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DYEING AND CALICO PRINTING.

peroxide of iron, or a basic insoluble salt of iron. We have already observedthat the substance just named is used as a colour by itself, for producingnankin, rust, and chamois colours; but the quantity of hydrated oxide of ironrequired to yield with madder pigments the utmost effedt is too small to pro-duce by itself any colour upon the fabric.

The means employed to fix peroxide of iron upon tissues are—(i), the useof basic salts of peroxide of iron, which give up a portion of the oxide as aconsequence of the capillary attraction of the fibre ; (2), the use of certainneutral salts of peroxide of iron, the oxide of which can be precipitated by theemployment of ammonia, caustic or carbonated alkalies, and some alkalinesalts (e.g., phosphates, arseniates) the acid of which forms, with the peroxideof iron, insoluble compounds ; (3), those salts of the peroxide of iron whichare spontaneously decomposed by the volatility of the acid, while the base isset free ; (4), the use of protoxide salts of iron, which, however, require higheroxidation simultaneously with or after the transferring of the oxide to thefibre ; (5), lastly, the alkaline solutions of peroxide of iron. While enume-rating all these possible means, we should also state that only one amongthem has been and is actually used, and after a lengthened experience hasbeen found the best, viz., the proto-acetate of iron, or, as it is technicallycalled, pyrolignite of iron. These preparations, after having been printed on,and after ageing, become changed, lose a portion or the whole of their aceticacid, and take up oxygen, with the result that there is deposited on the clothan insoluble hydrated peroxide of iron, or at least an insoluble subacetate ofperoxide of iron. It must be here remembered that, according to someauthorities, the intermediate or magnetic oxide of iron is actually formed onthe cloth, and is more efficient as a mordant than the peroxide. The tarryand other organic matters in ordinary iron-liquor have a decided effeCt in re-tarding the peroxidation of the protoxide present.

M. H. Schlumberger finds that good results may be obtained by the appli-cation of aceto-ferruginous solutions obtained by—(1), double decompositionbetween acetate of lead and sulphate of iron (green vitriol, copperas) ; (2), byacetic acid and iron (viz., the slow solution of scrap iron in crude aceticacid); (3), solution of iron in Bourgogne vinegar; (4), solution of iron inpurified pyroligneous acid ; (5), solution of iron in purified pyroligneous acid,and boiling for five minutes ; (6), solution of iron in crude pyroligneous acid;(7), by double decomposition between protosulphate of iron and pyrolignite oflime. Before being applied to cloth as a mordant, these solutions ought tocontain the iron in the state of protoxide : it is clear that the peroxidation ofthese liquids has to be guarded against as much as possible, because if it takesplace the mordants no longer combine with the fabric, and that which mayadhere is very readily removed by the subsequent cleansing and dunging.The effects of oxidation are especially injurious with blockwork, where fre-quently a small portion of mordant remains exposed over a large extent ofsurface to the adtion of the air. This change is far less perceptible inmachine work. The nature of the thickening substance exerts a very greatinfluence upon the fixation of oxide of iron. All things considered, starchfixes more of the oxide of iron than British gum, and the latter more than gumSenegal. The degree of viscosity of the mordant also greatly influences theresult, and it is hence necessary to give to every mordant that proper degreeof thickness which is required by the character of the design. The purified