These colors are not suitable for converting white wine into red, but
they can be used for giving wines a faint red tint, for darkening pale
red wines, and in making up a factitious bouquet essence, which is added
to red wines. The most suitable methods for the detection of magenta are
those given by Romei and Falieres-Ritter. If a wine colored with archil
and one colored with cudbear are treated treated according to Romei's
method, the former gives, with basic lead acetate, a blue, and the
latter a fine violet precipitate. The filtrate, if shaken up with amylic
alcohol, gives it in either case a red color. A knowledge of this fact
is important, or it may be mistaken for magenta. The behavior of the
amylic alcohol, thus colored red, with hydrochloric acid and ammonia is
characteristic. If the red color is due to magenta, it is destroyed by
both these reagents, while hydrocholoric acid does not decolorize the
solutions of archil and cudbear, and ammonia turns their red color to a
purple violet. If the wine is examined according to the Falieres-Ritter
method in presence of magenta, ether, when shaken up with the wine,
previously rendered ammoniacal, remains colorless, while if archil
or cudbear is present the ether is colored red. Wartha has made a
convenient modification in the Falieres-Ritter method by adding ammonia
and ether to the concentrated wine while still warm. If the red color of
the wool is due to archil or cudbear, it is extracted by hydrochloric
acid, which is colored red. Ammonia turns the color to a purple violet.
König mixed 50 c.c. wine with ammonia in slight excess, and places in
the mixture about one-half grm. clean white woolen yarn. The whole is
then boiled in a flask until all the alcohol and the excess of ammonia
are driven off. The wool taken out of the liquid and purified by washing
in water and wringing is moistened in a test-tube with pure potassa
lye at 10 per cent. It is carefully heated till the wool is completely
dissolved, and the solution, when cold, is mixed first with half its
volume of pure alcohol, upon which is carefully poured the same volume
of ether, and the whole is shaken. The stratum of ether decanted off is
mixed in a test-tube with a drop of acetic acid. A red color appears if
the slightest trace of magenta is present. The shaking must not be too
violent, lest an emulsion should be formed. If the wine is colored with
archil, on prolonged heating, after the addition of ammonia, it is
decolorized. If it is then let cool and shaken a little, the red color
returns. If the wool is taken out of the hot liquid after the red color
has disappeared, and exposed to the air, it takes a red color. But if
it is quickly taken out of the liquid and at once washed, there remains
merely a trace of color in the wool. If these precautions are observed,
magenta can be distinguished from archil with certainty according to
König's method. As the coloring-matter of archil is not precipitated
by baryta and magnesia, but changed to a purple, the baryta method,
recommended by Pasteur, Balard, and Wurtz, and the magnesia test, are
useless. Magenta may in course of time be removed by the precipitates
formed in the wine. It is therefore necessary to test not merely the
clear liquid, but the sediment, if any.--_Dr. B. Haas, in Budermann's
Centralblatt.--Analyst_.
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