_Cinchonia_, when obtained in an isolated form,[463] is distinguished by
the following characters and habitudes.
It is white, transparent, and crystallizes in the form of needles; it
has but little taste, circumstance depending upon its comparative
insolubility, as it requires no less than 7000 parts of cold water for
its solution; in boiling water it is soluble in 2500 times its weight,
but a considerable part separates, on cooling. In alcohol and the acids
it is much more soluble, and imparts to such menstrua the characteristic
bitter of the bark; it dissolves only in small quantities in the fixed
and volatile oils, or in sulphuric ether. Cinchonia restores the colour
of litmus which has been reddened by an acid. With acids it combines and
forms neutral salts, of which the solubility and crystalline form vary
with the acid employed.
_Sulphate of Cinchonia_, easily crystallizable and moderately soluble,
has been found to consist of _Cinchonia_ 100, _Sulphuric acid_ 13·02.
_Nitrate of Cinchonia_, uncrystallizable, and sparingly soluble.
_Muriate of Cinchonia_, crystallizes in very beautiful needles, and is
more soluble than the preceding salts.
_Oxalate of Cinchonia_, nearly insoluble; hence by pouring oxalic acid,
or oxalate of ammonia into solutions of any of the soluble salts of
cinchonia, we obtain a very white and abundant precipitate, which might
be mistaken for oxalate of lime; it is however soluble in an excess of
acid, and in alcohol.
_Gallate of Cinchonia_, equally as insoluble as the _Oxalate_, whence
the precipitate occasioned by pouring an infusion of galls into the
decoctions of genuine cinchona.
Cinchonia, when heated, does not fuse before decomposition. Its ultimate
elements are _oxygen_, _hydrogen_, and _carbon_; the latter being
predominant.
The _Kinic acid_, which exists in native combination with the
_Cinchonia_, amongst several other peculiar properties, is convertible
by means of heat into a substance (_acide pyrokinique_,) which is
crystallizable, and capable of producing with iron a most beautiful
green colour.