The operation of bleaching must from its very nature be of the same antiquity as the work of washing textures of linen, cotton, or other vegetable fibres. Clothing repeatedly washed, and exposed in the open air to dry, gradually assumes a whiter and whiter hue, and our ancestors cannot have failed to notice and take advantage of this fact. Scarcely anything is known with certainty of the art of bleaching as practised by the nations of antiquity. Egypt in early ages was the great centre of textile manufactures, and her white and coloured linens were in high repute among contemporary nations. As a uniformly well-bleached basis is necessary for the production of a satisfactory dye on cloth, it may be assumed that the Egyptians were fairly proficient in bleaching, and that still more so were the Phoenicians with their brilliant and famous purple dyes. We learn, from Pliny, that different plants, and likewise the ashes of plants, which no doubt contained alkali, were employed as detergents. He mentions particularly the StrutJιiιιm as much used forbleaching in Greece, a plant which has been identified by some with Gypsophila Struthium. But as it does not appear from Sibthorp’s Flora Groeca, published by Sir James Smith, that this species is a native of Greece, Dr Sibthorp’s conjecture that ↑ λιo Struthium of the ancients was ∖ heSapοnaria officinalis, a plant common in Greece, is certainly more probable.

In modern times, down to the middle of the 18th century, the Dutch possessed almost a monopoly of the bleaching trade, although we find mention of bleach-works at Southwark near London as early as the middle of the 17th century. It was customary to send all the brown linen, then largely manufactured in Scotland, to Holland to be bleached. It was sent away in the month of March, and not returned till the end of October, being thus out of the hands of the merchant more than half a year.

The Dutch mode of bleaching, which was mostly conducted in the neighbourhood of Haarlem, was to steep the linen first in a waste lye, and then for about a week in a potash lye poured over it boiling hot. The cloth being taken out of this lye, and washed, was next put into wooden vessels containing butter-milk, in which it lay under a pressure for five or six days. After this it was spread upon the grass, and kept wet for several months, exposed to the sunshine of summer.

In 1728 James Adair from Belfast proposed to the Scotch Board of Manufactures to establish a bleachfield in Galloway; this proposal the board approved of, and in the same year resolved to devote £2000 as premiums for the establishment of bleachfields throughout the country. In 1732 a method of bleaching with kelp, introduced by R. Holden, also from Ireland, was submitted to the board; and with their assistance Holden established a bleachfield for prosecuting his process at Pitkerro, near Dundee.

The bleaching process, as at that time performed, was very tedious, occupying a complete summer. It consisted in steeping the cloth in alkaline lyes for several days, washing it clean, and spreading it upon the grass for some weeks. The steeping in alkaline lyes, called bucking, and the bleaching on the grass, called crofting, were repeated alternately for five or six times. The cloth was then steeped for some days in sour milk, washed clean, and crofted. These processes were repeated, diminishing every time the strength of the alkaline lye, till the linen had acquired the requisite whiteness.

For the first improvement in this tedious process, which was faithfully copied from the Dutch bleachfields, manufacturers were indebted to Dr Francis Home of Edinburgh, to whom the Board of Trustees paid £100 for his experiments in bleaching. He proposed to substitute water acidulated with sulphuric acid for the sour milk previously employed, a suggestion made in consequence of the new mode of preparing sulphuric acid, contrived some time before by Dr Roebuck, which reduced the price of that acid to less than one-third of what it had formerly been. When this change was first adopted by the bleachers, there was the same outcry against its corrosive effects as arose when chlorine was substituted for crofting. A great advantage was found to result from the use of sulphuric acid, which was that a souring with sulphuric acid required at the longest only twenty-four hours, and often not more than twelve; whereas, when sour milk was employed, six weeks, or even two months, were requisite, according to the state of the weather. In consequence of this improvement, the process of bleaching was shortened from eight months to four, which enabled the merchant to dispose of lι is goods so much the sooner, and consequently to trade with less capital.

No further modification of consequence was introduced in the art till the year 1787, when a most important change was initiated by the use of chlorine, an element which had been discovered by Scheele in Sweden about thirteen years before. Berthollet repeated the experiments of Scheele in 1785, and by the prosecution of further investigations he added considerably to the facts already known. He showed that this substance (called by Scheele 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.

The property which this gas possesses of destroying vegetable colours, led Berthollet to suspect that it might be introduced with advantage into the art of bleaching, and that it would enable practical bleachers greatly to shorten their processes. In a paper on dephlogisticated muriatic acid, read before the Academy of Sciences at Paris in April 1785, and published in the Journal de Physique for May of the same year (vol. xxvi. p. 325), he mentions that he had tried the effect of the gas in bleaching cloth, and found that it answered perfectly. This idea is still further developed in a paper on the same substance, published in the Journal de Physique for 1786. In 1786 he exhibited the experiment to Mr James Watt, who, immediately upon his return to England, commenced a practical examination of the subject, and was accordingly the person who first introduced the new method of bleaching into Great Britain. We find from Mr Watt’s own testimony that chlorine was practically employed in the bleachfield of his father-in-law, Mr Macgregor, in the neighbourhood of Glasgow in March 1787. Shortly thereafter the method was introduced at Aberdeen by Messrs Gordon, Barron, and Co., on information received from M. de Saussure through Professor Copland of Aberdeen. Mr Thomas Henry of Manchester was the first to bleach with chlorine in the Lancashire district, and to his independent investigations several of the early improvements in the application of the material were due.

No very great amount of success, however, attended the efforts to utilize chlorine in bleaching operations till the subject was taken up by Mr Tennant of Glasgow. He, after a great deal of most laborious and acute investigation, hit upon a method of making a saturated liquid of chloride of lime, which was found to answer perfectly all the purposes of the bleacher. This was certainly a most important improvement, without which, the prodigious extent of business carried on by some bleachers could not possibly have been transacted. Such was the acceleration of processes effected by the new method that, it is stated, a bleacher in Lancashire received 1400 pieces of gray muslin on a Tuesday, which on the Thursday immediately following were returned bleached to the manufacturers, at the distance of sixteen miles, and were packed up and sent off on that very day to a foreign market.

In the year 1798 Mr Tennant took out a patent for his new invention, and offered the use of it to practical bleachers, for a fair and reasonable portion of the savings made by its substitution for potash, then in general use. Many of the bleachers, however, used it without paying lιim, and a combination was formed to resist the right of the patentee. In December 1802, an action for damages was brought against Messrs Slater and Varley, nominally the defendants, but who, in fact, were backed and supported by a combination of almost all the bleachers in Lancashire. In consequence of this action, the patent right was set aside by the verdict of a jury and the decision of Lord Ellenborough, who used very strong language against the patentee. The grounds of this decision were, that the patent included a mode of bucking with quicklime and water, which was not a new invention. It was decided that, because one part of the patent was not new, therefore the whole must be set aside. Lime was indeed used previous to the patent of Mr Tennant; but it was employed in a quite different manner from his, and he would have allowed the bleachers to continue their peculiar method without any objection, because it would have been productive of no injury to his emolument.

In consequence of this decision the use of liquid chloride of lime in bleaching was thrown open to all, and speedily came to be universally employed by the bleachers in Britain. Mr Tennant, thus deprived of the fruits of several years of anxious and laborious investigation, advanced a step farther, to what may be considered as the completion of the new method. This consisted in impregnating quicklime in a dry state with chlorine, an idea originally suggested by Mr Charles MTntosh of Cross-Basket, then a partner with Messrs Tennant and Knox. A patent for this was taken out on the 13th of April 1799, and he began his manufacture of solid chloride of lime at first upon a small scale, which has ever since been gradually extending, and the manufactory is now the largest of the kind in Great Britain.

The various processes for the preparation of the so-called chloride of lime, or bleaching-powder, as conducted at the present day, and its other applications in arts, will be found described under the head of Chlorine.

Bleaching of Cotton.

Of the two great staples, cotton and linen, to the whitening of which the art of the bleacher is directed, cotton is the more easily and expeditiously bleached. The basis of all vegetable fibres is cellulose or ligneous tissue, a pure white substance, and it is to obtain this body in a state of purity, free from the resinous matter naturally associated with it as well as from adventitious impurities imparted in the process of spinning and weaving, that is the object of bleaching. The operations, although apparently complex and numerous, are essentially simple, though frequently repeated, and the greatest variety of detail is connected with the finishing of cloth, which is in reality a separate industry, frequently conducted in distinct establishments under the name of calendering and finishing works. Bleaching proper resolves itself into washing with suitable detergents, and subjecting the washed material to the influence of chlorine, whereby the colouring matter either belonging to the fibre or imparted to it is oxidized and discharged.

The general arrangements of a bleach-house will be made plain from the ground-plan (fig. 1). The various pieces of apparatus, the positions of which are there indicated, will be described in connection with the sequence of operations through which the cloth passes in the process of bleaching. In the best arranged works, it should be mentioned, where power is required to work any machine, it is generally supplied by a separate engine attached to the machine itself, instead of by gearing carried from one engine for all the machinery. For this plan, as well as for the greater portion of the illustrations which follow, we are indebted to Mr William Mather, of the eminent firm of Mather and Platt, Salford, to whom we are also under obligation for much valuable practical information. We have also to express our indebtedness to Mr Alexander Crum of Thornliebank, for the fullest access to the important works of his firm, and for the cordial assistance afforded by the managers of its various departments.

The sequence of operations in the bleaching and finishing of calico has undergone no change in its general details since the bleaching-powder process was first introduced; but the mechanical arrangements by which the operations are conducted have been the subject of frequent improvements. The ingenuity of engineers and bleachers has been chiefly directed towards the decreasing of manual labour, economy of fuel and materials, and the rapid completion of the various processes. The application of factory legislation to bleach-works by the Bleaching and Dyeing Works Act of 1860, by imposing a necessity for regular and stated hours of work, still further stimulated the production of apparatus and arrangements for prompt and certain completion of the various operations. Consequently a great part of the old machinery and arrangements of a bleach-house have now disappeared, and the processes are carried on in a continuous series of operations by machinery and appliances to a large extent self-acting. Formerly each piece of goods was separately treated and carried by hand or on barrows from one stage to the next; now the pieces are sewn end to end, as many as 1000 pieces, measuring perhaps 20 miles, being operated on in one stretch.

As various pieces of old machinery are yet in use for certain kinds of work, it has been considered desirable to give descriptions and figures of some of them, and these, at the same time, will serve the further purpose of indicating the nature of the mechanical improvements which have been carried out, in recent years, in bleaching establishments. The important and frequently repeated operation of washing was formerly conducted either at the wash-stocks or washing-mill or in the dash-wheel. The wash-stocks, which are yet in use in many large works, especially where linen is the bleacher’s staple, consists of a trough or box for holding the goods to be washed, through which a constant stream of water is passing. A pair or more of heavy hammer-headed wooden beams, hung by long shafts, and playing into the trough, are alternately tilted, against the cloth, causing the water by their momentum to work through and squirt out of the mass. This process of washing is rather tedious, occupying on an average about half an hour, and requiring besides a great amount of manual labour. The dash-wheel (fig. 2) is a cylindrical box revolving on its axis. It has four divisions, as shown by the dotted lines, and an opening into each division. A number of pieces are put into each, abundance of water is admitted behind, and the knocking of the pieces as they alternately dash from one side of the division to the other during the revolution of the wheel effects the washing. The process lasts from four to six minutes. The dashwheel is used to the present day in the bleaching of curtain materials and fine muslins. In nothing have greater improvements been effected than in the arrangement of the kiers or vessels in which the cloth is boiled or “bowked.” An old form of kier is seen in fig. 3. It consisted of a cylindrical vessel AA, 9 feet wide, of wood or iron, having a false bottom BB, on which the goods were placed, about 6 inches from the real one. A small pipe E, in the centre of a wider one CC, conveyed the steam from the steam - boiler.

When the liquid boiled at the bottom, where the steam issued, the steam forced its way up the pipe CC, carrying with it a quantity of the lye, which was thrown back by the small cover D, spreading itself over the surface of the goods, and filtering through them into the space below the false bottom, where it was again heated by the steam, reascended the pipe CC, and so on in constant succession, till the boiling was completed. FF is a wooden cover which prevented the cooling of the materials below a boiling heat.

The bleaching of common calico is divided into two branches—lsi, print bleaching, in the case of which the goods are bleached as a preliminary to the process of calico printing; and 2<7, white bleaching, which applies to goods to be finished white or unprinted. The processes differ in some of their details, as in white bleaching it is only necessary to satisfy the eye, whereas in print-bleaching the material must be rendered chemically pure, otherwise the colours in the subsequent printing process would be dull and blotchy. The print bleaching must therefore be more thoroughly done than the other; but as the processes are generally the same, it will be sufficient to indicate the points of difference in the various stages through which the material in both cases passes. A process preliminary to bleaching is Singeing.— Gray calico aβ received from the looms is generally in lengths of 37∣ and 50 yards. A large number of these, sometimes as many as 1000, measuring more than 20 miles in length, are sewn into a continuous web. At the extremities of each owner’s lengths, the name of the firm, or some distinguishing mark, is either stamped on in tar, or marked by means of coloured threads. These long lengths are then submitted to the operation of singeing, which has for its object the removal of the downy pile and short threads from the surface of the cloth, which would interfere with the appearance of finished white goods, and with the uniformity and sharpness of patterns in the case of prints. Several methods of accomplishing this have been employed, but that most commonly used is the system of plate singeing illustrated in fig. 4. A pair of singe-plates, a and b, made of thick bent sheets of copper, are mounted over the flues of a fire sufficient to raise a white heat. The plate b is most highly heated, a being at the end of the flue furthest removed from the fire. The cloth enters over a rail a, and in passing over the plate a is thoroughly dried and prepared for the singeing it receives when it comes to the highly-heated plate b. A block d, carrying two rails in the space between the plates, can be raised or lowered at pleasure so as to increase or lessen the pressure of the cloth against the plates, or, if necessary, to lift it quite free of contact with them. The system of plate singeing is found generally sufficient in practice, but the caking of paste and dirt on the plates from the cloth as it passes over them, and variations in the heat of the plates, often lead to irregularities in singeing. A combination of plate and gas singeing is frequently employed to overcome the deficiencies of plate singeing alone. In this case the cloth is passed first over an ordinary plate, and then on to another, along the ridge of which is a long narrow slit, which allows the issue of a gas flame produced from coke burning immediately under it. By this means long loose threads are more effectually burned off than in plate singeing, and a more uniform heat is applied to the gray cloth. Fig. 5 is a sectional view of a very efficient singeing apparatus introduced by Messrs Mather and Platt. The figure represents the first half of the machine, the second portion being precisely similar in arrangement. The singeing in this case is accomplished by the burning of a mixture of coal-gas and atmospheric air admitted by a pipe a, and driven by a fan Diast to the burners b, b, which are regulated by stop-cocks. The mixture burns with an intense heat and a blue smokeless flame. The cloth is carried by a series of rollers to the gas jets, and in passing over the rollers c, c, c, c the one side of the cloth impinges laterally four times against the flame, which is never permitted to pass through the fabric, but only shaves its surface. The back is thus singed in the first portion of the apparatus,...