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DYEING

publication of the first original account, in the English language, of the methods employed in dyeing, entitled “ An apparatus to the history of the common practices of Dyeing.” Ten years later the French Minister Colbert sought to improve as well as control the operations of dyeing, by publishing a code of instructions for the use of the woollen dyers and manufacturers in France. From this time, too, a succession of eminent chemists were appointed by the French Government to devote some of their attention to the study of the industrial arts, including dyeing, with a view to their progress and improvement. Dufay, Hellot, Macquer, Berthollet, Hoard, and Chevreul (1700-1825) all rendered excellent service to the art, by investigating the chemical principles of dyeing, by publishing accounts of the various processes in vogue, by examining the nature and properties of the dyestuffs employed, and by explaining the cause of the several phenomena connected with dyeing. With the advent of the 18th century, certain old prejudices against the use of foreign dyewoods gradually disappeared, and very rapid progress was made owing to the birth of the modern chemistry and the discovery of several useful chemical products and processes—e.g., Prussian Blue (1710), Saxony Blue or Indigo Extract (1740), sulphuric acid (1774), Murexide (1776), picric acid (1788), carbonate of soda 11793), bleaching powder (1798). Experiments on the practical side of bleaching and dyeing were made during this period, in England by Thomas Henry, Home, and Bancroft, and in France by Damboumey, Gonfreville, and others, each of whom has left interesting records of his work. Down to the middle of the 19th century natural dyestuffs alone, with but few exceptions, were at the command of the dyer. But already in the year 1834 the German chemist Bunge noticed that one of the products obtained by distilling coal-tar, namely, aniline, gave a bright blue coloration under the influence of bleaching powder. Ho useful colouring matter, however, was obtained from this product, and it was reserved for the English chemist Perkin to prepare the first aniline dyestuff, namely, the purple colouring matter Mauve (1856). The discovery of other brilliant aniline dyestuffs followed in rapid succession, and the dyer was in the course of a few years furnished with Magenta, Aniline Blue, Hofmann’s Yiolet, Iodine Green, Bismarck Brown, Aniline Black, &c. Investigation has shown that the products of the distillation of coal-tar are very numerous, and some of them are found to be specially suitable for the preparation of colouring matters. Such, for example, are benzene, naphthalene, and anthracene, from each of which distinct series of colouring matters are derived. In 1869 the German chemists Graebe and Liebermann succeeded in preparing Alizarin, the colouring matter of the madder-root, from the coal-tar product anthracene, a discovery which is of the greatest historical interest, since it is the first instance of the artificial production of a vegetable dyestuff. Another notable discovery is that of artificial Indigo by Baeyer in 1878. Since 1856, indeed, an ever-increasing number of chemists has been busily engaged in pursuing scientific investigations with the view of preparing new colouring matters from coal-tar products, and of these a few typical colours, with the dates of their discovery, may be mentioned: Cachou de Laval, (1873); Eosin (1874); Alizarin Blue (1877); Xylidine Scarlet (1878); Biebrich Scarlet (1879); Congo Bed (1884); Primuline Bed (1887); Bhodamine (1887); Paranitraniline Bed (1889) ; Alizarin Bordeaux (1890) ; Alizarin Green (1895). At the present time (1901) it may truly be said that the dyer is furnished with quite an embarrassing number of coal-tar dyestuffs which are capable of producing every variety of colour possessing the most diverse properties. Many of the dyes produced are fugitive, but

a considerable number are permanent and withstand various influences, so that the general result for some years has been the gradual displacement of the older dyewoods by the newer coal-tar colours. During this period of discovery on the part of the chemist, the mechanician has been actively engaged in devising machines suitable for carrying out, with a minimum of manual labour, all the various operations connected with dyeing—e.g., washing, squeezing, dyeing, drying, &c. At the present time the meats. several textile fabrics may be dyed in each stage of their manufacture, e.g., as loose unspun fibres, slubbing, tops, yarn, cops, and cloth, each requiring special forms of machine. Loose wool, which was formerly stirred about in the dye solution, is now enclosed in perforated cylinders, &c., and remains stationary, while the dye-liquor is circulated through the material by means of a pump. Wool tops and cotton cops are dyed in a similar manner. Yarn is still suspended on wooden rods and turned in the dye-liquor by hand, or the rods of yarn are suspended on revolving reels. Cloth is dyed by circulating it as an endless band over a reel placed above the dye-vessel and through the dye solution. This introduction of machinery into the dyeing trade has resulted in the production of better work, it has effected considerable economy, and may be regarded as an important feature in modern dyeing. The art of dyeing is a branch of applied chemistry in which the dyer is continually making use of chemical and physical principles in order to bring about a permanent union between the material to be dyed and the colouring matter applied. If cotton or wool is boiled in water containing finely powdered charcoal, or principles. other insoluble coloured powder, the material is not dyed, but merely soiled or stained. This staining is entirely due to the entanglement of the coloured powder by the rough surface of the fibre, and a vigorous washing and rubbing suffices to remove all but mere traces of the colour. True dyeing can only result when the colouring matter is presented to the fibre in a soluble condition, and is then, by some means or other, rendered insoluble while it is absorbed by, or is in direct contact with, the fibre. There must always be some marked physical or chemical affinity existing between fibre and colouring matter, and this depends upon the physical and chemical properties of both. It is well known that the typical fibres, wool, silk,, and cotton, behave very differently towards the solution of any given colouring matter, and that the method of dyeing; employed varies with each fibre. As a general rule wool has the greatest attraction for colouring matters, and dyes most readily, cotton has the least attraction, while silk occupies in this respect an intermediate position. These differences are no doubt partly due to differences of physical structure in the fibres, but they are also in great measure owing to their different chemical composition. On the other hand, a given fibre, e.g., cotton, behaves' quite differently in dyeing towards various colouring matters. Some of these are not at all attracted by it, and are incapable of being used as dyestuffs for cotton. For others cotton exhibits a marked attraction, so that it is readily dyed by mere steeping in a hot solution of the colouring matter. Again, for other colouring matters cotton has little or no attraction, and cannot be dyed with them until it has been previously impregnated or prepared with a metallic salt, tannic acid, or some other agent which is capable of combining with the colouring matter and precipitating it as an insoluble coloured compound within or upon the fibre. Such differences of behaviour are to be ascribed to differences in the chemical constitution or atomic arrangement of the various colouring, matters.