DISCHARGE AND RESIST PROCESSES.

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by means of animal mordants, such as albumen, this has never been asuccessful operation, for the very good reason that the madder lakes, even thebest prepared, when thus employed, do not exhibit the same transparency andpleasing effedt as the dyed colours produced by madder; it is, moreover, verydifficult to prepare deep red madder lakes, while hitherto neither purple norbrown madder lakes have ever been made with anything like a satisfactoryresult even to serve as pigments.

We cannot enter fully into the details of the so-called discharge and resistprocesses destined to produce white patterns on a coloured ground; but althoughthis subjedt is in reality a speciality of technology, and therefore requiring aseparate treatise, it is hoped that the following particulars will give the readersome idea of these operations. By the word discharge (enlevage in French) isdesignated any compound or mixture which has the property of bleaching, ortaking away, the colour already communicated to a fabric. Their use as regardsmadder-dyed goods is chiefly confined to the Turkey-red dyed fabrics, but is appli-cable if required upon lilac and other madder shades. The process generallyknown as Monteith’s consists in the diredt application of a solution of chlorineto the dyed fabrics. The Turkey-red dyed fabrics are placed in folds properlysmoothed and arranged between two thick cast lead plates, both of which areperforated with the design to be produced, the perforations exadtly corres-ponding; the cloth is then pressed between these plates with considerableforce, and the plates secured. By this mechanical contrivance the wetting ofthe portions of the cloth tightly pressed between the unperforated parts of theplates is very effedtually prevented, while any liquid poured on the upperplate will gradually filter through the cloth from the perforation of one plateto the corresponding on the other. The passage of the discharging fluid(bleaching-powder with an excess of free acid) is assisted by currents ofair. When the colour is discharged clear water is passed through, and thepieces then washed and finished. As might be expedted from the nature of theprocess, the edges of the design are not sharp and clear, because, notwith-standing any practical amount of pressure, capillary attraction will assertitself, and consequently the edges of the designs are blurred.

The other process frequently used for this purpose is the discovery ofM. D. Koechlin and Mr. Thompson. It consists in printing a highly acidcolour upon the cloth to be discharged, and then plunging it into a solutionof bleaching-powder in water; the acid adts upon the bleaching-powder,causing a disengagement of chlorine, which destroys the colour upon the spotwhere the acid is printed. It will be readily understood that the difficulty inthis process consists in confining the discharge to the points printed on, forit is not possible to hit the quantity of chlorine just necessary to dischargethe colour, and any excess generated spends itself upon the colour in theneighbourhood, unless some precautions are taken. By having a considerableexcess of lime (chalk may be added with some advantage) in the bleaching-powder, and by not leaving the goods in any longer than is absolutely required,and also by care being taken that the cloth is properly dried before beingimmersed in the bleaching solution, very regular results can be obtained.Besides producing a white design, there are discharges which, whilst de-stroying the red colour, leave another in its place, or the basis for producinganother. As examples of the composition of some of these discharges, we