble soaps which are precipitated in
intimate mixture with the pulp, the sulphate of potash taking no part
in the reaction. The choice of a suitable alum is a matter of very
great importance; it should be free from excess of sulphuric acid and
from iron. The former is deleterious on account of its action upon the
colouring matter used to tone the paper, some colours being completely
discharged by it; and because {140} of its effect upon any metal work
with which it may come in contact, especially upon the brass wire-cloth
on which the paper is made. The iron is objectionable as it forms a
dark red precipitate of oxide of iron.

Alum as supplied by makers of repute is generally sufficiently pure for
even the best classes of paper.

Many years ago a substitute for alum was introduced, called Pochin’s
aluminous cake. It consisted principally of sulphate of alumina
Al_{2}3 SO_{4}, and was, provided it was pure, as suitable for the
papermaker as the more expensive potash alum. It was more economical
at equal price, as it contained about 14 per cent. of alumina, whereas
potash alum, even if absolutely pure, could only contain 10·85 per
cent. Pochin’s aluminous cake however, was liable to contain a
considerable amount of free sulphuric acid and soluble sulphate of
iron. Of late years, a number of different varieties of sulphates of
alumina have been introduced into commerce, of so pure a nature, and
at such a low price, that it is a matter of wonder that they have
not entirely superseded the more expensive alum. They are prepared
either from very pure native alumina (bauxite), or from China clay of
good quality. Methods have been discovered of eliminating almost the
whole of the iron and free sulphuric acid. The following analyses of
different specimens sufficiently indicate their purity.[12]

  Alumina (Al_{2}O_{3})        14·84  14·70  14·95  14·85  16·00  16·20
  Ferric oxide (Fe_{2}O_{3})     ·06    ·12    ·05  trace    nil  trace
  Sulphuric acid (SO_{3})      35·00  34·60  36·09  34·94  38·00  38·00
  Free sulphuric acid            ·32    ·40    nil    ·29    nil    nil
  Lime (CaO)                     ·11    ·11    ·17    ·14    ·16    ·14
  Water                        49·42  49·95  48·72  49·60  45·50  45·43
                               ─────  ─────  ─────  ─────  ─────  ─────
                               99·75  99·88  99·98  99·82  99·66  99·75

     [Footnote 12: Journ. Soc. Chem. Ind., Jan. 1886, p. 16.]

Sulphate of alumina possesses this advantage over alum, that it is more
soluble in water, and thus a stock solution of considerable strength
can be prepared. It is soluble in {141} 2 parts of cold water, alum
requiring 18 parts for complete solution.

The amount of alum or sulphate of alumina added to a pulp is largely
in excess of the quantity necessary to precipitate the rosin soap;
as a matter of fact, in the case of esparto or straw pulps, for
the bleaching of which considerable quantities of bleach have been
employed, and which therefore contain a certain amount of basic lime,
together with calcium chloride, complete precipitation of the size
is effected without the addition of alum. A certain amount is also
required to precipitate the starch. The excess of alum appears to be
necessary, however, not only to brighten the colour of the paper,
but also to render it capable of resisting the action of ink. From
experiments made by the authors, it appears that one part of rosin
requires 2·9 parts of alum for complete precipitation from its solution
in soda. One part of starch requires 0·40 part alum.


_Colouring._—Cellulose, except in rare instances, is never sufficiently
white to produce a perfectly white paper, and the manufacturer finds
it necessary to complement the slightly yellow colour which most
bleached pulps possess by the addition of small quantities of blue and
pink colouring materials. The blues usually employed are ultramarine,
smalts, and aniline blues; the pinks are generally preparations of
either cochineal or aniline dyes. Ultramarine is met with in commerce
as a bright blue powder; the shade of colour and the quality of which
vary considerably.

In choosing an ultramarine, attention should be directed not only to
its tinctorial power but to its behaviour with a solution of alum,
inferior qualities being entirely discharged by it. All ultramarines
are readily decomposed by free acids, hence the necessity of employing
an alum as free as possible from this impurity.

Smalts on the other hand resists the action of acids, but it is only
used for the finer qualities of paper, owing to its high price. The
aniline blues are perhaps scarcely so brilliant in colour as the
above-mentioned colours, and they {142} are moreover somewhat readily
discharged by the action of light; they have however the advantage of
cheapness.

The pink colouring matters are sold either as lakes, that is, compounds
of the colouring matter with alumina or as solutions. They are also
frequently to be met with mixed with starch in varying proportions.
Those made from cochineal are superior to those containing aniline
colours.

Ultramarine can be detected by means of its reaction with hydrochloric
acid, the colour being discharged and sulphuretted hydrogen evolved,
which can be recognised by its odour. Smalts is not acted upon by
acids. The latter contains cobalt, the presence of which can be
determined by its giving a blue bead with borax in a blowpipe flame.

The aniline blues are soluble either in hot water or hot alcohol,
the liquid being intensely coloured. Most of them are discharged
by treatment either with strong acids or alkalis, the colour being
restored by the reverse treatment.

Paper of any desired colour may be made either by using rags already
dyed the necessary colour or by adding to the bleached pulp in the
beater such dyes or pigments as will produce it. Any colouring matter
which can be obtained in the form of a fine powder or as a solution can
be used. Blue papers are usually coloured with ultramarine; the dark
blue papers used for wrapping sugar and other purposes are coloured
with Prussian blue, either added directly to the beater or produced in
it by the action of potassium ferrocyanide on ferric sulphate.

The so-called toned paper is produced by adding to the pulp a solution
of pernitrate of iron, from which a fine precipitate of oxide of
iron is deposited on the fibres; thus the slightly brown shade
characteristic of this kind of paper is produced. The same effect may
be produced by the addition of yellow ochre or some similar pigment.
The following are a few of the materials which are used for producing
coloured papers:—Methyl violet, eosine, chrome yellow, venetian red,
catechu. Useful receipts for the preparation of coloured papers will be
found in Dunbar’s ‘Practical Paper-Maker.’ {143}

During the time that the loading, sizing and colouring processes have
been going on, the pulp has been continually acted upon by the roll,
and if these operations have extended over a considerable time, it is
probably in a proper condition for making into paper. The amount of
“beating” depends, as has been stated before, upon the nature of the
fibre, and also to some extent on the nature of the paper for which
it is intended. The “beaterman” examines the pulp from time to time
by taking a portion from the engine and placing it in a hand-bowl
containing water: from its appearance when so diluted he is able to
judge of the time during which it may be necessary to continue the
disintegration. As soon as this is completed, the pulp is ready to be
let down to the stuff-chests, usually placed at a lower level than
the beaters, so that the pulp can flow into them by gravity. For this
purpose the valve at the bottom of the engine is opened: to remove the
last portion of pulp it is necessary to rinse out the engine with water.

  TABLE.—STRENGTH OF ALUM SOLUTIONS (17·5° C., 63·5° F.).

  +------------------------+-------------------+------------------+
  |Percentage of           | Specific Gravity. | Degrees Twaddle. |
  |K_{2}Al_{2}(SO_{4})_{4} |                   |                  |
  |+ 24 H_{2}O.            |                   |                  |
  +------------------------+-------------------+------------------+
  |   1·0                  |    1·0065         |      1·30        |
  |   2·0                  |    1·0110         |      2·20        |
  |   3·0                  |    1·0166         |      3·32        |
  |   4·0                  |    1·0218         |      4·36        |
  |   5·0                  |    1·0269         |      5·38        |
  |   6·0                  |    1·0320         |      6·40        |
  +------------------------+-------------------+------------------+

{144}




CHAPTER X.

PAPER MACHINES; HAND-MADE PAPER.


The pulp as it comes from the beaters is now ready to be made into
paper. We will first consider briefly the manufacture of hand-made
paper.

It is made on a mould of wire-cloth, with a movable frame of wood,
called the “deckle,” fitting on to the outside of the mould and
extending slightly above its surface.

The wire-cloth is generally supported by a much coarser wire-cloth,
or by pieces of thick wire, and these again by wedge-shaped pieces of
wood, the thin end being next to the wire.

To form a sheet of paper the workman dips the mould, with the “deckle”
in position, into a vat containing the prepared pulp diluted with
water, lifting up just so much as will make a sheet of the necessary
thickness. As soon as the mould is removed from the vat, the water
begins to drain through the wire-cloth, and to leave the fibres on
the surface in the form of a coherent sheet of paper. The felting or
intertwining is assisted by lateral motion in every direction given to
the frame by the workman. The movable deckle is then removed, and the
mould, with the sheet of paper, given to another workman, called the
“coucher,” who turns it over and presses it against the felt, by this
means transferring the sheet from the wire to the felt. In the meantime
the “vat-man” is engaged in the formation of another sheet with a
second mould.

[Illustration: THE FOURDRINIER PAPER MACHINE.

PLATE I.]

A number of the sheets thus formed are piled together, alternately
with pieces of felt, and when a sufficient number {145} have been
obtained, the whole is subjected to strong pressure, to expel the
water. The felts are then removed, and the sheets again pressed.

They are then sized, if required, by dipping them into a solution of
gelatine: again slightly pressed, and hung up on lines or poles to dry.
Such paper is called loft-dried.

When dry the sheets of paper are calendered. (See Chapter XI.)

The making of paper by hand involves considerable dexterity on the
part of the workman; on account of the expensive labour necessary, in
comparison with paper-machines, it is comparatively little practised in
the present day; certain kinds of paper, however, such as bank-notes,
various drawing papers, and printing papers intended for the production
of very elaborate editions are always made in this way.

Any pattern or name required on the paper is obtained by means of a
raised pattern on the wire-cloth mould: consequently, less pulp lodges
there, and the paper is proportionally thinner, thus showing the exact
counterpart of the pattern. Such devices are known as “water-marks.”
(See also p. 156.)


_The Paper Machine._—The paper machine of the present day, with all
its ingenious improvements, differs but little in principle from that
originally constructed by Fourdrinier. It consists essentially of an
endless mould of wire-cloth, on to which the prepared pulp flows, and
on which a continuous sheet of paper is formed. The sheet of paper
then passes through a series of rollers and over a number of heated
cylinders, where it is completely dried.

A modern Fourdrinier paper machine is shown in plan and side elevation
in Plates I. and II.

The pulp, after leaving the beaters, passes into a large vessel called
the stuff-chest, of which there are one or more to each machine. As
soon as the beater is empty, water is run in to thoroughly rinse out
the remaining pulp, the washings also going into the stuff-chests.
These may be {146} made either of wood or iron, and should be provided
with arms fixed on a vertical shaft, made to revolve by suitable
gearing. The arms are for the purpose of keeping the pulp thoroughly
mixed, and should only work at a moderate speed, otherwise they are
liable to cause the fibres to form into small knots or lumps. The
pulp is drawn from the stuff-chests by means of the pump A, and is
discharged into a regulating-box (not shown). The object of this box
is to keep a regular and constant supply of pulp on the machine. It
consists of a cylindrical vessel, having two overflow-pipes near the
top, and a discharge-pipe near the bottom. The pulp is pumped in
through a ball-valve in the bottom, in larger quantity than is actually
needed, the excess flowing away back into the stuff-chests, through
the two overflow-pipes. By this means, the box is always kept full,
and therefore the stream of pulp issuing out of the bottom pipe is
always under the same pressure. It flows from this pipe, the quantity
being regulated by means of a cock, according to the thickness of paper
required, directly on to the sand-tables. These may be of various
sizes and shapes, but should be so large that the pulp takes some
little time to travel over them. They consist of long shallow troughs,
generally of a sinuous form. The bottoms are sometimes covered with
woollen felt, or with thin strips of wood placed across the direction
of the flow of the pulp, and at a slight angle. These serve to retain
any particles, such as sand and dirt, that may have escaped removal
in the previous treatment of the pulp, and that are heavy enough to
have sunk down during the passage of the pulp along the sand-tables.
In some mills, where great care is exercised, the pulp is caused to
flow over sand-tables 200 yards in length. As the pulp, when it leaves
the stuff-chests, does not contain sufficient water for the purpose
of making paper, it is mixed, where it enters the sand-tables, with a
quantity of water from the “save-all” (see p. 154), flowing from the
box B placed at a higher level.

In some mills, instead of being pumped into the {147} regulating-box,
the pulp flows into a small vessel below the stuff-chest, and is lifted
on to the sand-tables by means of buckets fastened on the circumference
of a wheel.

The pulp, after leaving the sand-tables, passes on to the strainers.
These consist of strong brass or bronze plates, having a large number
of very fine V-shaped slits cut in them, the narrowest end being on the
outside.


_Strainers._—The strainers are for the purpose of removing from the
pulp all lumps formed by the intertwining of the fibres, and all pieces
of unboiled fibre, which, if allowed to pass on, would show in the
paper as inequalities in the surface, or as dark specks. The slits
are made narrow at the top, and gradually increasing in width, so as
to prevent them from getting choked up. These slits allow only the
individual fibres to pass through, and their width varies according to
the quality of the paper. They are from 2 to 3 in. long, and they vary
in width from ·007 to ·05 in. They are put at distances of about 1⁠/⁠4
in. apart. Several plates, each containing about 500 slits, are bolted
together, and form a strainer. The whole strainer receives a violent
shaking motion, to assist the passage of the fibres through the slits.
In the machine represented, two of these strainers are shown at C. The
shaking motion is produced by the ratchet-wheel or cams _a_ acting on
the hammer _b_. An improved form, called the “revolving strainer,” has
of late years been introduced. The pulp generally passes first through
one of these, and then through the ordinary or “flat” strainers, as
they are called. A revolving strainer is shown at D. It consists of a
rectangular box, the sides of which are formed of plates perforated
with slits. Inside this box, a slight vacuum is formed by means of an
indiarubber bellows worked by a crank on the shaft _d_. The vacuum is
intended to serve the purpose of the shake in the ordinary form. The
box revolves slowly inside a vat containing the pulp, and the strained
pulp flows into the box D^1, and thence on to the flat strainers.

[Illustration: FIG. 45.]

Various patents have been taken out from time to time for {148} flat
strainers worked by means of a vacuum underneath the plates caused by
the motion of discs of indiarubber or thin metal. Fig. 45 shows in plan
a set of strainers, as manufactured by Messrs. G. & W. Bertram, similar
to those in Plate II., but illustrated somewhat more in detail.

The pulp first passes through the flat strainer B, and from thence to
the two revolving strainers A. From these it flows along the shoots
placed at the side on to the paper-machine at E.

[Illustration: FIG. 46.]

Fig. 46 gives a view of a patent flat vacuum strainer made by the same
firm, which may also be used for cleaning straw or esparto previous to
its passage over a _presse-pâte_. The pulp flows on to the strainer
at _a_, and passes away by {149} the cast-iron pipes _f_. The valve
_g_ is for running off waste pulp. The plates are placed at a slope
of about 1 in. in their length; those nearest the supply of pulp are
provided with coarser slits, as the impetus carries the knots forward.
The vacuum pumps are worked by the rods _d_ from the shaft _e_. By
means of the tubes _c_ water can be directed on to the plates, whereby
the coarser particles of fibre are carried forward, and the slits are
kept clean. The plates can be removed in a few minutes.

Figs. 47 and 48 show in side and end elevation, Messrs. Masson, Scott,
& Bertram’s patent self-cleaning strainer. The novelty consists in
an arrangement by means of which the upper surface of the plates are
continually freed from those portions of the pulp which cannot pass
through the slits.

The scrapers _d_ are made of vulcanised indiarubber, and are
continually carried forward by an endless chain; the knots, &c.,
collect in a heap at the end of a strainer. The {150} pulp flows on at
_a_, and passes away through the pipe _b_. The pumps are driven from
the shaft _e_.

[Illustration: FIG. 47.]

[Illustration: FIG. 48.]

Messrs. C. H. & F. L. Roeckner’s patent strainer (No. 7932, 1885)
consists of a series of cylindrical tubes, open at one end and
perforated with slits. They are placed in a vat into which the pulp
flows. Inside the cylinders are placed two, three, or more plates,
fixed to the shafts on which the cylinders are supported, and extending
to the circumference. These plates form a kind of fan, which, together
with the cylinders, are caused to oscillate by means of a rod and
cranks. This oscillating motion serves to draw the fibres through the
slits, and at the same time to keep the outsides of the cylinders
clean. The cylinders are easily removable.

After a time, the slits in the plates get too large, owing to the plate
having been worn away by the constant friction of the fibres, and as
they are very expensive, various attempts have been made to invent
plans for partially closing them again. Hammering will effect this, but
is liable to break the plates. Annandale of Beltonford has introduced
a method of closing the plates, by means of heavy pressure acting on
small steel rollers moving on each side of the slit, in which is placed
a small sheet of metal the exact thickness of the width desired. {151}

Another method of closing the plates consists in filling them up by
means of electrically deposited copper or other metal. They can then be
recut in the usual way.

In the case of revolving strainers, all that cannot pass through the
slits falls to the bottom of the vat, in connection with which it is
customary to have an auxiliary strainer, or “patent knotter,” as it is
called, shown at E. All fibre that passes through this one, which is of
the ordinary flat kind with shaking motion, goes into a box near E′,
called the “low box” for “save-all” water (see p. 154).

The pulp, after passing through the strainers, should be perfectly free
from knots and impurities, and in a fit condition for making paper.
In the machine shown, it passes from the last strainer directly on
to the wire, its flow being regulated by a movable gate _e_. In some
cases, however, it first flows into a small vat, in the centre of which
revolves a rod carrying paddles, with the object of keeping the pulp
well stirred up. It is carried right on to the wire by means of the
apron, a piece of canvas, oil-cloth, or sheet rubber, one end of which
is fastened to the breast-board _e′_, the other end resting on, and
covering the wire to the extent of about 15 in. The edges of the apron
are rolled up to prevent the pulp from overflowing. After leaving the
apron, it passes under a gate, or “slicer,” as it is sometimes called,
made of two pieces of brass, overlapping each other in the centre,
and bolted together. It is made thus to enable it to be lengthened or
shortened according to the width of the paper; its height from the
wire-cloth can be altered by means of screws, and should be equal at
all points, in order to ensure a uniformly thick sheet of paper. The
ends of the two pieces forming the slicer are fastened to the frame _f_
or “deckle,” as it is called, and this again is carried by two or more
rods stretching right across the wire, and fastened by small upright
supports on both sides to the frame _g_. The deckle-frame also carries
the grooved pulleys _h_, along which the deckle-straps _i_, endless
square bands of indiarubber, move. {152}

[Illustration: FIG. 49.]

The object of the deckle-straps is to regulate the width of the paper;
they form, together with the wire-cloth, a kind of mould into which
the pulp flows, thus corresponding to the mould used in hand-made
paper-making. The width of the paper can be altered by shifting the
position of the frame _f_, and also the deckle-straps, which are
carried on it as described, the pulleys _h_ being so arranged that
they slide along the rods on which they revolve. In order to alter
the width of the paper it is necessary to stop the flow of pulp on to
the wire, and it not only consumes a considerable amount of time, but
generally necessitates a partial cleaning up of the machine. Various
attempts have, therefore, been made to devise an arrangement whereby
the change can be effected while the paper is being made. Several {153}
contrivances have lately been introduced, all similar to the one shown
in Figs. 49 and 50.

In it the frame _f_ carrying the deckle-strap is made to slide along
the rods _e_ by means of the small wheel _b_, and by a similar
arrangement on the opposite side and geared with it. The movable apron
_l_, Fig. 49, is wound round the spindle _g_, and is kept taut by the
cords _m_ connected with the springs _n_. As the deckles approach
each other, the excess of apron is wound up, when they are separated
it unwinds again. The flow of pulp is regulated by two slices _a a_,
which are kept in position by the screws _h_. The whole arrangement is
securely bolted to the frame of the machine; _c_ (Fig. 50) represents
the breast-roll, and corresponds to F, Plates I. and II.

[Illustration: FIG. 50.]

The thickness of the paper is regulated by altering the supply of pulp
to the wire-cloth, and by the speed at which the machine is working.
This speed may vary from about 60 feet to as high as 270 feet per
minute.

The “wire” is an endless cloth made of very fine wire, the fineness
depending much on the quality of the paper required. The mesh varies
from 60 to 70 and even more threads to the inch. It is not woven
endless, but is joined by very careful sewing with wire. Its width
varies considerably, some {154} being made as wide as 126 inches; the
length is generally 35–40 ft. It is carried by the breast-roll F, the
lower couch-roll G, and the small rolls _f′_, and by a large number
of small rolls _f″_. The latter and the breast-roll are supported by
the frame _g_, while the small rolls _f′_ are supported by brackets
attached to it. The course of the wire is indicated by the arrows. The
frame _g_ works on two pivots _g′_, and receives a shaking motion from
side to side from the rod _j_, in connection with a crank worked by
two conical drums H. The supports _g″_ are also pivoted at their lower
ends to allow for the shaking motion. This shaking motion is given for
the purpose of weaving or intertwining the fibres. One or more of the
rolls _f′_ can be moved up or down on the support which carries it, for
the purpose of stretching the wire. There is usually a large number of
the small rolls _f″_, as it has been found by experience that, probably
owing to capillary attraction, they, cause the water to leave the pulp.
Though a large quantity of water thus passes through the wire-cloth, it
is necessary to assist it by artificial means. This is done by means of
the suction-boxes I connected by pipes with the vacuum-pumps I′.

This part of the machine, which is called the “wet-end,” is placed at a
slight slope of about 1 in. in its entire length, the lowest end being
nearest the strainers.

Underneath the wire-cloth is placed a box called the “save-all” K,
connected with the box E′. The water that passes through the wire-cloth
contains a considerable quantity of very fine fibres, together with
size, alum, clay, and colouring materials, that have passed through the
wire, and which would be lost but for the arrangement now universally
adopted. It flows into the box E′, and is pumped, together with the
pulp that has passed through the knotter E (see p. 151), into the high
box B, whence the mixed stuff flows on the sand-tables, to be again
used to dilute fresh pulp from the stuff-chests. The following numbers
will give some idea of the nature and amount of fibre, &c., which
passes through. {155} The paper was made from esparto and straw, sized
with rosin and starch. It contained 12 per cent. of clay.

                Grains per Gallon
                 of Waste Water.
  Fibre               34·37
  Clay                37·10
  Starch               1·40

[Illustration: FIG. 51.]

[Illustration: FIG. 52.]

It is almost impossible to utilise the whole of the back-water passing
through the wire-cloth in the way described. In some mills a portion of
this water is made to pass through a “pulp-saver,” such as is shown in
Figs. 51 and 52. It consists of a conical drum A, the circumference of
which is covered with wire-cloth, and it is caused to revolve slowly by
suitable gearing. The water enters by the pipe B, and passes through
the meshes of the wire-cloth, the pulp gradually finding its way to
the wider end, where it is discharged into the box C. It can then be
returned to the beaters.

This pulp-saver can also be used for recovering the fibre from
other waste water, such as the wash water from the washing and
beating-engines; or it can be used for freeing bleached pulp from water
in cases where drainage or hydraulic pressure is not resorted to.

If any pattern or name is required on the paper, it is produced by
means of a light skeleton roll, called a “dandy-roll,” covered with
raised wires in the form of the desired pattern, {156} placed between
the suction-boxes, and pressing lightly on the still moist paper.
The paper is thinned where the wire pattern presses, and thus a mark
(water-mark) is produced. The other side of the paper has a mark
corresponding to the wire-cloth; by using a dandy-roll covered with
wire-cloth, the two sides can be obtained alike, such paper going by
the name of “wove.”

Paper in which a series of parallel lines are produced is called a
“laid” paper.

Some water-marks are produced by means of a dandy-roll in which the
pattern is formed by depressions in the surface. The paper is thus
_thicker_ where the pattern is formed than in the ground-work. De la
Rue (Patent No. 8348, 1884) has patented the use of dandy-rolls so
formed as to produce upon the paper the effects both of thickening and
thinning.

Imitation water-marks can be produced on the finished paper by
subjecting it to pressure in contact with plates on which the design
has been produced in relief. In this way very beautiful results can be
obtained. (See Patent No. 13,455, 1884.)

It sometimes happens that the wire-cloth slips slightly to one side.
This can be obviated by the machine-man shifting, by means of screws,
one of the rolls provided for the purpose with a movable journal, until
its axis is at a slight angle to that of the other rolls. An automatic
apparatus has been invented for this purpose. Two brass plates are
fixed, one on each side of the wire-cloth, to a long rod, connected
by suitable machinery with the screws working the movable journal, so
that, as the wire presses against one or the other of these plates, the
roll is shifted so as to correct this.

The paper, which, even after passing the suction-boxes, is still very
wet, passes with the wire-cloth between the couch-rolls G G′. These
are hollow copper or brass cylinders, covered with a tightly-fitting
endless jacket of felt. They may also be made of wood (sycamore or
mahogany) or of iron or iron and brass combined. The pressure of the
upper couch-roll upon the lower can be regulated by means of {157}
screws or levers. They serve to press out water from the paper, and to
detach the paper from the wire-cloth. By dexterous manipulation on the
part of the machine-men, the paper is transferred to the endless felt,
travelling over the rolls _k_ in the direction of the arrows. It is
known as the “wet felt,” from the condition of the paper at this stage.
In its passage along this felt, the paper passes between two iron rolls
K, called the first press-rolls, with the object of having the water
squeezed or pressed out of it. These rolls are sometimes covered with a
thin brass case, and the top one is provided with an arrangement called
the “doctor,” in order to keep it clean, and free from pieces of paper
that may have stuck to it. The lower press roll is sometimes covered
with an indiarubber jacket. The “doctor” is a kind of knife placed
along the whole length of the roll, and pressing against it at every
point. The pressure on the rolls can be regulated by means of levers,
or, as in the illustration, by the screw _k′_. It will be readily seen
that the under side of the paper that has been next to the felt will,
in its still moist condition, have taken to some extent an impression
from the felt, while the upper side will have been made comparatively
smooth by the pressure against the top roll of the 1st press. In order
to make both sides of the paper as nearly as possible alike, it is
passed through another set of rolls L, called the 2nd press. This time
it is reversed, and enters at the back of the rolls; thus the other
side of the paper is next the metal, being taken through by the felt
(called the “2nd press felt”) travelling on the small rolls _l_, the
paper, after leaving the wet felt, and before being taken on to the
2nd press felt, travels over the rolls _l′_. The 2nd press felt is
necessary, because the paper is too tender to withstand, unsupported,
the pressure of the rolls.

[Illustration: FIG. 53.]

The paper, after passing the 2nd press rolls, travels over the
drying-cylinders M, the number of which varies somewhat. In the
machine shown, there are in all eight cylinders. Sometimes as many
as twelve are employed. Between the {158} 2nd press rolls and the
cylinders, a passage S allows easy access to the other side of the
machine. The paper generally passes alone over the first two, which
are only slightly heated; afterwards it is led over the others by
means of felts, as shown. The arrangements shown at R are for the
purpose of stretching the felts. The cylinders are heated by means
of steam, and are generally divided into two sets, between which is
a pair of chilled-iron, highly-polished rolls N, called “smoothers,”
the function of which is sufficiently explained by their name. They
are also heated by means of steam. The cylinders are usually made of
slightly decreasing diameter, in order to allow for the shrinking of
the paper on drying. Messrs. G. & W. Bertram introduce into some of
their machines one or two small drying cylinders, over which the 2nd
press felt travels, the object being to drive off some of the moisture
absorbed from the paper. This contrivance is said to give excellent
results, and to ensure a considerable saving in felts. The arrangement
is shown in Fig. 53. It is especially useful in machines running at
a high speed, or in those having limited drying power. After leaving
the cylinders, the paper should be quite dry; it is then led through
the calenders, of which there are in some machines {159} as many
as three sets, though only one is shown. These are similar to the
smoothing-rolls, just described. Pressure is applied by the screws O′,
or by levers and weights. The friction of the hot calenders on the dry
paper develops a large quantity of electricity, which occasionally
discharges itself in bright sparks.

It is the practice in some mills to cool the paper before passing it
through the calenders. This is effected by passing it over a copper
cylinder, through which a stream of cold water runs.

The degree of smoothness or “finish” that can be given to the paper by
the calenders, depends to a large extent upon the degree of moisture
which it contains. As it leaves the last cylinder it is perfectly dry,
that is to say, it contains only that amount of water which cellulose,
from whatever source, always carries. This amount varies slightly with
the nature of the cellulose, and with the plant from which it has been
isolated, and also with the state of the atmosphere, it being greater
on damp days. It would be impossible so to regulate the drying action
of the cylinders that the requisite amount of water should always be
left in the paper; it is therefore better to dry it as thoroughly
as possible, and then to add the water, by artificial means, just
before it passes through the calenders. This method, moreover, has the
advantage of damping only the surface of the paper.

Fig. 54 shows a damping arrangement as manufactured by Messrs. James
Bertram & Son. The paper on leaving the last drying cylinder passes
on to two copper cylinders _c_, filled with cold water. Steam passes
through the pipe _a_, and issues through a number of fine holes in a
pipe running at right angles to the direction in which the paper is
travelling, and near to it. The steam condenses on the paper and on the
surface of the cylinders, from which the paper absorbs it. The supply
can be regulated by the cocks shown in the drawing. The troughs _d_
carry off any excess of condensed water.

Amongst other methods proposed is one by Annandale; it {160} consists
in breaking up jets of water into a very fine spray by means of a blast
of air.

The finished paper, after passing through the calenders, is wound on
the reels P. The gearing by which the whole machine is driven is shown
in Plate II.

[Illustration: FIG. 54.]

It sometimes happens that, owing to the increased tension due to the
contraction of the paper in drying, the paper breaks. It is therefore
necessary to alter the speed of some of the cylinders to compensate
for this. A rough expedient which is largely adopted, consists in
attaching, by means of a mixture of rosin and tallow, a piece of felt
to one or other of the pulleys (Plate II.), and thus altering its speed.


_Tub-sizing._—The foregoing description is of a machine for the
manufacture of engine-sized papers; some slight modifications are
necessary in the case of papers that are tub-sized on the machine. In
making the cheaper qualities of tub-sized papers, the paper, after
being partially dried over a few cylinders, is passed through a vessel
containing a {161} solution of gelatine (see p. 162). It then goes
between a pair of rollers, which press out the excess of size, and then
again over drying-cylinders. The vessel or trough containing the size
is filled to overflowing from a tank placed at a higher level; the
overflow passes into a lower vessel, from which it is pumped up to the
top tank. The size is kept warm by means of a coil through which steam
passes placed in one or other of the vessels containing it. The paper
passes between a pair of rollers placed in a trough and dipping into
the size. The size may be made to flow through a pipe pierced with a
number of holes, the stream running directly on to the web of paper.
In the other, and perhaps most general way, at least for the better
qualities, the paper is wound off immediately after leaving the last
drying-cylinder A (Fig. 55), and sized at some future time, or it may
be passed directly into the vat B containing the size. After passing
between the squeezing-rolls. C, it is generally wound off as at D; and
after having stood some time {162} to allow the size to be evenly
absorbed by the paper, it is wound off from F, and passed over the
cylinders H, of which there may be a very great number, some machines
having over 300 of them. These cylinders are made of light spars of
wood; inside them, and revolving rapidly in an opposite direction, are
the fans G. The paper, in travelling over these drums, is only slowly
dried, and is supposed by this means to be more perfectly sized, and
increased in strength. It is wound on to reels again at I. Only the
first and last two drums are shown. This method was devised to imitate,
as far as possible, the sizing process of hand-made paper. Even now,
paper that has been made on the machine is sized by hand, after having
been cut into sheets, much in the same way as hand-made.

[Illustration: THE FOURDRINIER PAPER MACHINE.

PLATE II.]

[Illustration: Fig. 55.]


_Preparation of Size._—Very pure gelatine can now be obtained in the
form of light-coloured cakes. It is, however, more economical for the
paper-maker to prepare his own: this is therefore done in the majority
of cases. A great many animal substances, such as clippings of hides,
horns, bones, &c., yield gelatine when heated with water. Any of these
substances may be used, the first being the chief raw material. They
are first softened by soaking in cold water for some days: they are
then cleansed by washing in a stream of water. The next operation is
that of heating with water. This is usually done in iron or copper
vessels provided with a false bottom or outer jacket, into which steam
may be passed. The hide cuttings are covered with water, and the mass
gradually raised to a temperature of about 85° (185° F.). In from 10
to 15 hours nearly the whole of the cuttings will have passed into
solution as gelatine. This solution is then drawn off and any insoluble
substance suspended in it is removed by subsidence or filtration. The
hides contain a certain quantity of fat, which collects on the surface
of the solution. The residue in the boiler is again heated with water
and the solution added to the bulk. It is of the greatest importance
that too high a temperature be avoided, as gelatine is liable, when
strongly heated with water, to lose its power of gelatinising. {163}

To the filtered solution of gelatine, which should be, if properly
prepared, of a pale colour, a quantity of alum solution is added.
The effect of alum upon gelatine is very remarkable. If added slowly
it will be found gradually to render it stiff until at a certain
point the mass will become almost solid; a further addition renders
it fluid again. It is in this state ready to be used for sizing
purposes. The amount of alum necessary to produce this effect is
about 20 per cent. of the weight of the raw material. The alum is
also useful in preventing the decomposition of the gelatine, but its
chief characteristic is to render the gelatine a more efficient sizing
material. There is no doubt that, besides its action upon the gelatine
itself, it has a considerable effect upon cellulose. It is of the
greatest importance that the alum or the sulphate of alumina, which can
be substituted, should not contain any free acid. This is especially
necessary in the case of papers made from rags, in the bleaching of
which an acid has been used; one effect of which is to remove all basic
substances derived from the boiling or bleaching processes. In the
case of esparto and similar fibres, a considerable quantity of such
substances are present in the pulp, the result being that the free acid
of alum is to a large extent neutralised, and its injurious effects
prevented.

The effect of the free acid is seen in the weakening of the paper and
the destruction of metal surfaces with which it comes in contact. The
effect of acid upon cellulose will be found more fully described in p.
12.

Many paper-makers add to the gelatine a certain quantity of soap,
the effect of which is to render the paper capable of taking a high
finish. The soaps employed should be white and firm, and should be free
from rosin. Some soap-makers prepare a special soap for paper-making.
They are usually made from tallow, or a mixture of this with a small
quantity of coconut oil.

If a solution of soap be added to one of alum, a double decomposition
immediately occurs, the fatty acid being thrown down in combination
with the alumina, and the soda {164} combining with the sulphuric
acid. If, however, the soap solution be previously mixed with a
solution of gelatine, no precipitation takes place, the mixture forming
an emulsion having somewhat the appearance of thin milk.

Various attempts have from time to time been made to size paper in the
engine with gelatine, by precipitating it in the pulp after the manner
of rosin sizing, but as yet no successful method has been devised.


_Single-cylinder Machines._—Modified forms of the original Fourdrinier
machine have been introduced to meet various requirements. One suitable
for the manufacture of very thin paper, or of papers one side only of
which is required to be glazed, called a single-cylinder or Yankee
machine, is shown in Fig. 56.

[Illustration: FIG. 56.]

It resembles the Fourdrinier machine as far as the couch-rolls A and
B. The paper is taken off the wire-cloth on to an endless felt running
round the upper couch-roll A, and travelling in the direction of the
arrows. It is taken from the felt on to the large drying-cylinder C,
of about 10 feet diameter, heated with steam. It is carefully turned
and polished so as to impart a high gloss to the surface of the paper
with which it is in contact. Calender-rolls are sometimes supplied in
addition.

The arrangement shown at D is for the purpose of washing the felt. This
is necessary to cool and open it out after passing between the cold
press-roll E and the hot cylinder. {165}

The paper, after passing over the greater part of the surface of the
cylinder, is sufficiently dried, and it is then wound off at F.

[Illustration: FIG. 57.]

A machine of a very different construction from the ordinary form is
shown in Fig. 57. The pulp, after passing through the strainer A,
enters the vat B, in the centre of which a large drum or cylinder C
revolves. This cylinder is covered with fine wire-cloth, and on it the
paper is made. As it revolves, the fibres attach themselves to the
wire, and the water passes through the meshes, being assisted by means
of a pump. The sheet of paper thus formed is taken on to the endless
felt passing round the couch-roll D, and travels along with it to the
large drying-cylinder E, heated by steam. It leaves the felt at F,
and is then taken on to the cylinder, after travelling round which
it is sufficiently dried, and is then wound off as at G. The felt on
its return journey passes through the washer H, where it is cleaned
and freed from adhering particles by the scraper I. It is squeezed
free from excess of {166} water by the rolls K. Paper made on such a
machine is weaker than that made in the ordinary way, because it has
not been found possible to give a shaking motion to the cylinder, and
thus the fibres are only imperfectly felted.

A modification of this machine is used for making millboards, the
difference being that it has no drying-cylinder. The felt carrying
the paper passes between a pair of press-rolls, which squeeze out
the water. The sheet of paper is then allowed to wind round the top
press-roll until of the required thickness. When this happens, it is
cut off the roll by a knife. The thick sheets so produced are dried
either in the open air or in a room heated for the purpose. (See p.
108, Fig. 31.)

{167}




CHAPTER XI.

CALENDERING, CUTTING, ETC.


The paper, as it leaves the machine, is for many purposes not
sufficiently highly glazed, and it is therefore necessary for it to
undergo a further process of calendering. This may be done in various
ways.

[Illustration: FIG. 58.]

One method, called “web glazing,” is to pass the paper between a number
of rolls, alternately of polished iron and very highly compressed paper
or cotton. The construction of such a calender will be understood by
reference to Figs. 58 (end elevation) and 59 (front elevation). The
reel of paper, as taken from the machine, is shown at A (Fig. 58), its
course over the rolls being indicated by arrows. After passing over
the bottom roll, it is wound off on a wooden or hollow iron cylinder
B (Fig. 58), driven by the toothed wheel shown by the dotted line C,
on the same shaft as the wheel D, which is driven by E, keyed upon the
bottom roll. The whole machinery is driven by the large toothed wheel
F (Figs. 58 and 59), which is itself driven by the small wheel G on
the main shaft H. The paper rolls are marked P, and the iron rolls I.
It will be seen that there are two paper rolls in the middle, for the
purpose of, as it were, reversing the paper, and so making both sides
alike. Pressure is applied to the rolls by means of the screws K, and
by the weight L (Fig. 58) acting on the compound lever M. The brake,
which consists of a strap of leather, pressing, by means of the weight
and lever N, on the circumference of the wheel O, connected by toothed
wheels with the cylinder A on which the paper is wound, is used for the
purpose of preventing the paper from leaving {168} the cylinder too
rapidly. But for this appliance, the paper would be apt to crease. The
paper rolls have an inner core of iron, the paper only extending to a
depth of about 5 in. The iron rolls are hollow, and are connected with
steam-pipes, by which they can be heated. {169}

[Illustration: FIG. 59.]

Another method, known as “friction-glazing,” employed for giving a
very high finish to paper, generally on one side only, is to pass it
between a large paper roll and a smaller iron one, the latter revolving
at a much greater speed than the {170} former. By this means a very
smooth surface can be obtained. It is sometimes assisted by rubbing a
small quantity of bees’-wax on the small iron roll. The above-mentioned
methods apply to the glazing of paper in the web. Paper cut into
sheets may also be treated in the same way. Various modifications of
these calenders have been devised; they do not, however, involve the
application of any special principle. Plate-glazing, a method that is
adapted to hand-made and the better qualities of paper, consists in
applying heavy pressure to sheets placed between polished plates of
copper or zinc. The metallic plates and the sheets of paper are made
into bundles, and the whole is passed between two strong rolls, heavy
pressure being communicated to them by means of screws or levers and
weights applied to the ends of the upper roll.

[Illustration: FIG. 60.]

A calender for this purpose is shown in Fig. 60. The bundle of plates
and paper is passed along the table _a_; after {171} passing through
the rolls _c_, it slides along the inclined table _d_, where it is
received by a workman. The pressure on the rolls is regulated by the
handle _e_ and the weights _b_.

By passing paper between rolls on which devices have been cut, the
“repped” and other similar papers are produced.

With calender rolls of the ordinary construction, as the pressure is
applied at the extreme ends, the roll is liable to assume a slightly
curved shape, the effect of which is to produce an uneven surface on
the paper, the outer portion of the web being more highly finished than
the centre.

[Illustration: FIG. 61.]

This defect is obviated to a very large extent by Schurmann’s Patent
Anti-Deflection Rolls (Fig. 61). The roll proper consists of an outer
shell _a_, through the centre of which and securely wedged in at _b_ is
the centre core _c_, the ends of which run in journals, and to which
pressure is applied in the usual way. The pressure is communicated to
the outer shell at the point of contact _b_, the result being that
the parallelism of the surfaces of the rolls is maintained, and in
consequence, the paper tends to be equally finished in every direction.


_Cutting._—Except for special purposes, such, for example, as for use
in a continuous printing machine, paper is usually sent from the mill
in the form of sheets. The form of cutter, called a revolving cutter,
generally used, is shown in Fig. 62. The paper from the webs A is drawn
forward by the rolls B; it is then ripped into widths of a convenient
size by means of two circular knives, the upper one of which is shown
at C. It again passes between a pair of rollers, after leaving which it
meets a knife D fastened to the revolving drum E, and pressing against
a fixed knife not shown. The cut sheets {172} then fall upon the
endless travelling felt F. The action of the knives will be understood
by reference to Fig. 63. The edges of the two knives are shown at A and
B. The knife B has a slot, in which the bolt D slides, and it is kept
in position by means of a spring. This spring causes the knife to slide
back slightly as it comes against the fixed knife A. The position of
the paper is shown by the dotted line C. The knife B is set on the drum
not quite horizontally, so that one end meets the stationary knife a
little before the other, thus acting in every respect like a pair of
scissors. Fig. 64 shows a pair of ripping-knives. The upper one A is
kept in position against the lower one B by means of the spring C. The
cutting surfaces are slightly hollowed out, so as to have a sharper
edge. The paper is shown by the dotted line D. By altering the relative
speed of the drum E {173} and the rolls B, by means of the expanding
pulley G, sheets of any desired size can be cut. The cutting-knives
are sometimes placed inclined to the drawing-in rolls B, so that the
sheet, instead of being cut into a rectangle, is cut into a rhomboid.
Such paper is used chiefly for the manufacture of envelopes, this shape
occasioning a smaller loss when the envelopes are cut out.

[Illustration: FIG. 62.]

[Illustration: FIG. 63.]

[Illustration: FIG. 64.]


_Single-sheet Cutter._—It is sometimes necessary, as in the case of
paper having a water-mark, that the sheet should be cut with great
exactness, so that the device shall come exactly in the centre. The
ordinary cutter cannot be relied on for this purpose, and, in its
place, a machine called a “single-sheet cutter” is used (Fig. 65). It
consists essentially of a large wooden drum A, fixed on a horizontal
axis, over which the paper is led by a pair of drawing-in rolls B. The
paper is held against the drum by a clamp worked by the arm C. The
paper is cut by the knife E moving against the stationary knife D.
After the cut, the drum describes part of a circle, the paper being
still held, so that it cannot go back with the drum. As soon as it has
gone far enough, the clamp is removed, and the drum returns, bringing
the paper with it. The length of the arc through which the drum moves,
and therefore the size of sheet, is regulated by the length of the
crank-arm F. If from any cause the cut should not take {174} place at
the right time, the man in charge can, by pressing against the clamp,
retard the motion of the paper, and thus bring back the cut to the
right place. The small roller G is for the purpose of keeping the paper
always tight.

[Illustration: FIG. 65.]


_Guillotine Cutter._—It is sometimes necessary to trim the edges
of sheets of paper or to divide them into smaller sheets. This is
done by means of a guillotine cutter, an improved form of which, as
manufactured by Salmon of Manchester, and called the “Victory” cutter,
is shown in Fig. 66.

The paper to be cut is placed on the table F, touching the back gauge
G, which can be brought backwards or forwards by means of the handle H,
thus regulating the size of sheet.

The machine is set in motion by means of the lever A, which acts upon
a friction-clutch connected with the driving-gear. This causes the
knife-bar B and the clamp C to descend. {175} When the latter meets
the paper its progress is arrested. The knife D, however, continues
to descend, and passes through the sheets of paper. By means of slots
placed at the back, the knife is made to take a diagonal course. The
pressure of the clamp is maintained upon the paper during the cutting
operation by means of a powerful spring contained in the tube E.

[Illustration: FIG. 66.]


_Sorting._—The sheets of paper are now ready to be examined
before being finally sent away from the mill. This is done in the
“Finishing-house,” or “Salle” as it is sometimes called. This sorting
is usually performed by women, who reject the inferior or damaged
sheets. These are sold at a reduced price under the name of “retree.”

Paper is sold in sheets of definite sizes, and is made up into reams
containing from 480 to 516 sheets. These sizes {176} correspond
to different trade names—such, for example, as crown, demy, royal,
imperial, &c. The weight per ream is usually expressed in addition to
the name, thus: 14-lb. demy, 18-lb. double crown, &c. In this way the
consumer is enabled to make a rough comparison of the thickness of the
different kinds of paper.

In making paper it is the duty of the machineman to examine and weigh
from time to time a sheet of the desired size, in order to ensure
uniformity. Special lever balances can be obtained, showing at a glance
the weight per ream of different numbers of sheets. {177}




CHAPTER XII.

CAUSTIC SODA, RECOVERED SODA, ETC.


As we have already pointed out, caustic soda and lime are the only
alkalis employed by the paper-maker for boiling fibres; the special
cases in which carbonate of soda is used have been mentioned in their
proper place.

The preparation of milk of lime requires little or no description, as
the operation is a simple and tolerably familiar one. Before using, it
should be passed through a fine wire sieve, to keep back sand, coal,
and similar impurities which the lime invariably contains.

Caustic soda is met with in commerce in four forms, differing from each
other in alkaline strength and colour, and of course in price. The
lowest quality is what is known as caustic “bottoms”: it consists of
that portion remaining at the bottom of the caustic-pot after the clear
fused caustic soda has been ladled out, and it contains a considerable
quantity of ferric oxide and other insoluble impurities. It is of a
dark reddish brown colour, and contains 50–60 per cent. of alkali
(Na_{2}O). Its use in paper-making cannot be recommended, except for
the preparation of the very lowest grade of pulp. The solution should
be allowed to remain at rest, in order that the insoluble matter may
subside.

The next in quality is known as cream caustic, so called from its
slightly brown colour. It is usually sold containing 60 per cent. of
alkali, in the form of a tolerably friable mass, having a crystalline
structure. It is a very suitable form of alkali for the paper-maker.

The next in order is what is called 60 per cent. white. It {178}
consists of a hard white mass, requiring considerable force to break
it. Though whiter in appearance than cream caustic, it is in reality
less pure, as it contains a considerable quantity of salt. It is made
by continuing the evaporation of the caustic liquor to a further point
than is the case with cream caustic, the result being that the whole
of the water is driven off. A small quantity of nitre is then added to
oxidise the sulphides and other compounds which impart the colour to
cream caustic. Common salt is then added to reduce its strength to 60
per cent., in order to satisfy the whim of the consumer, who insists
upon an article of a given definite strength. On this account it is
somewhat inferior to cream caustic, and is, moreover, more expensive.

The highest quality of all is white 70 per cent. This resembles white
60 per cent. in appearance, but is much purer, and more expensive.

A very pure form of caustic soda has within the last few years been
introduced by the Greenbank Alkali Company. It consists of small
fragments, more or less crystalline, of almost pure sodium hydrate. It
can be packed in wooden casks, and it dissolves very readily in water.
It contains 76 per cent. of alkali. It is, however, much too costly for
boiling purposes; it might, however, be used for the preparation of
rosin size.

The following analyses of different forms of caustic soda and their
relative prices will possibly be of interest:—

  -----------------+-----------------+-----------------+---------------
                   |   (Davis.)      |   (Davis.)      |  (Morrison.)
                   | White (70 Per   | White (60 Per   | Cream (60 Per
                   | Cent. Na_{2}O). | Cent. Na_{2}O). | Cent. Na_{2}O).
  -----------------+-----------------+-----------------+---------------
  Sodium hydrate   |     89·60       |     75·25       |     70·00
  Sodium carbonate |      2·48       |      2·53       |      5·00
  Sodium chloride  |      3·92       |     17·40       |      7·00
  Sodium sulphate  |      3·42       |      4·40       |      2·00
  Sodium sulphide  |      0·02       |      0·03       |       —
  Sodium silicate  |      0·30       |      0·30       |       —
  Sodium aluminate |     trace       |     trace       |       —
  Water            |      none       |      none       |     15·80
  Insoluble matter |      none       |      none       |      0·20
  -----------------+-----------------+-----------------+---------------

{179}

Their relative prices per ton f.o.b Liverpool, in December 1886,
were:—70 per cent. white, 8_l._ 5_s._; 60 per cent. white, 7_l._ 5_s._;
60 per cent. cream, 7_l._

All the above-mentioned forms of caustic soda occur in the form of more
or less hard masses, and are contained in thin wrought-iron drums,
which are filled with the caustic in a fused state. The soda is removed
by breaking the drum with a chisel and hammer. The lumps of caustic may
be put direct into the boiler, though it is better to dissolve them
previously in water and allow any insoluble impurities to settle to the
bottom of the solution.

Instead of buying caustic soda direct, it is the custom of some
paper-makers to prepare it for themselves from carbonate of soda, which
can now be obtained in various forms, some of great purity.

It occurs as caustic ash, containing about 40 per cent. of alkali as
carbonate, and about 10 per cent. as caustic soda; soda-ash containing
about 52 per cent. total alkali, nearly all as carbonate; and refined
soda-ash containing 57–58 per cent. of alkali as carbonate. Some forms
of carbonate of soda, such, for example, as those made by the ammonia
process, are of even greater purity. The method of converting sodium
carbonate into caustic soda will be described subsequently.

Unless the arrangements for washing and draining the lime-mud are very
perfect, it is probably cheaper for the paper-maker to buy his caustic
direct from the maker.


_Soda Recovery._—In former years, the liquors in which rags, esparto,
and other paper material had been boiled, was run into the nearest
watercourse; but now, owing partly to the fact that is insisted upon
by the Rivers Pollution Act of 1876, and partly because it can be
made remunerative, all these liquors are preserved, and the soda they
contain utilised. The method adopted is to evaporate to dryness and
ignite the residue. The soda during the process of boiling takes up a
large amount of non-cellulose fibre constituents and dissolves them as
resinous compounds. These on evaporation and ignition become converted
into sodium carbonate. Many raw {180} materials, especially esparto
and straw, contain a large amount of silica, a large proportion of
which is dissolved by the soda in the form of sodium silicate, in which
form also it is found in the recovered soda.

[Illustration: FIG. 67.]

[Illustration: FIG. 68.]

The apparatus for accomplishing the evaporation varies with almost
every mill. In some, it is very primitive and {181} crude, consisting
perhaps of only a furnace for incinerating the residue, and over it
a pan containing the liquor, the latter being heated and evaporated
by the heat from the furnace. It is obvious that, with such an
arrangement, a large quantity of heat must be wasted. To economise
as much as possible of this waste heat, various plans have been
suggested. That of Rœckner, of Newcastle, appears to be to a great
extent efficacious. It consists practically of a series of shallow
trays B (Fig. 67) placed in a brick chamber, alternated so as to allow
the heated air from the furnace below to play upon the surface of each
in succession, on its way to the chimney, with which the whole system
is in connection. Above the chamber containing these trays, is a large
tank C, containing a store of the liquor to be evaporated, placed there
so as still further to economise the heat, and from which the liquor
runs on to the trays. The furnace A is of the ordinary reverberatory
kind; below it, and connected with it by a kind of damper, is a large
chamber J, where the calcined residue from the furnace is put to cool,
thus preventing any nuisance from the smell of the burning mass. The
chamber is provided with a pipe L, through which the vapours pass
into the furnace. Several pipes E from the furnace pass through the
{182} tank, to assist in warming the liquor. The residue, when cold,
is drawn through doors from the chamber below the furnace. Rœckner
has devised an apparatus (Fig. 68), consisting of a small chamber
containing a series of pipes A, through which a stream of cold water
constantly runs, in connection with the flue from his evaporator, for
the purpose of condensing volatile bodies, and thus preventing, to a
certain extent, contamination of the surrounding air.

A very economical form of evaporator is that invented by Porion,
a French distiller, and named after him. It is shown in sectional
elevation and plan in Figs. 69 and 70. It is largely used on the
Continent, and also in England and Scotland. It consists of a large
chamber _k_, the floor of which is slightly inclined from the chimney
shaft, and through which the waste heat from the furnace _a_ passes.

[Illustration: FIG. 69.]

[Illustration: FIG. 70.]

The liquor to be evaporated is run in at the end nearest the chimney
from the tank placed above the chamber _c_. A number of cast-iron
fanners _i_, dip into the liquor and revolve rapidly, usually at the
rate of about 300 revolutions per {183} minute, producing and filling
the chamber with a very fine spray, thus presenting a very large
evaporating surface.

Between the furnace and the evaporator are placed the chambers _c_ and
_f_. In _c_ a number of brick walls _d_ are so placed that the flames
from the furnace are intercepted and broken up. The object of this
is to give time for all the products of combustion to be thoroughly
burnt up, which would not be the case without the “smell-consumer,” as
these chambers are called. This part is an addition to the original
evaporator, and was devised by Messrs. Menzies and Davis. The liquor
after having been concentrated in the chamber _k_ runs into a trough
placed alongside the doors _h_ and flows into one or other of the
furnace beds _b_ where it is still further concentrated, and the
residue ignited by the flames from the fires _a_. The draught can be
regulated by the damper _g_, and also by one placed near the shaft _j_.
The doors _e_, in the smell-consuming chamber, are for the purpose
of cleaning out. The fanners _i_ are worked by a small steam engine,
not shown in the drawing. Under properly regulated conditions very
excellent results can be obtained with this evaporator. The temperature
of the gases near the chimney should not be higher than about 85°. By
running the fanners at a very high speed the temperature of the gases
may be even further reduced, thus showing the completeness of the
evaporation.

This form of evaporator is open to the objection that the whole of the
sulphur in the coal employed for the furnaces, finds its way into the
recovered soda. It combines with the alkali to form sulphite of soda,
part of which is decomposed in the furnace with formation of sodium
sulphate, sulphide, and other sulphur compounds. The same objection,
of course, applies, though perhaps in a less degree, to all systems
of evaporation in which the flame is in contact with the liquor to be
evaporated.

The Porion evaporator can be erected at very small cost, and costs
but little for maintenance. It is capable of producing 3⁠/⁠4 ton
of recovered soda per ton of coal with liquors {184} of the usual
strength. It has proved itself to be perhaps the most economical
evaporator existing.

Some time ago there was erected in Lancashire an evaporator invented
and patented by Mr. Alfred Chapman. It is shown in Figs. 71, 72, 73,
and 74. The evaporation is effected at a low temperature in three
vacuum pans E, and with the unusual result that the concentrated liquor
gelatinises after leaving the third vacuum-pan, instead of taking the
ordinary form of the concentrated products of other evaporators. It is
said that this apparatus gives an excellent product, with great economy
of labour and water, and with no drainage of foul liquor from the
buildings. Observations extending over three months have proved that it
evaporates 22 lb. of water from the liquor per lb. of coal used under
the boiler. It is however very costly to erect.

[Illustration: FIG. 71.]

[Illustration: FIG. 72.]

[Illustration: FIG. 73.]

[Illustration: FIG. 74.]

The waste liquor is discharged into the tank A, whence it is pumped
by the donkey-engine B, through the feed-heater C, {185} into the
boiler D, which receives heat from the incinerating furnace H, and,
in case of need, from an auxiliary furnace shown on the plan, under
the feed-liquor-heater. The steam produced in D is taken to the first
vacuum-pan at E, and having heated its contents, the products of
evaporation pass over into the tubes of the second pan; this, in its
turn, gives up its products of evaporation to the third, whence they go
to the condenser of the vacuum-engine F. Thus the heat from the furnace
H is used for incinerating the concentrated liquor {186} on its bed,
for beating the feed-liquor in the feed-heater pipes, and for making
steam out of the liquor itself in the boiler; this steam finally drives
the donkey-pump and vacuum-engine, and causes the evaporation in the
three vacuum-pans E. One advantage of this evaporator is the fact that
the liquor is evaporated out of contact with the furnace gases.

Whatever be the method of evaporating or concentrating the liquor,
the final treatment in the furnaces is much the same in every case.
The furnaces shown in Figs. 69 and 70 may be taken to represent the
ordinary form. The concentrated liquor is run on to either of the beds
_b_, where the last portions of water are driven off by the heat from
the fireplaces _a_, and the residual mass is ignited until all the
organic matter contained in the liquors is carbonised and the soda is
converted into carbonate of soda. This takes place in about 4 hours,
according to the degree of concentration of the liquor as it is run
into the furnaces. The running in of liquor should be done with great
care, as explosions sometimes occur through the sudden liberation of
steam on the liquor coming in contact with the hot beds. The charge
should be allowed to remain in the furnace until it is thoroughly
carbonised and all volatile matters have been driven off, otherwise a
nuisance may be caused when the still burning mass is exposed to the
air. Rœckner’s evaporator is provided with a special chamber into which
the charge is drawn (J, Fig. 67).

The composition of the recovered soda varies with the nature of the
liquors from which it has been obtained, and, as has been already
pointed out, with the form of evaporator employed. It consists
essentially of carbonate of soda, together with a certain amount of
silicate of soda, if derived from liquors in which straw or esparto
have been boiled, chloride of sodium, sulphate of soda, sulphite of
soda, sulphide of sodium, and other sulphur compounds, the rest being
made up of carbon and insoluble impurities. The amount of soda varies
from 35 to 45 per cent. (Na_{2}O). The following analysis {187} will
give some idea of the composition of Recovered Soda:—

  [13]Sodium carbonate                      72·33
      Sodium hydrate                         1·93
      Sodium chloride                        8·30
      Sodium sulphate                        3·95
      Sodium sulphite                         ·63
      Silica                                 7·09
      Carbon                                 4·70
      Oxide of iron and alumina               ·50
      Other constituents (by difference)      ·57
                                           ──────
                                           100·00

The whole of the soda present as sulphur compounds is not lost, as a
large proportion of it is present as sodium sulphite, most of which is
converted into caustic soda by the causticising process.

     [Footnote 13: A certain quantity of potash derived from the
     mineral constituents of esparto and straw is always present in
     recovered soda.]

A certain amount of soda is carried forward, partly mechanically
and partly volatilised, to the flue leading to the chimney. This
accumulates, and may be from time to time removed in the form of
fine dust. It contains, besides carbonate of soda, much sulphate and
chloride. In two different samples examined by the authors, the amounts
of soda (Na_{2}O) present were 25·0 and 27·1 per cent.


_Causticising._—The next process consists in converting the sodium
carbonate in the recovered soda into caustic soda.

This operation is known as “causticising,” and consists in heating a
solution of the soda with lime. The decomposition which takes place is
shown in the following equation:—

  Sodium          Lime.      Water.      Caustic       Calcium
  Carbonate.                              Soda.       Carbonate.
  Na_{2}CO_{3} +  CaO   +   H_{2}O    =   2 NaOH   +    CaCO_{3}.

The recovered soda should be dissolved in separate vessels. Perhaps the
best form of apparatus is a series of lixiviating tanks such as are
used for dissolving the alkali in black ash. {188} By this means a
nearly perfect exhaustion of the mass can be effected with a minimum of
labour. Special tanks are sometimes made for the purpose, provided with
mechanical stirrers.

It is essential in dissolving the recovered soda that a high
temperature should be employed, as otherwise a portion of the soda
present as silicate of soda will be lost, as it is only with difficulty
soluble, and requires rather prolonged heating with water. Whatever the
form of apparatus employed it should be so arranged that, after running
off the strong liquor, the insoluble residue may be further treated
with water. In the case of the vats mentioned above, this process
is made continuous, pure water being run in at one end, and strong
liquor flowing from the other. If other forms are used, the liquor
after settling, may be run off by means of a pipe passing through the
bottom or side of the vessel, and near the bottom, and consisting of
two parts, one long, and one short. The short part is stationary, and
is connected to the longer part by means of a movable knee joint,
allowing it to be deflected. The liquor having settled sufficiently,
the movable limb is lowered beneath the surface of the liquor which is
then allowed to flow through. As the surface of the liquor falls, the
pipe is gradually lowered. In this way the clear solution can be run
off without disturbing the residue at the bottom. The open end of the
pipe is usually covered with coarse wire gauze, to keep back insoluble
impurities. With properly calcined recovered soda, the solution should
be bright and almost colourless. If at all brown in colour, and if
it has an empyreumatic odour, it indicates imperfect calcination.
The residue in the dissolving tanks consists chiefly of carbonaceous
matter, together with some soda, insoluble matter, &c.

The liquor is now ready to be causticised. This should be done in a
separate vessel, although it is the practice in many mills to perform
this operation in the same vessel in which the solution of the soda
has been conducted. A good form of causticiser can be made from an old
egg-shaped boiler, by cutting it in two along its length. {189}

It should be provided with two or more vertical steam pipes, connected
at the bottom of the boiler with a horizontal pipe perforated with
numerous holes. The vertical steam pipes should be furnished with
injectors, whereby air is drawn in, and forced with the steam through
the holes in the horizontal pipe. The stream of air serves the double
purpose of thoroughly agitating the liquor and of oxidising any sodium
sulphide in the recovered soda. The liquor before causticising should
be reduced in strength to about 20–25 degrees Twaddle, which may be
done with the washings of the residue from the recovered soda, or from
the washings obtained subsequently from the lime-mud. This strength
should never be exceeded, otherwise imperfect conversion into caustic
soda is the result. This is due to the fact that concentrated solutions
of caustic soda react upon calcium carbonate, forming sodium carbonate,
and calcium hydrate, the reaction being the reverse of that indicated
in the above equation. If the liquors are very strong in carbonate
of soda, and comparatively free from sulphate, they should not be
causticised at much over 20° Twaddle, if they contain much sulphate,
and therefore less carbonate, the higher strength can with safety be
adopted.

The causticising vessel should be provided with a stout iron cage
or basket, into which the lime can be put. This should be securely
fastened to the vessel, and should dip into the liquid.

The liquor having been properly diluted, is now heated by means of
the steam pipes, and the lime put into its cage. It should be put in
in lumps. As the liquor reaches the boiling point, the reaction will
proceed rapidly, and the lime will gradually disappear; fresh lumps
should be added if necessary. If the liquor is sufficiently heated
the causticising will be complete in from two to three hours. The
liquor should be tested from time to time; this is usually done by
a workman. He withdraws a sample of the liquor, and after allowing
the calcium carbonate to subside, pours off a portion of the clear
liquid into a glass vessel. He {190} then adds an excess of either
sulphuric or hydrochloric acid. If any effervescence takes place, due
to the evolution of carbonic acid gas, he knows that the operation of
causticising is incomplete; the heating must therefore be continued.
It is difficult, without an undue expenditure of time and steam, to
convert the whole of the soda into caustic: it should however be so
perfect, that on testing only a very slight effervescence occurs. It
is quite easy to convert as much as 95 per cent. of the soda, or even
more. The actual amount converted can only be ascertained by a careful
analysis of the liquor.

The amount of lime used is generally somewhat in excess of the
theoretical quantity; 106 parts of sodium carbonate (Na_{2}CO_{3})
require 56 parts of lime (CaO): it is necessary, however, to add
about 60 parts. A very good plan is to conduct two or even three
causticisings in the same vessel without cleaning out or removing the
calcium carbonate, using in the first operation a large excess of lime.
The causticising being completed, the calcium carbonate and excess of
lime are allowed to settle down, and the clear liquor run off by an
arrangement such as that already described in the dissolving process.
Fresh solution is then run in and the whole mass heated for some time,
until the excess of lime is converted into carbonate. Fresh lime is
then added if necessary until the conversion of the carbonate of soda
is complete. The liquor is then allowed to settle, and is run off as
before: this operation may again be repeated.

The residual calcium carbonate, or “lime-mud” as it is called in alkali
works, is then washed once or twice by running in water, boiling up,
allowing to settle, and running off the clear liquor. If these liquors
are too weak for use in boiling fibres, they may be used for diluting
fresh recovered soda liquor before causticising, or for dissolving the
soda.

Some arrangement should be provided for removing as much as possible
of the liquor from the lime-mud before throwing it away or otherwise
disposing of it. This is best done by throwing it on a filter made of
layers of stones, {191} ashes and sand, and covered at the top with
perforated iron plates. The filter is connected with a vacuum pump.
In this way very perfect draining is accomplished, and the mud forms
a hard mass on the surface of the filter, from which it can be easily
removed with spades. In this form it contains only 50–60 per cent. of
water. If properly washed it should contain in this state only about
2 per cent. of alkali (Na_{2}O). By careful manipulation, even this
amount can be reduced.

The importance of thoroughly washing the mud can hardly be too much
insisted upon. Where proper means are not employed for draining, the
washing should be made more perfect. The lime-mud consists chiefly of
carbonate of lime, together with silicate, free lime, &c. The following
analysis is of a mud obtained by causticising recovered soda derived
from the liquors in which esparto and straw had been boiled:—

  Calcium carbonate              40·02
  Calcium hydrate                 5·13
  Silica                          4·01
  Sodium hydrate                  2·13
  Oxide of iron and alumina       0·30
  Water                          48·10
  Other constituents              0·31
                                ──────
                                100·00

As already pointed out the liquors contain a certain amount of soda,
as sodium sulphide and other sulphur compounds. The presence of the
former, if in large quantities, is objectionable, as it is liable to
discolour fibres boiled in liquors containing it. It is therefore best
to remove it. This can be conveniently done by blowing air into the
liquors during the process of causticising: this has the effect of
oxidising it to sulphate of soda, in which form it is harmless.

The air can of course be blown into the liquor by means of a pump;
the most economical way is to connect with the steam pipe an injector
constructed on the principle of the injectors used for feeding boilers
and for other purposes. By this means a strong current of air is drawn
in, and {192} being forced with the stream to the bottom of the
liquor, passes through it in a number of fine streams.

If the amount of sulphide present be very high it may be necessary to
prolong the oxidising operation beyond the time necessary for complete
causticising.

In many paper-mills the causticising is conducted in circular vessels
furnished with mechanical agitators. These are more expensive than the
simple form described above, and they possess no special advantages.
The use of causticisers in which neither mechanical agitation nor
agitation by means of air is provided for is exceedingly wasteful of
labour, time, steam, and soda. The lime-mud settles at the bottom as a
hard mass, very difficult to manipulate. {193}




CHAPTER XIII.

PAPER TESTING.


There are two points of view from which a paper may be tested:
first, of physical or mechanical properties; secondly, of material
composition. We shall consider the subject according to this division.


(I.) Quantitative measurements of such properties as resistances to
breaking and tearing strains are seldom made by English paper-makers.
In Germany, on the other hand, the matter has been very thoroughly
investigated in connection with the work of the Königl. Techn.
Versuchsanstalt, Berlin, and through the agency and influence of Prof.
Sell, and C. Hofmann, a department has been organised exclusively for
the work of paper testing. The results of the tests are becoming widely
recognised by practical men and the trade in that country, as affording
a true index of the quality of a paper. It is therefore of importance
to give an outline of the methods employed.

The determination of the strain or weight which a paper is capable of
supporting is a very obvious measure of the strength of the paper.
Observations of the limiting strain or breaking weight are sometimes
made by paper-makers, but the apparatus and method employed are usually
crude. The simplest means consist in clamping the paper—a strip of
standard length and breadth, arbitrarily chosen—at one end, the clamp
being firmly held in a fixed support, and to the other attaching by
means of a similar clamp, an ordinary scale pan, the whole arrangement
hanging vertically. Into the pan, weights are added in due succession
until fracture of the strip is determined. It is scarcely necessary
to point {194} out that the errors of experiment with such a method
are very great: indeed it has been found that even with the refined
apparatus about to be described the errors are not inconsiderable.
However, by exhaustive investigation, according to the well-known
“law of errors,” these have been quantified, and a careful operator
can therefore obtain results which are trustworthy. The apparatus in
question is the Hartig-Reusch machine.[14] It is shown in sectional
elevation and plan in Figs. 75 and 76.

     [Footnote 14: A complete description of this machine is given in
     ‘Civil Engineer,’ 1879.]

The principle will be readily grasped by inspection of the diagrammatic
representation of its essential parts—Fig. 77. The strip of paper is
held horizontally by the clamps _a_ and _b_, _a_ being held by the
fixed support A, _b_ by the movable carriage B. B is connected by means
of a swivel with the spiral spring F, and this again is similarly
connected with the screw, which is made to rotate by the wheel D. By
turning D, therefore, the spiral may be extended, and a corresponding
strain communicated through B and _b_ to the paper. The paper undergoes
a certain elongation under the strain, and the carriage B moves from
right to left in consequence. The rotation of the screw is continued,
and the extension of the spiral proceeds until the paper is fractured.
At this point it is required to determine, (1) the elongation of
the spiral which is the measure of the breaking strain, and (2) the
distance through which the carriage has moved, i.e. the elongation of
the paper. Both these effects are communicated to the pencil G, the
latter directly, since the pencil-holder is in rigid connection with
B, the former through the rod I, from which, by a special arrangement,
the horizontal is converted into a vertical motion of the pencil.
This, therefore, traces a curve, of which the ordinates represent the
strains, and the abscissæ the elongations of the paper produced by the
strain.

The scale shown in Fig. 76 indicates the exact position of the clamp A.
{195}

[Illustration: FIG. 77.]

[Illustration: FIG. 76.]

{196}

The values for the spiral spring—i.e. extension for a given
load—having been determined by previous observations in a special
apparatus, the curve obtained is at once a measure and a permanent
record of these cardinal factors, breaking strain and elasticity. As
with all other such instruments, the recording apparatus introduces
certain errors, which, however, by careful investigation and
modification in accordance with the results, have been reduced to a
minimum. Nevertheless, the director, Dr. Martens, has recently adopted
a simpler instrument, altogether similar in principle, but based upon a
direct reading of the two movements, in which of course these errors do
not appear. For the student, however, the recording instrument is the
more instructive, and we have given it preference for description here,
more especially as no difference in essential parts is involved.

Those who wish to pursue the matter into the most interesting details
of the investigations made upon the subject, are referred to the papers
published by the Institute for 1885.[15]

     [Footnote 15: Mittheilungen a. d. Königl. Techn. Versuchsanst,
     Berlin.]

In testing the strength of papers by this or similar machines, it
is important to observe the hygrometric state of the atmosphere at
the time the trials are made, as this has been found to exert a
considerable influence on the results, a paper being weaker the moister
the atmosphere.

The results of the tests are expressed in the following terms:—The
elongation is given directly in percentage of the original length. This
is uniformly taken at 180 mm., a length arrived at after laborious
investigation, as minimising the errors of experiment; in other words,
as giving mean value with the minimum of variation. For the breaking
strain an ingenious expression has been arrived at, viz. the length of
the paper which suspended vertically, with one end hanging freely, the
other fixed, would determine fracture at the fixed end. As the breaking
strain would vary with the thickness, the numbers obtained in {197}
units of force or weight for strips of constant breadth, would need
correction in order to admit of strict comparison with one another.
By substituting an expression in terms of the paper itself—since a
paper of greater thickness, and requiring therefore a proportionately
greater force to fracture it, weighs more per unit of area, and in
the same proportion—all the numbers for breaking strains are strictly
comparative one with the other. In the same way also the question of
width may be disregarded.

A further mechanical test, forming a part of the scheme of
investigation, is the resistance of the paper to rubbing. This test
is an altogether empirical one, as the following brief description
will show:—A piece of the paper, about 6 inches square, crumpled by
successive folding in two directions at right angles, is grasped by the
thumb and forefinger of each hand, at a distance of 3–4 inches apart.
It is then rubbed upon itself across the thumbs a given number of times
(seven is the number chosen) and held up to the light. If no holes are
visible, the rubbing is repeated. The number of times necessary to
repeat the rubbing until holes appear is the measure of the resistance.
A sufficient uniformity in the results of this test has been observed
to make it the basis of a classification of papers, in regard to their
resistance to such disintegration; they are divided into the following
eight groups, beginning with the lowest:—

  0.  Extremely weak.
  1.  Very weak.
  2.  Weak.
  3.  Medium.
  4.  Moderately strong.
  5.  Strong.
  6.  Very strong.
  7.  Extremely strong.

The classification of papers on the results of these tests cannot
be more lucidly given than in the following scheme, under which the
results are officially recorded:—

          _Class_.                         1    2    3    4    5    6

  _a._  Mean breaking length (metres)
          not less than                  6000 5000 4000 3000 2000 1000
  _b._  Mean elongation (per cent.) at
          fracture not less than         4·5   4    3   2·5   2   1·5
  _c._  Resistance to rubbing             6    6    5    4    3    1

{198}

This classification is based on the results of some hundreds of
observations. It is interesting to note the differences observed in
the numbers for _a_ and _b_ according to the direction for the test
in which the paper is cut, i.e. in the direction in which it was run
on the paper machine, or at right angles (see Chap. XI. p. 171). The
mean ratio for the breaking lengths (strains) may be taken as 1 : 1·6,
i.e. the paper is about 40 per cent.[16] weaker across the web; the
elongation under strain on the other hand is about double.

     [Footnote 16: In the statement of results the mean of the numbers
     obtained in the two directions is given.]

It is also of interest to note the influence of the glazing process (p.
167) upon the quality of the paper as determined by these tests.

First, we must notice the effect of the treatment upon the substance of
the paper itself. The mean reduction of thickness is 23 per cent. On
the other hand, the reduction of weight, calculated per unit of surface
(square metre), is 6·7 per cent., whence we may infer an increase of
surface, flattening out, in the process. These quantities, but more
particularly the latter, will doubtless vary with the various methods
of glazing and with the materials of which the paper is composed.

The breaking length (strain) shows a mean increase of about 8 per
cent.; the elongation under strain, on the other hand, a diminution of
6 per cent.

For an interesting discussion of the question of the relative strengths
of machine and hand-made paper see ‘Paper,’ by Richard Parkinson.

[Illustration: FIG. 78.]

The thickness of a paper may be determined by means of an ordinary
micrometer, such as is shown in Fig. 78. The paper is placed in the
jaws of the instrument, and the screw {199} advanced until it touches
the paper. The thickness is then read off on the scale. Other forms of
apparatus are sold for the same purpose. In making a determination of
the thickness of a paper it is necessary to take the mean of a series
of observations at different points of the sheet, as the thickness may
vary somewhat.


_Determination of Composition of Papers._

(II.) The analysis of a paper naturally divides itself into two
parts:—(_a_) The determination of the nature of the fibrous material of
which it is composed; and (_b_) the identification of such adventitious
substances as size and filling material.


(_a_) This again is divided into two sets of observations—microscopical
and chemical.

A fragment of the paper is soaked for some time in glycerine, and is
then carefully teased out with a pair of needles, and the fragments
laid on a glass slip with a drop of glycerine. A cover-glass is then
laid on and lightly pressed down so as to spread the fibres in a thin
layer.

The microscopical features of the different fibres have been already
described, and it is only necessary now to summarise the chief
characteristics of the more important materials.


_Cotton._—Flat riband-like fibres, frequently twisted upon themselves.
The ends generally appear laminated. The fibres are frequently covered
with numerous fine markings (see Frontispiece).


_Linen._—Cylindrical fibres, similar to the typical bast fibre (see
Fig. 6). The ends are frequently drawn out into numerous fibrillæ (see
Frontispiece).


_Esparto._—Esparto pulp consists of a complex of bast fibres and
epidermal cells. These serrated cells are, as has been already pointed
out, characteristic of esparto, straw, and similar fibres. Certain
differences exist between those of esparto and straw, and even between
the different species of straw, which enable the microscopist to
identify their source. The most characteristic feature of esparto pulp
is the presence {200} of a number of the fine hairs which line the
inner surface of the leaf (_e_, Fig. 10), some of which invariably
survive the boiling and washing processes, although the greater portion
passes away through the wire-cloth of the washing engines. The presence
of these hairs may be taken as conclusive evidence of the presence of
esparto.


_Straw._—Straw pulp very closely resembles esparto-pulp in its
microscopical features. The hairs above alluded to are, however,
absent. On the other hand, a number of flat oval cells are always
present in paper made from straw (_b_, Fig. 13). It should be borne in
mind, however, that bamboo and similar pulps also contain these cells.


_Wood (Chemical)._—Flat riband-like fibres, showing unbroken ends
(see photographs, Frontispiece). The presence of the pitted vessels
(Frontispiece, and _a_, Fig. 15) is eminently characteristic of pulp
prepared from pine-wood. The fibres of other woods are not sufficiently
characteristic. They much resemble those of pine-wood, with this
difference, that the pitted vessels are absent.


_Wood (Mechanical)._—Mechanical wood-pulp may be recognised by the
peculiar configuration of the torn ends of the fibres, and from the
fact that the fibres are rarely separated, but are generally more or
less agglomerated (see Frontispiece). Pulp from pine of course shows
the pitted vessels already referred to. They are usually more distinct
than in chemical wood-pulp. Occasionally fragments are to be met with
connected together with portions of the medullary rays.

The microscopical examination of a paper is a matter of very great
difficulty, and one requiring much practice. The student is recommended
to study closely for himself the microscopical features of pulps
obtained from authentic specimens.

Some approximate idea of the relative proportion of the various fibres
present in a paper can be obtained from a careful microscopical
examination.

Vétillart maintains that a quantitative determination within a fair
limit of accuracy is possible. On the other hand, the {201} Berlin
Prüfungsanstalt do not profess to do more than merely identify the
fibres.

In examining a paper under the microscope, it should be observed
whether the fibres appear as fragments, or whether they consist of
whole bast cells in which the tapered ends appear.

Cotton and linen, owing to the great length of their ultimate fibres,
yield, when beaten, fragments showing where the fracture has taken
place. From the appearance of this fracture it is possible to ascertain
whether or not the beating operation has been properly conducted. If
the beater-knives have been too sharp, or have been let down to the
bed-plate too quickly, the fractures will appear as clean cuts, whereas
when the operation has been properly conducted the fracture will appear
ragged and drawn out. The bearing of this on the strength of the
finished paper is considerable.

Esparto, straw, and wood, whose ultimate fibres do not exceed 1–2 mm.,
should, in the majority of cases, appear as whole bast fibres with two
tapered ends; the beating, when properly conducted, being confined
merely to the separation into these ultimate fibres.


(_b_) For the chemical identification of the fibres in a paper, the
only available reactions are those with aniline sulphate solution. The
majority of fibres (celluloses) give no reaction, straw and esparto
celluloses and mechanical wood-pulp being the only ones that can be
identified by its means. The authors have found that when a paper
containing straw or esparto is treated for some time with a boiling
1 per cent. solution of aniline sulphate, a pink colour is produced.
Esparto gives the reaction with greater intensity than straw. In
this way the presence of a very small quantity of these pulps can be
detected with certainty.

Mechanical wood-pulp, when treated with a solution of aniline sulphate,
develops, even in the cold, a deep yellow colour. If a paper containing
mechanical wood-pulp so treated be examined under the microscope, the
fragments of wood will be found to be deeply stained, whereas the other
{202} fibres remain colourless or nearly so. It must be borne in mind
that cellulose obtained from lignified fibres, if the boiling and
bleaching processes have not been carried sufficiently far, will give
with aniline sulphate a more or less intense yellow coloration. Various
other reagents have been suggested for the identification of mechanical
wood-pulp, all based upon the production of a colour with lignose.

The reaction of lignose with chlorine and sodium sulphite solution
already referred to (p. 19) may also be made available for the
detection of mechanical wood-pulp in a paper. Imperfectly boiled or
bleached pulps sometimes give this reaction faintly.


_Quantitative Estimation of Mechanical Wood-pulp._—The determination of
the amount of mechanical wood-pulp present in a paper is sometimes a
matter of some importance, and it is also a matter of great difficulty.
Some idea of the amount present can be obtained by observing the depth
of the yellow colour produced with aniline sulphate or the intensity
of the magenta reaction with chlorine and sodium sulphite. It is also
possible to calculate approximately the percentage from the percentage
of cellulose contained in the specimen. Mechanical wood-pulp (pine)
may be taken to contain 60 per cent. of cellulose. If, therefore, a
paper ascertained to contain a pure cellulose in addition to this
constituent, yield 75 per cent. of cellulose on the ordinary test, it
may be assumed that about 62·5 per cent. of mechanical wood-pulp is
present.

The authors have proposed a method of estimating the amount of
mechanical wood-pulp present in a paper, based upon the absorption
of iodine in definite proportions by wood in a finely divided state,
under strictly regulated conditions. The paper is carefully reduced to
a fine pulp, and is then left in contact with a standard solution of
iodine in potassium iodide. At the end of twenty-four hours the amount
of free iodine is determined by titration with sodium thiosulphate and
by deducting this from the amount originally taken, the amount absorbed
is ascertained. As this amount, under {203} strictly comparative
conditions, always corresponds to a definite amount of mechanical
wood-pulp the amount present can be readily calculated.


2. _Loading, Sizing Materials, &c._—The determination of the amount
of loading material in a paper has been already described (p. 134).
The identification of the material can only be arrived at by a careful
chemical analysis. The principal loading materials are china-clay and
pearl-hardening (calcium sulphate). The ash from a paper containing
china-clay is insoluble in boiling dilute hydrochloric acid; that
from paper containing calcium sulphate is soluble: the solution on
cooling deposits long needle-shaped crystals of CaSO_{4} 2 H_{2}O and
gives with barium chloride a copious precipitate of BaSO_{4} (barium
sulphate) insoluble in acids, and with ammonia and oxalate of ammonia a
precipitate of calcium oxalate.

The presence of starch in a paper can be readily ascertained by
its behaviour with a solution of iodine. If starch be present the
well-known blue colour of the compound of iodine and starch will be
produced. The determination of the amount of starch present is a matter
of some difficulty, the details of which are somewhat beyond the scope
of the present work. It is based upon the conversion of the starch into
sugar, and the estimation of the latter with Fehling’s solution.

The nature of the material with which a paper is sized may be
ascertained in the following way:—

The sample, cut up into small fragments, is warmed for a few minutes
with alcohol containing a few drops of acetic acid. The alcohol is
allowed to cool, and is then poured into four or five times its bulk
of distilled water. If any precipitate or cloudiness is produced,
it indicates that the paper has been sized with rosin. The alcohol
dissolves the rosin, which, being insoluble in water, is thrown
down on dilution. The alcohol used should be previously purified by
distillation, as some samples contain a small quantity of shellac,
which would itself be precipitated with water. {204}

The paper after treatment with alcohol should now be boiled for some
minutes with water: the solution allowed to cool, and then filtered. To
the filtrate a few drops of a solution of tannic acid are added, when,
if the paper has been sized with gelatine, a white curdy precipitate
will be formed.

The estimation of the amount of sizing material in a paper is a very
complicated process and one which demands considerable chemical
experience for its proper conduct.

The amount of gelatine present is best ascertained by determining the
amount of nitrogen present by combustion with soda-lime, and from this,
calculating the amount of gelatine. Pure gelatine contains 18·16 per
cent. of nitrogen (Muntz). The comparison of one paper with another
with a view to ascertain the relative degree of sizing, is usually
performed in a more or less rough and ready way by moistening the
samples with the tongue for a certain time, and noticing the degree
of transparency produced, which is of course inversely to the degree
of hardness. A more accurate method consists in placing a drop of
a mixture of alcohol and water containing some colouring matter in
solution and determining the time necessary for the colour to make its
appearance on the other side. In this way more trustworthy comparisons
can be made.


_Colouring Matters._—The chemical reactions of the chief colouring
matters have been already described (p. 141).

{205}




CHAPTER XIV.

GENERAL CHEMICAL ANALYSIS FOR PAPER-MAKERS.


A knowledge of the methods usually employed for the qualitative and
quantitative analysis of the various chemical substances met with in
paper manufacture is of considerable importance. The scope of this
work will not allow us to enter fully into the necessary details of
manipulation; for these the reader is referred to standard works on
analysis; we will merely indicate the methods.


_Caustic Soda, Soda Ash, Recovered Soda, &c._—These substances are
always valued by the amount of real alkali (Na_{2}O) that they contain,
which is determined by titration with a standard acid.

In testing recovered soda, it is necessary to _boil_ the finely
powdered ash for some time with water; unless this be done, the amount
of alkali will probably be under-estimated, as part of the soda is
present as a difficultly soluble silicate.

It is sometimes desirable to determine the amount both of sodium
hydrate and carbonate in a sample of alkali. For this purpose an excess
of a solution of barium chloride is added to a solution containing a
known quantity of the substance under examination, and the mixture made
up to a definite volume. It is then filtered, and an aliquot portion
of the filtrate titrated with standard alkali. The filtrate contains
only the alkali that was originally present as hydrate, the carbonate
of soda having formed with the barium chloride, insoluble barium
carbonate, and sodium chloride.


_Bleaching Powder._—The value of bleaching powder {206} depends upon
the amount of available chlorine that it contains. This is determined
by means of a standard solution of arsenious acid. The standard
solution is prepared by dissolving pure arsenious oxide (As_{2}O_{3})
in sodium carbonate solution. To test the powder, a quantity, say about
5 grms., is taken, and is carefully ground up in a mortar with a small
quantity of water, more water is then added, and the coarser particles
allowed to settle for a few seconds. The milky liquid is then run off
into a graduated flask; the residue is again ground up with water, and
the operations repeated until the whole of the powder is transferred
to the flask. The flask is now filled up to the proper mark, carefully
shaken, and an aliquot portion withdrawn as quickly as possible. It is
necessary to take both the soluble and insoluble portions in order to
obtain uniform results. Standard arsenious acid solution is now run
in until the solution ceases to produce a blue colour with iodide of
potassium and starch papers.

The method of estimating the amount of available chlorine in bleaching
powder by determining the quantity of ferrous sulphate it is capable of
oxidising is fallacious, as by this means calcium chlorate is included
in the result.

Bleaching powder should contain about 35 per cent. of available
chlorine, but the percentage frequently falls below this amount,
especially in warm weather.

Great care should be exercised in the sampling of bleaching powder, as
indeed of all chemicals, in order to insure an average result. Small
portions should be taken from different parts of the bulk; the whole
should then be carefully mixed, and, if necessary, reduced to powder.
Portions of the mixture should be taken, pounded, and again thoroughly
mixed.

If this process be repeated once or twice, a perfectly uniform sample
will be obtained.


_Alum, Sulphate of Alumina, Alum Cake, &c._—The points to be considered
in an examination of these products are (1) the percentage of alumina
contained in them; (2) the {207} percentage of iron, and (3) the
amount of free sulphuric acid present.

(1) The alumina is estimated as such by precipitation with ammonia.
Ferric oxide is also thrown down with alumina, and must therefore be
deducted from the amount of the mixed oxides obtained.

(2) The percentage of iron oxide present is determined in the following
way. A considerable quantity of the sample under examination is
dissolved in water, and to the boiling solution a large excess of
caustic potash solution is added. The caustic potash precipitates both
the alumina and ferric hydrates, the former, however, redissolves.
The solution is filtered, and the precipitate of ferric hydrate
washed, dissolved in dilute hydrochloric acid, and reprecipitated
with excess of caustic potash. It is again thrown on to a filter,
washed, redissolved in hydrochloric acid, and again reprecipitated with
ammonia. In this way it is obtained free from alumina.[17]

     [Footnote 17: For a method of estimating minute quantities of iron
     in alums see ‘Journ. Soc. Chem. Ind.,’ April 1887, p. 276.]

(3) _Free Acid._—This can be estimated indirectly, i.e. by estimating
the alumina and ferric oxide, calculating the amount of sulphuric acid
necessary to combine with them, and deducting this from the total
amount of sulphuric acid obtained. In the case of alum it is of course
necessary to make due allowance for the sulphate of potash or ammonia
present. The sulphuric acid is estimated as barium sulphate in the
usual way.

It should be borne in mind that sulphates of alumina are sometimes met
with containing uncombined alumina. A convenient method of estimating
free acid consists in digesting a weighed quantity of the finely
powdered sample in strong alcohol. The alcohol dissolves away the free
acid, which can be estimated in the solution by means of a standard
solution of alkali.

Free acid can be detected by means of a solution of {208} Congo-red,
which is turned blue with free acid, but not with pure sulphate of
alumina.


_Antichlor, Sodium Thiosulphate, Sodium Sulphite, &c._—Sodium
thiosulphate can be estimated by means of a standard solution of iodine
in potassium iodide. The operation should be performed in dilute
solution (see p. 111).

The same solution serves also for the estimation of sulphurous acid in
sodium and other sulphites.


_Starches._—After having made a careful microscopical examination of
the sample, it should be examined for water by drying at 100°C., and
for mineral matter by igniting in a platinum crucible and weighing the
residue. The water should not exceed 18 per cent., and the ash ·50 per
cent. The samples should be carefully examined for insoluble matter
by dissolving in water and filtering. It is also useful in comparing
different samples of starch to convert the specimens into pastes, under
exactly similar conditions.

When perfectly cold, the “stiffness” of the pastes should be compared.
This may be done by noting the relative resistance to weights placed
upon their surface. Information on this subject is contained in a paper
by W. Thomson in the ‘Journ. Soc. Chem. Ind.,’ March 1886.

The identification of starches by means of their microscopical
appearances is tolerably simple, as each particular kind possesses
characteristic differences.


_Gelatine._—Samples of gelatine should be examined for water and ash.
The water should not exceed 16 per cent. and the ash 2·7 per cent. The
relative strengths of the jellies formed with water should also be
compared. This may be done in the way indicated above for starches.

Raw materials intended for the preparation of gelatine may be similarly
examined. They yield the whole of their gelatine on heating with water.
The effect of prolonged heating on solution of gelatine should be borne
in mind. The amount of residue left after treatment with water should
be carefully determined.


_Soaps._—The soaps most suitable for use in paper-making {209} are
those known as curd and mottled, the former being chiefly used for the
fine qualities. They should be carefully examined for free alkali and
unsaponified fat. Full descriptions are contained in Lant Carpenter’s
‘Treatise on Soap-making.’


_Dyes, Pigments, Loading Materials, &c._—These substances are best
examined from a physical and tinctorial point of view, by comparison
with specimens of undoubted purity and excellence.

The chemical examination is both difficult and somewhat misleading.
A microscopical examination will often throw much light on their
composition.

For comparing the tinctorial power of different samples, weighed
quantities should be ground up with starch or some other white powder.
In this way some idea of the intensity of colour can be readily arrived
at.

{210}




CHAPTER XV.

SITE FOR PAPER-MILL, WATER-SUPPLY, WATER PURIFICATION, ETC.


In choosing a spot on which to build a paper-mill, the manufacturer
has to take into consideration several very important circumstances.
Chief of these is the necessity for having a large supply of water at
command. Not only is a large quantity needful, but it should be free
from impurities, such as suspended matter and iron. The former, it is
true, can be removed by settling and filtration; the latter cannot, and
is liable to injuriously affect the colour of the paper. Again, as a
question of economy in working, it is advantageous to have convenient
water-power; therefore for this, as well as for the former reason,
paper-mills are usually situated on the bank of a stream. In choosing
such a site, paper-makers are probably also influenced by the fact that
it affords a ready means for the removal of impurities. In properly
conducted mills, where suitable apparatus is employed for evaporating
the liquors in which the raw material has been boiled, the stream
should not be polluted to any very great extent. Generally speaking,
the greater the pollution, the more are valuable materials being lost
to the manufacturer. It is obvious that the site for a mill should also
be chosen with reference to its proximity to means of transit for the
raw and manufactured materials.

The disposition of the different divisions of a paper-mill depends
of course upon the nature of the paper it is intended to make and to
a large extent upon local circumstances. Fig. 79 will give some idea
of the general arrangement of a mill for manufacturing esparto paper.
{211}


_Water Purification._—Arnot in his Cantor Lectures on the Technology of
the Paper Trade states that from 30,000 to 40,000 gallons of water are
required for the manufacture of each ton of paper. The importance of a
pure and copious supply is therefore very evident.

[Illustration: FIG. 79.]

The impurities of water consist of two classes, insoluble and soluble.
The former can be readily removed by processes of settling and
filtration. For this purpose most paper-mills are provided with large
ponds capable of holding several days’ supply. These are sometimes
supplemented by filtering beds. Insoluble impurities can also be
removed by passing the water through filter-presses.

Fig. 80 is an illustration of Rœckner’s patent clarifier, which may
also be applied to this purpose.

The cylinders C dip below the surface of the water to be purified,
which is contained in the reservoir A. They are open at their lower
ends, but are closed at the top by the domes D. These are connected
with the pump I by means of the pipes H. On starting the pump the water
rises slowly in the cylinders. As soon as it reaches the level of the
top, the action of the pump is stopped and the cocks K opened, when the
water commences to flow down the pipes G, which together {212} with
the cylinders form a kind of siphon. If the reservoir A be kept full,
the siphons can be made to act continuously. The flow of water being
slow, insoluble impurities have time to subside.

The impurities may from time to time be removed by means of the small
pump L connected with the bottom of the reservoir.

The clarifier can also be used for the purification of the effluent
water from paper-mills.

[Illustration: FIG. 80.]

Insoluble impurities can be removed from water by means of the Stanhope
purifier, shown in Fig. 81.

The soluble impurities of water consist mainly of carbonate and
sulphate of calcium and iron, and occasionally organic matter. It is
a moot point among paper-makers {213} whether or not the presence of
the two former in a water is objectionable. For boiling and bleaching
purposes it undoubtedly is, as when mixed with caustic soda or
bleaching liquor they form a precipitate of carbonate of calcium, which
lines the insides of boilers, breakers, and potchers as a hard scale,
which is always liable to become detached, and to find its way into the
finished paper. Moreover, carbonate of calcium is precipitated in the
fibre, and carries with it a certain quantity of colouring matter, the
subsequent removal of which is difficult.

Carbonate of calcium, though practically insoluble in pure water, is
soluble in water containing carbonic acid. When this carbonic acid
is neutralised by lime or soda, the carbonate is precipitated. The
sulphate of calcium is unacted upon by lime, but by the action of
caustic soda is converted into free lime and sodium sulphate. The
lime then neutralises the free carbonic acid in the water, and forms
carbonate of calcium, which is of course precipitated.

These reactions may be represented by the following equations:—

      Calcium     Carbonic  Lime.      Calcium
     carbonate.     acid.             carbonate.
  1.  CaCO_{3} +   CO_{2} + CaO  =  2 CaCO_{3}.

      Calcium      Caustic     Calcium         Sodium
     sulphate.      soda.      hydrate.       sulphate.
  2.  CaSO_{4} +   2 NaOH   =  CaH_{2}O_{2} +  Na_{2}SO_{4}.

      Calcium       Carbonic     Calcium      Water.
      hydrate.       acid.      carbonate.
      CaH_{2}O  +   CO_{2}  =    CaCO_{3}  +  H_{2}O.

If sodium carbonate be used instead of caustic soda, the decomposition
will take place thus:—

  Calcium       Sodium         Calcium       Sodium
  sulphate.    carbonate.     carbonate.    sulphate.
  CaSO_{4} +  Na_{2}CO_{3} =   CaCO_{3} +  Na_{2}SO_{4}.

It will be seen from the above equation that in the boiling processes
the lime salts are removed from the water at the expense of an
equivalent quantity of caustic soda. The amount thus decomposed is
not sufficiently large to make it advisable {214} on that account to
purify the water. It is indeed so small that processes of purification,
based upon the use of lime and caustic soda, are now largely used,
the cost for chemicals rarely exceeding 1_d._ per 1000 gallons. But
for the reasons we have stated above, and also from the fact that it
serves to remove dissolved iron and organic matter from a water, such a
purification process is in certain cases advisable.

The processes now in use consist, as we have indicated, in the addition
to the water of lime and caustic soda or carbonate of soda, the
quantities being regulated according to the hardness of the water, and
the relative proportions of carbonate and sulphate of calcium.

The method of removing carbonate of calcium from water by the addition
of lime is due to the late Dr. Clark, of Aberdeen, and the process
is still called after him. It is in use in its original form in many
places. The plant necessary consists simply of a tank for mixing the
water and the lime, and of large settling tanks in which the carbonate
of calcium subsides.

Various modifications of this process have been proposed, chiefly in
the direction of improved plant.

In the Porter-Clark process the carbonate of calcium is removed
by passing the water after the addition of lime (in the form of
lime-water) through a filter-press.

[Illustration: FIG. 81.]

In Fig. 81 is shown the Stanhope purifier, which is largely used for
the purpose of softening water. The following details will render its
action clear: A is a store tank containing caustic soda solution.
B is a tank into which the water to be treated flows, and which is
maintained at a constant level by means of a valve and float. C and C
are two tanks which are used alternately, and in which lime water is
prepared. A definite quantity of caustic soda solution is added from
B; this mixture forms the reagent by which the softening of the water
is accomplished. D is a small tank for the purpose of maintaining a
constant head of reagent. The reagent and the water are mixed together
in the pipe F, the quantities being regulated by the cocks {216}
shown at H. The pipe F leads into the vessel E, which is fitted with
a number of V-shaped shelves, placed at an angle of 45°, and riveted
alternately to opposite sides of the vessel. This arrangement causes
the water to take a serpentine course. The position of the shelves is
indicated by the dotted lines.

As soon as the mixture of water and reagent flows down the pipe F, and
enters the vessel E, the calcium carbonate commences to precipitate
and settles upon the V-shaped shelves. At the top of the tank a layer
of wood shavings, inclosed in wire-netting, is placed as shown by the
dotted lines. This acts as a filter, and intercepts any particles that
may not have subsided. The clear purified water passes away by the pipe
I.

The precipitate that collects on the V-shaped plates is from time
to time drawn off by the cocks shown at G; this may be done without
interfering with the working of the apparatus. While there can be
no doubt that the use of soft water is advantageous in the boiling,
washing, and bleaching processes, and also of course for supplying
steam boilers, it is probably an advantage to use a hard water for
diluting the pulp before running it into the machine.

In the case of papers which are loaded with any of the forms of calcium
sulphate (pearl-hardening, crystal-hardening, &c.) the use of very soft
water is objectionable from the fact that a certain quantity of calcium
sulphate is dissolved. This would not take place to the same extent
with water which is already charged with sulphate and carbonate of
calcium.

The removal of soluble iron from a water is effected by the softening
processes described.

{217}




CHAPTER XVI.

ACTION OF CUPRAMMONIUM ON CELLULOSE. PREPARATION OF WILLESDEN PAPER.


The action of a solution of copper oxide in ammonia upon cellulose
has been already referred to (see p. 5). Celluloses, and also
lignocelluloses, when treated with such a solution, gradually
gelatinise and finally dissolve. On evaporating the solution to
dryness, a gummy amorphous mass is obtained, containing the cellulose
intermixed with copper oxide.

If the cellulose be in excess, e.g. when the solution is evaporated on
the surface of paper, calico, &c., merely dipped in the solution, the
copper oxide is often not formed at all, but a green varnish-like mass
of cellulose combined with copper oxide, which coats the surface of
each filament, welding and cementing them together. This cement-like
_cupro-cellulose_, as it may be termed, being insoluble in water,
communicates water-resisting properties to the material so treated:
moreover, the presence of copper renders the fabric less prone than
before to be attacked by insects and mould, so that animal and
vegetable life of a parasitic nature and fungoid growths are rarely, if
ever, to be observed, even when the material is kept under conditions
where boring worms, ants, rot, and mould, would be likely to attack it.

As has been already indicated (p. 5), the solution of cuprammonium
hydroxide is preferable to one containing cuprammonium salts; not only
is the action on cellulose more energetic, but various other advantages
are obtained.


_Preparation of the Copper Solution._—The cuprammonium solution is
prepared according to the patent of Dr. C. R. Alder Wright (No. 737,
1883). {218}

A series of cast-iron towers, two to three feet in diameter and ten to
twelve feet high, is so arranged that a current of air can be blown by
a powerful engine successively through the whole series. The towers
are then nearly filled with fragments of metallic copper (crumbled
up sheet, cuttings, &c.), and solution of ammonia: the air-current
being turned on, oxidation of the copper and solution of the oxide so
produced are rapidly effected.

The ammonia solution employed is previously impregnated with a
considerable quantity of copper by passing a stream of water over
scrap copper in similar towers, a current of ammonia gas mixed with a
suitable proportion of air being at the same time forced in. The liquor
passing from one tower is used over again to supply a second instead of
water, and so on through the series: finally the liquor is brought up
to full copper strength in the series of towers described above.

The spent air issuing from the towers carries with it a notable
quantity of ammonia; this is intercepted by means of an “exhaust”
scrubber containing copper, and well supplied with water, whereby a
comparatively weak solution of ammonia and copper is obtained, which
can be used instead of water in the first series of towers.

In order to produce the maximum effect on the cellulose, the solution
should contain from 100 to 150 lbs. of ammonia, and from 20 to 25 lbs.
of copper per 100 gallons.

By decomposing a cuprammonium solution by means of metallic zinc, a
corresponding solution of zinc-ammonium hydroxide can be obtained. This
solution is also capable of gelatinising cellulose, but not to the
same extent as the copper solution. It may, however, be advantageously
employed in certain cases in conjunction with a copper solution. Such a
solution can be conveniently prepared by substituting brass for copper
in the dissolving-towers. It is worthy of note that although, as we
have seen, zinc has the power of replacing copper in a cuprammonium
solution, iron is without any action, although it readily replaces
copper in a solution {219} of copper sulphate. This fact is of very
great industrial importance, as it enables the manufacturer to employ
vessels and machinery of iron.

The “Willesden” goods may be divided into two classes. Goods of
the first class, such as rope, cordage, netting, &c., are prepared
by simply dipping the made-up materials in a bath of cuprammonium
solution, using certain precautions as to the mode of immersion and
its duration, and the strength of the solution. On subsequently drying
the dipped fabrics, they are obtained coated and impregnated with
cupro-cellulose, which thus not only forms a kind of varnish-like
surface dressing, but further adds strength to the fibres by more or
less intimately cementing them together.

Goods of the second class constitute a much more important group to
which at present the Willesden Company more especially devotes its
attention. These fabrics are essentially of three kinds, viz. Willesden
Canvas, Willesden Scrim, and Willesden Paper. The two former of these
classes are prepared in much the same way as the goods just described,
saving that the fabric to be treated is usually unwound from one roller
and rewound upon another, after passing through the bath and over a
succession of drying cylinders.


_Willesden Paper._—This may be divided into two departments, viz.
(1) Willesden unwelded; (2) Willesden welded, the first class being
prepared from a single web of paper by passing it through the bath,
rolling and drying. Certain coarse varieties furnish a waterproof
material excellently adapted for lining packages, &c. Finer qualities
furnish envelopes and stationery, possessing the valuable property
of not being affected by water. Letters written on such paper would
remain perfectly legible, even after prolonged immersion. It may be
interesting to point out here that the cuprammonium solution offers a
very simple means of fastening envelopes in such a way as to be proof
against any attempts at tampering. The method consists in using a
concentrated solution as the fastening material; the envelope {220} is
then closed and ironed with a warm flat-iron, whereby the gelatinised
cellulose is converted into an insoluble cupro-cellulose, and the cover
is fastened so securely that the only possible mode of opening is by
tearing the paper.


_Willesden Welded Goods_ are prepared by simultaneously dipping two or
more sheets of paper and pressing them into one compact homogeneous
sheet whilst the surfaces are still in a gelatinous state. In this way
a continuous length of fabric of extraordinary durability is produced
that is scarcely affected by water, even when heated in it for some
weeks at a pressure of 60 lbs. per square inch.

As, on drying fabrics treated with cuprammonium solution, the whole
of the ammonia in the solution absorbed by them is volatilised, it is
necessary, in order to make the process economical, to collect and
re-use this ammonia. This is effected by conducting the drying process
in closed chambers, from which the ammonia gas is conducted by suitable
appliances and recovered.

In addition to the advantages already mentioned, it may be stated that
Willesden paper is much less inflammable than ordinary paper.

Among the many uses to which Willesden goods can be applied, the
following may be cited:—Roofs and sheds; huts and tents; partitions;
tanks and pipes; damp-proof foundations; underlining slates; sails,
awnings, &c. &c.

{221}




CHAPTER XVII.

STATISTICS.


_Raw Materials._

The statistics concerning the trade in raw materials for paper-making
are not published in a detailed form, all the various kinds of fibre,
&c., being grouped under two heads, viz. rags (linen and cotton), and
esparto (which embraces other fibres, and probably wood pulps). The
figures for recent years are shown in the accompanying tables:—

  (_a_) Imports of cotton and linen rags:

                 tons.     _l._
      1880.    29,642     451,782

      1881.    26,773     396,274

      1882.    21,200     303,349

      1883.    28,543     401,922

      1884.    36,233     487,866

      1885.    35,470     466,928

  (_b_) Esparto and other material:

                 tons.     _l._
      1880.   228,580   1,642,903

      1881.   238,043   1,626,800

      1882.   251,594   1,784,078

      1883.   288,549   1,943,732

      1884.   260,544   1,638,564

But a portion of these imports was exported again, the figures being as
follows:—

  (_a_) Exports of rags and other paper-making material produced
  in the United Kingdom:

                 tons.     _l._
      1880.    55,792     673,523

      1881.    50,488     563,460

      1882.    49,352     526,554

      1883.    51,293     502,851

      1884.    60,924     562,903 {222}

  (_b_) Exports of ditto of foreign and colonial produce:

                 tons.     _l._
      1880.     6,965     102,499

      1881.    10,183     146,101

      1882.     7,004      84,515

      1883.    11,561     121,992

      1884.    26,498     274,664

The relative proportions of raw material furnished by the various
countries in 1884 (the latest available return) are shown in the
subjoined tables:—

  (_a_) Imports of linen and cotton rags in 1884:

             From           Tons.      £
  Germany                  21,280   294,883
  Holland                   4,406    56,537
  Belgium                   2,867    34,713
  Turkey                    2,036    16,228
  France                    1,875    28,133
  Russia                    1,784    33,293
  Channel Islands             282     3,972
  Norway                      261     3,377
  Denmark                     198     3,020
  British South Africa        133     1,615
  Australasia                 113     2,245
  Canary Islands               96     1,043
  Spain                        93     1,009
  Argentine Republic           64     1,280
  Other countries             745     6,518
                           ──────   ──────-
                           36,233   487,866
                           ━━━━━━   ━━━━━━━

  (_b_) Imports of esparto and other fibres in 1884:

            From            Tons.        £
  Algeria                  88,357     515,232
  Spain                    40,159     314,927
  Tripoli                  33,930     172,282
  Tunis                    20,526     117,374
  Other countries           1,033       5,738
                          ───────   ─────────
                          184,005   1,125,553
                          ━━━━━━━   ━━━━━━━━━

  (_c_) Imports of other materials, including rag and wood
  pulps, in 1884: {223}

        From              Tons.      £
  Norway                 47,923   276,204
  Belgium                 7,169    58,383
  Holland                 6,484    46,104
  Sweden                  5,178    48,523
  Germany                 3,732    36,582
  France                  2,128    14,667
  Denmark                 1,205    13,332
  British India           1,046     7,735
  Egypt                     870     4,933
  Other countries           804     6,544
                         ──────   ───────
                         76,539   513,011
                         ━━━━━━   ━━━━━━━

A considerable export of raw material for paper-making also takes place
from British shores, the figures, embracing rags and other materials,
for 1884 being as below:—

  (_a_) Exports of home produced rags and other paper-making
  materials in 1884:

         To              Tons.      £
  United States         59,222   550,924
  Holland                  649     2,703
  British America          390     4,255
  Germany                  262     1,673
  Other countries          401     3,348
                        ──────   ───────
                        60,924   562,903
                        ━━━━━━   ━━━━━━━

  (_b_) Exports of foreign produced ditto in 1884:

   (_i._) Linen and cotton rags.

            To            Tons.       £
      United States      14,191    167,801
      Other countries       514      5,519
                         ──────    ───────
                         14,705    173,320
                         ━━━━━━    ━━━━━━━

   (_ii._) Esparto and other fibres.

           To             Tons.        £
      All countries         140        701

   (_iii._) Pulps and other materials.

           To             Tons.       £
      United States      11,290     97,620
      Other countries       363      3,023
                         ──────     ──────
                         11,653    100,643
                         ━━━━━━    ━━━━━━━

{224}

Our imports of “rags and other paper-making materials” from Norway
increased from 23,483 tons, value 138,098_l._, in 1880, to 48,199 tons,
279,679_l._, in 1884, mainly owing to the development of the wood-pulp
industry. Later figures will probably show a similar increment. The
same articles from Denmark grew from 359 tons, 3406_l._, in 1880, to
1403 tons, 16,352_l._, from the same cause. German statistics have
even a stronger upward tendency: 11,587 tons, 196,051_l._, in 1880,
against 196,051 tons, 331,591_l._, in 1884. Our receipts of esparto
from Algeria show an advance, but not a marked one, being 60,612 tons,
421,343_l._, in 1880, and 88,357 tons, 515,232_l._, in 1884. But
shipments of the same fibre from Spain show a decline from 51,413 tons,
454,713_l._, in 1880, to 40,159 tons, 314,927_l._, in 1884; and from
Morocco they have fallen away from 2879 tons, 18,231_l._, in 1880, to
260 tons, 1290_l._, in 1884; while the figures relating to Tunis and
Tripoli also show a disposition to recede, though not at such a rapid
rate.

The wood-pulp industry of Norway for the year 1886 shows a very large
increase upon the figures of a few years back, albeit prices have
ruled very low. This latter circumstance is attributed, not so much to
over-production, as to excessive competition among the sellers of this
article. The quantity exported during the year 1886 is about 120,000
tons; in the year 1885 it was 107,651 tons; 1884, 88,220 tons; 1883,
70,464 tons; 1882, 58,884 tons; 1881, 42,194 tons; 1880, 26,055 tons.
Several of the old works have extended their production during the past
year, and several new establishments are in the course of erection, so
the production this year may probably be put at 150,000 tons wood pulp
with 50 per cent. water. The greatest part of the Norwegian wood pulp
is exported to England, France, and Belgium; in Russia, the increase
in the duty has stopped business, and the same can almost be said of
Germany. America, too, has drawn part of her supply from Norway, but
this trade is not expected to continue. {225}


_Manufactured Material._

Our import trade in manufactured paper has been growing of late years,
as the following figures will show:—

  Imports of paper and pasteboard, of all kinds except
  hangings:
                 cwt.        _l._
      1880.   1,021,952   1,159,646

      1881.   1,065,912   1,138,943

      1882.   1,098,118   1,202,905

      1883.   1,160,104   1,245,861

      1884.   1,447,335   1,403,446

At the same time, our exports of manufactured paper, though amounting
to only about one-third the weight, have very nearly as high an
aggregate value as the imports, and have increased in much the same
proportion in corresponding years. Thus:—

  Exports of paper of all kinds but hangings:

                 cwt.        _l._
      1880.     472,168   1,106,996

      1881.     555,219   1,242,962

      1882.     584,947   1,305,025

      1883.     597,923   1,284,862

      1884.     670,760   1,374,392

The above figures relate to paper manufactured in the United Kingdom.
In addition, there were re-exports of paper of foreign and colonial
manufacture to the following amounts:—

Re-exports of foreign-made paper:

             cwt.        _l._
  1880.      68,843     108,426

  1881.      68,861     101,197

  1882.      50,403      82,464

  1883.      49,526      76,620

  1884.      51,467      78,785

Taking the latest year for which detailed statistics are available,
viz. 1884, we find that the importations of paper {226} are derived
from foreign states in the following proportions:—

Imports of paper in 1884—

  (_a_)  Writing or printing paper:

               From       Cwt.        £
      Germany            92,681    129,112
      Belgium            42,139     68,370
      Sweden             27,747     36,682
      Holland            26,507     34,884
      France              6,463     28,925
      Austria             5,399      9,314
      Norway              4,300      4,771
      Other countries     3,174      5,655
                        ───────    ───────
                        208,410    317,713
                        ━━━━━━━    ━━━━━━━

  (_b_)  Unenumerated sorts:

               From       Cwt.        £
      Germany           139,156    209,916
      Sweden            116,488    120,793
      Belgium            82,263    124,476
      Holland            54,594     84,699
      Norway             32,294     26,765
      France             19,328     69,763
      United States      10,980     31,201
      Austria             5,927     12,012
      Spain                 736      4,059
      Japan                 421      4,736
      Other countries     3,547      5,995
                        ───────    ───────
                        465,734    694,415
                        ━━━━━━━    ━━━━━━━

  (_c_)  Pasteboard and millboard:

               From       Cwt.        £
      Holland           439,749    201,894
      Germany           235,658    116,185
      Belgium            51,235     25,350
      Sweden             32,331     20,241
      Norway              8,260      5,726
      France              3,262     19,259
      Other countries     2,696      2,663
                        ───────    ───────
                        773,191    391,318
                        ━━━━━━━    ━━━━━━━

The exports of home-made paper in the same year were distributed as
follows:— {227}

Exports of home-made paper in 1884—

  (_a_)  Writing, printing, and envelopes:

                 To               Cwt.        £
      Australasia               280,024    545,830
      France                     44,427    101,833
      Bengal and Burma           33,963     71,834
      Bombay and Scinde          29,767     64,227
      British South Africa       16,900     33,041
      British North America      14,871     44,511
      Madras                     10,532     25,651
      Argentine Republic          8,683     30,954
      United States               6,985     31,722
      Sweden and Norway           6,101     11,870
      Belgium                     5,981     13,926
      Germany                     5,969     14,188
      British West Indies         4,706     13,411
      Ceylon                      4,668     10,919
      Other countries            31,397     93,454
                                ───────  ─────────
                                504,973  1,107,371
                                ━━━━━━━  ━━━━━━━━━

  (_b_) Pasteboard and millboard:

                 To               Cwt.        £
      Australasia                14,542     20,771
      Bengal and Burma            5,147      4,589
      Bombay and Scinde           4,572      4,134
      France                        987      2,309
      Other countries             5,571     13,367
                                 ──────    ───────
                                 30,819     45,170
                                 ━━━━━━    ━━━━━━━

  (_c_) Unenumerated, and articles made of paper:

                 To               Cwt.        £
      Australasia                62,731     81,385
      British South Africa        9,341     11,809
      Bombay and Scinde           7,146     10,389
      Argentine Republic          6,283      8,113
      Germany                     5,147     11,394
      Belgium                     5,122     11,300
      France                      5,052     16,238
      Bengal and Burma            5,006      6,678
      United States               4,841     14,668
      British America             3,737      7,801
      Holland                     2,410      5,529
      Other countries            18,152     36,547
                                ───────    ───────
                                134,968    221,851
                                ━━━━━━━    ━━━━━━━

{228}

The re-exports of foreign and colonial-made papers during the same
period went to the following destinations:—

Re-exports of foreign paper in 1884—

  (_a_) Printing and writing:

                 To              Cwt.         £
      British India              10,488     14,643
      Australasia                 4,908      7,695
      Other countries             3,236      7,554
                                 ──────     ──────
                                 18,632     29,892
                                 ━━━━━━     ━━━━━━

  (_b_) Unenumerated:

                 To               Cwt.        £
      British India               5,852      7,354
      Egypt                       5,167      7,751
      Australasia                 2,131      4,398
      Russia                      1,560      7,829
      Other countries             8,465     15,825
                                 ──────     ──────
                                 23,175     43,157
                                 ━━━━━━     ━━━━━━

  (_c_) Pasteboard and millboard:

                 To               Cwt.        £
      All countries              9,660       5,736

{229}




CHAPTER XVIII.

BIBLIOGRAPHY.


  J. Murray.
      Practical Remarks on Modern Paper.            Edinburgh: 1829.

  L. S. Le Normand.
      Manuel du Fabricant des Papiers.                  Paris: 1834.

  G. Planche.
      L’Industrie de la Papeterie.                      Paris: 1853.

  L. Müller.
      Die Fabrikation des Papiers.                     Berlin: 1855.

  Proteaux.
      Manufacture of Paper and Boards.           Philadelphia: 1866.

  C. Hofmann.
      Manufacture of Paper.                      Philadelphia: 1873.

  Hugo Müller.
      Pflanzenfaser.                                  Leipzig: 1873.

  T. Routledge.
      Bamboo considered as a Paper-making Material.
                                          London and New York: 1875.

  Vétillart.
      Études sur les Fibres Végétales.                  Paris: 1876.

  Arnot.
      Technology of the Paper Trade (Cantor Lecture,
        Society of Arts).                              London: 1877.

  J. Dunbar.
      The Practical Paper-maker.                       London: 1881.

{230}

  Forestry and Forest Products (Edinburgh Forestry Exhibition).
                                                    Edinburgh: 1884.

  C. F. Cross and E. J. Bevan.
      Cellulose.[18]                                    London: 1885.

  R. Parkinson.
      A Treatise on Paper.                            Preston: 1886.

  C. T. Davis.
      Manufacture of Paper.                      Philadelphia: 1887.

  Tomlinson.
      Manufacture of Paper.

  Paper-makers’ Monthly Journal.                 London: since 1872.

  Paper Trade Journal.                         New York: since 1872.

  Papier Zeitung.                                Berlin: since 1876.

     [Footnote 18: Gives a list of works on Cellulose and its
     derivatives.]

{231}




CHAPTER XIX.

ADDENDA.


_The Yaryan Process of Evaporation._

This process, the invention of Mr. H. J. Yaryan, of Toledo, Ohio,
U.S.A., has been considerably developed in America in its several
applications, and as we have authentic information of its successful
working for the recovery of soda in some of the largest paper-mills
in the States, we think it deserving of mention. The principle of the
process is that of “multiple effects,” upon which, indeed, all the
modern methods of economic evaporation are based. The principle may be
briefly explained as follows:—A liquid is converted into vapour under
ordinary conditions of boiling, by overcoming the pressure of the
atmosphere upon its surface. The quantity of heat required to vaporise,
as also the temperature of the ebullition, will be less as the pressure
to be overcome is less. Further, the vapour continuously driven off
carries with it a quantity of heat, which is its heat of condition or
latent heat. This heat it imparts to any colder body (e. g. a further
quantity of the same liquid) with which it comes in contact, direct or
indirect; if the quantity of the latter be relatively small, it will
raise its temperature approximately to that of the ebullition of the
first liquid. If now the pressure (atmospheric) on the surface of the
latter be slightly reduced, by any means, it will boil. The vapour
from this can be made to boil a third quantity of the liquid, under a
further diminished pressure.

The successive effects in economic evaporation consist, therefore, in
utilising the latent heat of a vapour given off from a liquid under a
certain pressure (e. g. that of the atmosphere) to vaporise a further
quantity of the liquid under a pressure maintained by mechanical means
below that of the first. In the ordinary methods the vapour does its
work in the successive effects by passage through systems of tubes,
the liquid to be heated being in contact externally; in the Yaryan
system, on the other hand, the arrangement {232} is reversed. The
liquid to be evaporated traverses the system of tubes which are heated
externally by the vapours. At the end of each effect, the liquid is
caused to impinge, in a special chamber, upon a disc: in this way a
complete separation of liquid and vapour is effected, each then passing
on to the next effect, the former through the tube-system, the latter
to the chamber inclosing these. The flow of liquid is maintained by
a force-pump, and the diminished pressure by a vacuum-pump suitably
disposed. This system differs from that described on page 180, in
that the evaporation is continuous, the dilute liquors entering the
apparatus and the highly concentrated liquors leaving it in an unbroken
stream. The rate of flow is such that the evaporation of the caustic
liquors from wood boiling from 8–10° to 80° Twaddell, in a quadruple
effect, requires only a few minutes. At the latter concentration it is
ready for the incineration process, which by means of a rotary furnace,
such as that of Mr. J. W. Hammond, of the firm of S. D. Warren and Co.,
is also effected continuously. It is found, moreover, that the excess
of heat available from this process is sufficient for the evaporation.


_Ferric Oxide Causticising Process._

The principle of this process is the expulsion of the carbonic acid
from sodium carbonate by ferric oxide at high temperatures; this oxide
playing the part of a weak acid, entering into a loose combination with
the soda, which is overcome by water in the subsequent lixiviation
process, the ferric oxide being regenerated and a solution of caustic
soda obtained.

The ferric oxide is therefore continuously available. The main features
of the process, disregarding the question of commercial economy, are
(1) that it leaves no by-products to be disposed of, (2) that it
enables the manufacturer to produce directly, without evaporation, a
highly concentrated caustic lye.

This process has been worked out under the auspices of Messrs.
Brunner, Mond, & Co., and there is every reason to expect an extensive
application of so simple a method.

{233}




INDEX.


  Abaca, see Manilla hemp

  Abies pulp, 60

  Acetic acid in bleaching, 114

  Acid, action on paper, 163

  ― in alum, estimating, 207

  ― ― ―, evils of, 163

  ― processes for wood, 69

  ― radicles and cellulose, 8

  Acids added in bleaching pulps, 112

  ― and cellulose, 12

  Adansonia fibre, 53

  ― ―, boiling, 103

  ― ―, cutting, 103

  ― ―, willowing, 103

  Adipo-cellulose, 26

  Adulterating paper, 130

  Agalite loading, 133

  Agave americana fibre, 33, 44

  Alkali boiled with rags, 82

  ― process for isolating cellulose, early methods, 65

  Alkaline processes for isolating cellulose, 62

  Alkalis and cellulose, 14

  ― and ligno-cellulose, 21

  Aloe fibre, 33, 39, 44, 46

  ― ―, dimensions, 39

  ― perfoliata fibre, 39

  Alum, action on cellulose, 163

  ―,― on gelatine, 163

  ―, analysing, 206

  ― cake, analysing, 206

  ―, estimating acid in, 207

  ―, freedom from acid, 163

  ― in sizing, 139

  ―, proportion required, 141

  ― solutions, table of strengths, 143

  Alumina resinate, 137

  Alumina sulphate, analysing, 206

  ― ― in sizing, 140

  Aluminous cake, 140

  Ammoniacal solution of cupric oxide, 5

  Amyloid, 12

  Analysis of plant substances, 42

  Analysing alum, 206

  ― ― cake, 206

  ― alumina sulphate, 206

  ― antichlor, 208

  ― bleaching powder, 205

  ― caustic soda, 205

  ― dyes, 209

  ― gelatine, 208

  ― loading material, 203, 209

  ― paper, 199

  ― pigments, 209

  ― recovered soda, 205

  ― size, 203

  ― soaps, 208

  ― soda ash, 205

  ― sodium sulphite, 208

  ― ― thiosulphate, 208

  ― starches, 208

  ― wood pulp, 201

  Ananassa sativa fibre, 44

  Aniline blues, 141

  ― colours, solutions, 37

  ― for diagnosing plant substances, 43

  ― pinks, 142

  ― sulphate solution, 37

  Animal cellulose, 7

  Annandale’s damping method, 159

  Antichlor, analysing, 208

  ―, lime and sulphur, 129

  ―, proportion required to neutralise bleaching powder, 128

  ―, removing bleaching liquor by, 127

  Antichlor, sodium hyposulphite, 127, 129

  ―, ― sulphite, 125

  ―, ― thiosulphate, 127, 129

  ―, testing, 130

  Apparatus for microscopic examination of fibres, 35

  Ash of cotton pulp, 136

  ― of esparto pulp, 136

  ― of linen pulp, 136

  ― of paper, estimating, 134

  ― of paper, natural, 136

  ― of straw pulp, 136

  ― of wood pulp, 136

  Aspen for mechanical wood pulp, 108

  Available chlorine in bleaching powder, 110


  Bachet and Machard’s process forwood, 69

  Baobab fibre, 53

  ― ― composition, 54

  Barium hydrate and cellulose, 7

  Bark fibres, 2

  Barley straw, 98

  Barre’s acid process for wood, 69

  Bast fibres, 34

  ― ―, dimensions, 39

  ― filaments, 34

  ―, nature of, 2

  ― tissues, 53

  Beater bed-plate, 120

  ― knives, 120

  ― ―, cutting in situ, 121

  ―, lead-lined, 120

  Beaters, 117

  ―, direct-driven, 126

  ―, engine for driving, 126

  ―, water for, 125

  Beating esparto, 117

  ―, proportion of water to pulp, 118

  ― pulp, 117

  ― ―, duration of, 119

  ― wood pulp, 117

  Bed-plate of beater, 120

  Beech, composition, 61

  Bertram’s beater, 122

  ― damping cylinder, 159

  ― direct-driven beaters, 126

  Bertram’s rag boiler, 82

  ― smoothers, 158

  ― strainers, 148

  Bibliography, 229

  Birch, composition, 61

  ―, pulp yield, 77

  Bisulphite, action on cellulose compared with soda, 76

  ―, colour of pulp produced by, 77

  ― process, advantages, 76

  ― processes for wood, 71

  Bleached pulp, freeing from bleach, 114

  ― ―, improving colour, 114

  Bleaching, acetic acid in, 114

  ― action should be confined to non-cellulose, 113

  ― by chlorine, 114

  ―, electrolytic, 115

  ― pulp in potchers, 111

  ― pulps, 110

  ― rags, 115

  ― refractory pulps, 114

  ―, time required by, 113

  ―, with sodium hypochlorite, 113

  Bleaching-liquor, clear, 111

  ―, removing by antichlor, 127

  ―, removing from half-stuff, 127

  ―, storing, 111

  ―, strength, 111

  ―, washing out from half-stuff, 127

  Bleaching-powder, accelerating action of, 112

  ―, analysing, 205

  ― and cellulose, 10

  ―, available chlorine in, 110

  ―, keeping, 111

  ―, neutralising by lime and sulphur, 129

  ―, ― by sodium hyposulphite, 127, 129

  ―, ― by sodium sulphate, 128

  ―, ― by sodium thiosulphate, 127, 129

  ―, preparing, 110

  ―, proportion of antichlor required to neutralise, 128

  ―, quantities needed, 112

  Blitz’s sulphide process, 67

  Blondel’s acid process for wood, 69

  Blotting paper, starching, 139

  Blue colours, 141

  Boehmeria, 50

  ― nivea fibre, 39

  ― puya fibre, 44

  Boilers for esparto, 90

  ― for resolving wood, 74

  ― for straw, 99

  ―, iron, 76

  ―, lead-lining, 75

  Boiling adansonia fibre, 103

  ― esparto, 89, 91

  ― jute, 103

  ― manilla hemp, 103

  ― rags, 82

  ― straw, 100

  Boiling-liquors, recovering soda from, 179

  Bombax heptaphyllum fibre, 39

  Books on paper-making, 229

  Bottoms, caustic, 177

  Broke paper, grinding mill, 105

  ― ―, using up, 104

  Bromine and jute, 18

  Broussonetia kæmpferia fibre, 54

  ― papyrifera fibre, 39, 54

  Burning recovered soda, 186


  Calcining recovered soda, 186

  Calendering, 167

  Calenders, 158

  ―, deflection, 171

  Calcium carbonate mud, 190

  ― hypochlorite, removing from pulp, 114

  ― sulphate, estimating, 203

  ― ― loading, 131

  Cannabis sativa fibre, 39, 49

  Carbonic acid bleaching, 115

  Carbonising recovered soda, 186

  Caustic soda, analysing, 205

  ― ―, brands, 178

  ― ―, commercial forms, 177

  ― ― drums, emptying, 179

  ― ―, prices, 179

  ― ― solutions, table of strengths, 109

  Causticisers, 188, 192

  Causticising, 187

  ― by ferric oxide, 232

  ―, lime used, 190

  ―, oxygenating during, 191

  Cellular tissue in straw, 103

  Cellulose, 4

  ―, absorption of acids and basic oxides, 7

  ―, action of alum on, 163

  ―, ― of cuprammonium on, 5, 217

  ―, ― of lime on, 84

  ―, ― of soda and bisulphite compared, 76

  ―, ― of sulphur on, 130

  ―, ― on light, 6

  ― and acids, 12

  ― and alkalis, 14

  ― and barium hydrate, 7

  ― and bleaching powder, 10

  ― and chlorine, 10

  ― and humus, 15

  ― and hydrochloric acid, 13

  ― and lead solutions, 8

  ― and metallic salts, 8

  ― and nitric acid, 13

  ― and oxygen, 10

  ― and sulphuric acid, 12

  ― and water at high temperature, 14

  ― and zinc chloride, 13

  ―, animal, 7

  ―, behaviour under Schweitzer’s reagent, 5

  ―, bleaching should not affect, 113

  ―, burning, 23

  ―, characters, 4

  ―, combinations, 7

  ―, ― with acid radicles, 8

  ― compared with jute, 17

  ―, composition, 4

  ―, compounds, 7, 16

  ―, decomposition, 12

  ―, ― by ferments, 15

  ―, ― by heat, 23

  ―, destructive action of soda on, 64

  ― di-nitrate, 10

  ―, early form of alkali process for isolating, 65

  ― formed by vinegar plant, 16

  ―, formula, 4

  ― gelatinised, 5

  ―, general method of isolation, 4

  ― hexa-nitrate, 9

  ―, identification, 6, 18

  Cellulose in contact with iron, 13

  ― in fibre, estimating, 42

  ― in straw, 99

  ―, isolating by sulphurous acid, 64

  ―, ― from plant substances, 62

  ―, ― from wood, Schultze’s method, 21

  ―, lignification, 17

  ―, mineral constituents, 5

  ―, modifications of, in the plant, 16

  ―, nitration of, 8

  ―, oxidation, 10

  ―, penta-nitrate, 9

  ―, percentage yielded by jute, 19

  ―, proportion in esparto, 96

  ―, ― of, in well-boiled pulp, 113

  ―, reactions, 6

  ―, soluble in Schweitzer’s reagent, 5

  ―, ― sulphides for isolating, 67

  ―, solubility, 5

  ―, synthesis, 15

  ―, tetra-nitrate, 10

  ―, triacetyl, 8

  ―, tri-nitrate, 10

  ―, yield from esparto, 95

  ―, ― from straw, 98

  Celluloses, compound, hydrolytic resolution, 63

  ―, ―, treating for paper, 63

  Cellulosic fermentation, 16

  Chapman’s evaporator, 184

  Chemical analysis of plant substances, 42

  ― examination of paper, 201

  Chestnut, pulp yield, 77

  China clay, estimating, 203

  ― ― loading, 131

  ― grass, 39, 46, 50

  ― ―, character, 50

  ― ―, composition, 51

  ― ― fibres, dimensions, 39

  ― ―, forms in which employed, 51

  ― ―, general chemical characteristics, 51

  ― ―, micro-chemical reaction, 51

  ― ―, microscopic features, 51

  Chlorinating straw pulp, 102

  Chlorinating wood tissue, 19

  Chlorine and cellulose, 10

  ― and jute, 18

  ― as a bleaching agent, 114

  ―, available, in bleaching powder, 110

  ― water solution, 37

  Clarifying water, 125

  Classification of paper as to strength, 197

  Cleaning straw, 100

  Closing plates of strainers, 150

  Cochineal lakes, 142

  Collodion pyroxyline, 10

  Colophony, 137

  Colour, improving, 114

  ― of pulp produced by bisulphite, 77

  Colouring paper, 141

  Commercial statistics, 221

  Composition of paper, testing, 199

  Compound celluloses, hydrolytic resolution, 63

  ― ―, treating for paper, 63

  Conifer pulp, 60

  Constitution of plant fibres, 1

  Cooke and Hibbert’s beater, 123

  Corchorus capsularis fibre, 39, 44, 52

  ― olitorius fibre, 39

  Cork, 26

  Cotton, 46

  ―, classification, 46

  ―, composition of raw fibre, 47

  ― fibres, dimensions, 39

  ―, forms in which employed, 48

  ―, general chemical characteristic, 47

  ― in paper, detecting, 199, 201

  ―, micro-chemical reaction, 47

  ―, microscopic features, 46

  ―, nature of, 1

  ― pulp, ash, 136

  ― ―, beaten, 118

  ― ―, dimensions of fibre, 119

  ― rags, statistics, 221, 222

  ― ―, treatment for paper, 79

  ― sections, 47

  Couch rolls, 156

  Cream caustic, 177

  Cross’s boiler, 76

  Crotalaria juncea fibre, 44, 50

  Crystal carbonate, 138

  Cuprammonium, 217

  Cuprammonium solution, preparing, 217

  Cuticular tissue, 26

  Cutting, 171

  ― adansonia fibre, 103

  ― beater knives, 121

  ― jute, 103

  ― manilla hemp, 103

  ― rags, 81

  ― straw, 100


  Dahl’s sulphide process, 67

  Damping-cylinders, 159

  Dandy roll, 155

  Dark paper from jute, 103

  Deckle, 144, 152

  Densities, Twaddle, and sp. gr., 109

  Detecting adulteration, 203

  Diagnosis of plant substances, 42

  Dicotyledonous stems, fibres of, 33, 46

  Direct-driven beaters, 126

  Discoloration of paper from mechanical wood pulp, 108

  Doctor, 157

  Draining bleached pulp, 114

  ― boiled rags, 84

  ― straw pulp, 100

  Drum washer for boiled rags, 85

  Dry pulp, preparing, 119

  Drying cylinders, 157

  Dusting rags, 82

  Dyes, 141

  ―, analysing, 209


  Economy of sulphide processes, 68

  Edgerunner mill, 119

  Edgworthia papyrifera fibre, 54

  Ekman’s bisulphite process, 72

  ― process, preparing wood for, 73

  Electrolytic bleaching, 115

  Emptying soda drums, 179

  Engine for driving beaters, 126

  ― sizing, 137

  Esparto, 46, 55

  ―, amount of bleaching powder needed by, 112

  ―, beating, 117

  ―, boiled, washing, 95

  ― boiler, Roeckner’s, 93

  ― ―, Sinclair’s, 94

  ―, boiling, 89, 91

  ―, character, 55

  ―, cleaning machine, 90

  ―, composition, 57

  ― fibres, dimensions, 39

  ―, general chemical characteristics, 56

  ― in paper, detecting, 199, 201

  ― liquor, disposal of, 98

  ―, micro-chemical reaction, 56

  ―, microscopic features, 56

  ― paper mill, arrangement, 210

  ―, picking, 90

  ―, presse-pâte system, 96

  ―, pressure for boiling, 93

  ―, proportion of cellulose in, 96

  ― pulp, ash, 136

  ― ―, dimensions of fibre, 119

  ―, quantity of soda for, 92

  ― section, 56

  ―, soda required by, 89

  ―, statistics, 221, 222

  ―, substances removed from, by caustic soda, 97

  ―, time of boiling, 92

  ―, treating for paper, 63

  ―, yield of cellulose, 95

  Estimating acid in alum, 207

  ― added mineral matter in paper, 136

  ― mineral matter in paper, 134

  Evaporating soda liquors, 180, 231

  Evaporators, 180, 231

  ―, Chapman’s, 184

  ―, Roeckner’s, 181

  ―, Porion’s, 182

  ―, smell consumer, 183

  ―, Yaryan, 231


  Felting, 31

  ― caused in potchers, 113

  Fermentation, cellulosic, 16

  Ferments decomposing cellulose, 15

  Ferric oxide causticising process, 232

  Fibre bundles, 34

  ―, interweaving to form paper, 30

  ―, theoretical value in paper, 30

  Fibres, analysis, complete, 43

  ― and cells, 1

  ―, apparatus for microscopic examination, 35

  ― classified according to iodine reaction, 46

  ―, dimensions, 38

  ―,― in pulps, 119

  ―, estimating cellulose in, 42

  ―, ― purity, 39

  ―, isolating for examination, 38

  ―, microscopic features, 32

  ―, nature of, 1

  ― of dicotyledonous stems, 33

  ― of monocotyledonous stems, 33

  ―, physical structure, 30

  ―, raw, analysing, 42

  ―, reagents for examining, 36

  ―, sections for examination, 38

  ―, separation, 34

  ―, table of characters, 44

  ―, ― of length, 39

  ―, Webster on analysis of, 42

  Fibrous tissue, 34

  Fibro-vascular bundles, 2

  ― ― ―, dimensions, 39

  Filaments, 34

  ―, dimensions of cells and fibres, 39

  ―, table of lengths, 39

  Filter bags for water, 126

  ― paper, starching, 139

  Filtering lime mud, 190

  Finish, 159

  Finishing-house, 175

  Fir pulp, 61

  Flax, 39, 44

  ―, characters, 48

  ―, composition of raw fibre, 48

  ― fibres, dimensions, 39

  ―, forms in which employed, 49

  ―, general chemical characteristic, 48

  ―, micro-chemical reaction, 48

  ―, microscopic features, 48

  ― sections, 48

  Forbes’ beater, 122

  Fourdrinier machine, 145

  Francke’s bisulphite process, 72

  Friction-glazing, 169

  Fry, Ransome, and Wilkie’s wood-splitting machine, 74

  Furfural, 21


  Gaskell and Deacon’s crystal carbonate, 138

  ― sodium sulphite, 128

  Gelatine, action of alum on, 163

  ―, analysing, 208

  ―, estimating amount of, 204

  ― for sizing, 161, 162

  ― size, making, 162

  ― with soap, 163

  Glaser’s straw pulp chlorinating process, 102

  Glazing, 167

  ―, influence on strength, 198

  Gossypium fibres, 39, 46

  Gould’s beater, 122

  Greenbank soda, 178

  Grinding straw pulp, 101

  ― wood to pulp, 105

  Guillotine cutter, 174

  Gun-cotton, 9


  Half-stuff defined, 88

  ―, freeing from bleaching liquor, 127

  ―, removing bleaching liquor from, by antichlor, 127

  ―, washing out bleaching liquor from, 127

  Hand-made paper, 144

  Hartig-Reusch paper-testing machine, 194

  Hemp, 39, 46, 49

  ―, characters, 49

  ―, composition, 50

  ― fibres, dimensions, 39

  ―, forms in which employed, 50

  ―, general chemical characteristic, 50

  ―, micro-chemical reaction, 50

  ―, microscopic features, 49

  ―, section, 50

  Hermite’s electrolytic bleaching, 115

  Hibiscus strictus fibre, 44, 46

  Humus and cellulose, 15

  Hydracellulose, 12

  Hydrochloric acid and cellulose, 13

  ― ― ― ligno-cellulose, 22

  ― ― in bleaching pulps, 112

  Hydrolytic resolution of compound celluloses, 63


  Igniting recovered soda, 186

  Iodine and jute, 17

  ― ― lignified tissue, 17

  ― ― starch paper, making, 130

  ― reaction, details of manipulation, 40

  ― solution, 36

  ― ―, testing, 36

  Iron boilers, 76

  ― oxide causticising process, 232


  Jolly’s balance, 135

  Jordan beater, 121

  Jute, 33, 39, 44, 46, 52

  ― and bromine, 18

  ― ― chlorine, 18

  ― ― iodine, 17

  ―, boiling, 103

  ―, character, 52

  ― compared with cellulose, 17

  ―, cutting, 103

  ―, dark paper from, 103

  ― fibres, dimensions, 39

  ―, forms in which employed, 53

  ―, general chemical characteristic, 53

  ―, micro-chemical reactions, 52

  ―, microscopic features, 52

  ―, objection to acid in bleaching, 112

  ―, reactions, 17

  ―, treating for paper, 64

  ―, willowing, 103


  Kaolin, estimating, 203

  ―, loading, 131

  Kingsland beater, 121

  Knives for cutters, 171

  ― of beater, 120

  ― ― ―, cutting in situ, 121

  Knotter, 151


  Laid paper, 156

  Lead lining to beater, 120

  ― solutions and cellulose, 8

  Leaden boilers, 75

  Leaf fibres, 2

  Lignification estimated by aniline, 43

  ― of cellulose, 17

  Lignified tissue and chlorine, 18

  ― ― ― iodine, 17

  Ligno-cellulose, 20

  ―, aldehydic character, 25

  ―, and dilute alkalis, 21

  ― and dilute mineral acids, 20

  ― and hot water, 21

  ― and hydrochloric acid, 22

  ― and mineral acids, 20

  ― and nitro-sulphuric acid, 22

  ― and sulphuric acid, 22

  ―, animal digestion of, 23

  ―, decay of, 23

  ―, decomposition by heat, 23

  ―, distribution, 23

  ―, treating for paper, 64

  Lime, action on cellulose, 84

  ― and sulphur for neutralising bleaching powder, 129

  ― boiled with rags, 83

  ― for causticising, 190

  ―, milk of, 177

  ― mud, 190

  ― ―, composition, 191

  ― ―, filtering, 190

  ― salts in water, 212

  ― sulphate loading, 131

  ― unsuited for esparto, 89

  Lime-tree, composition, 61

  Linden bast fibres, 39, 54

  Linen, 46

  ― in paper, detecting, 199, 201

  ― pulp, ash, 136

  ― ―, beaten, 117

  ― ―, dimensions of fibre, 119

  ― rags, statistics, 221, 222

  ― ―, treatment for paper, 79

  Linum usitatissimum fibre, 39, 44, 46

  Literature, 229

  Loading, estimating, 134

  ― materials, analysing, 209

  ― paper, 130

  ― with agalite, 133

  ― with china clay, 131

  ― with lime sulphate, 131

  ― with magnesium silicate, 134

  ― with pearl-hardening, 131

  Loft-dried paper, 145

  Lunge’s bleaching method, 114

  Lygeum spartum fibre, 55


  Machine, 145

  Magnesium silicate loading, 134

  Manilla hemp, 44, 46, 59

  ― ―, boiling, 103

  ― ―, composition, 60

  ― ―, cutting, 103

  ― ―, micro-chemical reaction, 60

  ― ―, microscopic features, 59

  ― ―, sections, 60

  ― ―, treating for paper, 64

  ― ―, willowing, 103

  Masson, Scott, and Bertram’s beater, 123

  ― ― ― esparto-cleaning machine, 90

  ― ― ― strainer, 149

  Mechanical wood pulp, 105

  ― ― ―, quantitative estimation, 202

  Menzies and Davis’ smell consumer, 183

  Metallic salts and cellulose, 8

  Microscope equipment, 35

  Microscopic features of fibres, 32

  Microscopical examination of paper, 201

  Milk of lime, 177

  Mill, arrangement, 210

  ―, site for, 210

  Millboard machine, 166

  Mineral acids and cellulose, 20

  ― ― and ligno-cellulose, 20

  ― matter, added, estimating, 136

  ― ― in paper, estimating, 134

  Mixing pulps, 119

  Monocotyledonous stems, fibres of, 33, 46, 54

  Mounting solution, 36

  Musa paradisiaca fibre, 44

  ― textilis, 59


  Names in paper, 145, 156

  Nettle, 52

  Neutral mounting solution, 36

  New Zealand flax, 39, 44, 46, 59

  ― ― ―, dimensions, 39

  ― ― ― general chemical characteristics, 59

  ― ― ― micro-chemical reaction, 59

  New Zealand flax, microscopic features, 59

  Nilgherry nettle, 44

  Nitric acid and cellulose, 8, 13

  Nitro-sulphuric acid and ligno-cellulose, 22


  Oak, pulp yield, 77

  Oat straw, 98

  Oxidising sodium sulphide, 191

  Oxycellulose, 13

  Oxygen and cellulose, 10

  Oxygenating liquors while causticising, 191


  Paper ash, estimating, 134

  ―, broke, pulp from, 104

  ―, colouring, 141

  ― from mechanical wood pulp, faults of, 108

  ―, hand-made, 144

  ―, loading, 130

  ―, loft-dried, 145

  ― machine, 145

  ― makers’ soap, 163

  ― making and textiles, 3

  ―, measuring strength, 193

  ―, natural ash, 136

  ―, printed, pulp from, 105

  ―, sources of raw material, 1

  ―, thickness, 153

  ―, toned, 142

  ― trade, statistics, 225

  ― waste, pulp from, 104

  ―, width, 152

  Paper-mulberry fibres, 39, 46, 54

  Partington’s bisulphite process, 72

  Patterns on paper, 145, 156

  Pearl hardening, 131

  ― ―, estimating, 203

  Pectic acid, 28

  Pecto-cellulose, 28

  ― ―, treating for paper, 63

  Phormium tenax fibre, 39, 44, 59

  Physical structure of fibres, 30

  Picking esparto, 90

  Pictet’s sulphurous acid process, 70

  Pigments, 141

  ―, analysing, 209

  Pine, composition, 61

  ―, pulp yield, 77

  Pine, white, for mechanical wood pulp, 108

  ― wood fibre, 61

  Pineapple fibre, 44, 46

  Pink colours, 141

  Pinus fibre, 60

  Plant fibres, constitution, 1

  ―, structural elements, 1

  ― tissues mainly cellulose, 4

  Pochin’s aluminous cake, 140

  Poplar, composition, 61

  ― fibre, 60

  Porion’s evaporator, 182

  Porter-Clark process for water, 214

  Potchers, felting caused in, 113

  ― for bleaching pulp in, 111

  ― for rags, 80

  Presse-pâte system for esparto, 96

  ― ― ― for straw, 101

  Pressure for boiling straw, 100

  ― in relation to soda, 64

  Prussian blue, 142

  Pulp, beating, 117

  ―, bleaching, 110

  ―, ― refractory, 114

  ―, colour of, produced by bisulphite, 77

  ―, dimensions of fibre in, 119

  ―, dry, preparing, 119

  ―, duration of beating, 119

  ―, freeing from bleach, 114

  ―, improving colour, 114

  ―, mixing, 119

  ―, removing calcium hypochlorite from, 114, 127

  ― saver, 114, 155

  ― yield from straw, 99

  ― ― ― woods, 77

  Purification of water, 211


  Rags, bleaching, 115

  ―, boiled, draining, 84

  ―, ―, washing, 85

  ―, boiling, 82

  ―, ― with lime, 83

  ―, cutting, 81

  ―, dusting, 82

  ―, potchers, 89

  ―, proportion of alkali, 83

  ―, quantity of water for boiling, 84

  ―, sorting, 80

  ―, statistics, 221, 222

  ―, time of boiling, 84

  ―, treatment for paper, 79

  ―, ― in washer, 89

  ―, willowing, 81

  Ramie fibres, dimensions, 39, 50

  Raw material for paper, 1

  Reagents for examining fibres, 36

  Recovered soda, analysing, 205

  ― ―, carbonising, 186

  ― ― causticising, 187

  ― ―, composition, 186

  Refractory pulps, bleaching, 114

  Repped paper, 171

  Resinate of alumina, 137

  Retree, 175

  Rhea fibre, 50

  Roeckner’s esparto boiler, 93

  ― evaporator, 181

  ― strainer, 150

  ― water clarifier, 211

  Rosin, 137

  ― soap, 137

  Rotary boilers unsuited to esparto, 90

  Rubbing test for paper, 197

  Rye straw, 98


  Salle, 175

  Salmon’s guillotine, 174

  Save-all, 154

  Schultze’s method of isolating cellulose from wood, 21

  Schurmann’s calender rolls, 171

  Schweizer’s reagent, 5

  Sections of fibres for examination, 38

  Seed hairs, 46

  ― ―, dimensions, 39

  Self-cleaning strainer, 149

  Settling ponds, 125

  Seventy per cent. white caustic, 178

  Sheave, causes of, 90

  Silk fibre, 31

  Sinclair’s esparto boiler, 94

  Single cylinder machines, 164

  ― sheet cutter, 173

  Siphon washer for boiled rags, 87

  Site for mill, 210

  Sixty per cent. white caustic, 177

  Size, estimating amount of, 204

  ―, ― nature of, 203

  ―, making with gelatine, 162

  Sizes of sheets, 175

  Sizing, 137

  Slicer, 151

  Smalts, 141

  Smell consumer, 183

  Smoothers, 158

  Smoothness, 159

  Soaking wood, 107

  Soap, analysing, 208

  ― and gelatine, 163

  ― for paper-makers, 163

  Soda, action on cellulose compared with bisulphite, 76

  ― ash, analysing, 205

  ― bicarbonate for accelerating action of bleaching powder, 112

  ―, brands, 178

  ― carbonate for sizing, 138

  ―, commercial kinds, 177

  ―, destructive action on cellulose, 64

  ― drums, emptying, 179

  ― for esparto, 89

  ― for isolating cellulose, 63

  ― in relation to pressure, 64

  ― liquor from esparto, treatment of, 98

  ― ―, evaporating, 180, 231

  ― ―, removing sodium-sulphur compounds, 191

  ―, prices, 179

  ―, proportion for straw, 99

  ―, recovered, analysing, 205

  ― ―, carbonising, 186

  ― ―, causticising, 187

  ― ―, composition, 186

  ― recovery, 179

  ― solutions, table of strengths, 109

  ―, substances removed from esparto by, 97

  Sodium hypochlorite in bleaching, 113

  ― hyposulphite, analysing, 208

  ― ― for neutralising bleaching powder, 127, 129

  ― sulphide, oxidising, 191

  ― sulphite, analysing, 208

  ― ― to neutralise bleaching powder, 128

  ― -sulphur compounds in soda liquors, 191

  ― thiosulphate, analysing, 208

  ― thiosulphate for neutralising bleaching powder, 127, 129

  Soft water, objections to, 216

  Soluble sulphides for isolating cellulose, 67

  Solutions, alum, table of strengths, 143

  ―, aniline colours, 37

  ―, aniline sulphate, 37

  ―, chlorine water, 37

  ―, iodine, 36

  ―, neutral mounting, 36

  Sorting, 175

  ― rags, 80

  Specific gravity, Twaddle converted into, 109

  Spherical rag boiler, 82

  Stanhope purifier, 212, 214

  Starch and iodide paper, making, 130

  ―, estimating, 203

  ― paste for sizing, 138

  Starches, analysing, 208

  Starching blotting paper, 139

  ― filter paper, 139

  Statistics, 221

  Steam and ligno-celluloses, 21

  Steaming wood, 107

  Stipa tenacissima fibre, 39, 55

  Strainers, 147

  ―, closing plates, 150

  ―, knotter, 151

  Straw, 46, 57

  ―, amount of bleaching powder needed by, 112

  ―, boiled, washing, 100

  ―, boilers for, 99

  ―, boiling, 100

  ―, cellulose yield from, 98

  ―, cleaning, 100

  ―, composition, 59, 99

  ―, cutting, 100

  ―, dimensions of cells, 58

  ―, general chemical characteristics, 58

  ― in paper, detecting, 200, 201

  ―, microscopic features, 57

  ― paper, source of weakness, 103

  ―, pressure in boiling, 100

  ―, proportion of soda for, 99

  ― pulp, ash, 136

  ― ―, chlorinating, 102

  ― ―, dimensions of fibre, 119

  ― pulp, draining, 100

  ― ―, dry, preparing, 119

  ― ―, grinding, 101

  ― ―, yield, 99

  ―, soda treatment, 98

  ―, treating for paper, 63

  ― washer, 101

  Strengths of alum solutions, table, 143

  ― of paper, classification, 197

  ― ―, influence of glazing, 198

  ― ―, measuring, 193

  Sugar-cane fibre, 59

  Sulphide processes, economy of, 68

  ― ―, malodours of, 68

  Sulphite processes, objection to, 75

  Sulphur, action on cellulose, 130

  ― and lime for neutralising bleaching powder, 129

  Sulphuric acid and cellulose, 12

  ― ― and ligno-cellulose, 22

  ― ― in bleaching pulps, 112

  Sulphurous acid for isolating cellulose, 64

  ― ― processes for wood, 70

  ― ― processes, objection to, 75

  Sunda, see Sunn hemp.

  Sunn hemp, 44, 46, 50

  ― ―, characters, 50

  ― ―, composition, 50

  ― ―, general chemical characteristics, 50

  ― ―, micro-chemical reactions, 50

  ― ―, microscopic features, 50

  Synthesis of cellulose, 15


  Table of processes for resolving wood, 78

  ― of strengths of alum solutions, 143

  ― ― ― of caustic soda solutions, 109

  Teazing needles, 38

  Telegram paper, 104

  Test paper, making, 130

  Testing antichlor, 130

  ― iodine solution, 36

  ― paper, 193

  ― ― by rubbing, 197

  Textile trade waste, treating for paper, 62

  Thickness of paper, gauging, 153

  ― ― ―, measuring, 198

  Thompson’s rag-bleaching process, 115

  Thune’s mechanical wood pulp, 107

  Tilghmann’s sulphurous acid process, 70

  Tilia grandifolia fibre, 39, 54

  Time of boiling rags, 84

  Toned paper, 142

  Trade statistics, 221

  Triacetyl cellulose, 8

  Tub sizing, 137

  ― ― on the machine, 160

  Twaddle degrees, converting into specific gravity, 109


  Ultramarine, 141

  Umpherstoil’s beater, 123

  Urtica dioica fibre, 52

  ― heterophylla fibre, 44


  Vacuum strainer, 148

  Victory cutter, 174

  Vinegar plant forming cellulose, 16

  Vomiting boiler, 91


  Washing boiled esparto, 95

  ― ― rags, 85

  ― ― straw, 100

  ― out bleaching liquor from half-stuff, 127

  Waste paper, pulp from, 104

  Water and ligno-cellulose, 21

  ― at high temperature and cellulose, 15

  ―, clarifier, 211

  ―, clarifying, 125

  ―, filter bags, 126

  ― for beaters, 125

  ―, lime salts, 212

  ― marks, 145, 156

  ―, Porter-Clark process, 214

  ― proportion to pulp in beating, 118

  ―, purification, 211

  ―, quantity for boiling rags, 84

  ― resolving wood by, 65

  ―, settling ponds, 125

  ―, soft, objections to, 216

  ―, soluble impurities, 212

  Water supply, 210

  Web glazing, 167

  Webster on analysis of fibres, 42

  Weighing paper ash, 134

  Weight per ream, 176

  Weighting paper, 130

  Wet end of machine, 154

  ― felt, 157

  Wheat straw, 98

  White fir fibre, 61

  ― pine for mechanical wood pulp, 108

  Width of paper, gauging, 152

  Willesden canvas, 219

  ― paper, 219

  ― scrim, 219

  ― welded goods, 220

  Willowing adansonia fibre, 103

  ― jute, 103

  ― Manilla hemp, 103

  ― rags, 81

  Winding, 160

  Wire-cloth, 153

  ― in rag washer, 87

  ―, shifting, 156

  Wood, acid processes, 69

  ―, amount of bleaching powder needed by, 112

  ―, bisulphite processes, 71

  ―, boiling with sulphites, 74

  ―, chemical, in paper, detecting, 200

  ―, cutting up for pulp, 105

  ―, grinding, 105

  ―, mechanical, in paper, detecting, 200, 201

  ―, objection to acid in bleaching, 112

  ― processes, table of, 78

  ― pulps, 60

  ― ―, ash, 136

  ― ― beating, 117

  ― ―, dimensions of fibre, 119

  ― ―, dry, preparing, 119

  ― ― from aspen, 108

  ― ― from white pine, 108

  ― ―, mechanical, 105

  ― ―, ―, quantitative estimation, 202

  ― ―, statistics, 224

  ―, resolving by water, 65

  ―, Schultze’s method of isolating cellulose from, 21

  ―, soaking, 107

  ― splitting machine, 74

  ―, steaming, 107

  ― suitable for Ekman’s process, 73

  ―, sulphide treatment, 67

  ―, sulphurous acid processes, 70

  ―, treating for paper, 64

  Woods, pulp yield of, 77

  Wool fibre, character, 31

  Wove paper, 156

  Wrapping paper, 104


  Yankee machine, 164

  Yaryan evaporator, 232

  Young and Pettigrew’s acid process, 69

  Yucca gloriosa fibre, 44, 46


  Zinc chloride and cellulose, 13


LONDON: PRINTED BY WM. CLOWES AND SONS, LIMITED, STAMFORD STREET AND
CHARING CROSS.




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E. & F. N. SPON, 125, Strand, London.

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TRANSCRIBER’S NOTE:

Original spelling and grammar have been generally retained, with some
exceptions noted below. Original printed page numbers are shown like
this: {52}. Original small caps are now uppercase. Italics look _like
this_. Footnotes have been relabeled 1–18, and moved from within
paragraphs to nearby locations between paragraphs. The transcriber
produced the cover image and hereby assigns it to the public domain.
Original page images are available from archive.org—search for
“gri_33125007981968”.

Subscripts are indicated with underscore followed by curly brackets,
e.g. “H_{2}O”. Some missing full stops have been inserted. Many ditto
marks have been eliminated, replaced by repeated text. Enlarged curly
brackets “}{” employed to combine information in two or more lines or
columns have been eliminated, by restructuring text if necessary. One
such instance is the table on page 39. The table on page 44 and some
other large tables were moved from their original locations inside a
paragraph of text to nearby locations between paragraphs. The page 44
table was also divided into two parts, after column six. Illustrations
have also been moved from within paragraphs of text to nearby locations
between paragraphs.

Page 12. “tranformation” to “transformation”. “C_{12}H_{20}O_{11}” to
“C_{12}H_{22}O_{11}”.

Page 14n. The note had no anchor; a new one has been inserted after “in
sealed glass”.

Page 17. “chemisty” to “chemistry”.

Page 65. “revolution” to “resolution”.

Page 136. “being therefore equivalent to one mgrm” is retained, but
presumably should be read “being therefore equivalent to ten mgrm”.

Page 196n. The note had no anchor in the text. A new one has been
inserted after “papers published by the Institute for 1885.”, as a
plausible guess.

Page 197. “following seven groups” to “following eight groups”.

Page 220. “the following way” to “the following may”.

Page 245. A section of advertisements begins here. This section in
the original printed book depended heavily upon the advantages of
typography, graphics, and page-breaks. In this simple text edition, the
codes [advertisement] and [/advertisement] have been inserted fore and
aft, for each ad.

















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