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DYEING AND CALICO PRINTING.

Since it is of the highest importance that the dyed goods should be evenlycoloured, it is, in the first place, best to moisten the goods first uniformlywith water, and it is next very important that the goods should be veryuniformly fastened and stretched on the frames, and very uniformly pressed onemerging from the vat; lastly, inequalities in the exposure to air are to beavoided. As a rule, the time of exposure to air should be precisely the sameas that of the duration of immersion in the vats, and that operation may varyfrom five to fifteen minutes.

The fastness and uniformity of the shades is promoted by operating gra-dually,—that is to say, beginning with immersion in weaker vats, and goingby degrees to stronger, whereby the penetration of the indigotin into thecentre of the fibres is rendered more complete. The tissues to be dyed oughtto be very well bleached and very dean, since any fatty matter or dirt whichmay adhere adts as a resist, and thus prevents uniformity of shade. Afterdyeing and exposure to air, the goods are passed through a bath containingdilute sulphuric acid (sp. gr. 1-007 to i'Oi3), in order to remove any carbonateof lime which has been precipitated by the carbonic acid of the air, andalso to adt as a clearing. They are next washed in pure cold water, anddried.

Vat-dyed blue goods are considerably improved in appearance by beingpassed through hot milk of lime, or by treatment with alkalies, whereby, inall probability, some yellow matters are eliminated. It is on this accountthat such goods are frequently passed through a soap-bath.

Vat-dyed goods, consisting of fibres of vegetable origin, may be combinedwith white or otherwise coloured patterns, which can be done by two entirelydistindt processes:—In some instances there is printed on the goods, previousto blue vatting, a preparation technically called a resist , or reserve, wherebythe fixation of indigotin is prevented upon the spots where such preparationis deposited ; in other instances, again, the indigotin of the uniformly blue-dyed goods is removed by suitable means, viz., chemical compounds on suchportions of the cloth as are brought under the influence of these substances.This proceeding is termed a discharge method.

The resists are either such as adt mechanically only by preventing the pene-tration of the indigotin into the fibre,— in this way wax and pipe-clay adt,—orthey exert a chemical adtion, setting up an energetic oxidising adtion whichcauses the oxidation of the indigotin before it has had time to reach the fibre.Such is the mode of adtion of salts of copper and of bichloride of mercury; butthe reader should bear in mind that this classification does not apply rigorously,because we are acquainted with many substances which adt simultaneouslyas mechanical resists and chemical discharges ; the copper salts, for instance,while oxidising white indigo and precipitating on the tissue a thin layer ofblue indigotin (viz., in the vat itself), cause thereby the formation of a moreor less impermeable layer, that layer being the blue indigotin, which, however,does not adhere to, neither is in any way fixed on, the fibre. The salts ofzinc and aluminium, which are frequently employed, furnish simultaneously adeposit of white indigo and a gelatinous envelope, consisting of the hydratedoxide of either metal. The following materials adt more or less in a similarmanner:—Arsenic acid, acid arseniates and phosphates, boracic acid, salts oflead and of peroxide of iron. Copper and lead soaps adt simultaneously as