BLEACHING

BLEACHING

Is the art of depriving cotton, linen, silk, wool, wax, &c., of their colouring matter, and rendering them as white as possible. The word is probably derived from the French term blanchiment, which signifies the process of rendering white.

History. 1. The ancients, especially in Egypt, where white linen or cotton was a common article of clothing, must at an early period have been acquainted with the method of bleaching that substance; but none of their writers have left us any details on the subject. We know, however, from Pliny, that different plants, and likewise the ashes of plants, which no doubt contained alkali, were employed as detergents. Pliny mentions particularly the struthium as much used for bleaching in Greece. This plant has been considered by some as the gypsophila struthium. But as it does not appear from Sibthorp's Flora Græca, publish-

ed by Sir James Smith, that this species is a native of Greece, Dr Sibthorp's conjecture, that the struthium of the ancients was the saponaria officinalis, a plant common in Greece, is certainly more probable. Mr Parkes, in his Essay on Bleaching (Chemical Essays, vol. iv. p. 7), says, that Theophrastus states that lime was used by the ancients in bleaching; and that a ship, partly loaded with linen, and partly with lime for bleaching it, was destroyed by the water having accidentally found access to the lime. We endeavoured, with some pains, to verify this quotation; and, accordingly, turned over all the writings of Theophrastus with which we are acquainted, but without being able to find any thing bearing the least allusion to it.

Till about eighty years ago, the art of bleaching was scarcely known in Great Britain. It was customary to send all the brown linen 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 principal Dutch bleaching-grounds were in the neighbourhood of Haerlem; and the great success of their bleaching was ascribed to the superior efficacy of their water, which, according to the fashionable theory of the time, was sea-water filtered and rendered sweet by passing through their sand-downs. Indeed, it was long a prejudice on the Continent, that no water was efficacious for bleaching but sea-water.

The Dutch mode of bleaching was to steep the linen for about a week in a potash ley poured over it boiling hot. The cloth being taken out of this ley, 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 the year 1749, as we are informed by Mr Parkes (Chemical Essays, vol. iv. p. 26), an Irishman, who had learned something of the art of bleaching, settled in the north of Scotland, and established a bleaching manufactory. On applying to the principal Scotch makers of linen, they readily furnished him with a quantity of goods; but after keeping them a whole year, he failed in all his endeavours to bleach them, and the proprietors were obliged to send them to Holland to get the process completed. Next summer his efforts were not more successful; the linen was considerably injured, and even rendered tender by his management, but it was not whitened. Nevertheless, this man by perseverance became in a few years an excellent practical bleacher. He had the merit of introducing the art into Great Britain, and his descendants at this day figure among the higher ranks in the metropolis.

The bleaching process, as at that time performed, was very tedious, occupying a complete summer. It consisted in steeping the cloth in alkaline leys for several days, washing it clean, and spreading it upon the grass for some weeks. The steeping in alkaline leys, 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 ley, till the linen had acquired the requisite whiteness.

For the first improvement in this tedious process, which was faithfully copied from the Dutch bleachfields, manufacturers were indebted to Dr Francis Home of Edinburgh, who proposed to substitute water acidulated with sulphuric acid, for the sour milk previously employed. This suggestion was in consequence of the new mode of making 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. It is curious, that when this change was first adopted by the bleachers, there was the same outcry against its corrosive effects as we have seen some years ago, when chlorine was substituted for crofting. No allegation, however, could be worse founded, and it was completely destroyed by the publication of Dr Home (Essay on Bleaching), who demonstrated the perfect innocence and the superior efficacy and cheapness of sulphuric acid, when properly applied, as compared with sour milk. Another advantage resulted from the use of sulphuric acid, which was of the greatest importance to the merchant. 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 improvement, 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.

The bleaching art remained in this state, or nearly so, till the year 1787, when a most important change began to take place in it, in consequence of a discovery which originated in Sweden about thirteen years before. In the year 1774 there appeared in the Memoirs of the Royal Academy of Stockholm a paper on manganese, by Mr Scheele. Among other experiments to which he subjected this mineral, he mixed it with muriatic acid, put the mixture in a retort, and applied heat. He perceived a smell similar to that of aqua regia. This induced him to collect what came over in a receiver, and he found it to be muriatic acid, altered in a remarkable manner by the action of the manganese on it. Its smell was greatly heightened, it was become less soluble in water, and it possessed the property of destroying those vegetable colours on which it was allowed to act. M. Berthollet repeated the experiments of Scheele on this new acid in 1785, and added considerably to the facts already known. He showed that this new substance (called by Scheele dephlogisticated 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. When water impregnated with this gas is exposed to sunshine, it gradually loses its colour, while at the same time a quantity of oxygen gas is disengaged from the water. If the liquid be now examined, it will be found to contain, not the new acid, but common muriatic acid. This experiment Berthollet considered as exhibiting an analysis of the new acid, and as demonstrating that it is a compound of muriatic acid and oxygen. On that account he gave it the name of oxygenated muriatic acid, which was afterwards shortened into oxymuriatic acid, an appellation by which it was long known among bleachers.

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. At what time these ideas first struck his mind we do not exactly know; but at the end of 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 developed in a paper on the same substance, published in the Journal de Physique for 1786. In 1786 he exhibited the experiment to Mr Watt, who, immediately upon his return to England, commenced a practical examination of the subject, and was accordingly the person who first introduced the new method of bleaching into Great Britain.

Mr Parkes, in his Chemical Essays, published in 1815, has mentioned some facts upon this subject, which it will be proper to state. In the early part of the year 1787, Professor Copland of Aberdeen accompanied the Duke of Gordon to Geneva, and was there shown the discolouring property of chlorine gas by M. de Saussure. Mr Copland was much struck with the importance of the experiment; and on his return to Aberdeen in July 1787, he mentioned the circumstance, and repeated the experiment before some eminent bleachers in his own neighbourhood. These gentlemen were Messrs Milnes of the house of Gordon, Barron, and Company, Aberdeen. They immediately began the application of the process to the bleaching of linen on a great scale; and Mr Parkes assures us that they were the first persons who applied the new process to practical bleaching in Great Britain.

But this statement, though it may appear plausible at first sight, is quite incorrect. The writer of this article took the liberty of applying to Mr Watt himself for information on the subject. Mr Watt has preserved copies of all his letters since the year 1782, taken by means of his copying machine; and he allowed the writer of this article to peruse such of them as bore any reference to this subject. Now, two letters were found which entirely set the matter at rest. The first of these is to his father-in-law, Mr Macgregor, dated Birmingham, 19th March, 1787. In this letter he gives a particular detail of the new bleaching process, states its advantages, and says that he had sent Mr Macgregor a quantity of the whitening liquor. The second letter is to Berthollet, and is dated Birmingham, May 9, 1787. The following is a part of that letter, which we have transcribed verbatim: "Je ne sais pas si j'ai encore fait la liqueur acide si fort que vous avez fait, mais je vous donnerois les moyens de juger. Je trouve que 4 onces de mon acide mélangé avec la quantité nécessaire d'alkali de pearl-ash peut blanchir un gros de toile brune, telle comme j'ai vu chez vous. Il est vrai qu'il ne la fait tout-à-fait blanc; mais il le fait aussi blanc, que je puis le faire, même en ajoutant une seconde dose d'acide. Je bouille la toile par avance dans une solution d'alkali faible; et, à mi blanc, je la bouille une seconde fois. Je trouve que le savon est meilleur que l'alkali pur pour la seconde bouillie. J'ai blanchi tout-à-fait le coton, mais je ne suis encore parvenu à blanchir parfaitement la toile de lin." The reader will observe that the date of both of these letters is some months before Mr Copland's return from the Continent. M. Berthollet had published his process in 1785, and as Watt had brought it to England in the end of 1786, and had put it in practice, and introduced it into Mr Macgregor's bleachfield, near Glasgow, in the month of March 1787, it is clear that Saussure has no claim to the original discovery, nor Mr Copland to the first introduction of the new process into Great Britain.¹

Dr Henry quotes a letter of Mr Watt, dated February 23, 1788, in which he says, "I have for more than a twelvemonth been in possession and practice of a method of preparing a liquor from common salt, which possesses bleaching qualities in an eminent degree; but not being the inventor, I have not attempted to get a patent or exclusive privilege for it." (Annals of Philosophy, vi. 423.) This letter alone is sufficient to show that Mr Watt's experiments were of an earlier date than those of Messrs Milnes. He says further, that "at that very time 1500 yards of linen were bleached by the new process, under his directions." This great experiment was conducted in the bleachfield of his father-in-law, Mr Macgregor, near Glasgow; where, as he wrote to M. Berthollet, soon after, 500 pieces were bleached by the new method, and Mr Macgregor was so satisfied of the importance of the new process, that he had resolved to continue it. Mr Watt made several improvements in the method of M. Berthollet. Instead of employing muriatic acid and manganese, as had been done by Scheele and Berthollet, he had recourse to the cheaper mode of a mixture of common salt, black oxide of manganese, and sulphuric acid. He made use of wooden vessels to hold the water which was to be impregnated with the chlorine, coating them within with a mixture of wax and pitch, which rendered them air tight, and prevented the gas from acting on the wood. Mr Watt likewise contrived a test to indicate the strength of the wa-

ter impregnated with chlorine, as far as its bleaching effects were concerned. He took a determinate quantity of the infusion of cochineal, and ascertained how much of the bleaching liquor was necessary to destroy the colour. The strength of the bleaching liquor was obviously inversely as the quantity necessary to destroy the colour. But M. Welter hit upon another method about the same time, which has been considered as preferable, and has in consequence come into general use. He employed a solution of indigo in sulphuric acid, instead of the infusion of cochineal. In other respects the two methods were the same.

Mr Thomas Henry of Manchester began his experiments on bleaching by means of chlorine nearly as early as Mr Watt, and without any previous knowledge of what he had done. He was very assiduous, and very successful in his trials. At a meeting of the bleachers held at Manchester early in 1788, he exhibited half a yard of calico, bleached by the new method, which was considered as superior in whiteness to half a piece of calico bleached by the same process by Messrs Cooper, Baker, and Charles Taylor. In consequence of this exhibition he was applied to by Mr Ridgway of Horwich, to be instructed in the new process: and the instructions which the latter accordingly received were the first step of a series of improvements carried on by Mr Ridgway and his son, with an ability and spirit of enterprise which have raised their establishment to its present extent and importance. (See Annals of Philosophy, vi. 423.) These two gentlemen, Messrs Watt and Henry, had the chief merit of introducing the new mode of bleaching into Lancashire, and the neighbourhood of Glasgow.

In the year 1789 M. Berthollet published a memoir on the subject, in the second volume of the Annales de Chimie, p. 151. In this memoir, which constituted the first publication on the mode of bleaching by means of chlorine, Berthollet gives a detail of the progress of his experiments, and states the attempts that had been made to introduce the new mode of bleaching into France. M. Bonjour, who had assisted him in his experiments, associated himself with M. Constant, a manufacturer of cloth at Valenciennes, to form a bleaching establishment in that city upon the new plan. But their project was prevented by the prejudices of the inhabitants and by the jealousy of the bleachers, who were afraid of being injured by the introduction of any new improvements. M. le Comte de Bellaing, however, who approved of the project, granted a piece of ground possessed of all the requisite conveniences, but at rather too great a distance from Valenciennes. Mr Bonjour applied to the board of commerce for the exclusive privilege of bleaching for some years, according to the new method in Valenciennes and Cambray, and for two leagues around these places, offering at the same time to explain the new process in all its details to those who wished to make themselves acquainted with it. But the request was refused.

It does not appear from Berthollet's account that the new mode of bleaching had been successfully established in any manufactory in France before the publication of his Memoir. One of the great difficulties in the way of applying chlorine to bleaching, was the very disagreeable and noxious odour which characterized it, and which rendered it not only very offensive, but highly injurious to the health of the workmen. Berthollet describes, at consider-

¹ The writer of this article, when he drew up the preceding historical detail for the Supplement to the Fourth Edition of the Encyclopædia Britannica in the year 1816, thought it right to write to Professor Copland, stating the facts given in the text, and requesting him to say whether they were accurate. Mr Copland returned no answer to the letter. This silence may be considered, we think, as an admission of the accuracy of the statements.

able length, a vessel contrived for impregnating water with it, by M. Welter, and likewise the mode of preparing the gas from common salt, black oxide of manganese, and sulphuric acid. But his improvements, though considerable, were far from obviating the inconveniences complained of. Some method was wanted which should deprive water impregnated with this gas of its smell, without depriving it of its bleaching qualities. The first attempt to accomplish this object originated with M. Berthollet himself.

When he first began to bleach by means of water impregnated with chlorine, he employed that liquid as concentrated as possible; but he found that the texture of the cloth steeped in it was considerably injured. To prevent this effect, he at first added a little alkali to the liquid, in order to saturate a portion of the acid. But he found afterwards that it was better to dilute the liquid with water. Before this last method occurred to him, however, he was requested to go to Javelle, to show the bleachers there the method of preparing the chlorine and making the bleaching liquor. He went twice in consequence, prepared the liquor before the bleachers, and added some potash to prevent the acid from injuring the texture of the cloth. Some time afterwards the manufacturers of Javelle announced in the different journals that they had discovered a peculiar liquid which they called Lessive de Javelle, and which possessed the property of bleaching cloth immersed in it for a few hours. This liquid they prepared by dissolving potash in the water which they were going to impregnate with chlorine. The consequence was, that the liquid absorbed a much greater quantity of gas, and might be diluted with a considerable proportion of water, without losing its bleaching quality.

Being disappointed in their attempts to introduce this liquor among the French bleachers, they came over to England, and applied to parliament for the exclusive privilege of supplying the British bleachers with this liquid. The patent was to be given to MM. Bourboulon de Bonneuil and Company. In consequence of this application, a meeting of the bleachers of Lancashire was advertised in the beginning of the year 1788. It was at this meeting that Mr Henry exhibited the half yard of calico bleached according to the new method. Mr Watt had written a letter to Dr Percival on the subject, which was communicated to the meeting. He stated in it that he had been in possession of a new method of bleaching, by means of chlorine, for above a year; that he had learned it from Berthollet, and that he had every reason to believe that the liquor of MM. Bourboulon de Bonneuil and Company consisted of chlorine, or of some preparation of it. In consequence of this meeting, the county members of parliament were requested to oppose the intended monopoly. Mr Watt also exerted all his influence; and Mr Parkes informs us likewise, that one of the Messrs Milnes of Aberdeen, who had been informed of the use of chlorine by Mr Copland, happened to be in the gallery of the House of Commons when the application in favour of the French gentlemen was made. He took immediate measures to inform the principal members that this was not a new process; that he himself had long ago prepared an article equally advantageous; and that he was ready to substantiate the truth of his statement when required. (Parkes's Chemical Essays, iv. 62.) In consequence of the united exertions of all these different gentlemen, the bill was thrown out, and the monopoly prevented.

It seems to have been partly in consequence of this application of the French gentlemen that Mr Henry of Manchester was induced to attempt bleaching upon a large scale with chlorine. His attention had been first drawn to the subject by the papers of Berthollet, published in the Journal de Physique, during the years 1785 and 1786.

He was at that time engaged in a course of lectures on dyeing, printing, and bleaching. An acquaintance with the properties of chlorine, which he had repeatedly had occasion to exhibit in his course of lectures, and the general hints previously thrown out by Berthollet, led him to conclude that the liquor of Bourboulon and Company could be nothing else than chlorine, or some compound of it. His first operations on the large scale consisted in exposing the goods, in a moist state, in air-tight chambers, to the action of chlorine gas. He likewise began to prepare for sale a bleaching liquor, in which the gas was condensed in a very weak solution of potash; which, as we learn from Berthollet, was the very same with the Lessive de Javelle. This liquid possessed two advantages over water simply impregnated with chlorine gas. Its smell was less noxious, and it might be employed to whiten printed calicoes without destroying the colours which had been dyed upon the cloth. But these advantages were much more than counterbalanced by equivalent disadvantages. It was found not to go nearly so far as water impregnated with chlorine gas, and when kept for some time it lost its bleaching properties altogether. The reason of this last alteration is now sufficiently understood: the chlorine in the liquid was gradually converted into common muriatic acid and chloric acid; the water containing merely common muriate of potash and chlorate of potash. In consequence of these disadvantages, the addition of potash to the bleaching liquid was soon laid aside. The next attempt to destroy the noxious smell of the liquid, without destroying its bleaching property, was the addition of lime to the liquid. Mr Henry of Manchester was one of the first persons who thought of this addition. On the floor of his air-tight chambers rested a stratum of thin cream of lime, through which the goods were passed by means of a wince; and were afterwards exposed, on quitting the liquor, to chlorine acid gas. Hence the chloride of lime was formed upon the cloth. But this method was objectionable in the case of some coloured goods, the colours of which were injured or destroyed by that earth. It admitted, therefore, of only a partial application.

Other persons made similar attempts, none of which appear to have been attended with success. But Mr Tennant of Glasgow, 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 purposes of the bleacher. This was certainly a most important improvement. Without it, the prodigious extent of business carried on by some of our bleachers could not possibly have been transacted. To give some idea of the rapidity with which bleaching is conducted according to the new process, we may mention the following fact, which we state on what we consider as very good authority. 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 distance of sixteen miles, and they were packed up and sent off on that very day to a foreign market. The quick return of capital which is thus made is a benefit entirely to be ascribed to the new mode of bleaching.

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 combination was formed to resist the right of the patentees. In December 1802, Mr Tennant and Company brought an action for damages against Messrs Slater and Varley, nominally the defendants, but who, in fact, were

Bleaching. 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 patentees. 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. Had the writer of this article constituted the jury, the verdict would have been very different. 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 all of them to continue their peculiar method without any objection, because it would have been productive of no injury to his emolument. If the very same process as that of Mr Tennant was employed before he took out his patent, there could be no doubt that the process originated with him, and that those who used it had been induced to do so from the information which they derived from him. In the opinion of the writer of this article, Mr Tennant was hardly used, and the words employed by Lord Ellenborough were quite inapplicable to him. But when a very powerful combination is formed against any individual, the sentiments with which they are actuated propagate themselves with rapidity; and it is difficult for the most upright jury to avoid being swayed by prejudices, which are the more formidable, that their existence is not perceived.

In consequence of this decision, the use of liquid chloride of lime in bleaching was thrown open to all, and appears now 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.¹ He had taken out a patent for this on the 13th of April 1799, and his right fortunately was not contested. He began his manufactory of solid chloride of lime at first upon a small scale, which has been ever since gradually extending, and his manufactory is now the largest of the kind in Great Britain. During the whole period of the duration of his patent he laboured under great disadvantages. The chlorine gas with which the lime was impregnated was obtained from common salt. Now, his patent did not extend to Ireland, in consequence of which manufactures of dry chloride of lime were established in that kingdom. In Ireland the manufacturer obtained his salt duty free, while Mr Tennant was obliged to pay a duty of 7s. 6d. per bushel. Such, however, was the superiority of the methods employed by Mr Tennant, that he was able to compete with the Irish manufacturers in their own country.

In the year 1815, in consequence of the joint application of the bleachers, the duty on common salt, formerly charged upon all bleachers and others who employed that article in the preparation of a bleaching liquid, was taken off, and they were henceforth allowed to use it duty free. But this act, while it affords great advantages to bleachers on a large scale, precludes those who only work on a small scale from making their own chloride of lime; the consumption of the powder, therefore, is likely to increase very much among the little bleachers and calico printers. Its use is also considerable in partially discharging the colour of Turkey red cloth. The method was originally a French invention; but a patent was granted to

Mr Thomson, a Lancashire calico-printer, for the process, which, we believe, he imported from Jouy. The method is this: An acid paste, consisting of tartaric acid, or any other acid thickened with gum, is first printed on the Turkey red cloth, which is then passed through liquid chloride of lime. It becomes white only where the acid was applied. On this bleached part any other colour may be applied, and the combinations produced are exceedingly beautiful and striking.

Such, as far as we are acquainted with the subject, is the history of the progress of the new method of bleaching in Great Britain. We have said nothing of the Irish bleachers, because we are not particularly acquainted with the progress of the new method in that country, though we believe that chlorine was tried by the Irish bleachers almost as early as it was in Great Britain. Mr Parkes supposes that Mr Kirwan might have proposed the trial of the new re-agent, in consequence of some suggestion from Scheele or Saussure. (Parkes's Chemical Essay, iv. 43.) But we have no evidence that this was the case. Indeed, it would be quite unreasonable to attempt, by such vague suspicions, to detract from the merit due to Berthollet for his original suggestion of the application of chlorine to bleaching, a merit which he has enjoyed without a competitor for thirty years. Scheele was dead before any one attempted to introduce the new gas into bleaching, either in Great Britain or Ireland; and there is every reason for believing that Saussure's knowledge of the bleaching qualities of chlorine originated from Berthollet's publications on the subject in 1785 and 1786.

1.—Bleaching of Cotton.

Cotton is a kind of down which fills the seed-pods of various species of plants, particularly the Gossypium herbaceum, hirsutum, and arborescens, from all of which it is extracted in considerable quantity for the purposes of manufacturers. This substance was known to the ancients, and made by them into thread and cloth. Cotton cloth appears to have been generally worn in Egypt and the neighbouring countries at a very early period; and no doubt the plant was cultivated in India and China for similar purposes before the time at which the history of these nations, as far as we are acquainted with it, commences. Pliny gives a short description of the gossypium which grew in Upper Egypt, which is sufficient to show us that it was the same with our cotton plant. "Superior pars Ægypti in Arabiam vergens gignit fructicem, quem aliqui gossipion vocant, plures ylon, et ideo lina inde facta ylina. Parvus est, similemque barbatæ nucis defectum fructum, cuius ex interiore bombyce lanugo netur. Nec ulla sunt eis in candore mollitiae præferenda." (Pliny, Natur. Hist. lib. xix. c. 2.) The bysus mentioned in the same chapter was probably likewise a species of cotton; though the account of it given by Pliny is not sufficiently precise to enable us to make out the point with certainty.

Since the discovery and colonization of America and the West Indies, and our great connection with the East Indies, cotton has become a very common article of clothing in Europe. The manufacture of cotton cloth in consequence has increased prodigiously, and in Great Britain constitutes one of the great branches of manufacturing industry. The quantity of colouring matter in cotton is much less than in linen, and it is more easily removed. Hence the bleaching of cotton is much easier, and occupies less time, than that of linen. On that account it will answer best to give the reader a clear idea of the pro-

¹ The idea of saturating slacked lime with chlorine was first suggested by Charles McIntosh, Esq. of Cross-Basket, who was at that time a partner of Messrs Tennant and Knox.

cesses at present followed by the most skilful bleachers in Great Britain. The bleaching of cotton is practised chiefly in Lancashire and the neighbourhood of Glasgow, to which districts the cotton manufacture is almost confined. We shall describe the processes as they are followed in the most extensive bleaching-houses, where they have been brought to the state of greatest perfection. The processes are numerous, though each is sufficiently simple. Let us follow the cotton cloth, from the time that it comes into the hands of the bleacher till it is returned to the merchant fully bleached and ready for sale.

1. The first process is to stamp the proprietor's name upon the end of every piece of goods, that there may be no mistake from the mixture of the cloth belonging to different persons, but that every individual may have his own goods returned to him again without the least risk of error. The substance used for the purpose is coal-tar, which distills when pit-coal is heated in iron retorts for the purpose of obtaining coal-gas. It consists of a mixture, or rather solution, of black bituminous matter in naphtha. A quantity of coal-tar is spread over a woollen sieve with a brush. A wooden stamp containing the name of the proprietor of the cloth is pressed against the cloth. It takes up the requisite quantity of coal-tar, and when pressed against the end of the piece makes a black and very distinct impression of the name, which withstands all the subsequent processes to which the cloth is to be subjected without being obliterated; but which might be removed were the stamped part of the cloth to be well washed with soap, and rubbed hard between the hands of the washer.

2. The cloth thus marked is in the next place singed, in order to remove the numerous hairs or flocks of cotton, which would have the effect of injuring the look of the cloth. This is usually done by passing the pieces with a uniform velocity over an iron heated red-hot. The heat is sufficient to burn off the hairs; but the cloth passes too rapidly to be injured by the hot iron. Some years ago Mr Hall of Nottingham contrived a very ingenious apparatus, by means of which the cloth is singed by coal-gas. Some idea may be formed of the nature of the process by the following imperfect description. A represents the gas flame issuing from a pipe, and B the cloth drawn uniformly along, with the requisite velocity, to prevent it from catching fire from the flame; C represents the section of a kind of vessel terminating in a tube D, which is connected with an air-pump kept working during the whole process. The consequence is, that the cloth presses rather forcibly against the bottom of C, and the flame is cut off by the cloth without passing through it, singeing only one side of it.

3. If the cloth were thrown into a vessel of water, regularly folded into a number of plies, the water would not be able to penetrate through it, but the central folds would remain dry. To prevent this, each piece of cloth is pulled into a band, by drawing it between the hands so as to give it a slight resemblance to a rope. This band is folded loosely, and tied up by one of its ends into a kind of irregular bundle. These bundles are thrown one after another into a large square cistern or vessel, filled with cold water, and left in that situation till they are completely soaked. They are then washed in a wash-wheel, of which a representation is annexed. The wash-wheel is a cylindrical

box revolving on its axis. It has four divisions, as shown by the dotted lines, and an opening into each division. Two pieces are put into each, abundance of water is admitted behind, and the knocking of the pieces as they fall from one division to another constitutes the washing. The process lasts from four to six minutes. The object of it is to remove as much of the weaver's dressing as possible from the cloth before the regular bleaching processes commence.

4. The next process to which the cloth is subjected is boiling with lime. This is done in a large circular boiler, or kier as it is termed, of which a section is given in the margin. It has two parts: the pan of wrought iron A, set in brick-work, on which the fire acts; and the upper part B, which is of cast-iron, and which contains the goods to be boiled. These parts are separated by a cast-iron false bottom C. D is an iron pipe placed in the centre of the kier, and resting upon the false bottom. The liquid in the pan A, from the pressure upon it, does not boil till it is heated considerably above the boiling point. At last it begins to boil in a part of the pipe D, where the pressure is less than in the pan. A mixture of steam and water is formed there, producing a column of lower specific gravity than before. This rushes up the pipe, and is thrown back by the cap E into the boiler, making room for another portion of highly heated liquid, which rising also in the pipe, boils in its turn, making room for a third portion, and so on till the pan is emptied of all its liquid above the bottom of the pipe. The liquid then filters gradually through the goods in the vessel B into the pan, where in a few minutes it is again heated to the requisite degree, and again rushes up the pipe as before. This process lasts about eight hours after boiling commences.

Another kind of boiler, in which the water is heated by steam from a separate boiler, is now in very general use. It consists of a cylindrical vessel AA, 9 feet wide, of wood or iron, having a false bottom BB, on which the goods are placed, about six inches from the real one. A small pipe E, in the centre of a wider one CC, conveys the steam from the steam-boiler. When the liquid boils at the bottom, where the steam issues, the steam forces its way

Bleaching up the pipe CC, carrying with it a quantity of the ley, which is thrown back by the small cover D, spreads itself over the surface of the goods, and filters through them into the space below the false bottom, where it is again heated by the steam, re-ascends the pipe CC, and so on in constant succession, till the alkali is exhausted. FF is a wooden cover which prevents the cooling of the materials below a boiling heat.

The quantity of lime used in this process is 1 lb. of lime for every 35 lbs. of the cloth. This lime, previously slacked, is mixed with water in a separate vessel, till it has acquired the consistency of cream. A layer of pieces of cloth is deposited in the boiler, and over it is spread equally a portion of this cream of lime. Then another layer of goods is introduced over the former, which is covered with cream of lime as before. In this way the goods and cream of lime are introduced in alternate layers, till the whole has been put into the boiler; then the requisite quantity of water is introduced, and the process of boiling begun.

The cloth as it comes from the hands of the weaver is impregnated with the dressing, which consists of flour boiled with water into a paste. It contracts also unavoidably many greasy stains, which become visible to the eye when the piece is put into water, by remaining dry, while the remainder of the cloth is wetted. These two impurities are removed by the lime-boiling more effectually, it appears, than they would be if a potash or soda ley were used for the purpose.

The colouring matter of the cotton, which it is the object of bleaching to remove, is also acted upon by the lime, but certainly not removed; for the colour of the cloth after it has undergone the lime-boiling is darker than it was before it was wetted at all. Yet it cannot be doubted that this colouring matter has been acted on by the lime, and that it is rendered more easily removable by the future processes to which the goods are subjected.

After the lime-boiling, the cloth is carefully washed in the wash-wheel, in order to remove the lime, loaded as it is with impurities, as completely as possible from the cloth.

5. The cloth is now subjected to the action of the bleaching powder.

The bleaching powder, or chloride of lime as it is usually called, is made by exposing slacked lime to an atmosphere of chlorine gas till it refuse to absorb any more. Unslacked lime is incapable of absorbing this gas; but slacked lime, or hydrate of lime, absorbs it readily. Mr Tennant of Glasgow, who was the original contriver of the process, and is still by far the greatest maker in Great Britain, prepares it by covering the floor of a stone chamber with a layer of slacked lime to the height of a few inches. The stone of which the chamber is built is the Glasgow coal sandstone, which is rendered impervious to the chlorine by being coated externally with a layer of cement, made by melting together wax and rosin in the requisite proportions to make a stiff but very ductile cement. The wooden door of the apartment is then closed and made air-tight. There is an aperture above, which can be occasionally opened; the use of which seems to be to allow the common air of the chamber to make its escape. A mixture of native black oxide of manganese, ground to a fine powder, of common salt, and of sulphuric acid diluted with water, is put into a large leaden vessel, nearly spherical, and furnished at the top with a lid, which fits so as to be air-tight. From this lid a leaden tube passes into the lime chamber, to convey the chlorine gas as it is formed. This leaden vessel is cased on the outside with an iron vessel, between which and the leaden vessel there is an interval. At first the chlorine gas is extricated without any heat

being applied; but after the process has continued for some time, a current of steam is made to pass into the inside of the iron case, which heats the leaden still sufficiently high to continue the process till the whole common salt is decomposed, and of course the disengagement of chlorine gas is at an end.

The black oxide of manganese (supposing it pure) is a compound of

By the mutual action of the sulphuric acid and the acid of the common salt it is converted into protoxide of manganese, composed of

It therefore loses an atom of oxygen. This atom unites with the hydrogen of the muriatic acid evolved, forming water, and thus converting the muriatic acid into chlorine. It is obvious from this, that if the black oxide of manganese were pure, every 5.5 parts of it would be sufficient to generate 4.5 parts of chlorine, which is the quantity contained in 7.5 parts of common salt. Hence the proportions of black oxide and common salt which ought to be used are $5\backslash frac\{1\}\{2\}$ of the former to $7\backslash frac\{1\}\{2\}$ of the latter. But the black oxide of manganese employed in this country is never pure. It is always contaminated with a quantity of peroxide of iron, seldom less than one fourth of the weight of the ore, and often amounting to one third of that weight. It contains also not unfrequently barytes or lime, which seem to be in chemical combination with a portion of the oxide. On this account it is always necessary to use more than $5\backslash frac\{1\}\{2\}$ of manganese for every $7\backslash frac\{1\}\{2\}$ of salt. We believe that the quantity of black oxide for every $7\backslash frac\{1\}\{2\}$ parts of common salt ought not to be less than 8 parts, to make sure of obtaining the whole chlorine from the common salt.

The black oxide of manganese having a specific gravity of 4.97, and being insoluble in water, speedily falls to the bottom of the leaden still, and would soon cease to convert the muriatic acid into chlorine. To prevent this, there is an agitator in every leaden vessel, which is very frequently moved by the workmen whose province it is to take charge of these stills. By this means the manganese, which is in very fine powder, is mixed with the whole liquid, and thus brought into contact with the nascent muriatic acid, which it deprives of its hydrogen, and thus converts into chlorine.

To decompose $7\backslash frac\{1\}\{2\}$ parts of common salt completely, $12\backslash frac\{1\}\{2\}$ parts of sulphuric acid of the specific gravity of 1.843 are requisite. This acid should be previously diluted with at least its own bulk of water; or it is better (when the manufacturer of bleaching powder makes his own acid, which is generally the case) to employ the sulphuric acid in the state in which it comes from the leaden chambers, without any artificial concentrations. This, if the acid maker conducts his process properly, may be as high as 1.75. Mr Tennant finds it better to employ a still greater quantity of acid than $12\backslash frac\{1\}\{2\}$ for every $7\backslash frac\{1\}\{2\}$ of salt; because the decomposition goes on with the application of less heat, and the leaden stills are much less corroded than when a smaller quantity of acid and a stronger heat are employed. What remains in the still after the evolution of the chlorine gas is at an end, is a mixture of sulphate of manganese, bisulphate of soda, and free sulphuric acid. It would not do to lose the free sulphuric acid. The residue is therefore mixed with as much common salt as the sulphuric acid is able to decompose, and the whole is gradually

fused in a furnace. By this fusion the sulphate of manganese is decomposed as well as the common salt, and there remains sulphate of soda mixed with oxide of manganese and peroxide of iron. Lixivation gets rid of these two oxides, and leaves a solution of sulphate of soda, which is evaporated to dryness, mixed with pounded coal, and ignited in a reverberatory furnace. By this simple process the Glauber salt is converted into sulphuret of sodium, from which carbonate of soda is extricated by simple and well-known processes.

The bleaching powder, when first prepared, was a dichloride of lime, or a compound of one atom of chlorine and two atoms of lime. But of late years Mr Tennant has improved his process so much, that it is now a chloride of lime, or a compound of one atom chlorine and one atom lime; that is to say, it contains twice the quantity of chlorine which it originally did, and goes twice as far when employed in bleaching; and other manufacturers have been obliged to follow his example. Hence the value of the bleaching powder all over Great Britain is about doubled, while its price is reduced to less than one half of what it was originally; being sold at present at the rate of threepence per pound, containing nearly half its weight of chlorine.

With respect to the nature of bleaching powder, no experiments have been made sufficiently decisive to remove all doubts. The most commonly received opinion is, that it is a compound of chlorine and lime, or a chloride of lime. The objection to this opinion is, what happens when carbonate of soda is saturated with chlorine to form the disinfecting liquor used by Labaracque. If the solution be evaporated, a peculiar salt is obtained, which possesses bleaching properties. No chlorine gas is given off during the evaporation. The same phenomena take place when carbonate of potash is saturated with chlorine. From this it has been conjectured, that when chlorine acts upon slacked lime, a certain portion of the lime is converted into calcium, while a portion of the chlorine is converted into chlorous acid, or a compound of one atom of chlorine and three atoms of oxygen. On this supposition it is evident that three fourths of the lime are converted into calcium. The three atoms of oxygen thus evolved convert one atom of chlorine into chlorous acid. This chlorous acid unites with the one fourth of lime remaining, and converts it into chlorite of lime; while the three atoms of calcium evolved, uniting each with an atom of chlorine, constitute chloride of calcium. According to this view of the subject, the strongest bleaching powder will be a mixture of

So that about one third of the weight is chlorite of lime, to which alone the bleaching powers of the substance is owing.

It is rather inconsistent with this opinion, that bleaching powder does not attract moisture from the atmosphere with nearly so much rapidity as might be expected from a mixture containing two thirds of its weight of so deliquescent a salt as chloride of calcium; unless, indeed, this be prevented by the chloride and chlorite being united into a double salt. When sulphuric acid or muriatic acid, however diluted, are poured into a solution of bleaching powder, chlorine gas is given out in abundance. This seems rather inconsistent with the notion of its being a mixture of chloride of calcium and chlorite of lime; at least no such evolution takes place when these acids are mixed with solutions of chloride of calcium or chlorate of potash.

The bleaching powder, in order to be applied to the Bleaching. cloth, must be dissolved in water; and the quantity employed for the first process consists of a solution of 24 lbs. of bleaching powder in 60 gallons of water.

In general, a solution of one pound of bleaching powder in one gallon of water has a specific gravity of 1.05. But the specific gravity of the bleaching powder solution into which the cloth is put is only 1.02. The quantity of liquor of this specific gravity necessary for 700 lbs. of cloth is 971 gallons. Hence it is obvious that the quantity of bleaching powder required for 700 lbs. of cloth will be 388½ lbs.

But the specific gravity of the solution is not sufficient to determine its qualities as a whitening substance. The longer bleaching powder is kept, especially if it be not well shut up from the action of the atmosphere, the less bleaching power does it possess. We have purchased it from apothecaries in London a great many years ago almost totally inert; yet this inactive substance was soluble in water, and was capable of augmenting the specific gravity of the liquid as much or nearly as much as the best bleaching powder whatever; but the liquid was merely a solution of chloride of calcium. Some other method, accordingly, of judging of the goodness of bleaching powder is necessary for the bleachers. The method commonly employed by the bleachers is the indigo test, first brought into use by M. Welter.

The mode of applying the indigo test followed in this country is by means of the graduated glass tube, figured in the margin, which is known by the name of the Test-tube. The method is as follows: One part of the best indigo is dissolved in nine parts of strong sulphuric acid, and the solution is mixed with 990 parts of water, making a solution, $\backslash frac\{1\}\{1000\}$th part of which is indigo. Of this liquid a quantity is to be poured into the test-tube, so as to fill it up to 0, or the commencement of the scale. The bleaching liquor whose power is to be tried is then to be dropt gradually in, and mixed with the blue liquor by shaking the tube from time to time till the blue is changed into a clear brown. As soon as this takes place, the degree of the scale to which the mixture reaches is observed, and the figure marked at that degree indicates the strength of the steep-liquor. The lowest on the scale is, of course, the strongest in bleaching power, being capable of destroying most colour. The liquor whose strength is thus ascertained is denominated steep-liquor, of 1, 2, 3, 4, 5, and 6 degrees, the last of which is the weakest ever used for any kind of goods. By adding stock-liquor when the steep-liquor is too weak, and water when too strong, this liquor may be obtained of any strength which is required.

This mode of testing is obviously defective, because we have no good method of determining the goodness of the indigo itself employed as the test; and yet it is well known that different indigos vary considerably in the quantity of colouring matter which they contain. Various attempts have been made to improve it; but at best it can only be considered as enabling us to compare between the relative values of the different varieties of bleaching powder. It can never give us the absolute quantity of oxygen which the bleaching powder is capable of disengaging, upon which its bleaching powers must entirely depend.

But Mr Dalton, in his paper On Oxymuriate of Lime, in the Annals of Philosophy, vol. i. p. 15, has pointed out a

Bleaching process, which, when a little modified, as it has been by Mr Walter Crum, one of the most extensive bleachers in the neighbourhood of Glasgow, answers exceedingly well, and enables us to determine the true quantity of oxygen which the solution of the bleaching powder is capable of yielding to the cloth. Mr Crum's method is this. He dissolves four ounces of green sulphate of iron in hot water, and then adds solution of bleaching powder by small quantities at a time till the smell of chlorine begins to be perceptible. This is a proof that the whole of the protoxide of iron in the four ounces of green vitriol has been converted into peroxide. The strength of the bleaching powder liquid employed by Mr Crum, when the object is to test its value as a bleaching ingredient, is one pound of bleaching powder dissolved in one gallon of water. Of this he adds quantities by $\backslash frac\{1\}\{12\}$th of a gallon at a time to the solutions of green vitriol, till the smell begins to become sensible. Six of these measures may be added at once without any risk of evolving any smell; but on the addition of the seventh measure it is necessary to proceed with caution, adding only a little at a time, lest the point of saturation be exceeded. Let us suppose that $7\backslash frac\{1\}\{2\}$ measures were necessary to evolve the smell of chlorine; as 64 measures contain one pound of bleaching powder, it is obvious that $7\backslash frac\{1\}\{2\}$ measures will contain 820.3 grains. We learn from the experiment, that in the case in question 820.3 grains of bleaching powder, when placed in contact with protoxide of iron, are capable of converting all the protoxide of iron contained in four ounces of green vitriol into peroxide. Now, crystallized sulphate of iron is composed of

Consequently four ounces of the salt must contain 396.2 grains of protoxide of iron, to convert which into peroxide will require 44 grains of oxygen. This, of course, is the quantity of oxygen contained in 820.3 grains of the bleaching powder tried. If six measures had been sufficient instead of $7\backslash frac\{1\}\{2\}$, then 656.2 grains of bleaching would yield 44 grains of oxygen. In general, the bleaching powder employed by the bleachers is of about this strength. Hence it is obvious (admitting bleaching powder to be a mixture of one atom chlorite of lime and three atoms chloride of calcium) that 656.2 grains of bleaching powder, in the strongest state in which it is usually employed by bleachers, is composed of

This loss must be partly water, and partly perhaps owing to the presence of a greater quantity of chloride of calcium than ought to be present. If we suppose the whole of the loss to be water, then the best bleaching powder would be a compound of

But in general the whole lime is not accurately saturated with chlorine. Accordingly, when the bleaching powder is dissolved in water, a small residue almost always remains undissolved. Unless the powder be fresh made, a

portion of chlorite is always converted into chloride of calcium. It is probable, therefore, that the best bleaching powder, as it comes into the hands of the bleachers, consists of

If we consider the bleaching powder as a compound of chlorine and lime, our mode of calculating will not be altered. Instead of 1 atom chlorite of lime and 3 atoms chloride of calcium, we shall have 4 atoms chloride of lime, 6 atoms water, and 2.25 of impurity as before.

Sulphate of manganese might be substituted for sulphate of iron. The result would be the same, excepting that the protoxide of manganese is converted into the native black oxide, by uniting with an additional atom of oxygen. And as crystallized sulphate of manganese is composed of

it is obvious that 14 of sulphate of manganese will go twice as far, as a test of bleaching powder, as 17.375 of sulphate of iron. Thence $1\backslash frac\{1\}\{2\}$ oz. of crystals of sulphate of manganese will go just as far, as a test for bleaching powder, as 4 oz. of sulphate of iron. The manganese is thrown down in the state of native black oxide; not however pure, but every six atoms of it are combined with one atom of lime, constituting a compound which may be called sex-manganite of lime, composed thus:

Prussian blue might also be employed as a test for bleaching powder. A solution of bleaching powder dissolves prussiate of iron, and the solution, when just neutral, is green; when there is an excess of bleaching powder, the liquid becomes brownish yellow. But prussiate of iron can only be employed as a comparative test in the same way as indigo; although it is preferable to indigo, because it can always be obtained of the same relative strength or purity.

The cloth is left in the cold solution of bleaching powder about six hours. It is then taken out and washed with water. It has now assumed a kind of light grey colour. It is not yet white, but much whiter than when it came into the hands of the bleacher.

6. The next process to which it is subjected is called souring. Eight gallons of the sulphuric acid of commerce are mixed with 200 gallons of water. This constitutes a liquid having a decidedly sour taste, but too dilute to be in the least corrosive. In this liquid it remains cold for about four hours. It is then taken out and carefully washed in cold water, to remove the acid as completely as possible. By the souring the cloth is rendered much whiter than it was before. The sulphuric acid dissolves and removes the oxide of iron with which the cloth is always more or less contaminated. It removes also the lime which the cloth had imbibed partly from the lime-boiling and partly from the bleaching liquor in which it was so long immersed. The colouring matter of the cloth would seem to combine with the sulphuric acid, and to form a compound much whiter than the uncombined colouring matter itself. That it is not removed is obvious from this,

that if the cloth be steeped in an alkaline solution, the dark colour is again in some measure restored.

7. The cloth, after being well washed in cold water, is immersed in an alkaline ley, in which it is boiled for eight hours, precisely in the same way as was described when giving an account of the lime-boiling. Thirty-two pounds of potash made caustic by quicklime are used for every 2100 lbs. of the unbleached cloth. Of late years, in consequence of the reduced price of carbonate of soda, and its much greater purity, it has been substituted for potash by the bleachers. When the carbonate of soda is in crystals, 18 lbs. of it are equivalent to 9 or 10 lbs. of potash.

After this boiling the cloth is again carefully washed in cold water.

8. A solution of bleaching powder is now prepared, two thirds of the strength of the first bleaching powder liquid, in which the cloth is immersed, and left for five or six hours; but by this exposure the bleaching powers of the liquid are not exhausted, so that by an additional supply of strong liquor it may be rendered fit for another process.

If the cloth to be bleached has red ends, which is sometimes the case, it is carefully washed after this exposure to the action of the bleaching liquor before it is subjected to souring; but if there be no red ends this washing is dispensed with.

9. The next process is a souring. The mixture of sulphuric acid and water is nearly of the same strength as before, and the cloth is left immersed in it about four hours, or sometimes not so long. By this process the bleaching of the cloth is completed, for it comes out of the acid steep quite white.

It is a very material thing to remove all trace of the sulphuric acid from the cloth as completely as possible; because any portion of it remaining would corrode and destroy the cloth, especially when it was exposed to the action of heat. To accomplish this necessary result, the cloth is subjected to very careful washing; and this washing process is repeated two several times.

10. Such are the processes of bleaching cotton cloth when of the best quality, and carried to the greatest extent. In many cases several of the processes are omitted; but we thought it right to give a detail of them all as they are applied to cotton shirting, and to the better cotton fabrics that are to undergo the subsequent processes of calico printing. But after the bleaching is finished, the cloth is put through a variety of subsequent processes by the bleacher, in order that it may please the eye of the purchaser, and be in the best possible state for commanding a ready sale. Of the most important of these processes it will be requisite to give a short account.

The cloth is squeezed after washing, in order to remove a considerable portion of the water which it had imbibed in the washing. This is done by making it pass between two rollers, which by their pressure force out the water. There is something ingenious in this process, simple as it is, that deserves to be noticed. The pieces of cloth, as they come out of the washing wheel, are crumpled together, and frequently entangled in irregular knots. If these knots were allowed to enter between the rollers, they would, from their too great size, be apt to derange them, and might even stop the motion of the machinery altogether. To prevent this from happening, a water cistern, the top of which is on a level with the floor of the room, and which is constantly kept full of water, is placed immediately before the rollers. Over this water the cloth is made to pass on its way to the rollers. By the force necessary to drag it through this water, the piece is stretched, and any wrinkles or knots into which it may have been cast are effectually removed. Thus the cistern of water is made

to answer the purpose of one or rather of two workmen. Bleaching. For as two pieces of cloth pass through the rollers at once, were it not for the water, two persons would be required to unfold the cloth, one to each piece.

Plate CVII. fig. 1, exhibits a view of the machine called squeezers, employed to press as much water as possible from the piece after being bleached. It consists of a cast-iron framing, with two wooden rollers, which are pressed together by a double lever, and made to revolve by means of wheels connected with a shaft from a steam-engine or water-wheel. The wet piece is laid down at one side of the machine, and after passing between the rollers, is folded by a workman stationed at the opposite side.

11. The cloth after the squeezing process is still wet, and is crumpled together like a rope. The next process is to pull out each piece to its breadth. This is done by women, a number of whom are constantly employed in this simple but necessary process. But the edges of the piece still continue folded in. To make them straight, a workman knocks them against a smooth beating stock, first one edge and then the other. By this process the pieces are spread out to their full breadth, and all the folds and wrinkles removed as before the bleaching processes commenced. The pieces are then stitched end to end by women with a sailor's needle, to prepare them for the mangle.

12. The next step is mangling the cloth while still wet, by passing it successively between cylinders, forced towards each other by levers, to which a considerable weight is attached. These cylinders require all to be turned quite true, so as to be perfectly round. One of them is of brass, and two are of wood. 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.

13. Starching is the next process; and though it be well understood, yet it may not be superfluous to give a short sketch of the processes which the bleacher follows, the great object being to unite economy with exactness. Wheat starch would be too expensive; the bleacher therefore satisfies himself with flour. But the gluten of wheat flour renders it unfit for starching. The first step, therefore, is to get rid of that ingredient. Flour is mixed with water in the proportion of one pound of flour to the gallon of water, and allowed to remain for twenty-four hours. A brisk fermentation takes place, an acid, lactic, is generated, the texture of the gluten is destroyed, and the water acquires a specific gravity of 1.015. After twenty-four hours, the whole liquid is passed through a sieve. The starch passes along with the liquid, but the bran is retained upon the sieve. The starch is then boiled, a little indigo being added, and water also, so as to proportion the thickness of the liquid to the degree of stiffness which the goods are to acquire.

In many cases the starch is mixed with porcelain clay, about equal bulks of flour and porcelain clay being most commonly employed; though the proportion varies according to circumstances. The starch is applied in the state of a pretty thick paste, while the goods are passed between a pair of rollers.

In other cases equal quantities of porcelain clay and calcined sulphate of lime are mixed with the starch. These substances are applied only on one side; but by the rollers they are forced into the cloth, intermix themselves with its internal structure, and add greatly to its apparent strength and thickness. This method of thickening was undoubtedly intended at first as a fraudulent method of making the purchaser believe that the cloth was much

Bleaching, stouter and thicker than it really was. But it has been so long practised, and is now so universally known, that all purchasers must be aware of it, and of course not in any danger of being deceived. But it certainly serves the purpose of making the goods appear much more beautiful, and of a stouter fabric to the eye; and as long as they continue unwashed, they are really stronger than they would be without this artificial dressing. So far it is beneficial; and as it does not enhance the price, the purchasers have no reason to complain of imposition.

Plate CVII. fig. 2, represents the starching machine or stiffening mangle; the middle roller being of brass and the other two of wood. They are pressed together by means of levers, which are loaded less or more, so as to leave the requisite quantity of starch in the cloth that passes through the rollers. A is the roll of pieces as they come from the water mangle, B a box containing the starch. It is furnished with a roller fixed near the bottom. The piece, in passing under this roller, gets filled with starch, the superfluous part of which is pressed out again by the rollers of the mangle. The piece is then rolled up as before at the back of the machine.

14. The next process is to dry the goods after starching. This is done by hanging them on rails in an apartment heated by a flue passing round the room and down the centre, where it passes into the chimney. There are usually two furnaces, one at each corner of one of the sides of the apartment. The flues from these furnaces pass round the apartment in the way represented in the margin, and uniting in the centre of the side of the room farthest from the furnaces, pass down in one common

flue through the centre of the room to the chimney, which is situated midway between the two furnaces. The side flues are usually covered by thin brickwork, but the middle common flue is covered with plates of cast-iron. When the cloth is hung up in this apartment the temperature is at first low, but it gradually rises as the goods get dry. The workmen, while employed in hanging up the goods on the rails, &c. which occupies a considerable time, find themselves obliged to throw off part of their clothes, and even sometimes to work naked, with the exception of a pair of drawers or a cloth wrapt round their loins.

15. Nothing now remains but the process of calendering, which gives the goods their final gloss and texture. For this purpose they require in the first place to be damped. This is done by passing them leisurely over a machine, which scatters upon them, as they pass, an infinity of exceedingly small drops. When these drops are first applied, if we hold up the cloth between the eye and the light, we see a great number of small round wet spots, while the greatest part of the cloth is dry. But when the pieces are left for some time standing together in a heap, these spots gradually disappear, and the cloth acquires a uniform dampness, which fits it for assuming the gloss which it acquires by the calendering.

Plate CVIII. fig. 3, represents the damping machine. A is a box containing a circular brush B, which is made to revolve rapidly, its points just touching a surface of water which is kept of a uniform height. The goods, dry from the stove, are laid down at C; they are pulled in single folds over the surface of the box A, by the pair of rollers D, which are turned round by machinery. A shower of minute drops of water is thus thrown up upon

the cloth as it moves over the surface of the box, and the piece, folded up by a workman, is left in a heap till the drops have all disappeared, and the cloth acquired a uniform degree of dampness.

Calendering is making the cloth to pass between a pair of rollers forced against each other by the application of a considerable pressure. During this process the texture of the cloth is made to vary at pleasure. When the goods pass simply between the smooth rollers, the threads are flattened, and the whole piece assumes a soft and silky lustre. When two folds of the cloth are made to pass together through the rollers, the threads make an impression on each other, and assume a wiry appearance, with an intermediate hollow between each. Various degrees of this wiry appearance may be given at pleasure.

Plate CVIII. fig. 4, represents the calender. It consists essentially of a frame-work, arranged so as to retain a number of rollers parallel, one above another, with levers and pulleys to press them together, and wheels and shafts to make them revolve. Two of these rollers are of cast-iron, nicely turned and polished, and three (the largest) of wood with iron centres. The piece of cloth, after being damped, is laid down in front of the calender, and made to pass in various ways between these rollers, after which it is rolled round a cylinder behind, and taken away to be folded.

The goods, after being thus calendered, are folded, and various devices are stamped in red or in blue upon the end of the piece, according to the different markets in which they are to be exposed; for different stamps are requisite for different markets, South America, the West Indies, India, North America, the Mediterranean, &c. requiring each its own device; and, what is very curious, the sale of the goods in a great measure depends upon these stamps; so that if they were absent, the goods, however well prepared, and however excellent in every other respect, would not meet with a ready sale. Everywhere appearances are more attended to than realities. Man is essentially a gullible animal, and quackery is a most important principle in human nature in general. After the goods have been regularly folded, they are placed piece by piece into a Bramah's press, with a sheet of pasteboard between each; and after a certain interval an iron plate is substituted for the pasteboard, to prevent any inequality in the pile. After sufficient pressure in this machine, they are packed up between boards, to prevent any injury during the carriage, and sent to the merchant or manufacturer to whom they belong.

Such is a sketch of the processes at present followed in the most extensive bleaching establishments in Great Britain for bleaching cotton. The processes altogether amount to about twenty-five, and the whole expense of bleaching and finishing a piece of twenty-four yards in length is tenpence, which is somewhat less than one half-penny per yard.

The loss of weight sustained during the bleaching of fine cotton cloth in the bleaching houses round Glasgow amounts very nearly to ten per cent. Of this one half may be considered as weaver's dressing; so that the real loss sustained during the bleaching is not more than five per cent. But when some coarse cotton goods are bleached, we are informed, by a gentleman who tried the experiment, that the loss of weight, independently of the weaver's dressing, amounts to ten per cent.

2.—Bleaching of Linen.

16. From the experiments of Mr Lee, who took out a patent about the year 1810, it appears that the colouring matter of flax is not chemically combined with the fibrous

threads constituting the bark of the stalk; but that a chemical combination takes place while the plant is steeped in water. The object of this steeping is to rot the plant, and enable the fibres to separate readily from the stalk. It is a putrefaction, which goes on to a considerable extent, and generates so much noxious matter as to destroy the fish, if the flax be steeped in water containing them. This fermentation weakens very considerably the strength of the flax fibres, and even destroys many of them. Mr Lee's process, therefore, if it be practicable on a large scale, would be a prodigious improvement. It would render the flax fibres much stronger, it would increase their quantity, and it would save the expense of the materials employed in bleaching the linen. The writer of this article has been informed that Mr Lee's process has uniformly failed of success when tried in Ireland. If this account be true, it is extremely difficult to explain it. We have seen it performed by workmen under his own direction at Old Bow, near London, with the most complete success; not merely upon handfuls of flax, but upon whole fields of it. Indeed the whole is so extremely simple, that we cannot well see how it should fail, if properly conducted. We cannot, therefore, help suspecting that the prejudices of the Irish, with which it would have to contend, have been too powerful for it; but that, as soon as it shall meet with fair play, it will be found just as practicable, and certainly much cheaper and better than the methods at present in use.

That Mr Lee's process has hitherto failed, and that it has been abandoned by the patentee himself, is an undoubted fact; but we cannot avoid suspecting that this was in some measure the fault of the patentee himself. If, instead of attempting the process at Old Bow, at a distance from the linen manufactory, and where no person qualified to appreciate its importance was likely to be near,

he had tried it in a place where the linen manufactory existed, Dundee, for example, or Belfast,—and had he associated with himself some person who was conversant with machinery, and who could have applied a mechanical process more convenient and expeditious than the method of Mr Lee, which was simply beating off the woody fibre by means of wooden mallets,—we cannot but think that the process would have been attended with success. The object of Mr Lee was to save the expense of bleaching linen. For when the flax is separated from the plant without the putrefactive process induced by steeping it in water, nothing more is necessary in order to make it white than simply to wash it in water.

As steeping is uniformly practised, the colouring matter becomes chemically combined with the fibres of the flax, and the process of bleaching must be had recourse to in order to render it white. But we conceive it to be unnecessary to enter into any minute details about the method of bleaching linen, because it is similar to the processes for bleaching cotton. It is much more difficult indeed to bleach linen than cotton; hence the boiling with an alkaline ley, and the steeping in the solution of chloride of lime, must be repeated three or four times. In general, the linen is exposed upon the grass to the sun for some weeks, though this part of the process is not essential. The loss of weight which linen sustains during bleaching amounts to about one third part of the whole weight of the goods. Cotton scarcely sustains a loss of one tenth part. This shows at once the difference in the difficulty between bleaching linen and cotton.

The following experiments, made by Charles Tennant, Esq. of St Rollox, near Glasgow, in July and August 1831, point out the parts of the process in which the loss is sustained, and are so valuable that we cannot avoid inserting them here:—

Experiment 2d—On bleaching 12 cuts of linen yarn, of the quality denominated 2 lbs. per spindle, weighing 3460 grains from bundle, and when dried, 3350

In this experiment the white was fully equal to the former; the materials used were in the same proportion to the weight of yarn, although the time and operations were reduced one half; and this may account also for the saving of the weight of the yarn, 31.79, instead of 35.21, as in the first experiment.

17. Wool, like hair, of which it is a variety, is composed of filaments or tubes filled with a substance of an oily nature. The surrounding surface of these tubes is pierced with an infinite number of small holes which communicate with the internal cavity. It is very little altered by exposure to the air, and undergoes no change from the action of boiling water. It is of great consequence that the bleacher should attend to this circumstance, as will appear immediately.

18. A solution of caustic alkali or caustic ley destroys it altogether, and forms with it a kind of soap.

19. The wool, as it comes into the hands of the manufacturer, usually contains a large portion of the natural greasy matter, from which it must be purified before it can undergo the process of bleaching. Sometimes the farmer cleans it from most of its oil, so as to diminish its weight by fifty or sixty per cent., in order to enhance the value of the article; but care is taken to leave some portion, as the natural fat is found to be the best preservative against the attacks of moths and other insects.

20. The first object then is to carry off the whole of the oily matter, which is called the operation of scouring, and is performed by means of an ammoniacal ley, which is thus prepared. Five parts of river or other soft water are to be mixed with one part of stale purified urine, which is found to contain a large quantity of ammonia.¹ This mixture is to be boiled for a short time; and into this, at about the heat of fifty-six degrees, or so that the hand of the workman can be easily held in it for a considerable time, the wool is to be thrown. Four or five pailfuls will generally be sufficient for twenty pounds of wool. After steeping for a short time, the wool is to be stirred about in the mixture continually for about a quarter of an hour or twenty minutes, according to the quantity of greasy matter. 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 continued stream of clear water, while a workman is perpetually employed in stirring it with a pole, till the water passes off perfectly clear. The wool is then removed, and a fresh quantity put into the basket, which is to be treated in the same manner. The steeping and rinsing are to be repeated till the wool has attained as great a degree of whiteness as it is capable of receiving from this operation. It is necessary, in order to conduct this process to the greatest advantage, that the workman should attend to the following circumstances.

21. 1st, A quantity of fresh ley must be from time to time added to the bath, as the immersion of the wool is found to weaken its power; but it is better not entirely to renew the bath, as the grease abstracted from the wool during its immersion forms with the ammonia of the urine a kind of soap, which much increases the cleansing quality of the bath.

22. 2d, Increasing the temperature of the bath will augment its detergents powers, and may sometimes supply

the want of an addition of stale urine; but both these circumstances require caution, as too great a degree of heat hardens the greasy matter, and renders it more difficult of solution; and again, too much urine makes the wool harsh.

23. 3d, After being much used the bath becomes too foul, and must be entirely renewed.

24. The wool which has properly undergone the process of scouring should be white, soft, elastic, and open; whereas before it was hard, stiff, and greasy. By this operation the wool loses much more of its weight, so that 100 pounds of raw wool, when completely scoured, will not yield more than 30 or 40 fit for the manufacture of cloth.

25. After scouring, the wool is sometimes carried to the fulling mill, in which it acquires an additional degree of whiteness. The above is chiefly employed for the coarser wools, and wool that has yet to be carded for the making of broad cloth; but for the finer kind it is better to employ a bath in which soap has been dissolved. This method is more expensive, but the expense is compensated by the superior quality of the wool which is thus treated. This operation is performed by the combing, and is thus conducted. The wool is divided into parcels containing each about six pounds and a half. A bath is prepared with two pounds and a half of green or black soap dissolved in a sufficient quantity of boiling water; and in this bath a parcel of the wool is to be washed for a longer or shorter time according to its foulness. It is then wrung by means of a hook, and hung in the sunshine or air to dry. Before it is combed it must undergo a second scouring, which clears it of all the natural oily matter.

26. This quantity of wool is not to be washed all at once, but in successive portions; and fresh hot water is to be added from time to time, in order to free the wool more easily from the grease. For wringing it there is a hook fixed at each end of the washing-tub, on which the wool is fastened and turned round by means of a handle or winch, fixed to one of the hooks. As economy should be consulted in every manufacture, a method of scouring wool without soap would be of considerable advantage. Fullers have long been in the habit of employing a species of clayey earth, called from them fullers' earth, which has the property of combining with the greasy matter, and rendering it more soluble in water. Before the wool is quite dry it is combed, as this operation is found to succeed best when it is a little moist, it being then easier to form it into proper lengths of three or four feet. Considerable nicety is requisite in the conducting of these first processes, as much of the success of the succeeding operations depends on their proper management.

27. After combing, the wool sometimes undergoes two or three further washings, especially when it is required of a very delicate white.

28. It is known that the wool has been properly scoured by its filaments being smooth, long, and slender, white, and perfectly free from foreign substances, and not having lost their natural tenacity. The Dutch wool is generally the purest: the English is next in quality, but is much harsher and fouler. The German wool is still harsher than the English, and the French is inferior to them all.

29. The loss sustained by the wools in scouring is proportional to their impurity. Thus the French and German lose about a third of their weight, while the Dutch and English do not lose above a fourth.

30. But this scouring, whether it be performed with

¹ The detergent property of urine has been long known, and it is frequently employed in washing to save soap. At sea, where fresh water cannot be spared for the purpose of washing, the sailors are accustomed to scour their foul linens in stale urine, which so far cleanses them that a subsequent rinsing in salt water renders them tolerably pure and sweet.

urine, soap, or earth, is seldom sufficient to bring the wool to that brilliant whiteness which is desirable for some manufactures. This is given it by means of the vapour of sulphur, or by steeping it in sulphurous acid, which is called by the manufacturers sulphuring.

31. The usual method of sulphuring goods is to expose them in a very close apartment to the vapour of burning sulphur. The goods are hung on poles so disposed that the vapour can readily pass between the pieces, and when the chamber is filled, a quantity of sulphur placed in very flat and broad dishes is set fire to, and allowed to burn away gradually in the chamber, while every aperture by which the vapour could escape is carefully closed. The acid vapour generated by the combination of the sulphur with the oxygen of the air of the chamber penetrates to every part of the cloth to which it can get access, destroys the colouring matter, and thus completes the bleaching. Every thing is allowed to remain quiet till it is supposed that the effect of the sulphurous vapour has fully taken place, which requires from 6 to 24 hours.

32. The action of the sulphurous vapour leaves a roughness and harshness on the cloth, which are removed by passing it through a bath slightly impregnated with soap.

4. Bleaching of Silk.

33. Silk is a substance possessing some degree of transparency, and is spun by a caterpillar from a matter contained within its body, which has the property of hardening when exposed to the air. The silk-worm is an inhabitant of the southern climates, being originally brought from Asia, and naturalized in the south of Europe about the period of the decline of the Roman empire.

34. The filaments of silk, as left by the silk-worm, are rolled together into a kind of ball or clew, and in their natural, or what is called the raw state, are covered with a yellow varnish or gum, which obscures their lustre, and gives them an unpleasant roughness.

35. Water has no effect on silk at the boiling temperature, and no change is produced on it by alcohol; but alkaline leys, when tolerably strong, attack, and are capable of dissolving it. The yellow varnish is soluble also in alkaline leys, and it may even be separated by long-continued boiling of the silk. When the varnish is thus carried off, the silk is found to have lost about a fourth of its original weight.

36. Two methods are in practice for bleaching silk; the first, in which it is ungummed or deprived of the natural varnish; the second, in which this is retained, in order to give them that stiffness which is required for gauzes, blonds, &c.

37. In the first process, the silk is to undergo a scouring similar to what we have described as necessary for depriving wool of the natural oil. For this purpose a quantity of water is put into a boiler over a fire, and for every hundred pounds of silk to be scoured, thirty pounds 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 degrees of Fahrenheit, and at this temperature it must be kept during the process. The silks are to be hung in the liquor in 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 with the pin to clear them of the soapy water, then well shaken, and put into coarse linen bags, in parcels of from twenty to thirty pounds each.

38. 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 two or three hours, taking care to keep the bags from sticking to the bottom of the boiler, by frequently stirring them with a stick.

39. For silk that is intended to be dyed, the former steeping in the lukewarm bath is unnecessary, and the present boiling only is employed, using a greater quantity of soap in proportion to the fineness of the colour. Thus for the ordinary colours, the proportion above laid down, or even less, will suffice; but for the saffranum colours, and the poppy and cherry red, even 50 pounds are sometimes employed to the 100 pounds of silk.

40. After boiling, the silk is wrung as before, and then washed thoroughly in a stream of water; they are then examined, and if it appears they are not sufficiently or not uniformly scoured, they must be submitted to a fresh bath.

41. The white silk usually sold has a bluish shade. This is given it by a bath impregnated with litmus or indigo. This is prepared by dissolving a pound and a half of fine soap in about ninety gallons of water, in which a small quantity of litmus or indigo has been diffused. The bath is heated to about 90 degrees, and the silk is passed through it over rods or reels till it has acquired the requisite shade. Being taken out, it is wrung and dried.

42. From these processes the silk acquires a tolerably clear white, but the highest degree is given to it by the action of the sulphurous acid, either in the state of vapour, as is usually practised, or by immersing it in the liquid acid, according to the method of Mr O'Reilly.

5.—Bleaching of Rags for the Papermaker.

43. The rags to be whitened should be well washed in the engine, and when reduced to what is called half-stuff, the water should be run off, leaving just enough to allow them to be easily turned. While the rags are thus preparing, a solution of the bleaching-powder is to be got ready, by putting the powder into a pitcher or other convenient vessel, and pouring upon it two or three gallons of water, stirring and bruising it well, till every thing soluble is taken up. After it has stood some time to allow the insoluble sediment to fall down, it is fit for use, and the pure solution should be poured into the engine. The sediment may be repeatedly washed with fresh portions of water to exhaust any remains of soluble matter, which alone is useful in the whitening process. While this last operation is going on, the engine is to be kept moving, and to continue so for about an hour, which will generally be sufficient to produce the requisite degree of whiteness. The water may now be returned upon the engine, and the washing continued as usual till the process be completed. The quantity of powder usually allowed is from two pounds to four pounds for every hundredweight of rags, in proportion to the whiteness required and the difficulty of whitening the stuff.

Rags containing dyed colours to be discharged, should be well washed, and reduced to half-stuff. They are then removed from the engine and put into a puncheon made water tight, but having a sufficient opening in the side to admit with ease the putting in and taking out of the stuff, and capable of being shut up so as to retain the water. Having put the stuff into this puncheon, take for every hundredweight of the rags a solution containing from five to eight pounds of bleaching powder, according to the strength and fixedness of the colours to be discharged. Pour the solution into the puncheon among the stuff, allowing liquid enough to let the stuff float easily, and for each pound of powder used add half a pound of sulphuric acid. Then shut up and secure the opening so as to make