is so harmless to the fibre, and is easily driven off on steaming, etc.
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. Suppose we have a colour or dyestuff, such as
Magenta, which is of a basic character, and not of an acid or phenolic
character like the colours Alizarin, Hæmatein (logwood), or carminic
acid (cochineal), and we wish to fix this basic dyestuff on the tissue.
Can we then use "red liquor" (acetate of alumina), acetate of iron,
copperas, etc.? The answer is, No; for such a process would be like
trying to combine base with base, instead of base with acid, in order to
form a salt. Combination, and so precipitation, would not take place; no
lake would be formed. We must seek for an acid or acid body to use as
mordant for our basic colour, and an acid or acid body that will form an
insoluble precipitate or colour-lake with the dyestuff. An acid much
used, and very valuable for this purpose, is tannic acid. The tannate of
rosaniline (colour principle of Magenta) is a tolerably insoluble lake,
which can be precipitated by Magenta from a solution of tannate of soda,
the Magenta being capable of displacing the soda. But tannic acid,
alone, does not form very fast lakes with Magenta and the other basic
dyestuffs, and so a means of rendering these lakes more insoluble is
needed. It is found that tannic acid and tartar emetic (a tartrate of
antimony and potash) yield a very insoluble compound, a tannate of
antimony. Perchloride of tin, in a similar manner, yields insoluble
tannate of tin with tannic acid. These insoluble compounds, however,
have sufficient acid-affinity left in the combined tannic acid to unite
also with the basic aniline colours, forming very fast or insoluble
colour lakes. This principle is extensively used in practice to fix