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Page 90
* * * * *
ON THE COLORING-MATTERS OF FLOWERS.
BY FREMY AND CLOEZ.
Chemists possess only a very incomplete knowledge of the coloring
matters of flowers. Their investigation involves difficulties which
cannot be mistaken. The matters which color flowers are uncrystallized;
they frequently change by the action of the reagents employed for their
preparation; and, also, very brilliantly-colored flowers owe their color
to very small quantities of coloring matter.
On the nature of the coloring matters of flowers several opinions have
been expressed. Some observers have assumed that flowers owe their color
to only two coloring matters, one of which is termed anthocyan, and the
other anthoxanthine. Others will find a relation between the green
coloring of leaves, the chlorophylle, and the coloring matters of
flowers. They support their opinion generally on the results of the
elementary analysis of those different bodies; but all chemists know
that chlorophylle has not yet been prepared in a pure condition.
Probably, it retains various quantities of fatty and albuminous bodies.
Further, the coloring matters of flowers are scarcely known, so that it
is impossible to establish relations supported by the necessarily
uncertain composition of impure bodies.
Some time since the blue color of flowers was ascribed to the presence
of indigo; but Chevreul has shown, in a certain way, that the blue
substance of flowers is always reddened by acids; and that with indigo
it is quite different, which, as is known, retains its blue color even
when the strongest acids are allowed to act on it.
It is thus seen that the coloring matters of flowers have heretofore
only in a superficial manner been examined, and that it is important to
again undertake their complete examination, as these bodies are
interesting to the chemist, because they are employed as reagents in the
laboratory for the recognition of alkalies; and by an improved knowledge
of them the florist might find the way by which he could give to
cultivated flowers various colors.
We have believed that before undertaking their elementary analysis,
methods must be carefully sought for which can be followed for the
obtainment of the coloring matters of flowers, and that it should be
proved whether these substances are to be considered as independent
bodies, or whether they proceed from one and the same matter, which is
changed in various ways by the juices of the plant.
We now publish the results of our first investigations.
_Blue Coloring Matter of Flowers (Cyanine)._--The blue coloring matter
of flowers we propose to call cyanine. To obtain this substance we treat
the petals of _Centauria cyanus_, _Viola odorata_, or _Iris
pseudacorus_, with boiling alcohol, by which the flowers are
decolorized; and the liquid acquires immediately a fine blue color.
If the coloring matter is allowed to remain some time in contact with
alcohol, it is perceived that the blue of the liquid gradually
disappears, and soon a yellow brown coloration takes its place. The
coloring matter has in this case suffered an actual reduction by the
prolonged action of the alcohol, but it will again assume its original
color when the alcohol is allowed to evaporate in the air. Nevertheless,
the alcohol must not be allowed to remain in contact too long with the
coloring matter, because the alcoholic extract will not then again
assume its blue coloration by the action of oxygen.
The residue remaining from the evaporation of the alcohol is treated
with water, which separates a fatty and resinous substance. The watery
solution which contains the coloring matter is then precipitated by
neutral acetate of lead. The precipitate, which possesses a beautiful
green color, can be washed with plenty of water, and then decomposed
with sulphuretted hydrogen; the coloring matter passes into the watery
solution, which is carefully evaporated in a water-bath; the residue is
again dissolved in absolute alcohol; and lastly, the alcoholic solution
is mixed with ether, which precipitates the cyanine in the form of blue
flocks.
Cyanine is uncrystallizable, soluble in water and alcohol, insoluble in
ether; acids, and acid salts color it immediately red; by alkalies it
is, as known, colored green. Cyanine appears to behave as an acid, at
least it forms with lime, baryta, strontia, oxide of lead, &c., green
compounds insoluble in water.
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