We then dip the mordanted
piece of cotton into the colour bath, containing, for instance, Magenta,
and it is dyed a fine red, composed of a tannate of antimony and
Magenta. You now see, no doubt, the necessity of sharply discriminating
between two classes of colouring matters, which we may term _colour
acids_ and _colour bases_ respectively. There are but few acids that act
like tannic acid in fixing basic aniline dyestuffs, but oleic acid and
other fatty acids are of the number. A curious question might now be
asked, namely: "Could the acid colour Alizarin, if fixed on cotton
cloth, combine with a basic aniline colour, _e.g._ Aniline Violet, and
act as a mordant for it, thus fixing it?" The answer is, "Certainly";
and thus an Alizarin Purple would be produced, whilst if Magenta were
used in place of Aniline Violet, an Alizarin Red of a crimson tone would
result.
_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_.
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