Page:Encyclopædia Britannica, Ninth Edition, v. 4.djvu/760

of water to thesa pipes is regulated by the tap g. H is the framing, J stands, with the necessary appliances for turning over the pans to empty their contents, K a pipe and swivel tap for supplying water to the pans, L is the main steam pipe to f m the water pipe to / 2 and K, and n and o are

tips for washing out and for condense water respectively.

FIG. 3. Colour Pans.

The variety of methods by which colours are produced on calicoes is almost endless, and the processes employed, both chemical and mechanical, as well as the tinctorial agents used, are also very numerous and diversified. The processes are in practical works generally classified under the heads of numerous different styles, combinations of several of which are frequently employed in the production of a single pattern It is at once impossible and unneces sary to enter into details of these various styles here ; but they all resolve themselves into a few general groups, under which heads they will be briefly treated of. In certain styles a mordant, or chemical substance, which possesses an affinity for both the cloth and the dye-stuff, is the substance printed in the cylinder machine, and the calico has to undergo a subsequent process of dyeing by which those portions of the cloth which received the mordant are alone permanently dyed Again, the colour-box may con tain all the ingredients necessary for the production of the colour, but to develop it in the fibre it is necessary to expose the printed cloth to the oxidizing influence of the atmosphere, or otherwise produce an oxidation of the dye- stuff by which the colour is developed and fixed. By a third process the colour is prepared and applied direct to the cloth mixed with some agent which, under the in fluence of heat and moisture, either mechanically attaches or chemically precipitates the colour in the fibre. And a fourth process, which may be regarded as a modification of the third, consists of mixing the dye with powerful mordanting substances, which, after printing, are merely dried, the mordant volatilising sufficiently to fix the dye, not very fast, on the cloth. There are thus these four divisions—

I. Dye colours. II. Oxidation colours. III. Steam colours. IV. Spirit colours.

Along with these different methods patterns are also produced and modified by means of substances applied to cloth already dyed or printed in order to remove the colour from certain portions of it which are either intended to remain white, or to receive some other colour afterwards. These substances are known as " discharges," and examples of their action are seen in printed Turkey reds and bandannas.

Sometimes a substance is applied to cloth before it is dyed, in order to prevent the indigo, or any other colour, from being fixed on those parts to which it is applied, that they may remain white, or be afterwards made to receive other colours. Substances possessed of this property are called " resists."

Dye Colours.

Under this head are included prints prepared by printing the pattern in one or more mordants substances which have an affinity for the fibre on the one hand and the dye- stuff on the other. The mordanted cloth is subsequently submitted to a process of dyeing, when the dye-stuff is fixed only on such parts of the cloth as have been impregnated with the mordant. By using more than one mordant, by mixing them, or by employing the same at different degrees of strength, a variety of shades or colours is produced in the process of dyeing with one dye-stuff.

Mordants.—The principal mordants employed for dye colours are the following:—

1. Red Liquor.—The acetate of alumina mordant or " red liquor " of the calico-printer is prepared by partly decom posing alum, held in solution by impure acetate of lime, commonly called pyrolignite of lime ; sulphate of lime precipitates and acetosulphate of alumina is thus obtained. Red liquors thus prepared have a specific gravity of 1 08, and are composed as follows:—

Composition of four red Mordants per Gallon. Substances. Mordant A. Mordant B. Mordant C. Mordant D. Alumina .. grains. 1680 oz. grs. 3 367 grains, oz.grs. 1830 OJ4 80 grains, [oz.grs. 1239 0,2 364 grains. 2164 4 OZ. gl S- 4 414 Sulphuric acid 2642 5 6 20 1 2800 06 175 3017 06 392 1664 6 3 352 Acetic acid 3369 8 7 307 3970 09 32 1281 7:2 406 3679 2 8 179 Ammonia | and watei 674 1 1 236 910 02 35 693 11 255

In the manufacture of "red liquor," sulphate of alumina is frequently substituted for alum, and acetate of lead for pyrolignite of lime.

2. Iron Liquor.—The oxides of iron are much used as mordants, either in the state of protoxide or peroxide. The salt most employed is the impure pyrolignite of protoxide of iron, which is prepared either by decomposing green copperas with pyrolignite of lime, or by placing in large vats pyrolignous acid and old iron, when, after a few months, the iron, which is gradually oxidized, dissolves in the acid, and gives rise to pyrolignite of protoxide of iron. This valuable mordant is thickened with calcined farina, flour, starch, or gum, and applied on the calico. After being exposed for a few days in a moist atmosphere, it loses a part of the acid, and becomes partially peroxidized. Pyrolignite of iron of the specific gravity of 1*05 gives a black with madder and several " tannin " substances. Vari ous shades of purple are obtained by adding different pro portions of water to the mordant previously to applying it to the cloth ; and various shades of chocolates are pro duced by mixing this with the alumina mordant previously described, and then dyeing also with madder.

These two mordants are the principal employed for

madder colours ; but several others are employed for special

shades. Among these may be enumerated the aluminate