DYEING.

423

it has been dyed with sulphate of indigo; it will not be colored if it was dyed in the indigovat, but it will become yellow by nitric acid. Boiling water, without becoming coloreditself, will destroy the Prussian blue dye; an alkaline water will convert its color into aniron rust tint; nitric acid, which makes the indigo dye yellow, makes that of Prussianblue green. The liquor resulting from boiling alkaline water on the Prussian blue cloth,will convert sulphate of iron into Prussian blue.

9. Division. Of dyeing viewed in its relation to chemistry.

The phenomena of dyeing have been ascribed to very different causes; by some theywere supposed to depend upon mechanical causes, and by others upon the forces fromwhich chemical effects flow. Hellot, in conformity with the first mode of explanation,thought that the art of dyeing consisted essentially in opening the pores in order to admitcoloring matters into them, and to fix them there by cooling, or by means of a mordantimagined to act like a cement.

Dufay in 1737, Bergmann in 1776, Macquer in 1778, and Berthollet in 1790, had re-vourse to chemical affinities, to explain the fixation of the coloring principles upon stuffs,either without an intermedium, like indigo, walnut peels, annotto; or by the interven-li°n of an acid, a salifiable base, or a salt, which were called mordants. When bodiesPresent phenomena which we refer to an attraction uniting particles of the samenature, whether simple or compound, to form an aggregate, or to an affinity whichUnites the particles of different natures to form them into a chemical compound, thesebodies are in apparent contact. This happens precisely in all the cases of the mutualnation of bodies in an operation of dyeing; if their particles were not in apparent con-ta ct, there would be absolutely no change in their respective condition. When we seespiffs and metallic oxydes in apparent contact, form a mutual union of greater or lessorce, we cannot therefore help referring it to affinity. We do not know how many“las may be fixed upon the same piece of cloth; but in the operations of the dye-houseEfficiently complex compounds are formed, since they are always stuffs, composed ofJ~ ree or four elements, which are combined with at least binary acid or basic com-pounds ; with simple salts compounded themselves of two immediate principles at least"Ely; with double salts composed of two simple salts ; and finally with organic dye-t ®“ s containing three or four elements. We may add that different species belonging. °ne of these classes, and different species belonging to different classes, may uniteWultaneously with one stuff. The union of stuffs with coloring matters appears, in- heral, not to take place in definite proportions; though there are probably somex Eptions.

Plat ma 7 conclude this head by remarking, that, besides the stuff and the coloring,j a * er > it is not necessary, in dyeing, to distinguish a third body, under the name of mor-thi ’ *' or 'ii e idea of mordant does not rest upon any definite fact; the body to whichColo na . tne has been given being essentially only one of the immediate principles of the

jq c . om hination which we wish to fix upon the stuff.a n j ‘ Division. Of dyeing in its relation with caloric, mechanics, hydraulics, pneumatics,“optics.

d“ct h baths, or coppers, are heated directly by a furnace, or by means of steam con-v css 1 111 a P'P e f' rom a boiler at a certain distance from the bath. In the first case, thehelical 5 are “boost always made of copper; only, in special cases, for the scarlet and somefire i s le Sllk dyes, of tin; in the second case, they are of copper, iron, or wood. A directheat m ° re ec onomical than heating steam pipes, where there is only one or two baths tosteaiVhere the labors are often suspended. Madder and indigo vats, when heated byp binsr it aVe il; e ‘ther admitted directly into the liquor, or made to circulate through pipesof tii; lnto i [ , or between the copper and an exterior iron or wood case. See the end

jEis article.

ing a “ r 7tliing else being equal, dyeing with heat presents fewer difficulties towards obtain-b'HowinJp nly C ° lor ’ than dfeia? in the cold ; the reason of which may be found in thethe f,i, re " “ cts The air adhering to the surface of stuffs, and that interposed betweenone, anfi S th t ^ le * 1 const i tu cnt yarns, is more easily extricated in a hot bath than a coldSe cond d 1 aUS allow s the dye liquor to penetrate more easily into their interior: in thetender 6 ’ t * le curr O n ts which take place in a hot bath, and which tend incessantly tothe stutf “aatpnts uniform, by renewing continually the strata of liquid in contact witht° stir ud thh l 6 main, y to ren d er the dyeing evenly. In cold dyeing, it is necessaryy ully dipped e «u at “ l ' me to time: and when goods are first put in, they must be care-Un iformlv • en Eken out, pressed, and wrung, several times in succession till they be

The r m °‘stened.

firing, a„ e d Cl r iCal relations are to be found in the apparatus employed for wincing,“ An dan,i. Th SII !f i 1 * 10 ? 00< l s > as we have described under Calico Printing andPUfatUs, of which hydraulic relations refer to the wash-wheels and other similar ap-an account is givpn under the same articles. The optical relations