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To another portion of the solution we will add some caustic soda, NaOH, in order to rob the normal sulphate of alumina of some of its sulphuric acid. But what has all this to do with mordanting? is possibly now the inquiry.
Now if you imagine these reactions going on in a single fibre of a textile material, you have grasped the theory and purpose of mordanting.
I think we have now got a clue to the principle of mordants and also to the importance of a sound chemical knowledge in dealing most effectively with them, and I may tell you that the man who did most to elucidate the theory of mordanting is not a practical man in the general sense of the term, but a man of the highest scientific attainments and standing, namely, Professor Liechti, who, with his colleague Professor Suida, did probably more than any other man to clear up much that heretofore was cloudy in this region.
A further reason is that from the solution of acetate of iron or alumina, basic acetates are very easily precipitated on heating, and are thus readily deposited in the fibre. Mordanting and Fixing Basic Colours. Now let us ask ourselves a very important question. Combination, and so precipitation, would not take place; no lake would be formed.
Now you may easily understand that a structure like this, if it is to be completely and uniformly permeated by a dye liquor or any other aqueous solution, must have those scales not only well opened, but well cleansed, because if choked with greasy or other foreign matter impervious to or resisting water, there can be no chance of the mordanting or dye liquids penetrating uniformly; the resulting dye must be of a patchy nature.
If we desire to utilise the whole of the chromic acid in our mordanting liquor, we must add to it some sulphuric acid to set free the chromic acid from the potassium with which it is combined. Bichromate of potash with sulphuric acid gives sulphate of potash and chromic acid. The question of the proper exhaustion of bichromate baths is an important economic one. Mr.
Thus it is not really necessary to use basic aluminium sulphate for mordanting wool, since the latter itself decomposes the normal or neutral sulphate of alumina on heating, an insoluble basic sulphate being precipitated in the fibres of the wool. The presence of other added substances, as cream of tartar, etc.
The substantive colours fix themselves readily and directly on animal fibres and substances, but only a few amongst them will dye vegetable fibres like cotton and linen directly. Almost all substantive colours may, however, be fixed on cotton and linen by first preparing or mordanting those vegetable fibres.
Chrome Mordanting of Wool and Fur. In studying this subject I would recommend a careful perusal of the chapter on "Mordants" in J.J. Hummel's book, entitled The Dyeing of Textile Fabrics, and pages 337 to 340 of Bowman's work on The Wool-Fibre.
Now the use of certain coal-tar black dyes in place of logwood obviates this use of bichrome, and thus the heavy stress on the fibre in mordanting with it. It also effects economy in avoiding the use of bichrome, as well as of copper salts; but even thus, of course, other problems have to be solved before it can be finally decided which is best. Classification.
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