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compounds. Dyeing thus appears to be altogether a chemical process, and to require, for its due explanation and practice, an acquaintance with the properties of the elementary bodies, and the laws which regulate their combinations.

Bergmann appears to have been the first, who referred to chemical affinities the phenomena of dyeing. Having plunged wool and silk into two separate vessels, containing solutions of indigo in sulphuric acid, diluted with a great deal of water, he observed that the wool abstracted much of the coloring matter, and took a deep blue tint, but that the silk was hardly changed. He ascribed this difference to the greater affinity subsisting between the particles of sulphate of indigo and wool, than between these and silk; and he showed that the affinity of the wool is sufficiently energetic, to render the solution colorless, by attracting the whole of the indigo, while that of the silk can separate only a little of it. He thence concluded, that dyes owed both their permanence and their depth to the intensity of that attractive force.

We have, therefore, to consider, in dyeing, the play of affinities, between the liquid medium, in which the dye is dissolved, and the fibrous substance to be dyed. When wool is plunged in a bath, containing cochineal, tartar, and salt of tin, it readily assumes a beautiful scarlet hue; but when cotton is subjected to the same bath, it receives only a feeble pink tinge. Dufay took a piece of cloth, woven of woollen warp and cotton weft, and having exposed it to the fulling-mill, in order that both kinds of fibres might receive the same treatment, he then subjected it to the scarlet dye: he found that the woollen threads became of a vivid red, while the cotton continued white. By studying these differences of affinity, and by varying the preparations and processes, with the same or different dye-stuffs, we may obtain an indefinite variety of colors, of variable solidity and depth of shade.

Dye-stuffs, whether of vegetable or animal origin,

though susceptible of solution in water, and, in this state, of penetrating the pores of fibrous bodies, seldom possess, alone, the power of fixing their particles so durably, as to be capable of resisting the action of water, light, and air. For this purpose, they require to be aided by another class of bodies, already alluded to, which bodies may not possess any color, in themselves, but serve, in this case, merely as a bond of union, between the dye and the substance to be dyed. These bodies were supposed, in the infancy of the art, to seize the fibres, by an agency analogous to that of the teeth of animals, and were hence called mordants, from the Latin verb mordere, to bite. However preposterous this comparison is now known to be, the term derived from it has gained such a footing, in the language of the dyer, that all writers upon this art are compelled to adopt it.

Mordants may be regarded, in general, as not only fixing, but also occasionally modifying, the dye, by forming with the coloring particles an insoluble compound, which is deposited within the textile fibres. Such dyes as are capable of passing from the soluble into the insoluble state, and of thus becoming permanent, without the addition of a mordant, have been called substantive, and all the others have been called adjective, colors. Indigo and tannin are perhaps the only dyes, of organic origin, to which the title substantive can be applied; and even they, probably, are so altered by atmospheric oxygen, in their fixation upon stuffs, as to form no exception to the true theory of mordants. Mordants are of primary importance, in dyeing; they enable us to vary the colors, almost indefinitely, with the same dye; to increase their lustre, and to give them a durability, which they otherwise could not possess. A mordant is not always a simple agent; but in the mixture of which it consists, various compounds may be formed, so that the substances may not act directly, but through a series of transformations. Sometimes, the mordant is mixed with the coloring mat

ters; sometimes, it is applied by itself, first of all, to the stuff; and at others, both these methods are conjoined. We may dye, successively, with liquors which contain the same substances, which will act differently, according to the different mordants employed. One solution will give up its base to the stuff only when aided by heat; another acts better and more uniformly, when cold, though this is a rarer case.

When a mordant consists of a changeable metallic oxide, as of iron or tin, unless great nicety be used in its application, either no effect, or an injurious one, may be produced upon the dye. All these circumstances prove how necessary it is for the dyer to be thoroughly versed in chemical science. Each of the great dyeworks, in Alsace, celebrated for the beauty and fixity of their colors, is superintended, in the laboratory-department, by a gentleman, who has studied chemistry for two or more sessions in the universities of Paris, or some other eminent schools. The numerous complaints which have been made of the fugitiveness of the color of our calicoes, and especially of our cloth dyes, ought to rivet the attention of all great manufacturers and merchants on this important desideratum, and to lead them to supply it, by consulting qualified persons as to the best means of improving this great branch of national industry.

4. Calico Printing. This is the art of impressing cotton cloth with topical dyes, of more or less permanence. Of late years, silk and woollen fabrics have been made the subjects of a similar style of dyeing. Linens were formerly stained with various colored designs, but since the modern improvements in the manufacture of cotton cloth, they are seldom printed, as they are both dearer, and produce less beautiful work, because flax possesses less affinity than cotton, for coloring matters.

The principles of calico-printing have been very profoundly studied, by many of the French manufacturers, who generally keep a chemist, who had been educated in the Parisian schools of science, constantly at

work, making experiments upon colors, in a wellfurnished laboratory.

Calicoes, muslins, &c., intended for printing, must be, first of all, freed from their fibrous down, by the action of the singeing machine. This consists either of a semi-cylinder of cast-iron, laid horizontally, and kept at a bright red heat by a furnace, or of a horizontal range of gas-jet flames: over one of these, the plane of cloth is drawn, with a steady continuous motion, and at a rate suited to its texture. When gas flames are employed, a line of suction-tubes is placed over the extended web, to draw the flame up through the interstices of the cloth, which effectually cleans the threads. The cotton cloth must be next well bleached, because the whiter it is, the more light will it reflect from its surface, and the more brilliant will be the color of its dyes. The first step in the bleaching process is boiling the cloth in an alkaline bath, which, for delicate, fine goods, consists of a weak solution of soda, and for stronger articles, a mixture of slaked lime and water.

The goods are next steeped, for a few hours, in a leaden or wooden cistern, containing a weak solution of chloride of lime, usually called bleaching salt. They are once more rinsed. They are are now boiled in an alkaline lie, made of crude soda dissolved in water, and freed from its impurities by filtrations or subsidence. The goods are again rinsed, and finished by a steep in sulphuric acid, very largely diluted with water. This removes any adhering particles of lime or iron, which would be apt to give the cloth, after some time, a yellow tint. They are last of all rinsed, dried, and sometimes smoothed under the calender, a machine composed of rollers and beaters, by which the fibres of the cloth are thickened, and the surface is both smoothed and polished.

If they are not calendered, they are run through a machine, called in Lancashire the candroy, which spreads them smoothly in the act of rolling them upon a cylinder.

There are four mechanical modes of printing calicoes; first, by small wooden blocks, worked by hand; second, by large wooden blocks, set in a frame, and worked by a machine called the Perrotine, from the name of its ingenious inventor, M. Perrot, of Rouen; third, by flat copper plates, (a method now nearly obsolete ;) and fourth, by copper cylinders, mounted in a machine of great elegance and productive powers, but of no little cost and complexity, called a one, two, three, four, or five, colored calico-printing machine, according as it is mounted with one, two, or more, cylinders. The fifth color is generally applied, by what is called a surface-cylinder, covered with figures like types, in basrelief.

Calico-printing, by hand, is performed by applying the face of the block to a piece of woollen cloth, stretched over one end of a sieve-hoop, and imbued with the coloring matter, of a thin pasty consistence, by means of a flat brush. The block is then applied to the surface of the cotton cloth, while extended upon a flat table, covered with a blanket, and the impression is transferred to it by striking the back of the block with a light mallet. This method, besides the great cost of labor which it involves, has the inconvenience of causing many irregularities in the execution of the work. It has been superseded, to a considerable extent, both in France and Belgium, by the Perrotine, a machine of a most novel and elegant description. Three thin wooden blocks, engraved in relief, about three feet long, and from two to five inches broad, are successively brought to bear on three of the four faces of a prismatic roller of iron, round which the cloth is successively wound. Each block rests on springs, which enable it to press with the delicacy of a skilful arm; and each receives its peculiar colored paste from a woollen surface imbued by a mechanical brush in rapid alternation. "We have seen this machine," says Dr. Ure, "operate in many print-works, with surprising speed and precision; its moving shaft being driven,

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