THE MANUFACTURE
OF PAPER

BY

R. W. SINDALL, F.C.S.

CONSULTING CHEMIST TO THE WOOD PULP AND PAPER TRADES; LECTURER
ON PAPER-MAKING FOR THE HERTFORDSHIRE COUNTY COUNCIL, THE
BUCKS COUNTY COUNCIL, THE PRINTING AND STATIONERY
TRADES AT EXETER HALL, 1903-4, THE INSTITUTE
OF PRINTERS; TECHNICAL ADVISER TO THE
GOVERNMENT OF INDIA, 1905

AUTHOR OF “PAPER TECHNOLOGY,” “THE SAMPLING OF WOOD PULP”
JOINT AUTHOR OF “THE C.B.S. UNITS, OR STANDARDS OF PAPER
TESTING,” “THE APPLICATIONS OF WOOD PULP,” ETC.

WITH ILLUSTRATIONS, AND A BIBLIOGRAPHY OF WORKS
RELATING TO CELLULOSE AND PAPER-MAKING

NEW YORK
D. VAN NOSTRAND COMPANY
23 MURRAY AND 27 WARREN STREETS

1908

[PREFACE]

Paper-making, in common with many other industries, is one in which both engineering and chemistry play important parts. Unfortunately the functions of the engineer and chemist are generally regarded as independent of one another, so that the chemist is only called in by the engineer when efforts along the lines of mechanical improvement have failed, and vice versa. It is impossible, however, to draw a hard and fast line, and the best results in the art of paper-making are only possible when the manufacturer appreciates the fact that the skill of both is essential to progress and commercial success.

In the present elementary text-book it is only proposed to give an outline of the various stages of manufacture and to indicate some of the improvements made during recent years.

The author begs to acknowledge his indebtedness to manufacturers and others who have given permission for the use of illustrations.

[CONTENTS]

[LIST OF ILLUSTRATIONS]

THE MANUFACTURE
OF PAPER

[CHAPTER I]
HISTORICAL NOTICE

History.—The art of paper-making is undoubtedly one of the most important industries of the present day. The study of its development from the early bygone ages when men were compelled to find some means for recording important events and transactions is both interesting and instructive, so that a short summary of the known facts relating to the history of paper may well serve as an introduction to an account of the manufacture and use of this indispensable article.

Tradition.—The early races of mankind contented themselves with keeping alive the memory of great achievements by means of tradition. Valiant deeds were further commemorated by the planting of trees, the setting up of heaps of stones, and the erection of clumsy monuments.

Stone Obelisks.—The possibility of obtaining greater accuracy by carving the rude hieroglyphics of men and animals, birds and plants, soon suggested itself as an obvious improvement; and as early as B.C. 4000 the first records which conveyed any meaning to later ages were faithfully inscribed, and for the most part consigned to the care of the priests.

Clay Tablets.—The ordinary transactions of daily life, the writings of literary and scientific men, and all that was worthy of note in the history of such nations as Chaldea and Assyria have come down to us also, inscribed on clay tablets, which were rendered durable by careful baking. On a tablet of clay, one of the earliest specimens of writing in existence, now preserved in the British Museum, is recorded a proposal of marriage, written about B.C. 1530, from one of the Pharaohs, asking for the hand of the daughter of a Babylonian king.

Waxed Boards.—Bone, ivory, plates of metal, lead, gold, and brass, were freely used, and at an early period wooden boards covered with wax were devised by the Romans. In fact, any material having a soft impressionable surface was speedily adopted as a medium for the permanent expression of men's fancy, so that it is not strange to find instances of documents written on such curious substances as animal skins, hides, dried intestines, and leather. The works of Homer, preserved in one of the Egyptian libraries in the days of Ptolemæus Philadelphus, were said to have been written in letters of gold on the skins of serpents.

Leaves, Bark.—The first actual advance in the direction of paper, as commonly understood, was made when the leaves and bark of trees were utilised. The latter especially came speedily into favour, and the extensive use of the inner bark (liber) made rapid headway. Manuscripts and documents written on this liber are to be found in many museums.

Papyrus.—The discovery of the wonderful properties of the Egyptian papyrus was a great step in developing the art of paper-making. The date of this discovery is very uncertain, but one of the earliest references is to be found in the works of Pliny, where mention is made of the writings of Numa, who lived about B.C. 670. This celebrated plant had long been noted for its value in the manufacture of mats, cordage, and wearing apparel, but its fame rests upon its utility in quite a different direction, namely, for conveying to posterity the written records of those early days which have proved a source of unending interest to antiquaries.

Fig. 1.—Sheet of Papyrus, showing the layers crossing one another (Evans).

The Egyptian papyrus was made from the fine layers of fibrous matter surrounding the parent stem. These layers were removed by means of a sharp tool, spread out on a board, moistened with some gummy water, and then covered with similar layers placed over them crosswise. The sheets so produced were pressed, dried, and polished with a piece of ivory or a smooth stone. Long rolls of papyrus were formed by pasting several sheets together to give what was termed a volumen.

Roman Papyri.—The Romans improved the process of manufacture, and were able to produce a variety of papers, to which they gave different names, such as Charta hieratica (holy paper, used by priests), Charta Fanniana (a superior paper made by Fannius), Charta emporetica (shop or wrapping paper), Charta Saitica (after the city of Sais), etc. The papyrus must have been used in great quantities for this purpose, since recent explorations in Eastern countries have brought to light enormous finds of papyri in a wonderful state of preservation. In 1753, when the ruins of Herculaneum were unearthed, no less than 1,800 rolls were discovered. During the last ten years huge quantities have been brought to England.

Parchment.—Parchment succeeded papyrus as an excellent writing material, being devised as a substitute for the latter by the inhabitants of Pergamus on account of the prohibited exportation of Egyptian papyrus. For many centuries parchment held a foremost place amongst the available materials serving the purpose of paper, and even to-day it is used for important legal documents. This parchment was made from the skins of sheep and goats, which were first steeped in lime pits, and then scraped. By the plentiful use of chalk and pumice stone the colour and surface of the parchment were greatly enhanced. Vellum, prepared in a similar manner from the skins of calves, was also extensively employed as a writing material, and was probably the first material used for binding books. Until comparatively recent times the term “parchment” comprehended vellum, but the latter substance is much superior to that manufactured from sheep and goat skins.

Paper.—The Chinese are now generally credited with the art of making paper of the kind most familiar to us, that is from fibrous material first reduced to the condition of pulp. Materials such as strips of bark, leaves, and papyrus cannot of course be included in a definition like this, which one writer has condensed into the phrase “Paper is an aqueous deposit of vegetable fibre.”

A.D. 105.—The earliest reference to the manufacture of paper is to be found in the Chinese Encyclopædia, wherein it is stated that Ts'ai-Lun, a native of Kuei-yang, entered the service of the Emperor Ho-Ti in A.D. 75, and devoting his leisure hours to study, suggested the use of silk and ink as a substitute for the bamboo tablet and stylus. Subsequently he succeeded in making paper from bark, tow, old linen, and fish nets (A.D. 105). He was created marquis in A.D. 114 for his long years of service and his ability.

A.D. 704.—It has been commonly asserted that raw cotton, or cotton wool, was first used by the Arabs at this date for the manufacture of paper, they having learnt the art from certain Chinese prisoners captured at the occupation of Samarkand by the Arabs. The complete conquest of Samarkand does not, however, seem to have taken place until A.D. 751, and there is little doubt that this date should be accepted for the introduction of the art of paper-making among the Arabs.

Recent Researches.—Professors Wiesner and Karabacek have ascertained one or two most important and interesting facts concerning the actual manufacture of pure rag paper. In 1877 a great quantity of ancient manuscripts was found at El-Faijum, in Egypt, comprising about 100,000 documents in ten languages, extending from B.C. 1400 to A.D. 1300, many of which were written on paper. The documents were closely examined in 1894 by these experts, at the request of the owner, the Archduke Rainer of Austria.

Researches of a later date resulted in the discovery of some further interesting documents which appear to establish with some degree of certainty the approximate date at which pure rag paper, that is, paper made entirely from rag, was manufactured.

Chinese documents dated A.D. 768-786, which have been reported upon by Dr. Hoernle, and others dated A.D. 781-782-787, reported upon by Dr. Stein as recently as 1901, appear to show what materials were used by the Chinese paper-makers in Western Turkestan. The manuscripts mentioned were dug out from the sand-buried site of Dandan Uilig, in Eastern Turkestan.

Professor Wiesner found that all the papers of the Rainer collection were made of linen rag, with an occasional trace of cotton, probably added accidentally. The earliest dated paper was a letter A.D. 874, but two documents, which from other reasons could be identified as belonging to A.D. 792, proved that at the end of the eighth century the Arabs understood the art of making linen paper on network moulds, and further that they added starch for the purpose of sizing and loading the paper.

Professor Karabacek advances some ingenious explanations as to the origin of the idea that raw cotton was first used for paper-making, and he suggests that the legend owes its origin to a misunderstanding of terms. In mediæval times paper was known as Charta bombycina, and sometimes as Charta Damascena, the latter from its place of origin.

Paper was also made in Bambyce, and a natural confusion arose between the terms, since the word bombyx was used as a name for cotton, and the paper commonly in use suggested that material to the mind of the observer, and the name became corrupted to bombycina.

The suggestions of Professor Karabacek, together with the microscopical investigations of Dr. Wiesner, appear to show that paper made entirely from raw cotton fibre was not known.

Invention of Rag Paper.—Dr. Hoernle, in discussing this question, points out that, taking A.D. 751 as the date when the Arabs learnt the art of paper-making, and A.D. 792 as the date when paper made entirely of linen rag was produced, the date of the invention of rag paper must lie between these two dates. The documents discovered in Eastern Turkestan and bearing the dates mentioned, which papers fill up the gap between the years A.D. 751 and A.D. 792, were found to contain certain raw fibres, such as China grass, mulberry, laurel, as the main constituents, and macerated flax and hemp rags as the minor constituents.

The addition and substitution of rag evidently increased in course of time, and since the improvement thus effected soon became an obvious and established fact, the raw fibres were omitted. Hence the credit of the manufacture of pure rag paper would be given to the people of Samarkand, the date being between the years A.D. 760 and A.D. 792; and further the constitution of such paper has been shown by Dr. Wiesner to be linen, and not cotton, as commonly stated.

These researches are of such interest that we quote Professor Hoernle's translation of the summary of the principal results of Dr. Wiesner's examination of the Eastern Turkestani papers so recently discovered:—

“Taking into account the dates assigned to the papers on palæographic grounds, the following conclusions may be drawn from the examination of their material:—

“(1) The oldest of the Eastern Turkestani papers, dating from the fourth and fifth centuries A.D., are made of a mixture of raw fibres of the bast of various dicotyledonous plants. From these fibres the half-stuff for the paper was made by means of a rude mechanical process.

“(2) Similar papers, made of a mixture of raw fibres, are also found belonging to the fifth, sixth, and seventh centuries. But in this period there also occur papers which are made of a mixture of rudely pounded rags and of raw fibres extracted by maceration.

“(3) In the same period papers make their appearance in which special methods are used to render them capable of being written on, viz., coating with gypsum and sizing with starch or with a gelatine extracted from lichen.

“(4) In the seventh and eighth centuries both kinds of papers are of equal frequency, those made of the raw fibre of various dicotyledonous plants and those made of a mixture of rags and raw fibres. In this period the method of extracting the raw fibre is found to improve from a rude stamping to maceration; but that of preparing the rags remains a rude stamping, and in the half-stuff thus produced from rags it is easy to distinguish the raw fibre from the crushed and broken fibre of the rags.

“(5) The old Eastern Turkestani (Chinese) paper can be distinguished from the old Arab paper, not only by the raw fibres which accompany the rag fibres, but also by the far-reaching destruction of the latter.

“(6) The previous researches of Professor Karabacek and the author had shown that the invention of rag paper was not made in Europe by Germans or Italians about the turn of the fourteenth century, but that the Arabs knew its preparation as early as the end of the eighth century.

“The present researches now further show that the beginnings of the preparation of rag paper can be traced to the Chinese in the fifth or fourth centuries, or even earlier.

“The Chinese method of preparing rag paper never progressed beyond its initial low stage. It was the Arabs who, having been initiated into the art by the Chinese, improved the method of preparing it, and carried it to that stage of perfection in which it was received from them by the civilised peoples of Europe in the mediæval ages.

“(7) The author has shown that the process of sizing the paper with starch in order to improve it was already known to the Arabs in the eighth century. In the fourteenth century the knowledge of it was lost, animal glue being substituted in the place of starch, till finally in the nineteenth century, along with the introduction of paper machines, the old process was resuscitated. But the invention of it was due to the Chinese. The oldest Eastern Turkestani paper which is sized with starch belongs to the eighth century.

“(8) The Chinese were not only the inventors of felted paper and the imitators of rag paper—though in the preparation of the latter they made use of rags only as a surrogate by the side of raw fibres—but they must also be credited with being the forerunners of the modern method of preparing ‘cellulose paper.’ For their very ancient practice of extracting the fibre from the bark and other parts of plants by means of maceration is in principle identical with the modern method of extracting ‘cellulose’ by means of certain chemical processes.”

Fig. 2.—An Early Paper Mill (from “Kulturhistorisches Bilderbuch,” A.D. 1564).

Paper-making in Europe.—The introduction of the art into Europe seems to have taken place early in the eleventh century, when the Moors manufactured paper at Toledo. The early authorities who have studied this subject express the opinion that the paper produced in Europe at this time was made from cotton rags and from raw cotton, but, in view of the recent researches into the composition of paper, it is difficult to say how this idea arose, unless we accept the explanation offered by Professor Karabacek. In standard encyclopædias the following statements are made as to existing early documents printed on paper made in Europe:—

One of the most interesting books on this subject is the “Historical Account of the Substances used to describe Events from the Earliest Date,” by Matthias Koops, published in 1800. This writer appears to have obtained most of his information from German authorities.

The industry of paper-making passed through Spain into Italy, France, and the Netherlands. In 1189 paper was being manufactured at Hainault, in France, and the industry rapidly spread all over the Continent. In 1390 Ulman Stromer established a mill at Nuremberg, in Germany, employing a great number of men, who were obliged to take an oath that they would not teach anyone the art of paper-making or make paper on their own account. In the sixteenth century the Dutch endeavoured to protect their industry by making the exportation of moulds for paper-making an offence punishable by death.

The bulk of the paper used in England was imported from France and Holland, and it was many years before the industry was established in England. This is not surprising in view of the protective and conservative policy of the Continental paper-makers.

Fig. 3.—The Paper Mill of Ulman Stromer, A.D. 1390 (supposed to be the oldest known drawing of a Paper Mill).

Paper-making in England.—The actual period at which the manufacture of paper was first started in England is somewhat uncertain. The first mention of any paper-maker is found in Wynkyn de Worde's “De Proprietatibus Rerum,” printed by Caxton in 1495, the reference being as follows:—

And John Tate the younger, joye mote he brok,
Which late hathe in England, doo
Make thys paper thynne,
That now in our Englyssh
Thys booke is prynted inne.

John Tate was the owner of a mill at Stevenage, Hertfordshire. In the household book of Henry VII. an entry for the year 1499 reads, “Geven in rewarde to Tate of the mylne, 6s. 8d.”

In 1588 a paper mill was erected by Sir John Spielman, a German, who obtained a licence from Queen Elizabeth “for the sole gathering for ten years of all rags, etc., necessary for the making of paper.” This paper mill was eulogised by Thomas Churchyard in a long poem of forty-four stanzas, of which we quote two:—

I prayse the man that first did paper make,
The only thing that sets all virtues forth;
It shoes new bookes, and keeps old workes awake,
Much more of price than all the world is worth:
It witnesse bears of friendship, time, and troth,
And is the tromp of vice and virtue both;
Without whose help no hap nor wealth is won,
And by whose ayde great works and deedes are done.
Six hundred men are set to worke by him
That else might starve, or seeke abroad their bread,
Who now live well, and goe full brave and trim,
And who may boast they are with paper fed.
Strange is that foode, yet stranger made the same,
For greater help, I gesse, he cannot give
Than by his help to make poore folk to live.

The industry made but little progress for some time after Spielman's death, and up till 1670 the supplies of paper were obtained almost entirely from France. The first British patent for paper-making was granted to Charles Hildeyard in 1665 for “the way and art of making blue paper used by sugar bakers and others.” The trade received a great impetus on account of the presence of Huguenots who had fled to England from France in consequence of the revocation of the edict of Nantes in 1685.

In 1695 a company was formed in Scotland for the “manufacture of white and printing paper.”

Improvements in the art were slow until 1760, when Whatman, whose name has since become famous in connection with paper, commenced operations at Maidstone. Meantime the methods by which the rags were converted into paper were exceedingly slow and clumsy, so that the output of finished paper was very small.

Some interesting details as to the early manufacture of paper in England are given by Mr. Rhys Jenkins, and from his account of “Early Attempts at Paper-making in England, 1495-1788,” the following extracts have been made:—

Early Methods.—The most rapid development of the industry appears to have taken place in Holland. The rags used for paper-making were moistened with water and stored up in heaps until they fermented and became hot. By this means the dirt and non-fibrous matter was rendered partially soluble, so that on washing a suitable paper pulp was obtained. The washed rags were then placed in a stamping machine resembling an ordinary pestle and mortar. The mortars were constructed of stone and wood, and the stamps were kept in motion by levers which were raised by projections fixed on the shaft of a waterwheel. The operation of beating thus occupied a long period, but the paper produced was of great strength.

The invention of the “Hollander,” a simple yet ingenious engine which is deservedly known by the name of the country in which it first originated, gave a tremendous impetus to the art of paper-making, as by its means the quantity of material which could be treated in twenty-four hours was greatly increased. Unfortunately the date of the invention of this important machine has not been definitely traced. The earliest mention of it seems to occur in Sturm's “Vollständige Mühlen Baukunst,” published in 1718. It was in extensive use at Saardam in 1697, so that the invention is at least some years previous to 1690.

On this point Koops says: “In Gelderland are a great many mills, but some so small that they are only able to make 400 reams of paper annually, and there are also water mills with stampers, like those in Germany. But in the province of Holland there are windmills, with cutting and grinding engines, which do more in two hours than the others do in twelve. In Saardam 1,000 persons are employed in paper-making.”

The First Fourdrinier Paper Machine.

Up till the year 1799 paper was made entirely in sheets on a hand mould, but during the last few years of the eighteenth century a Frenchman, Nicholas Louis Robert, manager for M. Didot, who owned a paper mill at Essones, had been experimenting for the purpose of making paper in the form of a continuous sheet, and eventually produced some of considerable length.

The idea was taken to England by Didot's brother-in-law, Gamble, and introduced to the notice of Messrs. Fourdrinier, wholesale stationers, of London.

Fig. 4.—The First Paper Machine, A.D. 1802. Plan and Elevation.

The first machine was naturally a very crude affair. It consisted of an endless wire cloth stretched in a horizontal position on two rollers, one of which rotated freely in a bearing attached to the frame of the machine, the other being fitted in an adjustable bearing so that the wire could be tightened up when necessary.

The beaten pulp, contained in a vat placed below the wire, was thrown up in a continual stream upon the surface of the wire, and carried forward towards the squeezing rolls. A shaking motion was imparted to the travelling wire so as to cause the fibres to felt properly. A great deal of the water fell through the meshes of the gauze, and further quantities were removed by means of the press rolls. The wet paper was then wound up on to a wooden roller, which was taken out as soon as sufficient paper had been made.

Fig. 5.—The Improved Paper Machine of A.D. 1810.

The whole process was carried on under great difficulties, but substantial improvements were soon made by the enterprising Fourdriniers, who commenced operations in Bermondsey, employing Mr. Bryan Donkin, then in the service of Messrs. Hall & Co., of Dartford, who had shown himself keenly interested in the machine. In 1803 the first “Fourdrinier,” so called, was built at Bermondsey, and erected at Two Waters Mill in Herefordshire.

In this machine the mixture of pulp and water was carried forward between two wires, and, after passing through the couch rolls, transferred to an endless felt. This arrangement proved to be faulty because the water did not escape freely enough from the wire, and a great deal of the paper was spoilt.

Donkin, however, hit upon a simple but effective device for curing this fault by altering the relative position of the two couch rolls. Instead of keeping the two rolls exactly in a vertical position one over the other, he placed them at a slight angle so that the upper one should bear gently on the web of paper carried by the wire before receiving the full pressure of the rolls, and thus remove a greater proportion of the water. In this way the paper was firmer and less liable to break when pressed between the couch rolls, an additional advantage being secured in the fact that the upper wire could be dispensed with.

The various improvements effected resulted in a machine the details of which appear in the appended diagram, the device of the inclined couch rolls being fitted about 1810.

The mixture of water and pulp flowed from a stuff chest into a small regulating box and on to the wire over a sloping board. The pulp at once formed into a wet sheet of paper, the water falling through the meshes of the wire, being caught in a bucket-shaped appliance, and conveyed back to the regulating box. The stream of pulp was confined upon the wire by means of a deckle. Further quantities of water were removed by the aid of a pair of squeezing rolls before the web passed through the couch rolls after which the paper was reeled up on a wooden spindle.

From this date the success of the machine was assured, though the inventor and his colleagues were practically ruined, an experience only too common with the early pioneers of many great and useful industrial enterprises. In fact, the firm of Messrs. Donkin were the only people to profit from the invention, for they manufactured a number of machines, as stated in the report of the Jurors of the Exhibition of 1851, and from 1803 to 1851 no less than 190 Fourdriniers were set to work.

[CHAPTER II]
CELLULOSE AND PAPER-MAKING FIBRES

When plants such as flax, cotton, straw, hemp, and other varieties of the vegetable kingdom are digested with a solution of caustic soda, washed, and then bleached by means of chloride of lime, a fibrous mass is obtained more or less white in colour.

This is the substance known to paper-makers as paper pulp, and the several modifications of it derived from different plants are generally known to chemists as cellulose.

Although plants differ greatly in physical structure and general appearance, yet they all contain tissue which under suitable treatment yields a definite proportion of this fibrous substance. The preparation of a small quantity of cellulose from materials like straw, rope, hemp, the stringy bark of garden shrubs, wood, and bamboo can easily be accomplished without special appliances. Soft materials, such as straw and hemp, are cut up into short pieces, hard substances like wood and bamboo are thoroughly hammered out, in order to secure a fine subdivision of the mass. The fibre so prepared is then placed in a small iron saucepan, and covered with a solution made up of ten parts of caustic soda and 100 parts of water. The material is boiled gently for eight or ten hours, the water which is lost through evaporation of steam being replaced by fresh quantities of hot water at regular intervals. When the fibrous mass breaks up readily between the fingers, it is poured into a sieve, or on a piece of muslin stretched over a basin, and washed completely with hot water until clean and free from alkali. Hard pieces and portions which seem incompletely boiled are removed, and the residual fibres separated out. These fibres are placed in a weak, clear solution of ordinary bleaching powder, left for several hours, and subsequently thoroughly washed. This simple process will give a more or less white fibrous material.

The purest form of cellulose is cotton. A very slight alkaline treatment, followed by bleaching, is sufficient to remove the non-fibrous constituents of the plant, and a large yield of cellulose is obtained. For this reason the cotton fibre ranks high as an almost ideal material for paper-making, possessing the quality of durability.

Cellulose is an organic compound, containing carbon, hydrogen, and oxygen in the following proportions:—

Its composition is represented by the formula C₆H₁₀O₅.

The celluloses obtained from various plants are not identical either in physical structure and chemical constitution, or as to their behaviour when employed for paper-making. In fact, the well-known differences between the raw materials used for paper-making, and also between the numerous varieties of finished paper, are to be largely accounted for and explained by a careful study of the cellulose group, particularly with reference to the microscopic characteristics and the chemical composition of the individual species.

The only vegetable substance which may be regarded as a simple cellulose is cotton, all others being compound celluloses of varying constitution, the nature of which cannot be appreciated without a considerable knowledge of chemistry. The classification of such plants, therefore, in a book of this description must be limited to certain distinctions having some immediate practical bearing on the question of paper manufacture.

Cotton.—Regarded as the typical simple cellulose, containing 91 per cent. of cellulose, and remarkable for its resistance to the action of caustic soda.

Linen.—The cellulose isolated from flax by treatment with alkali or caustic soda cannot readily be distinguished from cotton cellulose by chemical analysis or reactions. The difference is almost entirely a physical one.

Flax is a typical compound cellulose, to which has been given the name pecto-cellulose on account of certain properties. Other well-known plants of this class are ramie, aloe, “sunn hemp,” manila.

Esparto.—The cellulose isolated from esparto differs in composition from cotton cellulose:—

It is regarded as an oxycellulose, being readily oxidised by exposure to air at 100° C. Other oxycelluloses familiar to the paper-maker are straw, sugarcane, bamboo.

Wood.—The difference between wood and the plants already mentioned is expressed by the term lignified fibre or ligno-cellulose. This term is used to indicate that the wood is a compound cellulose containing non-fibrous constituents, to which has been given the name lignone. Jute is another example of this class.

These distinctions may be exemplified by reference to a simple experiment. If three papers, such as a pure rag tissue or a linen writing, an ordinary esparto printing, and a cheap newspaper containing about 80 per cent. of mechanical wood, are heated for twenty-four hours in an oven at a temperature of 105° C., the first will undergo little, if any, change in colour, while the others will be appreciably discoloured, the mechanical wood pulp paper most of all.

This change is due to the gradual oxidation of the constituents of the paper, the ligno-cellulose of the mechanical wood pulp being most readily affected by the high temperature, and the pure cellulose of the rag paper being least altered.

The process of oxidation, brought about rapidly under the conditions of the experiment described, takes place in papers of low quality exposed to air in the ordinary circumstances of daily use, but of course at an extremely slow rate. The deterioration of such paper is not, however, due to the simple oxidation of the cellulose compounds, because other factors have to be taken into account. The presence of impurities in the paper on the one hand, and of chemical vapours in the air on the other, hastens the decay of papers very considerably.

Percentage of Cellulose in Fibrous Plants.—The value of a vegetable plant for paper-making is first determined by a close examination of the physical structure of the cellulose isolated by the ordinary methods of treatment. If the fibres are weak and short, the raw material is of little value, and it is at once condemned without further investigation, but should the fibre prove suitable, then the question of the percentage of cellulose becomes important.

There are several methods employed for estimating the amount of cellulose in plants. The process giving a maximum yield is known as the chlorination method, the details of which are as follows:—About ten grammes of the air-dried fibre is dried at 100° C. in a water oven for the determination of moisture. A second ten grammes of the air-dried fibre is boiled for thirty minutes with a weak solution of pure caustic soda (ten grammes of caustic soda in 1,000 cubic centimetres of water), small quantities of distilled water being added at frequent intervals to replace water lost by evaporation. The residue is then poured on to a piece of small wire gauze, washed thoroughly, and squeezed out. The moist mass of fibre is loosened and teased out, placed in a beaker, and submitted to the action of chlorine gas for an hour. The bright yellow mass is then washed with water and immersed in a solution of sodium sulphite (twenty grammes of sodium sulphite in 1,000 cc. of water). The mixture is slowly heated, and finally boiled for eight to ten minutes, with the addition of 10 cc. of caustic soda solution. The residue is washed, immersed in dilute sodium hypochlorite solution for ten minutes, again washed, first with water containing a little sulphurous acid and then with pure distilled water. It is finally dried and weighed.

The second process for estimating cellulose is based upon the use of bromine and ammonia. About ten grammes of the air-dried fibre is placed in a well-stoppered wide-mouthed bottle with sufficient bromine water to cover it. As the reaction proceeds the red solution gradually decolourises, and further small additions of bromine are necessary. The mass is then washed, and boiled in a flask connected to a condenser with a strong solution of ammonia for about three to four hours. The fibrous residue is washed, again treated with bromine water in the cold, and subsequently boiled with ammonia. The alternative treatment with bromine and ammonia is repeated until a white fibrous mass is obtained.

In practice the paper-maker is confined to two or three methods for the isolation of the fibres, viz., alkaline processes, which require the digestion of the material with caustic soda, lime, lime and carbonate of soda, chiefly applied to the boiling of rags, esparto, and similar pecto-celluloses; acid processes, in which the material is digested with sulphurous acid and sulphites. The latter methods are at present almost exclusively used for the preparation of chemical wood pulp.

Yields of Cellulose in the Paper Mill.—The object of the paper-maker is to obtain a maximum yield of cellulose residue at a minimum of cost. Usually the amount of actual bleached paper pulp obtained in the mill is less than the percentage obtained by careful quantitative analysis, for reasons easily understood.

In the first place, the raw material is digested for a stated period with a carefully measured quantity of caustic soda, for example, at a certain temperature. Now the conditions of boiling may be varied by altering one or more of these factors, the period of boiling, the strength of solution, or the steam pressure, and the paper-maker must exercise his judgment in fixing the exact relation between the varying factors so as to produce the best results.

In the second place, the mechanical devices for washing the boiled pulp and for bleaching cause slight losses of fibre, which cannot be altogether avoided when operations are conducted on a large scale. Frequently, also, a greater yield of boiled material may involve a larger quantity of bleaching powder, so that it is evident the adjustment of practical conditions requires considerable technical skill and experience.

The percentage of cellulose in the vegetable plants employed more or less in the manufacture of paper is given in the following table:—

Table Showing Percentage of Cellulose in Fibrous Plants.

The Properties of Cellulose.—Cellulose is remarkably inert towards all ordinary solvents such as water, alcohol, turpentine, benzene, and similar reagents, a property which renders it extremely useful in many industries, with the result that the industrial applications of cellulose are numerous and exceedingly varied.

Solubility.—Cellulose is dissolved when brought into contact with certain metallic salts, but it behaves quite differently to ordinary organic compounds. Sugar, for example, is a crystalline body soluble in water, and can be recovered in a crystalline state by gradual evaporation of the water. Cellulose under suitable conditions can be dissolved, but it cannot be reproduced in structural form identical with the original substance.

If cellulose is gently heated in a strong aqueous solution of zinc chloride, it gradually dissolves, a thick syrupy mass being obtained, which consists of a gelatinous solution of cellulose. If the mixture is diluted with cold water, a precipitate is produced consisting of cellulose hydrate intimately associated with oxide of zinc, which latter can be dissolved out by means of hydrochloric acid. The resulting product is not, however, the original substance, but a hydrated cellulose, devoid of any crystalline structure.

Cellulose is also soluble in ammoniacal solutions of cupric oxide, from which it can be precipitated by acids or by substances which act as dehydrating agents, e.g., alcohol.

Hydrolysis.—An explanation of the behaviour of cellulose towards the solvents already mentioned, and towards acid and alkali, requires a reference to its chemical composition.

The substance is a compound of carbon, hydrogen, and oxygen represented by the formula

C₆H₁₀O₅

being one of a class of organic compounds known as carbohydrates, so designated because the hydrogen and oxygen are present in the proportions which exist in water.

Water = Hydrogen + Oxygen
H₂ + O.

The H₁₀O₅ in the cellulose formula corresponds to 5 (H₂O).

When cellulose is acted upon by acid, alkali, and certain metallic salts, it enters into combination with one or more proportions of water, forming cellulose hydrates of varying complexity. This change is usually termed hydrolysis.

With mineral acids like sulphuric and hydrochloric acids, cellulose, if boiled in weak solutions, is converted into a non-fibrous brittle substance having the composition

C₁₂H₂₀O₁₀ 2 H₂O

to which the name hydra-cellulose has been given. Similar changes occur, but at a much slower rate, when cellulose is in contact with free acids at ordinary temperatures. For this reason it is important that paper, when finished, should not be contaminated with free acid.

The nature and extent of the chemical change can be varied by altering the strength of the acid and the conditions of treatment. The manufacture of parchment paper is an example of the practical utility of the chemical reaction between cellulose and acid. A sheet of paper is dipped into a mixture of three parts of strong sulphuric acid and one part of water, when it becomes transparent. Left in the solution it dissolves, but if taken out and dipped into water in order to wash off the acid the reaction is stopped, and a tough semi-transparent piece of parchment is obtained. The cellulose is more or less hydrated, having the composition

C₁₂H₂₀O₁₀ H₂O,

a substance having the name amyloid.

Oxidation.—Cellulose is only oxidised to any appreciable extent by acid and alkali if treated under severe conditions. It is remarkable that the processes necessary for isolating paper pulp from plants when digested with these chemical reagents do not act upon or destroy the fibre, and this capacity for resisting oxidation has rendered cellulose extremely valuable to many of the most important industries.

The resistant power of the cellulose is, however, broken down by the use of acid and alkali in concentrated form.

Oxalic and acetic acids are obtained when cellulose is heated strongly at 250° C. with solid caustic soda.

Oxy-cellulose, a white friable powder, is produced by means of strong mineral acids. Nitric acid at 100° C. attacks the fibre very readily and produces about 30-40 per cent. of the oxidised cellulose.

Cellulose Derivatives.

The great number of compounds and derivatives, i.e., substances obtained by chemical treatment, may be judged from the following list. The substances of commercial importance are suitably distinguished from those of merely scientific interest by the printing of the names in small capitals.

Acetic Acid.—An important commercial product obtained by the destructive distillation of wood. The crude pyroligneous acid is first neutralised with chalk or lime, and the calcium acetate formed then distilled with sulphuric acid. Wood yields 5 to 10 per cent. of its weight of acetic acid according to the nature of the wood.

Acetone.—A solvent for resins, gums, camphor, gun cotton, and other cellulose products. Prepared by distilling barium or calcium acetate in iron stills, the acetate being obtained from the crude acetic acid produced by the dry distillation of wood.

Acid Cellulose.—(See Hydral-Cellulose.)

Adipo-Cellulose.—A distinct compound cellulose present in the complex cuticular tissue of plants, and separated easily by suitable solvents from the wax and oily constituents also present.

Alkali Cellulose.—When cotton pulp is intimately mixed with strong caustic soda solution, this compound is formed. It is utilised in the manufacture of Viscose.

Amyloid.—Strong sulphuric acid acts upon cellulose and converts it into a gelatinous semi-transparent substance to which the name amyloid has been given. (See Parchment Paper.)

Ballistite.—A smokeless powder composed of nearly equal parts of nitro-glycerine and nitrated cellulose, with a small quantity of diphenylamine.

Carbohydrate.—A large number of important commercial products, such as cellulose, sugars, starches, and gums, consist of the elements carbon, hydrogen, and oxygen, associated in varying proportions. The ratio of hydrogen to oxygen in these compounds is always 2:1 (H₂ and O).

To all these substances the term carbohydrate is applied.

Celloxin (Tollens).—A substance having the stated composition C₈H₆O₆ considered to be present in oxidised derivatives of cellulose.

Celluloid.—This well-known material is made by incorporating camphor with nitro-cellulose, a plastic ivory-like substance being produced. In practice the process is as follows:—Wood pulp or wood pulp paper is saturated with a mixture of sulphuric acid (five parts) and nitric acid (two parts), which produces nitrated cellulose. The product is washed, ground, and mixed with camphor, the mastication being effected by heavy iron rollers. The mass thickens and can be removed in the form of thick sheets. These sheets are submitted to great pressure between steam-heated plates. The cake obtained is cut into sheets of any desired thickness, seasoned by prolonged storage, and afterwards worked up into boxes, combs, brush-backs, and many other domestic articles of a useful and ornamental character.

Cellulose Acetate (Cross).—If cellulose is heated with acetic anhydride at 180° C., viscous solutions of the acetates are obtained. The process yielding a definite acetate of commercial value is based upon the following reaction:—100 parts of cellulose prepared from the sulpho-carbonate are mixed with 120 parts of zinc acetate, heated and dried at 105° C. Acetic anhydride is added in small quantity, and 100 parts of acetyl chloride. At a temperature of 50° C. the mixture becomes liquid, and cellulose acetate is subsequently obtained as a white powder.

The compound can be used in the place of cellulose nitrate, and, being non-explosive, may gradually replace the latter in many industrial applications.

Cellulose-Benzoate.—When alkali cellulose is heated with benzoyl chloride and excess of caustic soda, this substance is obtained.

Cellulose Hydrate.—The substances produced by the action of acid and alkali on cellulose under certain strictly defined conditions are bodies containing cellulose united with water to form hydrates. The industrial applications of cellulose based upon this reaction are described under the special headings.

Cellulose Nitrate.—A considerable number of derivatives are obtained by bringing cellulose into contact with nitric acid. Variations in the strength of the acid, the temperature of reaction, and the time of contact determine the nature of the product. The best known nitrates are:—

Cellulose di-nitrate.

Cellulose tri-nitrate and tetra-nitrate, present chiefly in pyroxyline.

Cellulose penta-nitrate.

Cellulose hexa-nitrate, the chief constituent of gun-cotton.

Charcoal.—Not a cellulose derivative in the strict sense of the term, charcoal being a residue obtained in the dry distillation of wood.

Collodion.—A soluble nitrate of cellulose used in photography. (See Pyroxyline.)

Cordite.—A smokeless powder consisting mainly of nitro-glycerine and gun-cotton mixed with acetone. The materials are thoroughly incorporated and the resultant paste formed into threads which are dyed and then cut up into suitable lengths for cartridges.

Cuto-Cellulose.—Synonymous with adipo-cellulose.

Dextron.—A compound prepared from the waste liquors of the bisulphite process used for the manufacture of wood pulp. Resembles dextrin in its physical properties.

Dextrose.—A carbohydrate which can be obtained by the action of mineral acids on cellulose. Commercial dextrose, or glucose, is prepared by the conversion of starch with sulphuric acid. The starch is mixed with dilute acid at a fixed temperature, and the starch milk obtained poured gradually into a vessel containing dilute acid, which is maintained at boiling point. The conversion is complete and rapid.

Explosives.—The production of the several cellulose nitrates has given rise to a great number of highly explosive substances.

Blasting Gelatine.—A mixture of nitro-glycerine with cellulose nitrates.

Amberite, Ballistite, Cordite, and other smokeless powders, consisting of nitro-glycerine and cellulose nitrates in about equal proportions.

Sporting powders made by mixing nitro-cellulose with barium nitrate, camphor nitro-benzene, such as indurite, plastomenite, etc.

Glucose.—(See Dextrose.)

Gun-cotton.—An explosive prepared by the action of nitric acid on cotton. Selected cotton waste suitably opened up is immersed in a mixture of three parts of nitric acid by weight (1·50 sp. gr.) and one part of sulphuric acid by weight (1·85 sp. gr.) and submitted to a number of processes by which the nitration is properly effected so as to produce a nitro-cellulose of uniform composition. The material is washed, reduced to pulp, and moulded into various forms.

Hemi-Cellulose.—The constituents of plant tissues are extremely varied in character. Many plants contain substances which resemble true cellulose, but differing from it in being easily converted by hydrolysis, and by the action of dilute acids, into carbohydrates. Plants which contain a large proportion of such constituents are termed hemi-celluloses. In some cases certain crystallisable sugars can be obtained by hydrolysis under suitable conditions.

Hydral-Cellulose (Bumcke).—A compound of merely scientific interest, resulting from the treatment of cellulose with hydrogen peroxide. When acted upon by alkali it is decomposed into cellulose and acid cellulose, the latter a derivative of unstable composition.

Hydro-Cellulose.—This product, a white, non-structureless, friable powder, is obtained by treating cellulose with hydrochloric or sulphuric acid of moderate strength. The substance itself has no commercial value, but the reaction is useful in separating cotton from animal fabrics. If a woollen cloth containing cotton is soaked in dilute sulphuric acid, washed, and dried at a gentle heat, the cotton is acted upon, and can be beaten out of the fabric, the wool resisting the acid treatment.

Lignin.—The complex mixture of substances which is associated with cellulose in wood, jute, and other ligno-celluloses. The conversion of wood into chemical pulp effects the removal of this material more or less completely. The well-known “phloroglucine” test for mechanical wood in papers is based upon the presence of lignin in the wood.

Ligno-Cellulose.—Wood and jute are typical bodies consisting of cellulose and complex non-cellulose, generally described as lignin, associated together in the plant tissue. The chemistry of the non-cellulose portion of wood is a matter still under investigation, its importance from a commercial point of view being obvious from the fact that the removal of the lignin during the conversion of the wood into wood-cellulose results in a loss of 50 per cent. of the weight of wood.

Lustra-Cellulose.—Synonymous with and suggested as a more appropriate name for the material usually described as artificial silk.

Mercerised Cotton.—When cotton is immersed in strong solutions of caustic soda a remarkable change sets in. The physical structure of the fibre is entirely altered from the long flattened tube having a large central canal to a shorter cylindrical tube in which the canal almost disappears. Hydration of the cellulose takes place, and these changes are taken advantage of in the production of mercerised cloth (so named from the discoverer of the reaction, Mercer). Cotton goods, particularly those made of long stapled cotton, when mercerised, exhibit a beautiful lustre, and some magnificent crêpon effects are obtained by the process.

Methoxyl.—A constituent of the complex compound known as ligno-cellulose, which is present in wood and similar fibres. The amount of methoxyl in lignified tissue can be accurately determined, and it has been suggested that the proportion of methoxyl found in a cheap printing paper could be used as a measure of mechanical wood pulp present.

Muco-Cellulose.—This term is applied to certain compound celluloses present chiefly in mucilages, gums, and in seaweeds (Algæ). The natural substances are all of commercial importance—Iceland moss, Carragheen, Algin, etc.

Naphtha.—One of the products of the dry distillation of wood, usually described as wood-naphtha, or wood spirit.

Nitro-Cellulose.—The treatment of cellulose with nitric acid gives a number of nitro-celluloses according to the conditions of the process. (See Cellulose Nitrates.)

Oxalic Acid.—A substance of great commercial importance prepared by heating the sawdust of soft wood, such as pine, fir, and poplar, with strong solutions of mixed caustic soda and potash to dryness. The wood yields after six hours a greyish mass containing about 20 per cent. of the acid, which is separated out by water and then crystallised.

It is used for bleaching, and as a discharge in calico printing and dyeing.

Oxy-Cellulose.—A white friable powder produced by treating cellulose with nitric acid at 100° C. The oxidation of cellulose is brought about by several reagents such as chromic acid, hypochlorites of lime and soda, chlorine, and permanganates. The extent to which cloth has been damaged by overbleaching may be determined by a simple test with methylene blue solution, which is readily absorbed by oxy-cellulose present in such fabrics.

Parchment.—A tough paper prepared by the action of sulphuric acid on unsized paper. (See page [137].)

Pectins.—(See Pecto-Cellulose.)

Pecto-Cellulose.—A generic term applied to many important fibrous materials, such as flax, straw, esparto, bamboo, phormium, ramie, &c., which on alkaline treatment yield cellulose for paper-making, and a non-fibrous soluble residue of complex composition. These soluble derivatives are known as pectin (C₃₂H₄₈O₃₂), pectic acid (C₃₂H₄₄O₃₀), and metapectic acid (C₃₂H₂₈O₃₆). Although the soluble constituents of the pecto-celluloses amount to 50 per cent. by weight in most cases, no process for the recovery of the product in a commercial form has yet been devised. (See description of Soda recovery, page [78].)

Pyroxyline.—A substance prepared by nitrating cotton. The cotton is immersed in a mixture of nitric and sulphuric acids of carefully regulated strength, and subsequently washed free of the acid. Three volumes of nitric acid (sp. gr. 1·429) are diluted with two volumes of water and nine volumes of strong sulphuric acid (sp. gr. 1·839) added. To the solution when cool the cotton is added in small quantities at a time. The resultant pyroxyline is soluble in a mixture of equal quantities of alcohol and ether, and in the soluble form is utilised as collodion for photography.

Silk, Artificial.—A remarkable substance made from wood or cotton cellulose, closely resembling silk in appearance and physical properties.

Nitrated cellulose is dissolved in a mixture of equal parts of alcohol and ether.

The solution is forced through five capillary tubes under high pressure, and the filament so obtained solidifying at once is wound together with other similar filaments upon suitable bobbins. Various modifications of this general process are in use, such as the solidification of the solution into threads by passing it into water; the application of solvents less inflammable than ether and alcohol; the use of other forms of dissolved cellulose such as those prepared by means of zinc chloride, ammoniacal copper oxide, or acetic anhydride. In all cases the yarn or thread is submitted to further chemical treatment for the removal of nitric acid and to render the material non-explosive and less inflammable. The finished product is soft and supple, can be easily bleached and dyed, and is capable of acquiring a high lustre.

Smokeless Powders.—(See Explosives.)

Sulpho-Carbonate.—(See Viscose.)

Sulphate Cellulose.—Chemical wood pulp prepared by the sulphate process. (See page [107].)

Sulphite Cellulose.—Chemical wood pulp prepared by the sulphite process. (See page [107].)

Viscose.—A soluble sulpho-carbonate of cellulose, prepared by treating cellulose with a 15 per cent. solution of caustic soda, and shaking the product with carbon bisulphide in a closed vessel. The mixture forms a yellowish mass soluble in water, giving a viscous solution which has some remarkable and valuable properties.

This viscose, on standing, coagulates to a hard mass which can be turned and polished.

If spread on glass and coagulated by heat, films are obtained from which the alkaline by-products can be washed out. These films are transparent, colourless, very tough and hard.

Vulcanised Fibre.—Fibre or pulp treated with zinc chloride in acid solution, or otherwise, for the manufacture of hard boards. (See page [139].)

Willesden Goods.—Paper, fibre, and textiles when treated with cuprammonium oxide are partially gelatinised on the surface and rendered waterproof. (See page [139].)

Wood Spirit.—(See Naphtha.)

Xylonite.—(See Celluloid.)

Fibres for Paper-making.

Although the vegetable world has been explored from time to time for new supplies of cellulose, and some plants have been found serviceable in certain directions, yet the number of fibres in actual use is very limited.

The following table indicates the principal sources of the material required for paper-making:—

Exploiting New Fibres.—The exploitation of any new paper-making fibre requires attention to certain important details, which may be fairly considered in the following order:—

(1) Supply.—The supply of material must be plentiful and obtainable in large quantities. Too often this question is entirely neglected by those who bring new fibres to the notice of paper-makers, probably because they do not realise that enormous quantities of material are necessary to supply even a very small section of the paper trade, the fact being that few plants yield more than half their weight of paper-making fibre.

(2) Suitability.—The fibre should be properly examined as to its chemical and physical properties in a laboratory equipped with appliances for its conversion into bleached paper pulp on a small scale. The examination of the fibre would include tests as to the amount of pulp which can be obtained from one ton of raw material, the approximate cost of treatment, and details as to the value of the fibre for paper-making.

(3) Cost of Raw Material.—If the supply of material seems to be sufficient, and the paper pulp obtained possesses suitable qualities, then it is necessary to get accurate information as to the cost of the fibre delivered to some given spot at or near the place of collection.

The exploitation of any new fibre for paper-making purposes will involve a recognition of the fact that the raw material must be converted into pulp at or near the place where the material is most abundant.

The only interesting exception to this is the case of esparto fibre, which is imported into England in large amount, but this is only possible because esparto possesses most valuable paper-making qualities, and is obtained in countries close to England, where large quantities are consumed. It is doubtful whether other fibres could be utilised in the same way.

(4) The Cost of Manufacture at or near the place of collection requires to be carefully worked out, due consideration being given to the actual cost of chemicals on the spot, cost of labour, and the conditions under which the maintenance of machinery can be efficiently looked after.

(5) Carriage and Freight Charges are the last, but by no means the least, items of importance. It is not too much to say that the whole success of the exploitation of new paper-making fibre hangs entirely upon this item, the majority of many fibres which have been brought to the notice of the trade being suitable, but impracticable, solely on account of these and similar commercial considerations.

In the pages of the trade press for the last few years the following fibres have been noticed:—

(1) Flax Pulp.—This material was to be obtained from flax straw. Attempts were made on a commercial scale to produce quantities of flax fibre, but so far the efforts made have not been very successful.

(2) Ramie Fibre.—This material has been exploited over and over again, chiefly for textile trades, its application as a paper-making material being limited to small quantities used for special purposes such as bank notes. The fibre is too valuable, except for textile industries, and can only come into the paper trade as a waste material from such sources.

(3) Tobacco Fibre has been before the trade for some years, the idea being to utilise tobacco stems and other tobacco waste for the manufacture of paper suitable for use as wrappers for cigars, cigarettes, and similar purposes.

(4) Agave Fibre.—This name is given to a large and important genus of fibre-yielding plants found chiefly in Central America. It is also found in India, and in 1878 an experiment was made for the manufacture of paper at a mill near Bombay, but this did not give any satisfactory results, probably on account of the primitive methods used in treatment.

(5) Bagasse.—The waste material from sugar-cane has been looked upon for many years as a desirable fibre, much time and labour having been given to the utilisation of this material. In spite of these efforts bagasse still remains an almost useless and unworkable material. This is partly due to inferiority of the pulp and partly due to difficulties connected with its treatment. Probably cultivation of the plant for the sake of its fibre instead of the sugar might give better results.

(6) Peat.—The attempts made to utilise peat for paper-making are probably fresh in the minds of those paper-makers interested in the production of wrappers and boxboards. The nature of peat, however, is such as to exclude the hope of making any useful article. The material has been exploited by companies in Austria, Ireland, and Canada on a fairly large scale, with but a limited amount of success.

(7) Cotton-seed Hulls.—Many patents have been taken out for the chemical treatment of cotton-seed waste and having for their object the removal of the particles of seed hulls, so as to obtain a pure cotton pulp. The scheme sounds attractive, but there are so many conditions which have to be taken account of that the commercial success of any undertaking based on the use of cotton-seed hulls is very questionable. The fact is that the hulls have a market value quite apart from the possibility of their application to paper-making, and this initial cost would prevent paper-makers from buying the material owing to the large quantity necessary for the manufacture of one ton of pure pulp.

(8) Apocynum.—This plant is said to be utilised to some extent by the Russian Government in the manufacture of bank notes, the plant being cultivated at Poltava. This is an instance of the particular application of a fibrous material in limited quantities, a proposition which is always feasible in the case of special requirements.

(9) Cornstalk.—This fibre has been chiefly exploited in America, experts having been attracted by the enormous quantities of cornstalk available in the several wheat-producing States. The manufacture of paper pulp from this material on a large scale has yet to be established.

(10) Japanese Paper Fibres.—In Eastern countries a great number of fibrous plants are utilised in small quantities for the manufacture of special papers. It is obvious that in these Eastern countries the employment of fibres which are not cultivated in large bulk is readily possible when the question of price obtained for the paper and the cost of production are considered. Of such fibres may be mentioned the Mitsumata and Kodzu, easy of cultivation and giving a good yield of material per acre of ground. The waxed papers used for stencils in duplicating work on the typewriter are made from these fibres. The paper Mulberry is also a well-known fibre; while a third species particularly valuable for thin papers is the Gampi.

(11) Antaimoto Fibre.—The bark of this shrub is utilised in Madagascar in very small quantities for local purposes and possesses little interest for paper-makers.

(12) Refuse Hempstalk.—The suggestion of the use of this material comes from Italy, the hempstalk having been experimented with at San Cesario Mill. This also is a fibre of a local interest only. The percentage of cellulose is very high, being over 50 per cent.

(13) Papyrus.—The revival of this celebrated material is of comparatively recent date. It should be noted that the manufacture of papyrus as carried out by the Egyptians, by smoothing out layers of bark in order to utilise them as sheets of paper, and the present day proposals which involve the production of paper pulp from papyrus, are two entirely different propositions, and the success of the old Egyptian method cannot be referred to as any assurance of success for the production of paper from papyrus along modern lines. The exploitation of this fibre must follow the lines of modern research and commercial investigation, and its value, if any, could then be established.

(14) Pousolsia.—This is a fibre of the same family as hemp and ramie. The value of this material is at present unknown, but the ultimate fibre appears to possess a most extraordinary length. Very little information is available at present as to its value for paper-making.

(15) Bamboo.—This material has been before the paper trade for many years, having first been exploited seriously by Mr. Thomas Routledge in 1875. Since that date a good deal of work has been done in connection with the fibre, but not until recently has the investigation been made of a sufficiently extensive character to enable paper-makers to form some conclusions as to the best methods of obtaining a reliable paper pulp. The researches of the writer in India go to prove that with any fibre it is necessary to take into account all the factors likely to affect the final cost of the paper pulp delivered to any given paper mill.

The figures given in a report recently published, “The Manufacture of Paper and Paper Pulp in Burma,” show the necessity of thorough investigation into all the points likely to affect the final results, viz., the price at which the paper pulp can be sold in England, assuming that the fibre in question is suitable for the manufacture of paper.

Examination of Fibres.—The exact chemical analysis of a new fibre is necessary in order to establish completely its value for textile and paper-making purposes, but the investigation of the suitability of the fibre for paper-making may be simplified by simple reduction of the raw material with caustic soda. The following process is sufficient for all practical purposes:—

Condition of Sample.—A record should be made of the general appearance of the sample, its condition and the amount available for the investigation. Any information available as to the source of supply and the growth of the plant should also be noted.

Preparation of Sample.—The material is cut up into small pieces. The most convenient appliance for this purpose is a mitre cutter as used by picture-frame makers. If the sample is a piece of wood, sections one inch thick cut across the grain of the wood are most suitable, as they can be readily cut up into thin flakes by this machine.

Moisture in Sample.—A small average sample should be dried at 100° C. for the determination of moisture.

Treatment with Caustic Soda.—About two hundred grams of the raw material is closely packed into a small digester or autoclave and covered with a solution of caustic soda having a specific gravity of 1·050. A perforated lead disc should be placed above the sample in the digester to prevent any of it from floating above the level of the solution. The material should be digested for five or six hours at a pressure of 50 lbs. The conditions of treatment here given will need to be varied according to the nature of the fibre. Some materials can be readily converted into pulp with weaker liquor and at a lower pressure, while others will require prolonged treatment. These conditions must be varied according to judgment or according to the effects produced by the conditions already set out.

Unbleached Pulp.—The contents of the digester are emptied out into an ordinary circular sieve provided with a fine copper wire bottom, having a mesh of about sixteen to the inch. The sieve is immersed in water and the contents partially washed with hot water. The partially washed material is squeezed out by hand and tied up in a strong cloth and then kneaded thoroughly by hand in a basin of water which is repeatedly renewed until the fibre is thoroughly washed. The process of kneading at the same time reduces the fibre to the condition of pulp. The water is carefully squeezed out of the pulp by hand, and the moist pulp is then divided into two equal parts, the first of which is made up into sheets of any convenient size, care being taken that none of the fibre is lost. These sheets are then dried in the air and preserved as samples of unbleached pulp, a record being made of the weight produced.

Bleached Pulp.—The second portion of the moist pulp is mixed with a solution of bleach, the strength of which has been accurately determined by the usual methods. The amount of bleach added should be about 20 per cent. of the weight of air-dry fibre present in the moist sample of pulp. The pulp should be bleached at a temperature not exceeding 38° C., and when the colour has reached a maximum the amount of bleach remaining in solution is ascertained by titration with standard arsenic solution. In this way the amount of bleaching powder required to bleach the pulp is determined. The product is then made up into sheets of pulp which are dried by exposure to air and subsequently weighed.

Yield of Pulp.—The percentage yield of finished pulp obtained from the raw material is determined from the figures arrived at in the experiment described, and the weight of raw material necessary to produce one ton of bleached pulp is readily calculated.

Examination of Bleached Fibre.—The fibre should be carefully examined under the microscope and a record made of general microscopic features, especially with reference to the length and diameter of the fibres, and the proportion of cellular matter present, if any.

Sample of Paper.—It is only in the case of short-fibred material similar to esparto and straw that sheets of paper capable of giving comparative results as to strength can be made. The figures obtained with fibrous materials of this kind are only comparative, because it is possible in practice to make a much stronger sheet of paper when the material is beaten properly under normal conditions.

A similar investigation should be made by submitting the fibre to treatment with bisulphite of lime, that is to say, if the fibre lends itself to such a process. A lead-lined digester is necessary, and the solution employed is bisulphite of lime prepared according to the directions given on page [160].

The preparation of sulphite pulp requires more attention than the manufacture of soda pulp. It is most important that the digester should be absolutely tight in order to prevent the escape of any free sulphurous acid gas, and the contents of the digester must be heated slowly until the maximum pressure has been reached.

[CHAPTER III]
THE MANUFACTURE OF PAPER FROM RAGS

Fig. 6.—A Rag Sorting House.

The word rag is used to designate a very wide range of raw material suitable for conversion into paper. In the case of high-class hand-made writing papers only the best qualities are employed, such as new linen and cotton cuttings from factories, or well-sorted rags of domestic origin. The usual classification adopted by merchants who supply the paper mills is somewhat as follows:—

New white linen cuttings (from textile factories).
New white cotton cuttings (from textile factories).
Fine whites (domestic rags).
Outshots (a quality between fines and seconds).
Seconds (a grade inferior to fines).
Thirds (inferior and dirty well-worn rags).
Coloured prints (of all grades and colours).
Fustians and canvas.
Manila and hemp rope.
Baggy, gunny, and jute.

The total amount of rag used in England for paper-making is not known. The only figures available refer to rags imported; and these cannot be regarded as a measure of consumption, which could only be arrived at by first ascertaining the quantity of home rags used. The imports of rag at stated periods are given in the appended table:—

Rags Imported into England.