Practical paper-making; a manual for paper-makers and owners and managers of paper mills, to which are appended useful tables, calculations, data, etc

Preface

THE Author is well aware that the subject of Practical Paper-making is one to which a much larger and fuller work than the present might have been devoted. He trusts, however, that this little volume, slight as is the treatment of most portions of the subject, will in some measure supply a need which he has himself felt for several years, and more especially during the first years of his apprenticeship — namely, the need of a work on Paper-making which, while not neglecting those teachings of theoretical and practical chemistry, the understanding of which is necessary for the successful and economic production of paper, should at the same time give due consideration to the practical working of the Paper Mill.

He is aware, also, that to carry out this plan, even

on the unambitious scale of the present work, there

iii

IV PREFACE.

is required of an author intimate knowledge' of the actual working of the mill, such as can only be obtained by years of practical work in the various departments. His own experience, he is able to say, having been such as should qualify him for the task he has here undertaken, he ventures to hope that many Paper-makers and Millowners will find in these pages knowledge and information of no little value, which has not hitherto been accessible in a similar form. To what extent the work answers his desires, his readers will be best able to judge.

Special attention may be invited to the illustrations of the Microscopical Examination of Paper and Paper-making Materials, which have been reproduced from micro-photographs.

In the Appendix will be found some useful Tables, Data, etc., compiled from various sources.

Blackburn, Penicuik.

March 1894.

NOTE TO SECOND EDITION.

For the present edition, the work has been carefully revised and some additions made (enlarging the volume by about i8 or 20 pages), so as to bring the information fully up to date.

November igo6.

Chapter I. Chemical And Physical Characteristics Of Various Fibres

PAGE

Cellulose : its Composition and Chemical Properties — Effect of Bleach — Of Atmosphere — Oxycellulose — Action of Solvents — Detection — Relation to Plants — Incrusting Substances — Cotton — Compound Celluloses — Pectocellulose — Lignocellulose — Adipocellulose — Isolation — Rags and Thread — " Bast " Fibres, Fibro- Vascular Bundles — Physical Features of Cotton, Linen, Hemp, Jute, Manilla, Esparto, Straw, Wood , , i

CHAPTER n.

CUTTING AND BOILING OF RAGS.— JUTE BOILING AND BLEACHING.

Grading — Cutting Machine — Rationale of Boiling — Caustic Soda

— Lime — Jute Boiling and Bleaching ..... 8

Chapter III

WET PICKING— WASHING, BREAKING, AND BLEACH- ING.— ELECTROLYTIC BLEACHING.— ANTICHLOR.

Wet Picking — Washing Drum — Management of Breaker, Plates, and Rolls — Weak Liquor — Bleaching Powder — Rationale of Bleaching — Effect of Steam, Sulphuric Acid, Alum, Acetic

V

CONTENTS.

PAGE

Acid — Jute, Reaction with Chlorine — Amount of Bleach for Various Qualities — Preparation of Bleaching Liquor — Apparatus — Lime Mud — Electrolytic Bleaching — Ozone Bleach — Hermete's Method — Bleaching and Draining Chests — Antichlor — Hyposulphite of Soda — Sulphite of Soda — Dangers from Excess— Test for Bleach . ■ . . . 1 7

Chapter IV. Cellulose From Wood.— Mechanical Wood Pulp

Composition of Wood — Classification of Processes — Mechanical Treatment — Alkali- Processes — Watt and Burgess's — Effect of Caustic Solutions — Sulphite Processes — Ekman's — Partington's— Mitscherlich's — Sulphate Processes, Dahl's — Method Employed in Scotch Mill — Mechanical Wood-Preparation—Properties 31

Chapter V. Esparto And Straw

Percentage Composition — Nature and Combination of Cellulose — Dusting — Sorting — Eff'ect of Caustic Solution, of Pressure, Boiling — Amount of Caustic Required — Concentration ot Boiling Solution — Washing Under Pressure — Steepers — Potchers — Drum Washer — Loss in Washing — Bleaching Effect of Steam — Duration — Straw, Pressure and Strength of Boiling Solutions— Nature of Finished Pulp — Loss in Washing — Yield of Cellulose — Effect on Paper . . .44

CHAPTER VL

BEATING.

Stuff for Bank, Loan, Chromo, and Litho Papers — Condition and Management of Plates and Rolls — Tempering the Stuff for Various Qualities — Marshall's Perfecting Engine — Intermediate Engines — Spanish Grass — Wood — Soft-sized Papers — Blottings — Construction of Beater. Forbes' Beater — Rusting 52

CONTENTS. vu

Chapter VII. Loading.— Starch.— Colouring Ma Tter

PAGE

Legitimate and Necessary Use — Selection of a Loading — China Clay, Preparation for the Engine — Effect on Paper — Loading Chromo and Plate Papers — " Pearl Hardening," Application — Properties — Barium Sulphate — Properties — Retention — Effect on Paper — Barium Chloride — ^Agalite, Nature and Properties — Retention — Starch, Properties — Application — Colour, Ultramarine — Carnation — Standard Samples — ^Alum Resisting Power — Fading in Chests and Engines — Amounts Necessary to Counteract Fading — Smalts — Iron — Aniline Colours, Greens 67

Chapter VIII. Resin Size And Sizing

Theories of Sizing — Proportions of Resin and Soda — Recipe for Neutral Sodium Resinate — Preparation — Test for Complete Saponification — Dilution for the Engine — White Size — Preparation — Effect of Beating on Sizing — Alum — Sulphates of Alumina — Solubility — Percentage of Alumina — Effect of Hard Water on Size — Neutralising Hardness in Water — Amount of Alum Consumed by Hard Water — Effect of Machine Drying Cylinders on Sizing — Caseine Sizing . . 80

Chapter IX. The Fourdrinier Machine And Its Management

Unequal Weight— Chests— Agitators— Knots— Stuff Pump— Sandtrap — Strainers— Working of Revolving Strainers- Strainer Plates — Knots — Breast-box — Deckles — Making Good Edges — Knees — Leathers — Apron — Slices — Wove — Laid— Speed— Dandy "Lifting"— Free and Long Stuff—

VUl CONTENTS.

PAGE

Soft and Fine Stuff— Sticking— Length of Wire— Pitch of Frame — Shake — Breast-roll — Pump Boxes — Slack Edges — Froth — " Bells " — Froth-killers — Cracks and Breaks — Named Dandies — Unequal Shrinkage — Brown's Patent Laid Dandy — " Blowing " — Wet and Dry Felts — " Cockling " — Altering Draws — Unsteady Wires — Making Webs — Breaking at Calenders — Changing Strainers — iPutting on and Starting Wire — A Raised Seam — Putting on Coucher Jacket — Starting Calenders • 93

Chapter X. Animal Sizing.— Drying

Extraction of Gelatine — Alum — Soap — Chests — Sizing Tub — Effect of Beating — " Peeling " — Envelope Papers — Use of Steam — Drying — Steam Heat — Fans — "Cockling" — "Spangling " — Speed of Drier — Loft Drying 137

CHAPTER XL

GLAZING AND BURNISHING.

Smoothing Rolls — Long versus Fine Stuff — Damper — Alkaline Soap — Super-Calender — Effect of Heat — Pressure — Wood and Straw Papers — Coloured Papers — Burnishing — Plate Glazing 146

CHAPTER Xn.

CUTTING.—FINISHING.

Revolving Angle and Square Cutter — Loading — Starting — Overloading — Circulars — Cross-cutting Knives — Feeding- Rolls — Tube-Rolls — Burnished Papers — Creasing — Tissue Papers — Squaring the Sheets — Double Draw — English Cutter — Starting New Knife — Circulars — Feeding-Rolls — " Dancer" — Lined Papers 152

CONTENTS. IX

CHAPTER XIII.

MICROSCOPICAL EXAMINATION OF PAPER.

PAGE

Use of Iodine — Apparatus — Standard Specimens — Objectives — Physical Characteristics — Cotton — Linen — Hemp — Manilla — Jute — Wood — Esparto — Straw — Mechanical Wood — Quantitative Analysis — Mounting Standard Specimens . . . 163

CHAPTER XIV.

TESTS FOR INGREDIENTS OF PAPER.

Animal Size — Alum — Starph — Chlorides — Engine Size — Mineral

Substances i73

CHAPTER XV.

RECOVERY OF SODA.

Incineration — Porion Roaster — Evaporator— Pan — Burning Off — Lixiviation — Tanks — Method of Working — Causticising — Chemical Action — Proportions of Soda and Lime — Plant — Method of Working — Test — Air. Blast— Sodium Sulphide — ' Aluminate and Silicate — Effect of Sodium Bi-carbonate — Ferric Oxide Causticising Process — "Multiple Effects" Rationale — Yaryan System — Chapman and Fawcett's Evaporator — Gaunt Evaporator — Scott Evaporator — Warren Rotary Furnace , 178

CHAPTER XVI.

TESTING OF CHEMICALS.— TESTING WATER FOR IMPURITIES.

Caustic and Recovered Soda — Normal Sulphuric Acid — Actual Test — Examples — ^Grades of Commercial Caustic Soda — Electrolytic Manufacture — Alum — Antichlor — Preparation of Iodine Solution — Actual Test — BleachingPowder — Arsenious Acid Solution — Actual Test^Weak Liquors — Lime Mud — Tables of Percentage of Caustic Soda and Alum — Testing Water I9S

X LIST OF ILLUSTRATIONS

Appendix

PAGE

Equivalent Weights and Sizes of Writing Papers . . . 209

Equivalent Weights and Sizes of Printing Papers . . .210

Sizes of Book and Drawing Papers 2 10

Sizes of Cartridge Papers . 211

Sizes of Lined Papers 21 1

Various Calculations relating to Weight of Reams and Webs . 211 Data for Ascertaining the Number of Gallons of Caustic Liquor required to give the Number of Pounds of NajO necessary

for a Boiling 212

Table showing the Strength of Bleaching Powder Solutions . 213 Weights and Measures of the Metric System . . . .214

French and English Thermometer Scales 215

Useful Data 215

LIST OF ILLUSTRATIONS.

PAPER-MAKING MATERIALS UNDER THE MICROSCOPE.

Plate L Cotton, Manilla, and Hemp . . . Frontispiece.

„ II. Linen and Flax Facing page 6

„ III. Chemical Wood and Mechanical Wood . „ 31

„ IV. Esparto and Straw i, 44

„ V. Chemical Wood and Esparto. — Cotton,

Linen, Wood, and Esparto ... „ 163

„ VI. Linen, Cotton, and Esparto. — Manilla

AND Cotton ,, 166

„ VII. Cotton and Pearl Hardening. — China

Clay ,171

„ VIII. Pearl Hardening. — Terra Alba . . „ 172

Note. — Plates I. to V. represent the various fibres in the state of half-stuff, while the illustrations on Plates VI. to VIII. are from the finished papers.

Practical Paper-making.

Chapter I, Errata

Page 77, in line 12. for "like precipitate," read "lake precipitate." >' >' )> » 26 „ "Amamine" .. " Am-amino "

'Amamine" „ "Auramine."

available paper-making material — varies with the plants from which it is obtained, and the treatment to which it is subjected in the process of freeing it from its combination with the non-cellulose or non-available material with which it is so intimately bound up.

The chemical formula for cellulose is CeHmOj, which means that 6 equivalents of carbon, lO of hydrogen,

X LIST OF ILLUSTRATIONS

APPENDIX.

PAGE

Equivalent Weights and Sizes of Writing Papers . , . 209

Equivalent Weights and Sizes of Printing Papers . . .210 Sizes of Book and Drawing Papers . . . . . ,210 Sizes of Cartridge Papers . . . . . . . 2H

Sizes of Lined Papers 211

Various Calculations relating to Weight of Reams and Webs . 211 Data for Ascertaining the Number of Gallons of Caustic Liquor required to give the Number of Pounds of NajO necessary

for a Boiling 212

Table showing the Strength of Bleaching Powder Solutions . 213 Weights and Measures of the Metric System . . .214

French and English Thermometer Scales 215

Useful Data ■ • • 215

.,' - M,mvim..„ Linen, Wood, and Esparto^^ i,,«,.,,..,-.- „ 163 „ VL Linen, Cotton, and Esparto. — Manilla

AND Cotton „ jgs

„ VIL Cotton and Pearl Hardening. — China

Clay

„ Vin. Pearl Hardening. — Terra Alba

Note. — Plates L to V. represent the various fibres in the state of half-stuff, while the illustrations on Plates VI. to VIIL are from the finished papers.

Practical Paper-making.

CHAPTER I.

CHEMICAL AND PHYSICAL CHARACTERISTICS OF VARIOUS FIBRES.

As the chemical and physical characteristics of the materials from which the paper-maker draws his supply determine to a marked degree the quality of the finished product, a thorough grasp of these characteristics is indispensable to all who aim at the production of the best possible results with the minimum of cost.

, The percentage of cellulose — or, to use a term more readily understood by paper-makers, the amount of available paper-making material — varies with the plants from which it is obtained, and the treatment to which it is subjected in the process of freeing it from its combination with the non-cellulose or non-available material with which it is so intimately bound up.

The chemical formula for cellulose is CgHioOs, which means that 6 equivalents of carbon, lO of hydrogen, and 5 of oxygen are united together to form the substance known by that name. These proportions are constant, though the physical characteristics may differ very widely, and it is of the first importance that great care be taken, in the different processes through which the raw material must pass, that none of the chemicals employed have the effect of changing its nature by adding to or taking from its constituents, thus giving rise to serious complications.

Cellulose which has been in contact with bleaching solution for a lengthened period, or even exposed to the action of air and light for any length of time, will be found to have lost much of its original strength and firmness, and in addition to have acquired properties that were wanting in its pure state. This change is due to the action of the atmospheric oxygen in entering into combination with the cellulose molecule to form what is technically known as the oxy-cellulose obtained by the action of a weak oxidising agent on cellulose.

The oxy-cellulose has the property of extracting basic colouring matters froin their solutions and being permanently dyed by them, and further possesses an extraordinary affinity for vanadium compounds, uniting with them from solutions containing infinitesimal proportions.

Pure cellulose is insoluble in all simple solvents. A solution of cupric hydrate in ammonia alone acts on it, first causing it to swell up and finally dissolving it. The reaction with a solution of iodine in potassium

ISOLATION OF CELLULOSE. 3

iodide is mostly used for its detection ; but in order to render it effective it is necessary to employ a dehydrating agent, such as sulphuric acid, when the characteristic deep blue or violet colour will be produced.

Before the cellulose can be made available for the manufacture of paper, it must first be freed from its combination with the non-cellulose constituents with which it is united to form the plant structure.

Plants may be designated as an aggregation of fibres and cells bound together by gummy, resinous, and waxy substances, which have a function similar to that performed by lime in cementing and rendering durable the stones or bricks of which a house is built ; and as the stones, in order to be used in the building of another house, would first have to be freed from the lime with which they were bound together in the previous structure, similarly the fibres and cells must be freed from all substances which, though indispensable to their existence in the plant life, would tend to impair their value as paper-making material.

Cotton differs from the other plants in this, that by the natural process of ripening the fibres are so freed as to yield a pure cellulose, which is available without the preliminary treatment which the compound celluloses must undergo. These compound celluloses are classed under the following heads : —

(i) Pecto-celluloses, so named because they yield pectic acid on the breaking up of their combination.

The flax plant may be taken as typical of the celluloses comprising this group.

(2) Ligno-celluloses, which owe the designation to their yielding non-cellulose or lignine as the result of their disintegration. Jute is the typical cellulose of this group, in which are included all the different forms of woody tissue.

(3) The third group exist in such a small proportion in paper-making materials, that, as compared with the preceding compound celluloses, they are of little importance. They are known by the name adipo-celluloses, and are so termed because on reduction they yield acids analogous to those obtained by the reduction of fats and cork tissue. This group embraces the cuticular tissue of such plants as straw, esparto, and cotton.

The problem, then, which presents itself to the practical paper-maker for solution is not simply to become acquainted with the physical features of the fibres he desires to use for the production of his paper, but to arrive at the most economical method by which he can best secure the liberation of such fibres in the form most suited to his particular purpose, while preserving as far as possible the original strength.

Such materials as rags and thread, which have already been subjected to retting, boiling, and bleaching by the textile manufacturer, require no very drastic treatment to render them suitable to the needs of the paper- maker, as they are already in a more or less pure state before coming to his hands.

CHARACTERISTICS OF PLANT STRUCTURES. 5

It is for this reason, coupled with the physical characteristics of their fibres, that they are so much valued by him. It will be readily understood that it is with such materials as esparto, straw, and wood that the chief difficulties in the way of extracting the available cellulose exist.

In addition to the fact that esparto and straw have been subjected to no previous disintegration, there is another reason which renders them less valuable as a paper-making material. In the process of the building up of their plant structure the fibro-vascular bundles, from which the available fibres are obtained, are scattered irregularly throughout the main mass, and are more closely connected with the non-cellulose constituents than are the " bast " fibres ot flax, hemp, and jute, the fibre bundles or " filaments " of which form a separate and cohesive tissue, and are thus more easily freed from the surrounding non-available material.

Before taking up the different processes through which the materials are passed, in order to render them fit for the production of paper, a glance at the physical features of the various fibres will be of material assistance in enabling the paper-maker to obtain a knowledge of the conditions best suited to their successful treatment. ,

The ultimate fibres of the cotton plant consist, as before stated, of pure cellulose, and on examination under the microscope will appear as long, flattened tubes always more or less twisted upon themselves. The side walls are rough and granulated, which is most easily seen when dry. They are strong and flexible, and suited for the production of the finest qualities of paper, though from the spongy nature of the fibre the finished sheet is less hard than that made from linen. When the tubular form of the fibres is' borne in mind, it will be at once understood why the colouring matter is so difficult to remove from coloured cotton rags. (See Plate I., Frontispiece, fig. i.)

Linen, the fibre of the flax plant, is, like cotton, tubular, but the side walls are much thicker, the central canal is smaller, and, consequently, the fibre is harder and less spongy. (See Plate II., figs. 3 and 4.)

Papers made from linen rags are hard, strong, and firm to handle. The fibres obtained from ropes and bags are mostly hemp, and are somewhat like linen, but much more coarse and harsh ; as they are seldom completely freed from the incrusting matters they require to be boiled with a larger percentage of caustic.

Jute fibres are strong but very difficult to bleach white, and, indeed, if subjected to such treatment as will dissolve all the extraneous matter, and reduce to ultimate fibres, their original strength is much impaired.

Manilla hemp yields strong fibres, easily detached, but, like jute, somewhat difficult to bleach white. (See Plate I., Frontispiece, fig. 2.)

The ultimate fibres of esparto are short, smooth, and tubular, but in some placea the central canal is

Plate II.

Fig. 3. — Linen x 130.

Fig. 4. — Flax x 130.

[ To fact: f>agc 6.

CHARACTERISTICS OF FIBRES. 7

completely hidden by the thickening of the side walls. (See Plate IV., fig. 7.)

Straw fibres are very similar in appearance to esparto, but they are shorter and more highly polished, thus tending to make their felting power much less, and rendering paper made from them very brittle. (See Plate IV., fig. 8.)

Wood fibres vary with the different species from which they are obtained and the methods used to isolate them. Pine wood is capable of yielding long, soft, transparent, flexible fibres, well suited to the production of strong well-felted papers. Ash and similar trees yield short, hard fibres, possessed of no great felting properties. (See Plate III., fig. 5.)

Chapter II. Cutting And Boiling Of Rags— Jute Boiling And Bleaching

Grading of Eags.— As the quality of the finished paper is dependent on the successful carrying out of the different processes through which the stock must pass, it is indispensable to the production of a uniform and satisfactory result that the greatest care be taken in each department to ensure the intelligent application of the principles on which each process depends.

Nowhere would a neglect of the requirement of each particular class be more disastrous than in the rag room, which may not inaptly be termed the birthplace of the varied qualities of beautiful papers which are met with in the market.

Carelessness in the regulations of the standard of each particular grade of rags cannot fail to lead to mischievous results, as in such circumstances the stock may at one time be above the usual quality intended for the paper made, and, at another, much inferior; and yet with such manifest defects the paper produced

RAG-GRADING AND CUTTING. 9

is expected "to be equal to last making in every respect.''

The only remedy for such a state of matters, which is not an uncommon one, is that the official in charge of the department should insist that the cutters and sorters give the necessary attention to the strength and cleanliness recognised as the standard of each grade. If this be done consistently and intelligently, it will soon make itself known in the smoothness with which the subsequent processes will go forward, and in uniformity in the purity, strength, and shade of the paper made which will far more than repay the extra time and care involved.

Rag-cutting. — Though the rag-cutting machine has been much improved of late years, it cannot be said to have superseded cutting by hand, especially for the better qualities of paper.

As will be readily understood, the rags in being cut by the machine come far less under the supervision of the women whose duty it is to grade the different quaUties used in the mill ; and this, together with the fact that in the tearing and cutting on the machine much of the best of the fibres is damaged, presents a serious drawback to its adoption.

In cutting strong, coarse material, such as canvas and bagging, these defects do not exist to the same extent, and, though they did, would be of less importance ; consequently it is more suited to that class of stock.

lo PRACTICAL PAPER-MAKING.

When the rags are run straight from the cutter into the dusting-machine, as is often the case, the carrying felt should be long enough to admit of standing room for sorters on either side, so that any extraneous material, such as wool, silk, etc., which may have escaped detection when feeding in the rags, may be removed, and thus prevented from finding its way into the boilers and, it may be, into the finished paper.

Eag Boiling. — The object in subjecting rags, or other paper-making material, to the process of boiling is that the reducing action of the water, aided by the temperature and pressure employed, may break up the combination of the cellulose with non-available substances.

Caustic soda is the chemical usually employed to render this action more thorough, and to ensure the complete removal of all the incrusting substances which by their presence tend to render the subsequent bleaching process much less effective, and to otherwise impair the value of the material.

Rags, which have already been subjected to such a process before coming into the hands of the papermaker, require to be treated with a much smaller amount of caustic compared with such raw materials as esparto and straw. In the case of rags, the function of the soda is to remove the size, which is often applied to the fabric, together with any dirt which may have become attached to the interstices of the material

RAG-BOILING. II

in its journey from the textile factory to the rag store, and also to destroy, as far as possible, any colouring matter and render it more susceptible to the action of the bleaching solution. Caustic soda has, in addition, the effect of softening the fibres, thus rendering them more flexible.

As the feel and look of a paper depend quite as much on the elasticity and complete freedom from all incrusting matters of the original fibres, as upon the treatment they receivfe in the subsequent operations of breaking and beating, it becomes at once apparent that what at first sight seems a very simple matter — namely, the determination of the amount of caustic soda most suitable for each material — is in reality a somewhat difficult problem, and one which requires much greater consideration than is usually given to it.

The physical nature and condition of some rags may be such as to render them quite inert, and of little felting power, should they be boiled with the amount of caustic necessary to the production of a good colour when bleached. The wisdom of continuing to use such materials, even though obtained at a comparatively low price, is, to say the least, very questionable.

Some rags, again, which from the standard of cleanliness may not require a large proportion of soda, will often be found to be greatly improved by using a little extra per hundredweight, especially when the fibres are harsh. The softening which is thus obtained will make itself apparent in producing a closer and more evenly felted sheet.

With regard to the economy of using low quality rags for papers in which a good colour is indispensable, it has been shown, as the result of very exhaustive experiments carried out by Messrs. Wiirster and Zugler, that bleached half-stuff from cheap rags is in the end much more costly than that obtained from the better qualities, notwithstanding the great difference in the price. As much as i8 per cent, of loss was found in the boiling and washing of such materials.

Some paper-makers prefer to boil their stock with lime, in place of caustic soda, and this is especially the case in America. For the better qualities of paper, however, its use is attended with very serious drawbacks. A larger proportion of lime than is actually necessary to reduce the stock must always be used, and as this excess must be properly washed out of the rags before bleaching, both time and water are thus consumed.

Gritty matters, such as sand and coal-dust, are invariably present, even in the best qualities of lime, and these are apt to become fixed in the fibres in such a way as to render their complete removal a matter of some difficulty.

Lime, as is well known, is but sparingly soluble in cold water, and still less so when the water is heated. One part of lime requires seven hundred parts of cold

RAG-BOILING. 13

water to dissolve it, and fifteen hundred parts when the temperature is raised to boiling point.

During the boiling process, however, a much larger quantity is dissolved than would appear possible at first sight. As the dissolved lime enters into combination with the non-cellulose portion of the stock, the water becomes capable of dissolving a further quantity, and so the dissolving action is repeated until all the fatty and resinous matters have entered into combination with the lime.

In preparing coarse, dirty stock, such as jute and the lower grades of flax, in the subsequent application of which a high degree of cleanliness is not of the first importance, lime may be used with advantage, both on account of its cheapness and its reducing qualities.

In selecting a lime to boil with, it should be borne in mind that grades showing the same percentage of actual lime do not always produce a uniform result in treating the stock. Lime which is light to handle, of a uniformly white colour, and which slacks easily, seems to possess greater reducing power than a dullcoloured, heavy lime, as less of it is required for boiling, and the pulp produced has a softer feel.

Caustic lime when exposed to the atmosphere quickly absorbs carbonic acid, and the carbonate of lime thus formed, in addition to possessing no boiling power, is very liable to cause serious complications in the subsequent operations by adhering to the fibres even after much washing, and is frequently the source of the spots which at times appear so unaccountably on the machine wire.

Stationary boilers are very suitable for the finer grades of cotton and linen rags, but for coarse, dirty stock the rotary action of the revolving boiler is of advantage, as the shaking thus given to the stock has the effect of loosening the dirt. For this reason it is usually employed for such materials. It is an additional advantage if the boiler can be fitted with a system of pulleys, which will enable the revolving action to be quickened during the washing which follows the running off" of the spent liquor.

Jute Boiling and Bleaching. — Jute is a material which, on account of its strength and cheapness, would receive much more extensive application in the manufacture of paper were it not for the almost insurmountable difficulties which lie in the way of producing from it, at a reasonable cost, a pulp of sufficient whiteness to be used in the making of fine papers.

The chief difficulty in bleaching lies in the fact that, unless the boiling process has been conducted so as to ensure that all the incrusting matters have been dissolved, the amount of chlorine consumed before these incrusting substances can be effectively bleached more than counterbalances the low price of the raw material. Apart from the cost of bleaching, the use of such a large amount of chlorine tends to impair the strength of the fibres.