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DYEING AND CALICO PRINTING.

1. The insoluble substance may be only very weakly retained in solution byits solvent, and the molecular attradtion of the fibre may be stronger thanthat of the solvent menstruum. In this case there will be precipitation of thedissolved matter without any extraneous aid. This adtion is instanced withan alkaline solution of reduced indigo in which cotton is immersed; decom-position and precipitation take place, and the dissolved (white) indigo isattradled so strongly that the amount of indigo taken up increases withtime. According to M. Persoz, a solution of alumina with excess of basecedes to cotton fibre its excess of alumina.

2. But if the affinity of the solvent for the dissolvedfmatter be greater thanthat of the fibre it becomes necessary to employ means by which this resistancemay be overcome, and the colour precipitated in an insoluble condition uponthe fibre.

The explanations of the modes of adtion under these principles are verymany and various. According to some, the fixation of the insoluble colouringmatter is mechanical—the solid molecules being considered to have penetratedthe pores of the fibre by endosmose, and by becoming precipitated to havelost their motive power. This theory, first promulgated by Hellot, le PileurD’Apligny, and Macquer, has been urged with great ingenuity and talent byMr. Walter Crum, with, however, essential modification of the erroneous viewsof the previous theory. According to others, who have at their head M. Chevreul,a true chemical combination takes place between the fibre and the colouringmatter. It does not appear possible to assimilate the dyeing of cotton bymeans of indigo, oxide of iron, or oxide of chromium, &c., with a chemicalphenomenon of the same order as the union of oxygen and hydrogen, ofsulphur and iron, which takes place in definite atomic proportions, and afterwhich the constituents have entirely or partially lost their distinctive individualcharadters. It is true there exists for the fibre a state of saturation beyondwhich it is not capable of retaining a further quantity of colouring matter;but there does not appear to exist between the quantity of fibrous matter andof colouring matter any atomic or relative proportion. On the other hand,neither fibre nor colour loses after fixation any single distindtive quality thatit before possessed.

The colouring matter can be removed from the fibre to which it )has beenfixed by any solvent which would adt upon it in its free state, leaving the fibreperfedtly intadl. This would show at most only a molecular attradtion similarto that exhibited by carbon and many other porous bodies. Should it beurged that the precipitation of indigo or of basic alumina is evidence thatthere exists in cloth fibre a chemical affinity capable of overpowering anothersimilar affinity, it may be answered that the force of diffusion alone is capableof determining the dissociation of compounds, the elements of which exertpowerful mutual attradtion. For an instance may be cited the combinationof sulphuric acid and sulphate of potash in the bisulphate of that base.

Summing up our evidence, it appears that the fixing of colouring mattersand insoluble substances upon fibre may be best considered from the point ofview taken by Mr. Walter Crum. It may be added that molecular attradtionaids permanent adhesion. The theories propounded by M. Persoz andMr. Walter Crum are not diametrically opposed, as would appear at first sight;indeed, it might be urged that their views are compatible. The essential