The bleaching process, as at that time performed, was very tedious, occupying a complete summer. It consisted in steeping the cloth in alkaline lyes for several days, washing it clean, and spreading it upon the grass for some weeks. The steeping in alkaline lyes, called bucking, and the bleaching on the grass, called crofting, were repeated alternately for five or six times. The cloth was then steeped for some days in sour milk, washed clean, and crofted. These processes were repeated, diminishing every time the strength of the alkaline lye, till the linen had acquired the requisite whiteness.
For the first improvement in this tedious process, which was faithfully copied from the Dutch bleachfields, manu facturers were indebted to Dr Francis Home of Edinburgh, to whom the Board of Trustees paid 100 for his experi ments in bleaching. He proposed to substitute water acidulated with sulphuric acid for the sour milk previously employed, a suggestion made in consequence of the new mode of preparing sulphuric acid, contrived some time before by Dr Roebuck, which reduced the price of that acid to less than one-third of what it had formerly been. When this change was first adopted by the bleachers, there was the same outcry against its corrosive effects as arose when chlorine was substituted for crofting. A great advantage was found to result from the use of sulphuric acid, which was that a souring with sulphuric acid required at the longest only twenty-four hours, and often not more than twelve ; whereas, when sour milk was employed, six weeks, or even two months, were requisite, according to the state of the weather. In consequence of this improve ment, the process of bleaching was shortened from eight months to four, which enabled the merchant to dispose of his goods so much the sooner, and consequently to trade with less capital.
No further modification of consequence was introduced in the art till the year 1787, when a most important change was initiated by the use of chlorine, an element which had been discovered by Scheele in Sweden about thirteen years before. Berthollet repeated the experiments of Scheele in 1785, and by the prosecution of further investigations he added considerably to the facts already known. He showed that this substance (called by Scheele dephlogisti- cated muriatic acid) is a gas soluble in water, to which it gives a yellowish green colour, an astringent taste, and the peculiar smell by which the body is distinguished.
The property which this gas possesses of destroying vegetable colours, led Berthollet to suspect that it might be introduced with advantage into the art of bleaching, and that it would enable practical bleachers greatly to shorten their processes. In a paper on dephlogisticated muriatic acid, read before the Academy of Sciences at Paris in April 1785, and published in the Journal de Physique for May of the same year (vol. xxvi. p. 325), he mentions that he had tried the effect of the gas in bleaching cloth, and found that it answered perfectly. This idea is still further de veloped in a paper on the same substance, published in the Journal de Physique for 1786. In 1786 he exhibited the experiment to Mr James Watt, who, immediately upon his return to England, commenced a practical examination of the subject; and was accordingly the person who first intro duced the new method of bleaching into Great Britain. We find from Mr Watt s own testimony that chlorine was practically employed in the bleachfield of his father-in-law, Mr Macgregor, in the neighbourhood of Glasgow in March 1787. Shortly thereafter the method was introduced at Aberdeen by Messrs Gordon, Barron, and Co., on informa tion received from M. de Saussure through Professor Copland of Aberdeen. Mr Thomas Henry of Manchester was the first to bleach with, chlorine in the Lancashire dis trict, and to his independent investigations several of the early improvements in the application of the material were due.
No very great amount of success, however, attended the efforts to utilize chlorine in bleaching operations till the subject was taken up by Mr Tennant of Glasgow. He, after a great deal of most laborious and acute investigation, hit upon a method of making a saturated liquid of chloride of lime, which was found to answer perfectly all the pur poses of the bleacher. This was certainly a most important improvement, without which, the prodigious extent of business carried on by some bleachers could not possibly have been transacted. Such was the acceleration of pro cesses effected by the new method that, it is stated, a bleacher in Lancashire received 1400 pieces of gray muslin on a Tuesday, which on the Thursday immediately following were returned bleached to the manufacturers, at the dis tance of sixteen miles, and were packed up and sent off on that very day to a foreign market.
In the year 1798 Mr Tennant took out a patent for his new invention, and offered the use of it to practical bleachers, for a fair and reasonable portion of the savings made by its substitution for potash, then in general use. Many of the bleachers, however, used it without paying him, and a combination was formed to resist the right of the patentee. In December 1 802, 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 pre vious to the patent of Mr Tennant ; but it was employed in a quite different manner from his, and he would have allowed the bleachers to continue their peculiar method without any objection, because it would have been pro ductive of no injury to his emolument.
In consequence of this decision the use of liquid chloride of lime in bleaching was thrown open to all, and speedily came to be universally employed by the bleachers in Britain. Mr Tennant, thus deprived of the fruits of several years of anxious and laborious investigation, advanced a step farther, to what may be considered as the completion of the new method. This consisted in impregnating quicklime in a dry state with chlorine, an idea originally suggested by Mr Charles M Intosh of Cross-Basket, then a partner with Messrs Tennant and Knox. A patent for this was taken out on the 13th of April 1799, and he began his manu facture 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 ble aching-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.
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