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DYEING AND CALICO PRINTING.

As regards the ordinary red mordant (red liquor), as generally made up, itappears that there remains a mixture of hydrate of alumina and neutral sul-phate of that base. By treating the cloth upon which these substances aredeposited with water, the neutral sulphate of alumina is dissolved, and whilein solution reads upon the hydrate of alumina, dissolves a portion thereof,and basic alum is again formed. The iron mordant is oxidised by the loss ofacetic acid, and there remains a basic acetate of peroxide of iron.

The second portion of the process of fixing the mordants comprises theoperations of clearing and dunging ( degommage , taking away the thickeners ;bousage , from bouse de vache , treating with cow’s dung). If the alumina andperoxide of iron were perfectly fixed on leaving the ageing-room, so that these ^

substances were present in the fibre in an insoluble state, the only operationthe goods would have to undergo previous to dyeing would be a washing intepid water, in order thereby to remove the thickeners and other soluble sub-stances which have served their purpose during the printing and are now ofno further utility, and a thorough rinsing in fresh cold water. Experiencehas, however, taught that this simple operation is not sufficient, and doesnot yield in practice good results. We will illustrate this point by taking asexample the ordinary red mordant, in the preparation of which only half ofthe sulphuric acid of the alum has been precipitated by acetate of lead.

M. Schiffert’s experiments proving that the goods ready for the cleansingprocess contain alum and hydrate of alumina, what will happen when thepieces are washed in water ? The alum will of course dissolve, and corrode,so to speak, a portion of the hydrate of alumina already fixed. This cor-rosion will be, it is quite clear, irregular,—that is to say, at one spot more,and at another less, of the hydrate of alumina will be eaten away, and, as a }consequence, the depth and uniformity of the colours will suffer. The whiteportions of the pattern will, moreover, when brought into contact with abasic solution of alum, take up more or less of the basic sulphate of alumina,and will consequently attract colouring matters in the dye-beck. Somethinganalogous will of course take place with regard to the iron mordants; thoughas yet incompletely fixed, subacetate of peroxide of iron will—on beingbrought into contact with water—become resolved into soluble neutral acetateand sesquioxide of iron, and the acetate rendered soluble will of course a& asmordant upon the white portions of the pattern. All these effeds are increasedby the incomplete decomposition which the mordants undergo in some por-tions of the goods. Indeed, if the heat and moisture are not very regularlydiffused over the whole ageing-room, it is possible that in some portions of thegoods the mordants are not thoroughly aged, and have consequently retaineda great deal of their solubility. Taking all this into consideration, it is quiteclear that a simple washing, to dissolve thereby the thickeners, would lead tothe produdion of spotted and irregular shades and to the staining of the )white portions of the pattern. The manufacturers, dyers, and calico-printershave overcome these difficulties of the cleansing by substituting for water atepid bath of cow-dung. Cow-dung contains mineral salts and insolubleorganic matter, and by the joint adion of these substances it causes the com-plete saturation of the mordant, the precipitation of the metallic oxides, andprevents the adhesion of any oxide which may become detached (mechanicallyloosened) or dissolved, to the white portions of the pattern. As a matter ofcourse cow-dung is always plentifully mixed with the urine of the animal, and