BLEACHING

BLEACHING.

BLEACHING is the art of whitening thread and cloth. It has been treated at considerable length in the Encyclopædia. Our business here is merely to supply the defects of that article. These are chiefly two; namely, 1. A very incomplete historical detail of the improvements in bleaching, at least as far as this country is concerned; and, 2. The omission of any description of the present mode of bleaching, as practised by the most enlightened manufacturers of Great Britain.

History.

I. The Ancients, especially in Egypt, where white linen 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, published 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 Essay, 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 accidental access of water to the lime. We endeavoured, with some pains, to verify this quotation; and, for this purpose, turned over all the writings of

Theophrastus with which we are acquainted, without being able to find any thing bearing the least allusion to it. We have doubts whether lime could be employed as a detergent of linen, without injuring the texture of the cloth; and, on that account, it would have gratified us exceedingly to have found such a statement in so respectable and correct a writer as Theophrastus.

About sixty or seventy 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 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 bleachings 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 es-

Bleaching. 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 bleach-fields, manufacturers were indebted to Dr 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 oxymuriatic acid 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, over 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 so much 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 acid (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 acid is distinguished. When water, impregnated with this acid, 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 is still known among bleachers.

The property which oxymuriatic acid 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 acid in bleaching cloth, and found that it answered perfectly. This idea is developed still farther in a paper on the same acid, 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 present Duke of Gordon to Geneva, and he was shown the discolouring property of oxymuriatic acid by M. de Saussure. Mr Copland was much struck with the importance of the experiment, and on his return to Aberdeen in July 1787, 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

Bleaching 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.

New Process introduced into Britain by Mr Watt.

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. 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, March 19, 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 bouillon. J'ai blanchi toute 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.

Dr Henry quotes a letter of Mr Watt, dated 1788, February 23, 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, farther, 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 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 oxymuriatic gas, coating them within with a mixture of wax and pitch, which rendered the air light, and prevented the gas from acting on the wood. Mr Watt likewise contrived a test to indicate the strength of the water impregnated with oxymuriatic acid, 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 oxymuriatic acid, 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 he 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 oxymuriatic acid, 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 conven-

Bleaching. niences; but rather at too great a distance from Valenciennes. M. 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 able to establish itself in any manufactory in France, before the publication of his Memoir. One of the great difficulties in the way of applying oxymuriatic acid to bleaching was the very disagreeable and noxious odour which characterizes it, and which rendered it not only very offensive, but highly injurious to the health of the workmen. He describes, at considerable 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 from M. Berthollet himself.

When he first began to bleach, by means of water impregnated with oxymuriatic acid, he employed that liquid as concentrated as possible; but he found that the texture of the cloth steeped in this liquid was considerably injured. To prevent this effect, he at first added a little alkali to the liquid, 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, he was requested to go to Javelle, to show the bleachers there, the method of preparing the oxymuriatic acid, 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. Sometime after 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 oxymuriatic acid. 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 Bonnueil 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 ^Bleaching. 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 oxymuriatic acid, 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 Bonnueil and Company, consisted of oxymuriatic acid, or of some proportion 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 oxymuriatic acid by Mr Copland, happened to be in the gallery of the House of Commons when this application in favour of these 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 in the large way with oxymuriatic acid. 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 oxymuriatic acid, 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 oxymuriatic acid, 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 oxymuriatic acid 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 oxymuriatic gas. Its smell was less noxious, and it might be employed to whiten printed calicos 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 oxymuriatic acid, and when kept for some time, it lost its bleaching properties altogether. The reason of this last alteration is now sufficiently understood; the oxymuriatic acid in the liquid was gradually destroyed, and converted into common muriatic acid and chloric acid; the water containing merely common muriate of potash and chlorate of potash. In conse-

Bleaching. quence 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 oxymuriatic acid gas. Hence the oxymuriate 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, but none of them appear to have been attended with success. But Mr Tennant of Glasgow, after a great deal of most laborious and acute investigation, hit upon the method of making a saturated liquid of oxymuriate 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 grey muslin on a Tuesday, which on the Thursday immediately following were returned bleached to the manufacturers, at the distance of 16 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, the nominal 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 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 or 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 so much the more formidable, because their existence is not perceived.

In consequence of this decision, the use of liquid oxymuriate of lime in bleaching was thrown open to all, and appears now to be universally employed by all the great 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 oxymuriatic acid. 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 oxymuriate of lime at first upon a small scale, which has been ever since gradually extending, and is now very considerable indeed. During the whole period of the duration of his patent, he laboured under great disadvantages. The oxymuriatic acid 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 oxymuriate of lime were established in that kingdom. In Ireland, the manufacturer obtained his salt-duty free, while in Scotland 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 oxymuriate 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 has been lately granted to Mr Thomson, a Lancashire bleacher, for the process, which, we believe, he imported from Iony. The method is this: An acid paste, consisting of citric acid, or any other acid thickened with gum, is first printed on the Turkey red cloth, which is then passed through liquid oxymuriate of lime. It becomes white only where the acid was applied. On this bleached part any

Bleaching. 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 oxymuriatic acid 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 reagent, in consequence of some suggestion from Scheele or Saussure. (Parkes's Chemical Essays, 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 oxymuriatic acid to bleaching,—a merit which he has enjoyed without a competitor for 30 years. Scheele was dead before any one attempted to introduce the new acid into bleaching, either in Great Britain or Ireland. And there is every reason for believing that Saussure's knowledge of the bleaching qualities of oxymuriatic acid, originated from Berthollet's publications on the subject in 1785 and 1786.

There are three different ways of employing oxymuriatic acid in bleaching, still followed by different manufacturers; the first, the simplest, and we may add, the most economical and efficacious mode, is to impregnate water with oxymuriatic acid, and to use this liquid without any addition in a sufficiently diluted state. Mr Rupp, long ago, demonstrated the superior economy of this process, and even at present it is used by the great house of Oberkampf, Widmer, and Company, of Iony, near Versailles, who have contrived a very ingenious apparatus for its preparation. The only objection to this mode of using the gas, is its suffocating odour, which renders it injurious to the health of the workmen employed.

But the method universally employed by the great bleachers of Britain and Ireland, is to form a liquid oxymuriate of lime, and to immerse the goods in it. The gas is always obtained from common salt, by the joint action of sulphuric acid and black oxide of manganese. Various proportions of these ingredients have been recommended by different persons; but none of them seem to have founded their numbers on scientific considerations. Berthollet, in his dissertation on this subject, pub-

lished in 1789 (Annales de Chimie, II. 165), recommends the following proportions as the best:

6 parts of black oxide of manganese,
16 parts of common salt,
12 parts of sulphuric acid,
8 or 12 parts of water.

Boullon La-Grange, in his Elementary Chemical work, recommends

3 parts of common salt,
2 parts sulphuric acid,
1 part of black oxide of manganese,
2 parts of water.

Mr Rupp directed

3 parts of manganese,
8 parts of common salt,
6 parts of sulphuric acid,
12 parts of water.

Mr Tennant of Glasgow directs

3 parts common salt,
3 parts of manganese,
3 parts of sulphuric acid,
3 parts, by measure, of water.

The usual proportions in France are,

3 parts manganese,
10 parts common salt,
7 parts sulphuric acid,
9 parts water.

The numbers recommended by Mr Dalton, as agreeing with the atomic theory, are,

100 sulphuric acid of the specific gravity 1.850,
76 water,
40 common salt,
35 black oxide of manganese.

These numbers are founded on the supposition, that two atoms of sulphuric acid are requisite to disengage one atom of muriatic acid from common salt, which, at the common temperature of the atmosphere, or when the heat of boiling water is only applied, is probably true; though at higher temperatures we know, that one atom of sulphuric acid will drive off one atom of muriatic acid. If we consider the state of the common salt, as it is employed, and the frequent impurity of the oxide of manganese used, pro-

* We may notice here, what we consider as a very improper restriction in the new act of Parliament, which takes off the duty on the common salt used by bleachers. They are prohibited from using the rock-salt as it is dug out of the mine, but must employ what has been refined, and which, of course, amounts to four times the price. Surely the framers of the act might have easily seen that, if it was their object to prevent smuggling, it would have been answered much better by prohibiting the use of refined salt, than by restricting the bleachers to it. It would be impossible to smuggle rock-salt without actually refining it, which no bleacher could do without the certainty of detection. Indeed, such a smuggling trade could only be followed on a scale totally below the attention of a bleacher.

Since the preceding note was written, this absurd restriction has been withdrawn, and the use of rock-salt permitted.

Bleaching. bably the bleachers would find the following proportions the most economical and advantageous :

• 2 parts sulphuric acid,
• 2 parts water,
• 1 part common salt,
• 1 part black oxide of manganese.

At present there can be no doubt that the proportion of common salt used by the bleachers is too great. It is well known, that what remains in the stills after the process, contains still a considerable proportion of muriatic acid. Thus Mr Wilson found the salt which crystallized in the liquid residuum, after distillation, was composed of

This residue was obtained from a mixture of

• 3 parts common salt,
• 1 part black oxide of manganese,
• 4 parts sulphuric acid of the sp. gr. 1.500.

See Annals of Philosophy, I. 365.

Dr Henry of Manchester found very large proportions of common salt and muriate of manganese in the residue left after distillation; and he informed the writer of this article, that he had known a bleacher, when in want of common salt, to work twice from the same ingredients, by adding fresh manganese and oil of vitrol. This is a sufficient proof that vastly too much common salt is employed. Indeed, the consumption of common salt by the bleachers is enormous. One bleacher in Lancashire, for example, uses, every six weeks, four waggon loads of common salt, each load containing 3 tons 13 cwt. This is almost at the rate of two tons and a half of salt per week. He employs, for his process, 22 leaden stills, each 22 inches deep, and about 2 feet 4 inches in diameter. Eleven of these are worked on alternate days.

The temperature of steam, under the pressure of the atmosphere, is sufficient to expel the whole of the oxymuriatic acid, and nothing is gained by employing a stronger heat. Accordingly, the stills are universally heated by steam. The calculation is, that 25 square feet of surface in the boiler, is sufficient to heat six stills of the dimensions given above, into each of which are put 112 lbs. of common salt. The gas is received into cream of lime, in which the lime is kept suspended by mechanical agitation. When the process is finished, the undissolved lime is allowed to subside, and the clear liquid is drawn off. Its specific gravity is, generally, about 1.0125. Liquid of this strength is usually mixed with five or six times its bulk of water, before the goods are immersed in it. It has been said, that muriate of lime always injures the texture of cloth immersed in it. But this is true only when the solution is concentrated, and when it is used boiling hot; but

by no means applies to the processes of the bleacher.

The third state in which the oxymuriatic acid is employed by bleachers, is combined with lime, constituting dry oxymuriate of lime. Hitherto the manufacture of this salt in Great Britain has been confined to Mr Tennant of Glasgow, the inventor of the process. But his patent being now at an end, other persons have begun to make it in the neighbourhood of Manchester. For the manufacture of this salt, leaden stills are employed similar to those used in making liquid oxymuriate of lime, and likewise cast-iron stills. The gas is conveyed into a close wooden vessel, on the bottom of which is spread some quicklime, newly slaked and sifted. As the gas passes over, it combines with the lime, and gradually forms the salt required. It is a soft white powder, possessing little smell. When heated it gives out oxygen gas; but if it be mixed with sulphuric acid, oxymuriatic gas is given out when the heat of a lamp is applied. It is partially soluble in water, and the solution gradually disengages bubbles of oxygen gas, while the salt is changed into common muriate of lime. This change appears to take place gradually, even when the salt is kept in a dry state. Mr Dalton has analyzed this salt, and found it composed of

When the salt is dissolved in water, one-half of the lime is precipitated, so that the compound which was formerly a subchloride of lime, is now converted into a chloride. Its constituents are,

When a current of oxymuriatic gas is passed to saturation through water in which lime is suspended, a bichloride of lime is formed. It is composed of

See Annals of Philosophy, I. 15, and II. 6.

From Mr Dalton's experiments, the oxymuriate of lime of commerce contains one-third of its weight of common muriate of lime; but this portion varies according to the age of the salt, always increasing, till at last the whole is converted into common muriate of lime.

II. In the article BLEACHING in the Encyclopædia, Present very copious extracts have been given from Kirwan, Method of Berthollet, Decharmes, Oreilly, Rupp, &c. with descriptions and drawings of the different apparatus recommended by them. But the reader of that article will be at a loss to form any idea of the method

Bleaching. of bleaching at present employed by the most en-
lightened bleachers in Great Britain. On that ac-
count, we conceive that it will be requisite to give a
concise sketch of the different processes as they oc-
cur in a practical bleachfield. We shall omit most
of the descriptions of apparatus, which would oblige
us to repeat many things contained in the article to
which this is a supplement. The bleaching appar-
atus is sufficiently simple to be easily conceived by
the reader without many particular descriptions.
Cotton being much more easily bleached than linen,
it will be requisite (though the processes are nearly
the same) to give the method of bleaching each se-
parately, because the quantity of materials employed
differ for each.

1. Bleaching of Linen.

It would appear from the new process of Mr Lee,
who separates the woody matter from the fibre of
flax without steeping it, by means of mechanical ac-
tion, and then bleaches his flax by simply washing it
in warm water, that the colouring matter is not che-
mically combined with the fibrous matter, while the
plant is vegetating, or after it is pulled, but that the
chemical combination takes place while the plant is
steeped in water. The object of this steeping is to
induce a fermentation, which loosens and destroys a
cement which bound the fibres of flax to each other
and to the wood. This fermentation weakens con-
siderably the strength of the flax fibres, and even
destroys many of them. Mr Lee's process, there-
fore, 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 quan-
tity, and it would save the expence 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 Mr Lee's process per-
formed 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 proper-
ly conducted. We cannot, therefore, help suspect-
ing 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 pre-
sent in use.

It is during the steep, then, that flax acquires its
permanent dark colour; and four processes, which
we shall now briefly describe, are requisite to re-
store it to its original white colour, or to separate
the colouring matter, which is chemically combined
with the fibres of the flax.

1. When the flax is converted into thread, it is
repeatedly moistened with the saliva of the spinner,
which leaves attached to it a quantity of albumen.
When the thread is woven into linen, it is covered
with the weaver's dressing, which consists of a paste,
made of flour and water. The first step of the
bleacher's process is to remove these foreign bodies,

that the colouring matter of the flax itself may be laid open to his subsequent operations. For this
purpose, the goods are immersed in warm water, or
in a warm alkaline ley, which has already been used
in the bleaching processes to be described imme-
diately. In this situation they are allowed to remain
till some degree of fermentation appears on the sur-
face of the liquid with which they are covered.
This appearance takes place sooner or later, accord-
ing to the nature of the goods and the heat of the
weather, and it is allowed to continue longer or
shorter according to circumstances. The goods are
then taken out, and well washed in pure water, which
now removes all the foreign matter added during the
spinning and weaving.

2. The second process consists in exposing the
goods to the action of alkaline leys.

The alkali universally employed by the bleachers
in Great Britain is Russian or American potash,
which contains about two-thirds of its weight of
caustic potash, according to the experiments of
Vauquelin (Annales de Chimie, XL. 273). The other
ingredients are sulphate of potash, muriate of potash,
carbonic acid, and siliceous earth. It has been alleged
that the potash of commerce is often adulterated ar-
tificially with common salt. This the bleacher should
always ascertain before employing it. Indeed, every
bleacher, who wishes to be exact, ought to be in pos-
session of a mode of determining the exact quantity
of potash which the alkali that he intends to use
contains. There are two methods which may be
employed for this purpose. The first is to dissolve
a certain quantity of the potash in water, and to try
how much acid of a known strength is requisite to
saturate the alkali contained in this solution. Ample
directions for reducing this method to practice, are
contained in the dissertation of Vauquelin above re-
ferred to. The second mode of testing the alkali is
more rapid; but would be less convenient for the
bleacher, unless he were in possession of a mercurial
pneumatic trough; but if he is supplied with this part
of chemical apparatus, the method is very easy; and,
perhaps, in the hands of persons not very conversant
with chemical experiments, more to be depended on
than the first described method. It is this. A glass
tube of the capacity of 10 or 12 cubic inches, shut
at one end, and flat at the other, so as to stand on
the mercurial trough when filled with mercury, is to
be graduated into cubic inches and tenths. The
tube, when the strength of the alkali is to be tried,
is to be filled with mercury, and placed inverted on
the trough. Then let up 20 grains of the alkali to
be examined, which will rise to the top of the tube.
Add now about 50 grains of sulphuric acid. As soon
as the acid comes in contact with the potash, an ef-
fervescence takes place, and the carbonic acid is ex-
tricated. Observe the number of cubic inches and
tenths of this gas extricated, taking care to sink the
tube so far in the trough that the mercury in the
tube and trough are upon the same level. Multiply
the bulk of the carbonic acid by the number 0.46313;
the product is the weight of carbonic acid present
in grains. Multiply this weight by 2.18; the pro-
duct is the weight in grains of real potash contained
in 20 grains of the pearl ashes under examination.

Bleaching. This last method is founded upon several chemical facts which have been sufficiently established. The potash, as it exists in American or Russian potash, is combined with carbonic acid in such a proportion, that one atom of acid is combined with one atom of alkali. An atom of carbonic acid weighs 2.750, and an atom of potash 6. The weight of a cubic inch of carbonic acid gas is 0.46313 grains. Hence, if we multiply the bulk of carbonic acid in cubic inches and tenths, by 0.46313, we obtain its weight in grains. The numbers 2.750 and 6, are very nearly to each other as 1 to 2.18. Hence, if we multiply the weight of carbonic acid, found by 2.18, we obtain the weight of potash with which it was combined. It is proper to know, that this method will give the proportion of potash rather below the truth, because, a little of the carbonic acid will be held in solution by the acid employed. If we add such a quantity of sulphuric acid, that, after the expulsion of the gas, the whole shall remain in a liquid state, the result will be almost perfectly exact, if the bulk of the liquid be added to that of the gaseous product, and the whole be considered as carbonic acid gas.

Formerly, the Irish bleachers were in the habit of using barilla instead of potash. But there are two objections to the use of this alkali. In the first place, the weight of real alkali contained in the same proportion of barilla, is much smaller than in pearl-ash; and, in the second place, the weight of an atom of soda being greater than that of an atom of potash, it is probable, that the second will go farther in bleaching than the former. When to this fact we add the difference of the price, which is always in favour of potash, there can be no hesitation in affirming, that no bleacher who studies the principles of economy, would make use of barilla if he can be supplied with pearl-ash. In trying the strength of barilla, the second of the two methods above described cannot be employed, because barilla contains both carbonate of lime and carbonate of magnesia. Hence the quantity of carbonic acid will always be much greater than it would be, if barilla contained only carbonate of soda. According to the experiments of Kirwan, a great proportion of the soda in barilla is in a caustic state. But if we attend to the way in which this substance is procured by burning the salcola vermiculata, we shall scarcely be induced to adopt this opinion. For, during the combustion of vegetable substances, carbonic acid is always evolved in considerable quantities, this acid would, of course, combine with the alkali, and the heat of the combustion is insufficient to decompose the carbonate of soda when once formed.

Two methods of applying pearl-ash to the purposes of bleaching, are generally followed. These methods are called Boiling and Bucking.

Boiling needs no description. The alkaline ley and the goods are put together into a boiler, and the whole kept at the boiling temperature for the requisite length of time.

Bucking is somewhat more complicated. It consists in making the alkaline ley, raised to a boiling heat, to pass repeatedly through the goods. Various modes of performing this process are followed in

different bleaching-houses. But they may be all reduced to one or other of the following three: 1. The goods are placed loosely in a proper vessel, the heated ley is made to run upon them, and to pass through them. As it comes to the bottom of the vessel containing the goods, it is pumped back again into the boiler, where it is heated a second time, and then made to pass through the goods as before. This process is repeated as often as is thought requisite. 2. The alkaline solution is put into the bottom of a large boiler, having a platform of wood, with holes through it, placed a little way above the surface of the ley. Through the middle of this platform there passes a pipe of a convenient size, the lower end of which reaches nearly to the bottom of the boiler, being immersed deep in the ley, while the upper end rises as high as the mouth of the boiler. The goods are placed upon the platform, and round the tube within the boiler to a convenient height. When heat is applied to the boiler, the steam generated is prevented from making its escape by the wooden platform and the goods. It, therefore, acts upon the surface of the ley, and forces it to ascend through the tube. A kind of umbrella is suspended over the top of the tube, which assists in spreading the ley over the surface of the goods. By this contrivance, it is made to spread over and trickle down through the goods, till it gets again to the bottom of the boiler, to be heated and forced up by the steam as formerly. This method is more efficacious than simple boiling, because the temperature of the ley is heated some degrees higher than 212°, which has a considerable effect upon the goods.

The following are sections of the vessels used for these two different methods of bucking: This figure shows the vessels employed, when the ley is simply pumped back into the boiler. A is the boiler

for heating the alkaline ley. B is the large wooden vessel in which the goods are placed. C the cock and pipe, by means of which the ley is conveyed upon the goods. D a square box designed for spreading the ley over the goods within the vessel B. E the pump for raising the liquor again out of the vessel B, from which it is conveyed by the

Bleaching. spout I back again into the boiler. F is the furnace for heating the ley. G represents the false bottom of the wooden vessel, full of holes, for the passage of the ley when it has run through the goods. H is a round wooden staff, which completely fits a hole at the bottom of the bucking vessel. It is called a duck, and is intended to be pulled up whenever the spent alkaline liquor is to be run off.

This figure represents the second kind of bucking apparatus. A is a metallic boiler to be fixed in brick work, as in the preceding figure. BB is the top part of wood, called a crib, with the bottom full of holes. In this, the goods are placed one above another, often amounting to many hundred pieces at one operation. C is the pipe through which the leys boil up, and dd is the umbrella suspended over the pipe, for the purpose of spreading the ley more effectually over the goods.

The third method of bucking is a modification of the second. It is considered as preferable, and is perhaps most generally used by experienced and extensive bleachers. The platform and its ascending pipe are placed, not in the boiler, but in a convenient tub or cistern. The requisite quantity of ley is put into the cistern below the platform. A tube passes into it, which conveys steam from a steam-boiler, in such quantity as first to heat up the ley to the boiling point, and then to force it up through the central tube, to be deposited over the surface of the goods, and to filter through them into the space below the platform. This method of bucking so nearly resembles the last, that the nature of the vessel employed will be easily understood without a figure.

The quantity of pearl-ash required for bleaching linen in general, amounts to $\backslash frac\{1\}\{10\}$th or $\backslash frac\{1\}\{12\}$th of the weight of the goods to be bleached. This quantity, however, is not to be used all at once; but is to be divided into six or eight portions, to be employed each in as many bucking processes. When the goods are boiled in an alkaline ley, the boiling is usually continued for four or six hours. In bucking, the process is generally continued till the liquor is so far evaporated, that the whole of it which remains is retained by the goods themselves. This generally requires from six to eight hours.

Heavy yarns for making ducks and similar fabrics are most advantageously bleached before being woven into cloth. These yarns are usually boiled with from 16 to 20 per cent. of their weight of pearl-ash, divided among two, three, and sometimes four boils, in proportion to the nature of the fabric, and the degree of whiteness required. When two boils are required, $\backslash frac\{1\}\{2\}$th of the weight of the goods may be used in the first, and $\backslash frac\{1\}\{6\}$th in the second boil. If the goods are difficult to bleach, or if a greater degree of whiteness be required, it is sometimes customary

to give them a third, or even a fourth boil, diminishing the allowance of potash each time. In the last boil, one-third or one-half of the potash is frequently kept out, and its place supplied by an equal quantity of soft soap. When the weather is favourable, the goods are sometimes exposed on the grass after each boiling.

3. The third process is to expose the goods to the action of oxymuriatic acid in some one of the three states described in a preceding part of this article,—namely, dissolved in water, combined with lime in the state of liquid oxymuriate of lime, or in the state of solid oxymuriate of lime. The first of these states is the most economical; but its very noxious odour renders its application scarcely practicable on a great scale. The second state consists of two atoms of oxymuriatic acid, combined with one atom of lime, or it is a bichloride of lime; and the third state, or the dry powder, is a compound of one atom of oxymuriatic acid and one atom of lime, or it is a chloride of lime. Of these two last substances there can be little doubt that the first, or the one made in the liquid way, is the most efficacious. But we shall suppose the dry chloride of lime to be the substance used; as its employment is likely to increase very much, especially among those bleachers who are the most likely to require instructions. Besides, it is not difficult to apply the observations made on chloride of lime to the liquid bichloride.

The quantity of oxymuriate of lime required for bleaching linen varies considerably, according to the nature of the linen operated upon,—according to the season of the year, and the degree of exposure on the grass,—and according to the whiteness required. But we may state the average quantity as varying between $\backslash frac\{1\}\{10\}$th and $\backslash frac\{1\}\{12\}$th of the weight of the goods employed. This quantity may be divided into three or four processes. If three processes be reckoned sufficient, $\backslash frac\{1\}\{3\}$ths of the oxymuriate may be expended on the first operation, $\backslash frac\{1\}\{3\}$ths in the second, and $\backslash frac\{1\}\{3\}$ths in the third. If four processes are considered as requisite, then $\backslash frac\{1\}\{4\}$ths of the oxymuriate should be used in the first operation, $\backslash frac\{1\}\{4\}$ths in the second, $\backslash frac\{1\}\{4\}$ths in the third, and $\backslash frac\{1\}\{4\}$ths in the fourth. Two wine pipes may be employed for the solution of the bleaching powder. They should be placed on one end, the other end being open; and a plug-hole should be made in each, about 10 or 12 inches above the bottom. From 20 lbs. to 100 lbs. of the bleaching powder is to be put into a small tub or bucket, where it is to be well bruised and mixed with a little water. This mixture is to be thrown into one of the wine pipes, more water is to be added, and the whole carefully stirred together for a few minutes. A cover is then to be put upon the pipe, and the whole is allowed to stand till the insoluble part of the powder, consisting of quicklime, subsides below the plug-hole. The clear solution, called stock-liquor, is now to be drawn off through the plug-hole, and may either be used immediately, which is most expedient, or it may be kept under a close cover till wanted.

Repeated portions of powder may, in this manner, be dissolved in the same pipe, till the sediment ac-

Bleaching. cumulate to the height of the plug-hole. When this happens, fresh stock-liquor must be prepared in the other pipe. But instead of using pure water, as in the first operation, the sediment in the first pipe should be repeatedly washed, by filling up the pipe with water, stirring the sediment well, allowing it to settle, and then drawing off the clear liquor by the plug-hole. These washings, as long as they show any bleaching power, are to be used in the second pipe, instead of pure water, for preparing stock-liquor. The sediment, in every future operation, should be exhausted in a similar manner.

The strength of this liquor is determined 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, $\backslash frac\{1\}\{1000\}$ 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 dropped 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.

The bleacher's operations should go on in regular rotation. The whitest goods are put into the clean fresh steeps. As these goods do not exhaust the bleaching power of the liquor, its strength is restored after they are taken out, by the addition of fresh stock-liquor. It is then used for goods in a less advanced state of whiteness. If the second operation has not exhausted its bleaching powers, or rendered it foul, it may be used a third time by another addition of stock-liquor. But if it has been rendered very foul, and indicates only 12 or 15 degrees in the test-tube, it is not worth preserving or using.

One pound of the bleaching powder, as it is prepared by Mr Tennant and Company of Glasgow, is capable of forming from ten to twelve gallons of liquor of one degree.

The exposure of the goods to the action of the oxymuriate of lime should not commence till after the third boil or buck, if they are to be exposed three times to the action of this substance; and after the second, if they are to be exposed to four operations,

with muriate of lime. These operations should alternate with the last bucks or boils. In all cases, the oxymuriate of lime must be dissolved in such a proportion of water as to allow the goods immersed in it to float loosely and easily in the solution, that the liquid may come into free contact with every part of them.

Though the method of immersion or steeping the goods in the solution of oxymuriate of lime is most generally used, yet, in some cases, great advantage is obtained by wincing the goods through the solution, instead of allowing them to rest for any length of time in it. When the method of wincing is followed, a solution of twice or thrice the ordinary strength may be safely used, and much time in consequence saved. When the goods are coarse and heavy, such as yarn for ducks, this last method is almost universally preferred. These heavy yarns require from $\backslash frac\{1\}\{15\}$th to $\backslash frac\{1\}\{10\}$th of their weight of oxymuriate of lime, divided into a number of operations corresponding to that of the boils, and following these boils, or these boils with exposure on the grass, when such exposures are employed. In the first oxymuriatic operation, they are winced through a strong solution, produced by adding about three or four ounces of dry oxymuriate of lime to each gallon of water. The yarns are hung over a roller fixed in the mouth of the trough or tub that contains the solution, which covers part of its surface. This roller being then turned rapidly round by means of a crank fixed on one of its ends, the yarn is made to pass rapidly and repeatedly through the liquor for the space of thirty or forty minutes. Fresh parcels of yarn are, in succession, passed through the liquor, its strength being restored by additions of oxymuriate when necessary, and the whole changed when exhausted of bleaching powers and foul. In this way, a very powerful bleaching effect is produced, and yarns which have undergone one process in this way, may receive the remaining oxymuriatic processes to which they are to be exposed in the ordinary way of immersion, which is less expensive in point of labour, though less efficacious.

The oxymuriatic process then is repeated three or four times, beginning after the second or third boil or buck, and alternating with every subsequent boil or buck. The time during which the goods are exposed to the oxymuriatic solution during each process, is from six to twelve hours.

4. The fourth process consists in steeping the goods in an acid solution. This is called the acid process. We have already observed, that the acid at first used for this purpose was sour milk; but that, when Dr Roebuck contrived his new method of preparing sulphuric acid, Dr Home proposed this acid as a substitute for sour milk; that it speedily came into general use, and very much improved and shortened the tedious bleaching processes at that time in general use. This steeping in sulphuric acid is repeated twice, and sometimes thrice, once after each of the last two or three immersions in the oxymuriate of lime. For this purpose, a quantity of strong sulphuric acid is taken, amounting to about $\backslash frac\{1\}\{10\}$th or $\backslash frac\{1\}\{15\}$th of the weight of the goods to be immersed. This acid is diluted with 60 or 80 times its weight

Bleaching of water, which reduces it to the specific gravity of about 1.015. Now, sulphuric acid of this specific gravity contains about $1\backslash frac\{1\}\{2\}$ per cent. of its weight of real sulphuric acid. In this liquid they are steeped from eight to twelve hours. When linen fabrics are intended for printing, they require two or three additional processes in alkali, and one in acid, and the solution of the sulphuric acid is generally made one-third stronger when the goods are intended for the madder copper.

Such are the different processes at present followed by the practical bleachers in Great Britain. After each of them, whether boiling or bucking in an alkaline solution, immersion in oxymuriate of lime, or steeping in sulphuric acid, the goods must be carefully washed in pure water, either by machinery or otherwise, till all the materials employed are completely washed out of them. Upon this much of the economy and success of bleaching depends. It is likewise of great advantage to free the goods from the water which they contain after each washing, before subjecting them to the next operation. For this purpose, Bramah's press is employed in almost all the large bleaching-houses, and constitutes one of the greatest improvements introduced of late years.

2. Bleaching of Cottons.

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 fruticem, quem aliqui gossipion vocant, plures ylon, et ideo lina inde facta ylina. Parvus est, simileque barbatæ nucis defert fructum, cujus ex interiori bombyce lanugo netur. Nec ulla sunt eis in candore mollitiave præferenda." (Plinii, Natur. Hist. Lib. xix. c. 2.) The byssus 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 East India, 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. As it does not go through the complicated processes of flax and hemp, and is naturally (for the most part at least) of a lighter colour, the art of bleaching it is much more

easy and less expensive. The processes are nearly the same as those for linen; but it will be requisite to go over them shortly, in order to point out the difference in the proportions of the ingredients employed, and some other little circumstances which ought to be generally known.

1. The first, or fermenting process, is the same for cottons as for linens. This must be the case, because the weaver's dressing, which it is the object of the process to remove, is the same in both cases.

2. But there is a difference in the second process, which consists in exposing the goods to the action of alkaline leys.

Cotton goods are generally exposed to the action of lime diffused through water, so as to constitute what is called milk of lime. The liquid is heated to the temperature of $200^\{\backslash circ\}$, and the cloth is kept in it from four to six hours. Two or three alkaline processes will be required after this, and the quantity of potash which ought to be used should amount to $\backslash frac\{1\}\{20\}$th of the weight of the goods. When the application is to be made at twice, the first of the operations should have $\backslash frac\{1\}\{4\}$ths, and the second $\backslash frac\{1\}\{4\}$ths of the whole potash. If three processes are to be gone through, the first and second should have $\backslash frac\{1\}\{8\}$ths each, and the third $\backslash frac\{1\}\{8\}$th of the potash.

When heavy cottons are bleached, either boiling or bucking may be employed, as described under the head of linens. When the cotton fabrics are light, or contain dyed colours, boiling is generally preferred, and the proportion of alkali diminished one-third, while a quantity of hard or soft soap, equal to the diminution of the alkali, is added to the ley.

3. The third, or oxymuriatic process, is nearly the same for cottons as for linens. The quantity of oxymuriate of lime used, should amount to $\backslash frac\{1\}\{20\}$th or $\backslash frac\{1\}\{30\}$th of the weight of the cotton cloth to be bleached. This quantity is divided among two or three operations, an oxymuriatic process following each alkaline process. When three operations are to be performed, the first must have $\backslash frac\{1\}\{3\}$ths, the second $\backslash frac\{1\}\{3\}$ths, and the third $\backslash frac\{1\}\{3\}$ths of the whole oxymuriate of lime. When only two operations are to be performed, the first should contain two-thirds, and the last one-third of the whole. The duration of each steep should be from six to twelve hours, but not longer. If wincing through the solution be preferred, a stronger liquor may be used, and the operation may be finished in fifteen or twenty minutes.

4. The fourth, or acid process, is pretty much the same for cottons as for linens; the quantity of sulphuric acid should amount to about $\backslash frac\{1\}\{20\}$th or $\backslash frac\{1\}\{30\}$th of the weight of the cotton goods. It must be diluted with water till its specific gravity be reduced to 1.010. A steep in this diluted acid from six to twelve hours after each of the two last oxymuriatic processes is generally made use of.

When the fabrics are very light, or contain dyed colours, the souring is only once used, and the strength of the acid is reduced to 1.008. This souring is applied after the last oxymuriatic process. In this case thorough washing or rinsing in water, is most strictly to be attended to before exposure to the sulphuric acid in souring. When cotton fabrics

Bleaching. are intended for printing with madder colours, they require one or two additional hucks or boils, and the sours should be one-third stronger.

The intermediate washings in pure water, and the proper draining of the goods after washing, must be observed with as much care in bleaching cotton as in bleaching linen. It is only in the bleaching of those goods intended for printing, that any exposure to the light and air is now used, and that but seldom even in this case.

3. Bleaching of Rags for the Papermaker.

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 hundred weight 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 cwt. 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 the puncheon air tight; then turn the puncheon round upon its axis, by means of a crank fixed at one end of it. Moving it in this manner gives facility and uniformity to the discharging process.

We have now finished the sketch which we proposed to give of the processes at present followed by the practical bleachers of Great Britain. For several

other applications of the same operations, we refer Bleaching. to the article BLEACHING in the Encyclopædia. But probably a few words will be expected from us on the theory of the art. Upon this subject, the following observations are all we have to offer:

The fibres of hemp, linen, and cotton, are naturally Theory of white; but, before bleaching, they are combined with Bleaching. a substance which gives them their grey or brown colour. The object of bleaching is to remove this substance. From the experiments which have been made upon the subject, it would appear that this substance is partly in the state of resin, and partly in a state analogous to that of the volatile oils. Resins dissolve readily in the alkalies, which they neutralize and convert into a species of soap. But this is not the case with the colouring matter, which is in a state analogous to that of volatile oil. After the weaver's dressing has been removed, the cloth is boiled or bucked repeatedly in alkaline leys, which dissolve and separate the whole of the colouring matter, which possesses the characters of resin. The alkaline ley, after this process, is turbid, has a brownish red colour, a strong smell, and has lost its alkaline properties. When muriatic acid is poured into it, a copious flocky precipitate subsides, consisting of the colouring matter. This substance, when properly edulcorated, has a greenish grey colour, which it retains when separated from the water by the filter. But, when dry, it becomes blackish externally, though it retains internally its greenish tint. It is soluble in alcohol, insoluble in oil of turpentine, but dissolves readily in the alkalies. It tinges the strong acids, but does not readily dissolve in them. When thrown upon a red-hot iron, it burns with a yellow flame and a black smoke, leaving a charry residuum. These properties, for the knowledge of which we are indebted to Mr Kirwan,* are sufficient to show us that the substance which the alkalies separate from linen is analogous to the resins.

By repeated boiling in alkaline leys the cloth is rendered whiter. But it is not yet bleached; because a colouring matter still remains, which the alkalies are incapable of dissolving. The action of oxymuriatic acid, or exposure to the air and light, produces a change on this colouring matter, and renders it capable of being dissolved in alkalies. In short, by these processes it is converted into a resinous matter, similar to that which the alkalies had previously removed. There can be no doubt that this change is produced by the union of the colouring matter with oxygen. When the oxymuriatic acid is used, the oxygen is supplied by the water which is decomposed by the mutual action of the chlorine and the colouring matter. The chlorine combines with the hydrogen of the water, and is converted into muriatic acid; while the colouring matter combines with the oxygen of the water, and is converted into resin.

It would appear, that this change in the colouring matter renders it white; for linen will appear bleach-

* See his Experiments on the Colouring Matter of Linen Yarn and its Solvents, in the Transactions of the Royal Irish Academy for 1789.

ed if it be treated with a sufficient quantity of oxymuriate of lime. But this state of the colouring matter is not permanent. If it be allowed to remain in the cloth it speedily becomes yellow. Hence the reason why cloth, bleached with oxymuriatic acid alone, soon loses its white colour again. This happened to Berthollet, in his first trials to bleach in the large way, by means of oxymuriatic acid. It happened likewise, at first, to several bleachers in this country. It is requisite, that the colouring matter, now become soluble, should be removed by alkalies. Hence we conceive, contrary to the practice of bleachers, that the last process ought always to be boiling in an alkaline ley. In great towns, as in London, where linen cannot be exposed to the air and sun upon the grass, it would be a great advantage, if it were steeped, for some time before it is washed, in a solution of oxymuriate of lime. It might then be boiled in an alkaline ley. Linen or cotton, thus treated, would not become yellow by age, as is too often the case with linens in large towns.

The precise use of the steeping of the goods in sulphuric acid has not been ascertained; though it is known to be indispensable. It is supposed, that both linen and cotton contain a portion of iron, and that the acid removes this substance, which both renders the colour whiter and the cloth fitter for the subsequent processes of dyeing and calico-printing.

This explanation is not improbable, though we are not aware of any accurate experiments, by means of which, the presence of iron in the sulphuric acid solution, employed as a souring, has been ascertained. But, probably, the great use of the acid is to remove or neutralize the alkali, which, if allowed to remain in the cloth, would gradually injure its texture.

We have taken no notice, in the preceding article, of a proposal, made a good many years ago in Ireland, and, in support of which, a pamphlet was published by Mr Higgins of Dublin; we mean the substitution of the hydrogureted sulphuret of lime for the alkali. The reason of this omission is, that we are not in possession of any facts on the subject. But we consider the circumstance of no British bleacher having introduced this substitute into his work, as sufficient to entitle us to infer, that the substitute would not answer the purposes for which it was recommended. Several objections to its use will readily present themselves to those who consider the subject. Among others, we may mention, that if any metallic substance, as iron, were to come in contact with the goods which are under the influence of hydrogureted sulphuret of lime, this last substance would act as a mordant, and fix the metal on the cloth; from which it could not be again removed without some expence, and without the risk of injuring the strength of the substance. (J.)

BLOCKADE, in war, the shutting up of any place or port by a naval or military force, so as to cut off all communication with those who are without the hostile line.

There is, perhaps, no part of the law of nations which, in practice, presents so many perplexing questions, as that which concerns the respective rights of neutral and belligerent states. No definite line of distinction has yet been drawn between the privileges of war and peace; and the consequence has been, that, in all the wars which have been waged in Europe, the general tranquillity of the world has been endangered by the jarring of these two different interests. It has commonly happened, too, that all these important questions have been agitated during a season of war, when the passions of the contending parties were keenly engaged in the dispute,—when principles were already subverted,—and when the minds of men, exasperated by the glaring infraction of acknowledged rights, were not in a state to agree on any system of general equity, by which to regulate and reform the erring policy of states. In these circumstances, many points of international law, which appear to rest on the most obvious principles, and which are very clearly settled in the writings of civilians, have, nevertheless, been the occasion, in practice, of no small controversy, and have frequently involved nations in all the miseries of protracted war. This has been, in some measure, manifested in the case of the Rights of Blockade; respecting which, though no difference of opinion has ever prevailed among speculative

writers, a controversy arose during the late contests in Europe, which, along with other points, ultimately involved Great Britain in a war with the neutral powers. We propose, in the course of the subsequent observations, to state, 1st, The general principles from which the most approved writers have deduced the rights of blockade; and, 2d, To give a short account of the recent differences which have taken place between the neutral and the belligerent states, respecting the extent of those rights.

In regulating the respective privileges of the neutral and the belligerent, it has been generally held as a fundamental principle, by writers on the law of nations, that those rights, from the exercise of which less benefit would accrue to the one party than detriment to the other, should be abandoned; and in all cases where the rights of peace and the rights of war happen to come into collision, the application of this rule will decide which of the two parties must yield to the convenience of the other. Thus the neutral state is debarred from carrying on any trade with either of the belligerents in warlike stores. The general right to a free trade is modified, in this particular instance, by the paramount rights of the belligerent. To refrain, for a time, from trading with an individual state in warlike stores, can, at most, only impose a trifling inconvenience on the neutral power, while the continuance of such a trade might terminate in the destruction of the belligerent. The detriment occasioned to the one party, by the existence of such a trade, is,