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1902 Encyclopedia > Bleaching
BLEACHING is the process of whitening or depriving objects of colour, an operation incessantly in activity in nature by the influence of light, air, and moisture. The art of bleaching, of which we have here to treat, consists in inducing the rapid operation of whitening agencies, and as an industry it is mostly directed to cotton, linen, silk, wool, and other textile fibres, but it is also applied to the whitening of paper-pulp, bees'-wax, and some oils and other substances. The term bleaching is derived from the Anglo-Saxon bloscan to bleach, or to fade, from which also comes the cognate German word bleichen, to whiten or render pale. Bleachers, down to the end of last century, were known in England as " whitsters," a name obviously derived from the nature of their calling.
The operation of bleaching must from its very nature be of the same antiquity as the work of washing textures of linen, cotton, or other vegetable fibres. Clothing repeatedly washed, and exposed in the open air to dry, gradually assumes a whiter and whiter hue, and our ancestors cannot have faded to notice and take advantage of this fact. Scarcely anything is known with certainty of the art of bleaching as practised by the nations of antiquity. Egypt in early ages was the great centre of textile manufactures, and her white and coloured linens were in high repute among contemporary nations. As a uniformly well-bleached basis is necessary for the production of a satisfactory dye on cloth, it may be assumed that the Egyptians were fairly proficient in bleaching, and that still more so were the Phoenicians witn their brilliant and famous purple dyes. We learn, from Pliny, that different plants, and likewise the ashes of plants, which no doubt contained alkali, were employed as detergents. He men-tions particularly the Struthium as much used for bleaching magnetism left in the in Greece, a plant which has been identified by some with Gypsophila Struthium. But as it does not appear from Sibthorp's Flora Grceca, published by Sir James Smith, that this species is a native of Greece, Dr Sibthorp's conjec-ture that theStruthium of the ancients was theSaponaria offi-cinalis, a plant common in Greece, is certainly more probable.
In modern times, down to the middle of the 18th century, the Dutch possessed almost a monopoly of the bleaching trade, although we find mention of bleach-works at South-wark near London as early as the middle of the 17th century. It was customary to send all the brown Linen, then largely manufactured in Scotland, to Holland to be bleached. It was sent away in the month of March, and not returned till the end of October, being thus out of the hands of the merchant more than half a year.
The Dutch mode of bleaching, which was mostly con-ducted in the neighbourhood of Haarlem, was to steep the linen first in a waste lye, and then for about a week in a potash lye poured over it boiling hot. The cloth being taken out of this lye, and washed, was next put into wooden vessels containing butter-milk, in which it lay under a pressure for five or six days. After this it was spread upon the grass, and kept wet for several months, exposed to the sunshine of summer.
In 1728 James Adair from Belfast proposed to the Scotch Board of Manufactures to establish a bleachfield in Galloway; this proposal the board approved of, and in the same year resolved to devote £2000 as premiums for the establishment of bleachfields throughout the country. In 1732 a method of bleaching with kelp, introduced by R. Holden, also from Ireland, was submitted to the board ; and with their assistance Holden established a bleachfield for prosecuting his process at Pitkerro, near Dundee.
The bleaching process, as at that time performed, was very tedious, occupying a complete summer. It consisted in steeping the cloth in alkaline lyes for several days, washing it clean, and spreading it upon the grass for some weeks. The steeping in alkaline lyes, called bucking, and the bleaching on the grass, called crofting, were repeated alternately for five or six times. The cloth was then steeped for some days in sour milk, washed clean, and crofted. These processes were repeated, diminishing every time the strength of the alkaline lye, till the linen had acquired the requisite whiteness.
For the first improvement in this tedious process, which was faithfully copied from the Dutch bleachfields, manu-facturers were indebted to Dr Francis Home of Edinburgh, to whom the Board of Trustees paid £100 for his experi-ments in bleaching. He proposed to substitute water acidulated with sulphuric acid for the sour milk previously employed, a suggestion made in consequence of the new mode of preparing sulphuric acid, contrived some time before by Dr Roebuck, which reduced the price of that acid to less than one-third of what it had formerly been. When this change was first adopted by the bleachers, there was the same outcry against its corrosive effects as arose when chlorine was substituted for crofting. A great advantage was found to result from the use of sulphuric acid, which was that a souring with sulphuric acid required at the longest only twenty-four hours, and often not more than twelve; whereas, when sour milk was employed, six weeks, or even two months, were requisite, according to the state of the weather. In consequence of this improve-ment, the process of bleaching was shortened from eight months to four, which enabled the merchant to dispose of his goods so much the sooner, and consequently to trade with less capital.
No further modification of consequence was introduced in the art till the year 1787, when a most important change was initiated by the use of chlorine, an element which had been discovered by Scheele in Sweden about thirteen years before. Berthollet repeated the experiments of Scheele in 1785, and by the prosecution of further investigations he added considerably to the facts already known. He showed that this substance (called by Scheele dephlogisti-cated muriatic acid) is a gas soluble in water, to which it gives a yellowish green colour, an astringent taste, and the peculiar smell by which the body is distinguished.
The property which this gas possesses of destroying vegetable colours, led Berthollet to suspect that it might be introduced with advantage into the art of bleaching, and that it would enable practical bleachers greatly to shorten their processes. In a paper on dephlogisticated muriatic acid, read before the Academy of Sciences at Paris in April 1785, and published in the Journal de Physique for May of the same year (vol. xxvi. p. 325), he mentions that he had tried the effect of the gas in bleaching cloth, and found that it answered perfectly. This idea is still further de-veloped in a paper on the same substance, published in the Journal de Physique for 1786. In 1786 he exhibited the experiment to Mr James Watt, who, immediately upon his return to England, commenced a practical examination of the subject, and was accordingly the person who first intro-duced the new method of bleaching into Great Britain. We find from Mr Watt's own testimony that chlorine was practically employed in the bleachfield of his father-in-law, Mr Macgregor, in the neighbourhood of Glasgow in March 1787. Shortly thereafter the method was introduced at Aberdeen by Messrs Gordon, Barron, and Co., on informa-tion received from M. de Saussure through Professor Copland of Aberdeen. Mr Thomas Henry of Manchester was the first to bleach with chlorine in the Lancashire dis-trict, and to his independent investigations several of the early improvements in the application of the material were due.
No very great amount of success, however, attended the efforts to utilize chlorine in bleaching operations till the subject was taken up by Mr Tennant of Glasgow. He, after a great deal of most laborious and acute investigation, hit upon a method of making a saturated liquid of chloride of lime, which was found to answer perfectly all the pur-poses of the bleacher. This was certainly a most important improvement, without which, the prodigious extent of business carried on by some bleachers could not possibly have been transacted. Such was the acceleration of pro-cesses effected by the new method that, it is stated, a bleacher in Lancashire received 1400 pieces of gray muslin on a Tuesday, which on the Thursday immediately following were returned bleached to the manufacturers, at the dis-tance of sixteen miles, and were packed up and sent off on that very day to a foreign market.
In the year 1798 Mr Tennant took out a patent for his new invention, and offered the use of it to practical bleachers, for a fair and reasonable portion of the savings made by its substitution for potash, then in general use. Many of the bleachers, however, used it without paying him, and a com! nation was formed to resist the right of the patentee. In December 1802, an action for damages was brought against Messrs Slater and Varley, nominally the defendants, but who, in fact, were backed and supported by a combination of almost all the bleachers in Lancashire. In consequence of this action, the patent right was set aside by the verdict of a jury and the decision of Lord Ellenborough, who used very strong language against the patentee. The grounds of this decision were, that the patent included a mode of bucking with quicklime and water, which was not a new invention. It was decided that, because one part of the patent was not new, therefore the whole must be set aside. Lime was indeed used previous to the patent of Mr Tennant; but it was employed in a quite different manner from his, and he would have allowed the bleachers to continue their peculiar method without any objection, because it would have been pro-ductive of no injury to his emolument.
In consequence of this decision the use of liquid chloride of lime in bleaching was thrown open to all, and speedily came to be universally employed by the bleachers in Britain. Mr Tennant, thus deprived of the fruits of several years of anxious and laborious investigation, advanced a step farther, to what may be considered as the completion of the new method. This consisted in impregnating quicklime in a dry state with chlorine, an idea originally suggested by Mr Charles M'Intosh of Cross-Basket, then a partner with Messrs Tennant and Knox. A patent for this was taken out on the 13th of April 1799, and ha began his manufacture of solid chloride of lime at first upon a small scale, which has ever since been gradually extending, and the manufactory is now the largest of the kind in Great Britain.
The various processes for the preparation of the so-called chloride of lime, or bleaching-powder, as conducted at the present day, and its other applications in arts, will be found described under the head of CHLORINE.
BLEACHING OF COTTON.
Of the two great staples, cotton and linen, to the whitening of which the art of the bleacher is directed, cotton is the more easily and expeditiously bleached. The basis of all vegetable fibres is cellulose or ligneous tissue, a pure white substance, and it is to obtain this body in a state of purity, free from the resinous matter naturally associated with it as well as from adventitious impurities imparted in the process of spinning and weaving, that is the object of bleaching. The operations, although appa-rently complex and numerous, are essentially simple, though frequently repeated, and the greatest variety of detail is connected with the finishing of cloth, which is in reality a separate industry, frequently conducted in distinct estab-lishments under the name of calendering and finishing works. Bleaching proper resolves itself into washing with suitable detergents, and subjecting the washed material to the influence of chlorine, whereby the colouring matter either belonging to the fibre or imparted to it is oxidized and discharged.
The general arrangements of a bleach-house will be made plain from the ground-plan (fig. 1). The various pieces
FIG. 1.Ground-Plan of Bleach-House
of apparatus, the positions of which are there indicated, will be described in connection with the sequence of opera-tions through which the cloth passes in the process of bleaching. In the best arranged works, it should be mentioned, where power is required to work any machine, it is generally supplied by a separate engine attached to the machine itself, instead of by gearing carried from one engine for all the machinery. For this plan, as well as for 1 the greater portion of the illustrations which follow, we are indebted to Mr William Mather, of the eminent firm of Mather and Piatt, Salford, to whom we are also under obligation for much valuable practical information. We have also to express our indebtedness to Mr Alexander Cram of Thornliebank, for the fullest access to the impor-tant works of his firm, and for the cordial assistance afforded by the managers of its various departments.
The sequence of operations in the bleaching and finishing of calico has undergone no change in its general details since the bleachinf;-powder process was first introduced; but the mechanical arrangements by which the operations are conducted have been the subject of frequent improvements. The ingenuity of engineers and bleachers has been chiefly directed towards the decreasing of manual labour, economy of fuel and materials, and the rapid completion of the various processes. The application of factory legislation to bleach-works by the Bleaching and Dyeing Works Act of 1860, by imposing a necessity for regular and stated hours of work, still further stimulated the production of apparatus and arrangements for prompt and certain completion of the various operations. Consequently a great part of the old machinery and arrangements of a bleach-house have now disappeared, and the processes are carried on in a continuous series of operations by machinery and appliances to a large extent self-acting^' Formerly each piece of goods was separately treated and carried by hand or on barrows from one stage to the next; now the pieces are sewn end to end, as many as 1000 pieces, measuring perhaps 20 miles, being operated on in one stretch
As various pieces of old machinery are yet in use for certain kinds of work, it has been considered desirable to give descriptions and figures of some of them, and these, at the same time, will serve the further purpose of indicating the nature of the mechanical improvements which have been carried out, in recent years, in bleaching establishments.
The important and frequently repeated operation of washing was formerly conducted either at the wash-stocks or washing-mill or in the dash-wheel. The wash-stocks, which
are yet in use in many large works, especially where linen is the bleacher's staple, consists of a trough or box for holding the goods to be washed, through which a constant stream of water is passing. A pair or more of heavy hammer-headed wooden beams, hung by long shafts, and playing into the trough, are alternately tilted against the cloth, causing the water by their momentum to work through and squirt out of the mass. This process of washing is rather tedious, occupying on an average about half an hour, and requiring besides a great amount of manual labour. The dash-wheel (fig. 2) is a cylindrical box revolving on its axis. It has four divisions, as shown by the dotted lines, and an opening into each division. A number of pieces are put into each, abundance of water is admitted behind, and the knocking of the pieces as they
Era. 2.-Section of a Dash-Wheel.
alternately dash from one side of the division to the other during the revolution of the wheel effects the washing. The process lasts from four to six minutes. The dash-wheel is used to the present day in the bleaching of curtain materials and fine muslins. In nothing have greater im-provements been effected than in the arrangement of the kiers or vessels in which the cloth is boiled or " bowked" An old form of kier is seen in fig. 3. It consisted of a cylindrical vessel AA, 9 feet wide, of wood or iron, having a false bot-tom BB, on which the goods were placed, about 6 inches from the real one. A small A pipe E, in the cen-tre of a frider one CC, conveyed the steam from the steam - boiler. When the liquid boiled at the bottom, where the steam issued, the steam forced its way up the pipe CC, carrying with it a quan-tity of the lye, which was thrown back by the small cover D, spreading itself over the surface of the goods, and filter-ing through them into the space below the false bottom, where it was again heated by the steam, reascended the pipe CC, and so on in constant succession, till the boil-ing was completed. FF is a wooden cover which prevented the cooling of the materials below a boiling heat.
The bleaching of common calico is divided into two branches1st, print bleaching, in the case of which the goods are bleached as a preliminary to the process of calico printing; and 2d, white bleaching, which applies to goods to be finished white or unprinted. The processes differ in some of their details, as in white bleaching it is only necessary to satisfy trie eye, whereas in print-bleaching the material must be rendered chemically pure, otherwise the colours in the subsequent printing process would be dull and blotchy. The print bleaching must therefore be more thoroughly done than the other ; but as the processes are generally the same, it will be sufficient to indicate the points of difference in the various stages through which the material in both cases passes. A process preliminary to bleaching is
Singeing.Gray calico as received from the looms is generally in lengths of 37£ and 50 yards. A large number of these, sometimes as many as 1000, measuring more than 20 miles in length, are sewn into a continuous web. At the extremities of each owner's lengths, the name of the firm, or some distinguishing mark, is either stamped on in tar, or marked by means of coloured threads. These long lengths are then submitted to the operation of singe-ing, which lias for its object the removal of the downy pile and short threads from the surface of the cloth, which would interfere with the appearance of finished white goods, and with the uniformity and sharpness of patterns in the case of prints. Several methods of accomplishing this have been employed, but that most commonly used is the system of plate singeing illustrated in fig. 4. A pair of
FlQ. 4.Section of Singe-Stove.
singe-plates, a and 6, made of thick bent sheets of copper, are mounted over the flues of a fire sufficient to raise a white heat. The plate 6 is most highly heated, a being at the end of the flue furthest removed from the fire. The cloth enters over a rail a, and in passing over the plate a is thoroughly dried and prepared for the singeing it receives when it comes to the highly-heated plate 6. A block d, carrying two rails in the space between the plates, can be raised or lowered at pleasure so as to increase or lessen the pressure of the cloth against the plates, or, if necessary, to lift it quite free of contact with them. The system of plate singeing is found generally sufficient in practice, but the caking of paste and dirt on the plates from the cloth as it passes over them, and variations in the heat of the plates, often lead to irregularities in singeing. A combination of plate and gas singeing is frequently employed to over-come the deficiencies of plate singeing alone. In this case the cloth is passed first over an ordinary plate, and then on to another, along the ridge of which is a long narrow slit, which allows the issue of a gas flame produced from coke burning immediately under it. By this means long loose threads are more effectually burned off than in plate singeing, and a more uniform heat is applied to the gray cloth. Fig. 5 is a sectional view of a very efficient singe-ing apparatus introduced by Messrs Mather and Piatt. The figure represents the first half of the machine, the second portion being precisely similar in arrangement.r The singeing in this case is accomplished by the burning of a mixture of coal-gas and atmospheric air admitted by a pipe intense heat and a blue smokeless flame. The cloth is carried by a series of rollers to the gas jets, and in passing over the rollers c, c, c, c the one side of the cloth impinges laterally four times against the flame, which is never permitted to pass through the fabric, but only shaves its surface. The back is thus singed in the first portion of the apparatus, and being turned over on roller d it is carried forward to another pair of jets, where, being thoroughly dry, the face side of the cloth is completely singed by going over exactly the same course through which the back is carried in the first part. By an arrange-ment not shown in the illustration, the attendant of the machine can instantaneously lower the gas burners by a treadle movement in case of any stoppage or accident, and thus prevent the cloth from being burned. With a proper pressure of gas this machine singes at the rate of 60 yards per minute.
At this stage the cloth has now in addition to the brown coloured incrusting substance and the resinous material proper to the fibre, a dark-coloured carbonized surface, caused by the singeing process, the weaver's paste or dressing, tallow or other fat introduced in the pro-cess of weaving, and the accumulation of dirt which the handling of weavers and others may have produced. The object of the subsequent processes is to wash out the mechanical impurities and resinous substances from the cloth, to render soluble by chemical agencies such as are otherwise insoluble in water, and to oxidize the colour-ing matter of the cotton by the chloride of lime as already explained.
Liming.In some cases it is the practice immediately after singeing to steep the pieces in water and pile them up wet for a night, in order to loosen and partly ferment the weaver's paste, which is then in large part removed by washing in a machine to be subsequently described. The " gray-backs " which have been used in calico-printing have always to be thus steeped, and at one time it was the practice to leave the cloth so long in this steep that it acquired a most offensive odour. This preliminary steeping and washing facilitates the percolation of the liquor through the fabric in the process of boiling, but notwithstanding this advantage it is generally dispensed with, and the goods pass direct from the singeing to the liming process. The pieces are formed into a loose coil or rope by being passed through circular rings of glass or pottery called " pot-eyes," and worked up and down several times in a strong milk of lime, in order that the whole may be uniformly and thoroughly impregnated. The arrangement for liming will be understood from fig. 6, which is a sectional view of a " squeezer," an apparatus used repeatedly in subsequent operations as well as in this of liming. The cloth passes up and down as indicated by the arrows, dipping several times into the solution, and before passing finally on to the kiers for boiling it is slightly " nipped " between the "bowk" of the squeezer to extract superfluous moisture. These bowls are thick cylinders of wood, usually in this case made of beech. From the lime squeezer the cloth is carried over winches, and guided through pot-eyes into the kiers.
Flu. 6.Section of Lime Squeezer.
Bowking.A bowking kier is an apparatus in which the cloth is boiled. To one old form of kier allusion has already been made. Bowking is now mostly accomplished in closed kiers worked up to a considerable pressure of steam. In the boiling for white bleaching about 80 & of lime are required for 2700 B> of cloth, and the boiling is continued for ten hours at a pressure of about 30 lb. A form of kier very generally employed consists of a strong vessel made of boiler plate, with a man-hole in the upper part, which can be screwed tightly down. The vessel is about 10 feet in depth, and 5 or 6 feet in diameter, and has a false bottom made of a gird of wood or iron, on which the lowest layer of cloth rests. Up the centre of the kier passes a pipe or tube which reaches higher than the cloth can be piled, and is surmounted by an umbrella-shaped plate. Steam is admitted at the lower part of the kier,
FIG. 7.Taylor's Circulating Keir.
and as the pressure accumulates it gradually forces the liquor upwards through the central pipe till, by-and-by, it in daahed with great violence against the umbrella-shaped plate, and thrown over the upper surface of the cloth. It gradually percolates down through the cloth to the bottom, where it is again caught and forced up through the central pipe, and thus a constant circulation is maintained. A very efficient circulating kier, the invention of Mr Taylor of Berchvale, has recently been introduced, of which a sectional representation is given in fig. 7. This kier in outline is like the previous, but it has no central distribut-ing pipe. Instead, the liquor is carried by an external pipe to the top of the kier, where it enters and is forcibly thrown against the surface of the cloth. The kier A has a false bottom B as in the previous case, and when filled with cloth and liquor, the liquor percolates by a pipe C into the receiver D, where it finds its own level in the ascending pipe E. Steam is admitted at the lower part of the receiver by the steam-pipe F, and forces the liquor upwards through the pipe E to the top of the kier. The vacuum created in the receiver is supplied from the lower part of the kier, and the flow is facilitated by the pressure of steam from above, and thus a constant steady circulation is maintained. This kier is very useful in cases where a comparatively low pressure is desirable, as in white bleaching, where the coloured headings of the cloth (Turkey red or other coloured threads introduced at the end of a web) have to be preserved
The bowking apparatus generally used by printers is Barlow's high-pressure kiers, an arrangement in which the kiers are worked in pairs. A pair is shown in fig. 8, one
Fia. 8.Barlow's High-Pressure Keirs.
being seen in section; the dimensions of the vessels are inserted in the figure.
The novelty these kiers introduced when first brought out, was that in using steam of 40 lb instead of 5 lb, » greater economy of time and drugs would be effected. Their world-wide application has proved that the inventor's theory has found ample confirmation. The cloth is carried or rather drawn by winches, and dropped into the wrought iron boilers or kiers AA', through the man-holes in the top, two pieces in all cases running side by side. As the pieces are delivered continuously in the kiers, a lad in each spreads a pile of the cloth all round the kier, as equally as possible, so that, when full, the kier shall be packed uniformly to the top. This cloth rests on what is termed a false bottom, simply a grid or plate with holes in it, as shown at B. Upon the grid are generally placed a few smooth stones, through the spaces between which the liquor drains from the cloth.
Down the centre of the kier is a pipe C, perforated with holes, for the purpose of distributing the liquor freely into the mass of cloth. The kiers are connected by a pipe D, leading from the bot-tom of one to the top of the other, and vice versa. The steam is introduced through the valves EE'. After the kiers are filled with cloth, each holding about 6000 lb, the man-hole lids are screwed down and all made steam tight. A little steam is then turned OE to discharge the air from the cloth, which escapes through the pipes FF'. This steam, moreover, gradually warms the goods. The alka-line liquor or lime water, having been mixed to the proper strength, is then let into the kier A, through the tap 6, until the necessary quantity has been supplied, about 20 gallons of caustic soda at 70° Tw., and 400 ft> lime for the full charge being U3ed. The steam is then turned on slowly, and by its pressure the liquor in kier A is made to pass with great force through the cloth, and then up the
ipe D, through the 3-way valve, into the kier A'. When all the quor has passed over, the steam valve E' is reversed, steam is shut off from A, communication is opened to pipe D', and valve E' turned so as to admit steam to A', when the action of forcing the liquor through the cloth up the pipe E' into kier A is performed. This alternate passing of the liquor backwards and forwards, see-saw fashion, through the cloth, constitutes the operation of boiling. The steam also has great effect if left in contact with the cloth for a few minutes in one kier, after the liquor has gone over to the other kier. This process is continued for eight hours (nearly one-third the time formerly required in what are termed low-pressure kiers), with steam of from 30 to 50 lb, during which time the liquor passes about 16 times from one kier to the other ; then the valves HH' are opened, and all the liquor expelled by the steam from the cloth into a drain. The steam is then shut off, the man-hole lids removed, and the ends of the two chains of cloth taken out and passed through pot eyes, which guide the pieces to the washing-machine.
Washing.The cloth as it issues from the kiers is found to have assumed a very dirty brown aspect. Formerly, the apparatus used for washing was either the wash-stocks or the dash-wheel, to which allusion has already been made. The machine now generally employed is represented in section in fig. 9. It consists of a pair of wooden bowls
FlG. 9.Section of Washing-Machine.
or cylinders a and 6, about 9 feet long, mounted in a strong framework, and arranged to press against each other in their revolution. Plane tree is the wood most suitable for making these bowls. Running underneath the whole length of the bowls is a box or trough e filled with water, near the bottom of which a rectangular roller d is fixed. The water in the box is constantly renewed during washing operations by a current flowing in at the middle and escaping at each end Two chains of cloth are washed in this machine at the same time, one being introduced at each extremity of the roller. The cloth passes down into the water under the roller d and up to the wooden bowls, between which it is caught and nipped, and down again into the water, working its way in a spiral manner from the end to the centre of the machine, passing nine times through the water and between the bowls in its progress. Its course inwards is guided by a strong wooden rail, from which pegs project, arranged according to the number of turns to be given to the cloth. In the centre part of the upper bowl there is a lapping of cotton rope, which projects a little above the surface of the wood, and serves to give the cloth, as it finally issues from the machine, a much stronger squeeze than it would obtain between the long even bowls, and thereby expels a large proportion of mois-ture. As the cloth travels inwards towards the centre of the trough, while the flow of water is outward to escape at each end, the cloth on each revolution is meeting water more nearly pure, till just at the point where it issues from the trough for the last time, the clean water entering the trough is powerfully spurted upon it, thus giving it a thorough rinse before it is finally squeezed. It is usual to pass the cloth from the lime boil either through a pair of such washing-machines, or twice through the same, in order to expel the last trace of calcareous soap and uncombined lime from the texture.
In addition to this machine various other devices have from time to time been proposed and introduced to perform the important operations of washing. Among these the continuous washer of Mr Henry Bridson of Bolton-le-Moors, Lancashire, patented in 1852, is deserving of notice as a simple and efficient washing-machine. Mr Bridson's washer consists of an oblong tank or trough of cast-iron which, in use, is kept about half filled with water. Within this tank, just dipping into the water, two cross shafts are fixed, which are geared to revolve in the same direction by spur-gearing mounted outside the trough Each shaft carries a pair of discs of large diameter, and between the discs of the two shafts a pair of bars placed diametrically opposite each other are mounted. These bars form flat winces or revolving frames, by the revolu-tion of which the fabric is not only carried forward, but is in its progress caused to strike with great violence against the surface of the water. The intermittent flapping and shaking motion thus communicated to the material has a powerful effect in detaching adhering impurities from the cloth. Another form of washing-machine in use in Lancashire consists of a row of eight vats or troughs arranged in an ascending series, so that the overflow of water from the highest or last runs into the second highest, and so downwards till it escapes from the lowest or first. The cloth enters at the lowest trough, and is carried by guide-rollers up and down through the entire series, issuing at the top between a pair of squeezing rollers.
Gray Sour.From the washing-machine the chain of cloth is passed through a pair of squeezers, by which a large proportion of moisture is expelled. The operation of souring, which comes next, is performed in an apparatus of the same construction as the washing-machine, the trough under which contains the souring liquor. For white bleaching a solution of hydrochloric acid of a strength of 2° Twaddle (sp. gr. 1010) is used, and for print bleaching the solution is made up to 4° Tw. Through this the cloth is passed up and down twice by the revolution of the bowls, and piled up in the sour in stillages for some hours. The object of the souring is to dissolve any traces of free lime which may have been left in the washing, and to decompose the calcareous soap.
Second Boil.After having lain in the sour for a sufficient length of time the cloth is passed through squeezers to expel as much as possible of the acid, and again washed in the machine. It is next passed into a kier or set of kiers, precisely as after liming, for the second boil, which in the case of print bleaching is done with a solution of soda-ash and rosin. For a pair of Barlow kiers boiling 12,000 lb of cloth, the quantities used are 350 lb of soda-ash and 200 H> of rosin dissolved with 30 gallons of caustic soda at 70° Tw. The boiling is carried on for ten hours, in a like manner and at the same pressure as in the case of the lime boiling. The soda-ash and rosin form a soap, which dissolves out the free fatty acid in the cloth, and acts on the calcareous soap remaining by forming carbonate of lime and a soluble soda soap. In the white bleaching of 2700 fi> of cloth, the boiling solution is 8 gallons of caustic soda at 70° Tw., but by some bleachers soda-ash is employed in the proportion of 80 & to 2700 lb of cloth. From this boil the cloth is passed on to the washing-machine, and then squeezed, when it is ready for "chemicking" with the bleaching-powder solution.
Chemicking.When the previous processes have been efficiently carried out, the cloth will, at this point, have attained a considerable appearance of whiteness and purity; The " chemicking" or liquoring with bleaching-powder which it now undergoes is conducted in a similar manner to the souring already described. The chemick is used as weak as possible, the solution varying from \° to J° Tw. (sp. gr. 1'000625 to 1-00125) according to the weight and condition of the cloth under treatment. It is run through this liquor, gently squeezed, and piled up for four or six hours. It is then squeezed and washed; and at this stage the bleacher has to judge whether the cloth requires to be chemicked a second time, which, in the case of heavy goods, is frequently necessary. If a repetition of the process is required, the cloth is again passed into the kiers, boiled with a solution of soda-ash, and the other processes repeated as before.
White Sour.After lying in the chemick the goods are again washed and squeezed, and afterwards soured in machine with sulphuric acid, used at a strength of about 4° Tw. (sp. gr. 1 -020), and piled up for a period of at least three hours. Thereafter, in order thoroughly to expel all acid the goods are twice washed, and finally squeezed, which concludes the operation of bleaching proper. The calico should now present a snow-white aspect, and should be fit to take the most delicate shades of colour when it is to be used for printing purposes.
Opening.In passing through the numerous processes detailed in the foregoing statement, the cloth has been always in the form of a coil or loose rope. In the drawing from one machine to another it has been also pulled some-what to the length at the expense of breadth, and in places it is likely to have become a little twisted. The pieces have therefore now to be opened out to their full width, and, if necessary, evened. The opening.out is effected by passing the pieces to a winch placed at a considerable height when the weight of the cloth itself in passing upwards unfolds it, and the selvedges are caught and extended by a boy just before it passes on to the winch. When necessary it is caught beyond the winch by an opening-machine, such as that patented in 1871 by Mr Wm. Birch of Salford. It is a complex apparatus, working by endless bands, on which are toothed projections, and these, travelling from the centre to the sides in opposite directions, open and spread out the cloth before it passes over the roller which is mounted on the machine. From the opener the cloth passes at once to the drying-machine (hereafter described), after passing over which cloth intended for printing is folded or batched on rollers, and its further treatment belongs to the art of calico-printing.
Finishing.So far as regards bleaching proper the pro-cess is now at an end, and the further operations which white calicoes undergo have only for their object the improvement of their appearance for the market. But although the finishing adds in no way to the quality of the material, it is regarded as of great value by the merchants, and the finish of a bleacher is of more importance than his bleaching. A great variety of finishing operations have to be employed, according to the different qualities of textiles, and the purposes to which they are devoted. Finishes are " beetled," "calendered" (either "stiff," "medium," or "soft,"or "glazed,") and,fordress muslins,<fec, "elastic." As the processes and appliances for these finishing operations are very numerous and varied, they cannot here be described in detail. In most cases they are the same as used in the finishing of calico prints, and more information will be found under that head. We shall here confine our remarks chiefly to the finishing of ordinary white beetled calicoes.
Water Mangle.The cloth, when brought into the finish-ing-room, is passed over a stretching rail into a trough of boiling water and between a series of calender rollers, in which it is powerfully pressed. A common arrangement of the cylinders of the water mangle is to have a series of four, two of small diameter being made of copper, and two larger of condensed cotton ; but wooden bowls are also sometimes employed with only a single intermediate copper cylinder. By this mangling process the water is equalized throughout the whole piece, the threads are flattened, and the cloth stretched, smoothed, and wound upon a roller, and thus rendered fit for receiving the starch.
Starching.It is in this stage that so much is done by some bleachers to give cloth a factitious appearance of weight and bulk by filling up the interstices between the fibres with compounds which have no other object than to please or deceive the eye, and some of which have a decidedly deleterious influence on the tissue they are intended to improve in appearance. A great variety of mixtures, both cheap and nasty, are used by some finishers in place of starch with a view to produce weight and appearance, but, naturally, as little information as pos-sible on this point is permitted to leak out to the public What ought to be, and by reputable bleachers really is, used is pure starch, either of Indian corn or wheat, or both, made up into a stiff mucilage and blued with ultramarine or indigo. The cloth passes over a stretching rail into a trough of this starch, in which a roller is mounted. As it comes out of the starch it is caught between a pair of bowls, by which the superfluous starch is squeezed out and thrown back into the trough, the cloth passing on to the drying machine. The starching mangle and drying-machine are seen together in fig. 10
Drying.The drying-machine (fig. 10), consists of a
Fig. 10.Starching Mangle and Drying Cans.
number of cylinders made of tinned iron or copper, and filled with steam, of low pressure. The cloth passes alter-nately back and face over one and the other, and emerges to be placed down at the end perfectly dry. This system of drying was introduced among the first mechanical appli-ances used in cahco-printing, and has not as yet been superseded by any other plan. Various improvements in detail, we learn from Mr William Mather, as to the con-struction of the cylinders and the mode of applying steam to them have been recently introduced, but the machine remains the same. One important defect has been recently removed by an alteration in the construction of the cylinders, to prevent collapse, in case a vacuum were formed by the rapid condensation of the steam. A spiral rib or stay is made to run from end to end of the body of the cylinder, giving support uniformly the whole length, and serving at the same time as a screw to drive the condensed water, as the cylinder revolves, to one end, where it is ejected through a nozzle. The steam enters at a nozzle, from the framing which is cast hollow, and serves as a pipe to distribute the steam to all the cylin-ders in the machine, while the framing on the other side serves in like manner to receive and discharge the water.
Damping.From the drying cans the cloth is passed on to the damping-machine, where it is uniformly moistened by an exceedingly fine spray of water thrown upon it. The spray is thrown up by a circular brush, the tips of which are allowed to dip into water in a trough over which it revolves. Mather and Piatt have introduced a manifest improvement on this plan by throwing the water in fine jets on the brush from a pipe which runs parallel with it. By this means the quantity of water and degree of moisture can be regulated with the utmost nicety. Fig. 11 shows the damping-machine in section as modified by an iron or wooden beam e, when it is ready for the process of beetling. When goods are to be finished of any parti-cular width, they are at this stage breadthened by such an apparatus as the belt-stretching machine of Mather and Piatt shown in elevation in fig. 12 and in plan in fig, 13. In Mather and Piatt, a represents the circular brush revolv-ing in a trough, and 6 is the pipe from which the water is squirted on the brush. The spray from the brush is confined by two sloping boards c, c, which work on quadrants, and the lever d raises or depresses the brush at
FIG. 12.Elevation of Belt-Stretching Machine.
pleasure. The course of the cloth over the machine is indicated by arrows, and after damping it is batched on this machine the full width of the cloth is obtained by the selvedges being held firmly by a belt and pulley on each side, the pulleys revolving at such an angle that the stretch on the cloth has to compensate for the difference in distance between these pulleys at A and B.
Beetling.The beetles ordinarily employed are a series of long heavy wooden piles arranged in a frame. These piles are alternately raised and allowed to fall with their full weight against the beamed cloth by the revolution of a. roller having a spiral series of notches, which catch a corresponding range of projections on the piles. The beam with the cloth is made to revolve gently by a ratchet motion as it is submitted to this hammering, which goes on for two or three hours. Recently Mr John Patterson of Belfast has patented and introduced a form of beetling-machine (fig. 14), which from its highly effective action
FIG. 14.Patterson's Patent Beetle.
is likely to come into very extensive use. The advantages claimed for his machine over the common beetle Mr Patterson thus states : " Heretofore, the beetling of textile fabrics has been done by means of beetles, or stampers, falling upon the fabric by the action of gravitation, each stamper or beetle falling 55 or 60 times per minute through a space of 13 to 15 inches. This rate of speed cannot be accelerated by gravitation, and the consequence has been that in order to increase the quantity of work done by the ordinary beetles, very bulky and massive machinery has been employed, requiring large and expensive buildings and driving gear. The new beetling-machine requires not one-tenth of the space, very much lighter gearing, and instead of making 60 blows per minute, each beetle makes from 420 to 500 blows per minute. The blows are not by the action of gravitation, but are actuated by a series of cranks cut upon a solid steel shaft. There are connecting rods from the steel cranks to semicircular springs. The beetles are attached to, or suspended between, the points of the semicircular springs by means of leather straps. When the crank shaft is set in motion the beetles are snatched up in regular sequence by the upward motion of the cranks, and the springs are compressed by the weight of the beetles, as in fig. 15, and by the combined upward motion of the cranks and the springs the beetle is thrown upwards with great impetus. The upward motion is stopped as the cranks pass the top centres, and the beetles are thus met by the springs and thrown violently into them, causing them to be again compressed, as in fig. 16.
Hammers of Patterson's Beetle.
When by the downward motion of the cranks the springs are allowed to throw the beetles on the cloth beam, a rapid forcible whipping blow is imparted to the cloth, which does not cut or injure it in the manner often done by the slow dropping blows of the ordinary beetles. The weight of the blows can be instantly varied by varying the speed of the crank shaft, from the slightest touch to the heaviest penetrating blow. It is found that twice or thrice the number of folds of cloth can be beetled effectively on the cloth beams more than can be done on ordinary beetles, that is, instead of 200 folds on the beam, 400 or 600 folds can be equally well beetled on the new machine."
Calendering.When it is desired to finish cloth with a stiff or with a glazed finish, instead of being submitted to the operation of beetling, it is finished in the calender. The calender, as its name icvXivSpos implies, is a series of cylinders mounted above each other in a strong frame-work. The number of cylinders and the material of which they are constructed vary. In some only three cylinders or bowls are employed, and in others they are four or five. One or two of the bowls are made of metal, and two or three are either of wood, of condensed cotton, or of paper, and they must always be turned with great accuracy and be free from all warping. Cylinders of paper or con-densed cotton have a very smooth surface and a consider-able amount of elasticity. Between these cylinders the cloth as it comes from the damping-machine is passed, and twice, thrice, or four times, according to the construction of the calender, it is powerfully pressed. The pressure gives the cloth a very even surface, condensing the fibres, and produces a shining lustre. When the cloth is submitted to friction, as well as to pressure in a heated calender, a glazed finish is produced. The frictional effect is produced by the cylinders being geared to move at different rates of rapidity, so that in their revolution they rub over the sur-faces of each other in addition to communicating pressure. Fig. 17 shows a finishing or friction calender in section. The metal cylinder a is made hollow so that it may be heated by the introduction of steam or gas, h and d are of compressed cotton or paper of the same diameter as a, and c is a smaller metal cylinder. The pressure of the cylinders is regulated by means of the screw e, and the compound lever /, which is adjusted by the double screw on the connecting rod at g. The cloth enters over stretching rails and rollers, passes through the calender in the manner indicated by the arrows, and is batched on roller L
Mastic Finish.This particular kind of finish is applied to muslins and similar thin fabrics, and has to be done in highly-heated apartments called stentering stoves. Formerly the work was entirely done by manual labour, and con-sisted in holding the fabric by the selvedges, and pulling it forward and backward while it was drying in the heated air. In this way the threads were made to rub against each other, and the cloth was thus deprived of the hard, stiff board-like appearance it would have possessed if left motionless when drying. Mr Ridgway Bridson was the first who introduced a machine which successfully supplanted hand labour in producing the elastic finish in muslins. His stentering frame is thus described:Two horizontal rails or frames extend side by side the whole length of the machine, carrying at each end a large wheel or pulley, with small pins fixed at equal distances in its periphery. These pins pass through corresponding holes in an endless band which passes round the pulleys. On the surface of the endless bands are fastened very fine needle or tenter points to hold the selvedges of the fabric as it passes through the machine. The horizontal rails can be moved away from each other laterally, so as to stretch the fabric breadthwise. The rails are of equal length with the fabric to be treated, which is fastened by the selvedges at one end to the centre pins, and the pulleys being set in motion, the entire piece is carried on and stretched out over the machine, and the rails are then moved outwards to breadthen the fabric. The elastic finish is given by communicating alternate vibrating motions to the two rails, by which a diagonal stretching is given to the muslin while in the process of drying.
At the conclusion of any of these various finishing processes, the goods are folded either in a plaiting-machine or by girls hooking plaits of definite length by the selvedges on steel spikes. The end of each separate piece is then stamped with some device or motto intended to serve as a trade-mark. After the goods have been regularly folded, they are placed piece by piece, separated by sheets of pasteboard, in a Bramah press, and after a certain interval an iron plate is substituted for tbe pasteboard, to prevent any inequality in the pile. Finally, the folded pieces are prepared for the market by fastening a band of gilt and ornamented paper around each end, which with the imprinted device is in some way regarded as a guarantee of good quality.
The whole operations of bleaching and finishing occupy on an average eight days, although goods can be hurried through much quicker if occasion arises. The cost, which of course will vary with the price of fuel and other circum-stances, is very small as compared with the value of the material, and does not on an average, for shirting calicoes and the like, exceed l|d. per lb weight of cloth.
BLEACHING OF THREAD.
We have been favoured by Messrs J. and P. Coats of Paisley with the following outline of the processes in the bleaching of thread :
1. The various N03. of thread are prepared before boiling.
2. The first boil. The kier used is a common vomiter, into which are put water and a solution of caustic lye,the proportions being regulated by the number of pounds of thread to be treated.
3. The first bleach. The thread is placed in a box, and a sieve let down upon it. Underneath the box is a well which is filled with water and chlorine. The liquor is drawn up by a pump, and thrown upon the sieve, through which it passes, and filters through the thread into the well.
4. The thread is next moved into a souring-box, also covered with a sieve, where it is washed to take out the chlorine of the pre-vious process.
5. A souring-well under the souring-box is now filled with water and sulpliurio acid, and this mixture, called the sour, is pumped up on the sieve over the souring-box, through which it runs back into the souring-well, in the same manner as described in process No3.
6. Before removing the thread from the souring-box it is washed with water through the sieve.
7. It is next washed in a washing-machine.
8. The scald, or second boil in kier. Various mixtures are used
for it. Some prefer black soap and crystals of soda; others use
9-13. Repetition of N03. 3, 4, 5, 6, and 7.
14. The thread is now extracted, i.e., dried in hydro-extractors.
15. Stocking. The stocks are boxes about 3 ft. long, by 2 ft.
wide, and 2 ft. deep, with a large wooden mallet hung in each,
similar to those used in bleaching linen. The thread hanks having
been properly prepared, so that they will not get loose, are put into
the stocks with a mixture of hot soap and water, and beat there till
of the proper colour. It is then taken out, and
16. "Washed in washing-machine, and
18. The blueing process is done in a box filled with a solution of
water and extract of indigo. As much thread is put in as the box
will contain. It is let stand for a time, after which it is taken out
and thrown on a barrow.
19. It is next taken to extractor and dried, and
20. Placed in the stove. After being a sufficient time there it is
21. Removed to cooling shed, where it is hung up to cool.
22. It is now taken to stretching-machine, where it is passed over hot rollers to take out the curl and moisture received in cool-ing shed.
23. Taken to warehouse, where Nos. are classed and made up in bundles.
BLEACHING OF LINEN.
The bleaching of linen is a much more tedious and difficult operation than the bleaching of cotton. The process of water-retting, or rotting, by which the fibre is separated from the woody portion of the stalk, lodges a large proportion of colouring matter in the fibre, with which it enters into very intimate combination. The amount of colouring matter which has thus to be dealt with in the bleaching of linen is very great, being as much as one-third of the entire weight of the fibre. In the early part of the century a great amount of public attention was given to a plan proposed by Mr James Lee for preparing flax fibre without the process of steeping or retting, by which it was affirmed that, among other advantages, it would only be necessary simply to wash, in soap, linen fabrics made from fibre so prepared, to render them pure and white. Mr Lee obtained a special Act of parliament allowing the specification of his patent to remain sealed for seven years, and his plans were entered into in a most full and laborious manner by the Irish Linen Board. After the expenditure of many thousands of pounds on his machines and experi-ments, the plan had to be entirely abandoned as a failure. More recently, Chevalier Claussen renewed the attempt to prepare flax without steeping, by breaking it by means of machinery, separating the refuse part of the stalk from it, and then by a chemical process splitting the hollow fibres, so as to reduce them to a soft cottony state fit for spinning by means of the cotton-spinning machinery. The fibre was proposed to be split by steeping the prepared flax in a solution of carbonate of soda, and then plunging it into dilute sulphuric acid. The sudden evolution of carbonic acid gas within the hollow tube of the flax was said to have the effect of splitting up the fibre and reducing it to fine flat threads possessing the felting properties of cotton. Sir Robert Kane, in his Report to the House of Com-mons, May 20, 1852, states that the whole process failed. The machinery for the beating and cleansing of the flax failed to separate it sufficiently from the refuse part of the stalk; and the chemical process for the splitting of the hollow tube only broke up small portions of the exposed ends, leaving the greater portion untouched Various other plans of preparing flax fibres without water or dew-retting have from time to time been proposed and patented, but hitherto none of them has stood, the test of extended practical operation. Till towards the end of last century the bleaching of linen both in the north of Ireland and Scotland was accomplished by bowking in cow's dung and souring with sour milk. In the year 1764 Dr James Ferguson of Belfast received a premium of £300 from the Irish Linen Board for the application of lime in the bleaching of linen. Notwithstanding this reward the use of lime in the bleaching of linen was for a long time after-wards forbidden in Ireland under statutory penalties, and so late as 1815 " Mr James Barklie, a respectable linen-bleacher of Linen Vale, near Keady, was prosecuted for using lime in the whitening of linens in his bleach-yard." The bleaching of linen to the present day is conducted much more in the primitive fashion of last cen-tury than is the practice with cotton-bleaching. Owing to the stiffness and inelasticity of flax fibres, a great part of the machinery used for cotton is not available for linen, and solutions of acid and bleaching-powder require to be used in a very dilute condition for linen fabrics, involving frequent repetitions of the various processes before a satisfactory white is produced. " Crofting," or exposure to the air on grass, is also very largely resorted to in the bleaching of linens, especially for plain shirting and sheeting, which necessitates the possession of very extensive grass parks in connection with works, and renders the pro-cess both tedious and subject to the influences of the weather. A large proportion of linen cloth is half-bleached or improved in the yarn before being woven, and it con-sequently requires less bleaching than that which comes in its original'" green " condition. The following is an outline of the two chief methods, with and without crofting, as pursued in the principal Scotch linen bleachfields at the present day:
I. WITHOUT CROFTING.
2. Boiled in open kier for about 6 hours.
3. Washed at washing-mill or stocks.
4. Soured with hydrochloric acid, and piled in sour for some hours.
5. Washed at stocks.
6. Boiled in soda-ash for 8 or 10 hours.
7. _____ boiled.
8. Liquored in chlorine solution and piled up.
10. Boiled in alkali for 6 or 7 hours.
11. Liquored in chlorine solution.
13. Soured with sulphuric acid.
When necessary the processes from 10 to 14 are repeated; whole processes occupy, on an average, four weeks.
II. WITH CROFTING.
== TABLE ==
BLEACHING OF PAPER-MAKING MATERIALS.
In addition to cotton and linen rags, esparto or Spanish grass (Macrochloa tenacissima) is now very largely used for the manufacture of the better classes of paper. Wood, especially the wood of the aspen (Populus tremula), is also now applied as a paper-making material Jute has been used for printing paper, and straw is very largely employed, but chiefly for brown and packing papers. These and the numerous other substances used for paper-making are all reduced to the condition of "half-stuff" before they come to undergo the operation of bleaching, and the treatment they receive in this stage varies only in the amount of whitening required, and consequently in the proportions of bleaching solution used. It is therefore unnecessary to notice more than the process followed in the bleaching of the " half-stuff," which in Great Britain is very frequently prepared from a mixture of esparto fibre and rags. The bleaching solution of chloride of lime is either prepared in specially constructed cisterns, fitted with revolving agitators and stored in a reservoir for use, or prepared for immediate use in a wooden vessel. When the solution is made up to the requisite strength, and all insoluble sediment has sunk to the bottom of the vessel, it is ready for pouring into the engine. Prom 4 to 10 B) of ordinary bleaching-powder are used for every 100 lb of rag half-stuff, but a much larger proportion is required for esparto. Sulphuric acid in not more than a proportion of 1 lb to 4 lb of bleaching-powder is thereafter added in a highly dilute condition, and the whole, after mixing in the engine, is turned into the drainer, which is a large tank provided with a false bottom of per forated wood covered with wire-netting or bagging. In some cases the bleaching-liquids are not added to the pulp material till it is deposited in the drainer; and the acid solution may be poured in first, or both solutions may be alternately used in small quantities. The bleaching process is sometimes carried on in separate engines constructed of materials not affected by the corrosive action of acid sub-stances. Drained half-stuff may also be bleached in a suitable apparatus by the direct application of chlorine gas.
It is of the greatest importance to free the pulpy material from the last traces of chlorine before it is made into paper, as it would react upon the manufactured product and render it brittle. To eliminate the free chlorine and acid, <fcc., the pulp is washed in the beater with pure water till it ceases to redden litmus paper, or give other characteristic indications of the presence of such compounds. The pre-judicial effects of chlorine and its combinations are also overcome by the addition of " antichlor," the hyposulphite of soda or of lime, which forms with them compounds that do not affect the colour of the paper, although it is desir-able, as far as possible, to remove such compounds also by washing with water.
BLEACHING OF STRAW.
The fine wheat-straw used in Tuscany and elsewhere for straw-plaiting, after being cut, dried, and tied up in bundles, is stacked for a month. It is then spread out in a meadow, and exposed to the action of the sun and air, being frequently turned during that period. The lower joint of the straw is then separated, leaving only the upper joint with the ear attached,this being the only part of the straw used. It is then steamed, and after that exposed to the action of sulphurous acid gas prepared by burning sulphur, which complete the bleaching. It is then tied up in bundles, in which state it is ready for the market. In the strawplait-making centres of Great BritainLuton, Dunstable, &c, in Bedfordshirestraw is bleached, chiefly after plaiting, by the influence of sulphurous acid gas.
WHITENING AND CLEANING PRINTS, MAPS, BOOKS, AND OTHER ARTICLES OF PAPER.
Chlorine was first applied to this purpose by Chaptal, and his method was employed with the greatest success by Vialard and Heudier, who by Chaptal's process restored several of the most valuable books of the French National Library. Chaptal's modus operandi is thus described in his own words :
"They begin by unsewing the book and separating it into leaves, which they place in cases formed in a leaden tub, with very thin slips of wood or glass, so that the leaves, when laid fiat, are separ-ated from each other by intervals scarcely sensible. The acid is then poured in, making it fall on the sides of the tub, in order that the leaves may not be deranged by its motion. When the work-man judges, by the whiteness of the paper, that it has been suf-ficiently acted upon by the acid, it is drawn off by a cock at the bottom of the tub, and its place is supplied by clear fresh water, which weakens and carries off the remains of the acid, as well as its strong smell. The leaves are then to be dried, and, after being pressed, may be again bound up.
"The leaves may be placed also vertically in the tub; and this position seems to possess some advantage, as they will then be less able to be torn. With this view I constructed a wooden frame, which I adjusted to the proper height, according to the size of the leaves which I wished to whiten. This frame supported very thin slips of wood, leaving only the space of half a line between them. I placed two leaves in each of these intervals, and kept them fixed in their place by two small wooden wedges, which I pushed in be-tween the slips. When the paper was whitened, I lifted up tho frame with the leaves, and plunged them mto cold water, to remove the remains of the acid, as well as the smell. This process I prefer to the other.
"By this operation books are not only cleaned, hut the paper acquires a degree of whiteness superior to what it possessed when first made. The use of this acid is attended also with the valuable advantage of destroying ink spots. This liquor has no action unon spots of oil, or animal grease; but it has been long known that a weak solution of potash will effectually remove stains of that kind.
' When I had to repair prints so torn that they exhibited only scraps pasted upon other paper, I was afraid of losing these fragments in the liquid, because the paste became dissolved. In such cases I enclosed the prints in a cylindrical glass vessel, which I inverted on the water in which I had put the mixture proper for extricating the oxygenated muriatic acid gas. This vapour, by filling the whole inside of the jar, acted upon the print, extracted the grease as well as ink spots, and the fragments remained pasted to the paper."
A solution of peroxide of hydrogen (H202) has been used with great success in the restoration of valuable prints, as well as for cleaning and reviving oil painting darkened by the action of sulphurous vapours.
BLEACHING OF WOOL.
The bleaching of wool and animal fibres generally is a much simpler and less important operation than is the whitening of vegetable fibres. Wool is covered with a peculiar varnish or greasy matter which impairs its qualities, and which it is the object of the bleacher to remove. To this varnish the name of " yolk " or " suint" is given. It is a fatty unctuous matter, chiefly derived from the cutaneous perspiration, but, no doubt, also secreted by the pores of the wool itself; and it imparts that peculiar heavy odour to sheep with which all must be familiar. From the researches of Vauquelin it would appear that this unctuous varnish consists chiefly of a kind of soap, together with a small quantity of waxy matter, a peculiar odorous animal substance, a mixture of potash salts, and a little lime. This varnish, in consequence of its soapy nature, is soluble in water, so that washing in pure water would remove the greater portion of it; but it is found more advantageous to remove it by the process termed " scour-ing."
Scouring is performed by means of an ammoniacal lye, prepared of river or other soft water mixed with stale purified urine, which is found to contain a large quantity of ammonia, upon which its action probably depends. The mixture is heated by steam to a temperature at which the hand of the workman can be easily held in it for a considerable time. In this bath the wool is left for from half an hour to two hours, according to the quantity of greasy matter it contains. It is then to be taken out and drained into a basket, so that the drainings may drop into the vessel in which it was steeped, that nothing may be lost. It must now be completely rinsed by exposing it in baskets to a continuous stream of clear water, while a workman is perpetually employed in stirring it with a pole, till the water passes off perfectly clear. As a substitute for urine pig's dung is sometimes used, and various other substances have been proposed and introduced, such as ammoniacal salts, soda-ash, phosphate of soda, and soluble glass. Recently a machine, Petrie's wool-washer, has been introduced for scouring wools. It consists of a range of three or four long tanks, clean water entering at one end of the series and flowing through the whole. The wool is introduced at the end of the range where the water escapes, and where it is consequently most highly charged with the impurities of the washing process, and it is carried forward from one tank to another till it is lifted out at the point where the pure water enters.
It is known that the wool is properly scoured by its filaments being smooth, long, slender, white, and perfectly free from foreign substances, and not having lost their natural tenacity. If this scouring be properly done there is no need of further washings in soaps, or otherwise, till the wool is subjected to the process called " sulphuring f and in point of fact it is very rarely passed through any other pro-cess. Some, however, recommend for the finer wools, where a very delicate white is wished, that they should be passed through one, two, or more baths of soft soap. No caustic alkaline lyes can be employed, as they destroy the wool altogether, dissolving it, and forming with it a kind of soap.
The process of sulphuring is applied to yarns and woven goods only when they are intended to be finished white or light bright colours. Formerly, the method of sulphuring woollen goods was to expose them in a close apartment to the vapour of burning sulphur. The goods were hung on poles, and when the chamber was filled, a quantity of sulphur placed in very flat and broad dishes was allowed to burn away gradually in the chamber, while every aperture by which the vapour could escape was carefully closed. After exposure to the sulphurous acid vapours from six to twenty-four hours the bleaching process was complete, and the goods withdrawn from the chamber. The same process is now much more expeditiously performed by Thorn's sulphuring process. The goods are passed on a long chain up and down over a series of rollers in a small chamber filled with sulphurous acid vapours, and a few minutes suffice for the operation. Sulphite of soda acidified with hydrochloric acid is also used in France for the bleaching of woollen fabrics.
Cloth which is to be finished white after the sulphuring process is run through a bath containing some indigo carmine, which increases the brilliancy of the white. When it is to be dyed it is treated with dilute sulphuric acid, thoroughly washed, and dried.
BLEACHING OF SILK.
Raw silk is covered with a kind of varnish, the nature of which was first thoroughly investigated by M. Roard. He showed that this varnish, instead of being a gum, as was usually believed, resembled a mixture of bees' wax and oil, with a resinous colouring matter, and in raw silk constituted 23 or 24 per cent, of the weight. The varnish is soluble in water, and affords a solution which forms a lather like soap. The yellow varnish is of a resinous nature, and is insoluble in water, but is soluble in alcohol The waxy substance exists in all silks, but the whiter the silk the less wax does it contain.
The comparative composition of yellow and white raw silk is shown by M. Mulder's analysis :
Fibroine 53-87 64-04
Gelatine 20-66 19-08
Albumen 24-43 25 47
Wax 1-39 1-11
Colouring matter 0'05
Fatty and resinous matter 0'10 0"30
This varnish, or " gum," as it is technically called, gives the silk a stiffness and elasticity which, for many of the purposes to which silk is applied, it is desirable to remove. This is called " ungumming" by the bleachers of silk. Though many different processes have been suggested for this purpose, none seems to answer so well as the old pro-cess of scouring in a weak solution of soap. If, however, the silk be kept in the soap too long after the varnish is removed, it begins to lose body, and has its qualities impaired, becoming dull, stiff, and discoloured, in conse-quence of being partly dissolved. White or yellow silks may be completely scoured in one hour in the soap bath, using about 15 lb of water for each pound of silk, and a suitable quantity of the finest soap. The soap and silk should be put into the water half an hour before it is brought to the boiling point, and then be boiled one hour. They are then removed, wrung out, washed in pure water, and either exposed to the vapour of sulphur or passed through a solution of sulphurous acid gas in water.
The following is the process usually followed by the scourer of silks. A quantity of water is put into a boiler over a fire, and for every 100 fi) of silk to be scoured, 30 lb of very fine soap are dissolved. The solution is generally boiled; but before the silk is put into it, the heat must be lowered to about 90° Fahr., and at this temperature it must be kept during the process. The silks are to be hung in the liquor on rods or frames, and left till the gum is sufficiently destroyed,care being taken to alter their position now and then, so that every part may be exposed to the action of the bath. When perfectly ungummed, they are flexible and of a dull whiteness ; in this state they are to be wrung out to clear them of the soapy water, then well shaken, and put into coarse linen bags, in parcels of from 20 to 30 lb each.
These bags are now to be steeped in a fresh bath, or, as the workmen say, are to be baked. The bath is prepared in a manner and proportion much as before, except that the quantity of soap may be somewhat diminished as the heat is to be increased; for the silk is now to be boiled for an hour and a half, taking care to keep the bags from sticking to the bottom of the boiler, by frequently stirring them with a stick. For silk that is intended to be dyed, the former steeping in the lukewarm soap-bath is unneces-sary, and the boiling only is employed, using a greater quantity of soap in proportion to the fineness of the colour. After boiling the silk is wrung as before, and then washed, and if it is found to be not sufficiently or not uniformly scoured, it must be submitted to a fresh bath.
The white silk usually sold has a bluish shade given it by a bath impregnated with htmus or indigo. This is prepared by dissolving a pound and a half of fine soap in about 90 gallons of water, in which a small quantity of litmus or indigo has been diffused. This process gives to the silk the tints known by the names of " silver white," " azure white," and "thread white," according to the depth of shade which has been imparted. The " China white " tint is given by adding arnotto to the bath instead of indigo.
From these processes the silk acquires a tolerably clear white, but the highest degree is given to it by the action of sulphurous acid, the silk being either, as is usually the case, subjected to the acid in the state of vapour, or immersed in a solution. At Lyons no soap is used in the tinting process; but, after being boiled, the silk is washed, wrung dry, sulphured, and then passed through water properly blued.
BLEACHING OF BEES'-WAX, &C.
Bees'-wax in its raw condition, as it is first melted up from the comb, is a yellowish coloured substance somewhat greasy to the touch, and having a faint honey-like odour. It often contains mechanical impurities, besides traces of honey, and to remove these and discharge the colour the following process is adopted :The wax is broken up into small pieces and melted in a copper boiler, with water sufficient to keep it from burning. When melted it is run into a tub containing hot water, and while in the hot fluid condition the mechanical impurities it may have contained subside to the bottom. From this tub the melted wax flows into a vessel, the bottom of which is perforated with small holes. Through these thin streams of wax are received on a cylinder kept revolving in water below ; and thus fine threads of solid wax are produced. These are exposed on moistened sheets to the air and light for some days, during which they are occasionally turned and watered. By thia exposure the wax loses much of its colour. It is then melted up into solid blocks and left for some time, after which the operations of melting, forming into threads, and bleaching in the light are repeated till it has attained a pure white translucent lustre, is of very firm consistency, and is free from all odour. Yellow wax is also decolorized by treatment with nitric acid , but chlorine, although it bleaches most expeditiously, is not available, as it leaves traces incorporated with the wax, which on burning evolves irritating fumes of hydrochloric acid. Palm oil, used in the manufacture of soap and candles, is bleached by the action of bichromate of potash and acid.
For bleaching generally, but especially for the bleaching of animal fibres and substances, the use of a considerable variety of processes, and of chemicals other than chlorine and sulphur compounds, have from time to time been proposed and to some extent put into operation. To some of these proposals incidental allusion has already been made, and generally their success has not been such as to warrant special notice. Among other substances which have been recommended for scouring wools and silk are feeble solutions of sulphides of sodium and of potassium, or aluminates of these alkalies, the cyanide of potassium, and a mixture of common salt and oxalic acid. The alkaline permanganates have also been frequently regarded as hopeful bleaching chemicals ; and a few years ago the permanganate of potash was introduced and used by MM. Tessié du Motay and Maréchal, who, in connection with the permanganate, used a solution of the peroxide of hydrogen.
To this latter substance a peculiar bleaching application has recently been given. Under the name of golden, hair water, or auricome, a liquid is sold by hair-dressers which is found to hold in solution a large percentage of peroxide of hydrogen. The use of this solution gives to the hair the brilliant golden yellow tinge which has come to be regarded as a highly fashionable colour. Other applications of this powerful oxidizing and re-ducing agent have been suggested by its toilet use, and it has been employed for the bleaching of ornamental feathers, hair, &c. Doubtless, if it could be prepared in stable solution at moderate price it would be found extensively useful in bleaching and other industrial applications. It has also long been hoped that a means of applying ozone as a direct bleaching agent might be devised, but hitherto little success has been attained in this direction. In Germany ivory is bleached by steeping it a week in light naphtha or other volatile oil, and exposing it thereafter to the air and sunlight, by which the atmospheric oxygen becomes ozonized in contact with the ivory and thus whitens it. (J. PA.)
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