he most productive. Dissolve benzoin in strong alcohol, by the aid of
heat, and add to the solution, whilst hot, hydrochloric acid, in
sufficient quantity to precipitate the resin. When the mixture is
distilled, the benzoic acid passes over in the form of benzoic ether.
Distillation must be continued as long as any ether passes over. Water
added towards the end of the operation will facilitate the expulsion of
the ether from the retort. When the ether ceases to pass over, the hot
water in the retort is filtered, which deposits benzoic acid on cooling.
The benzoic ether and all the distilled liquids are now treated with
caustic potash until the ether is decomposed, and the solution is heated
to boiling, and super-saturated with hydrochloric acid, which
afterwards, on cooling, deposits, in crystals, benzoic acid.

Benzoic acid, as it exists in the resin, is the natural production of
the plant from which the resin is derived. It may also be produced
artificially. Abel found that when cumole (C_{18}H_{12}) was treated
with nitric acid, so dilute that no red vapors were evolved for several
days, this hydro-carbon was converted into benzoic acid. Guckelberger
has, by the oxidation of casein with peroxide of manganese and sulphuric
acid, obtained as one of the products benzoic acid. Albumen, fibrin, and
gelatin yielded similar results when treated as above. Woehler has
detected benzoic acid in Canadian castor, along with salicin. It is also
formed by the oxidation of the volatile oil of bitter almonds. Benzoate
of potash results when chloride of benzoyle is treated with caustic
potash. Benzoic acid in the animal economy is converted into hippuric
acid, which may by the action of acids, be reconverted into benzoic
acid.

Benzoic acid should be completely volatile, without leaving any ash or
being carbonized when heated. When dissolved in warm water, to which a
little nitric acid has been added, nitrate of silver and chloride of
barium should produce no precipitates. Oxalate of potash should give no
turbidity to an ammoniacal solution of this acid. When heated with an
excess of caustic potash it should evolve no smell of ammonia,
otherwise, it has been adulterated with sal ammoniac. In spirit, benzoic
acid is easily soluble, and requires 200 parts of cold and 20 parts of
boiling water to dissolve one part of it.

* * * * *

ON THE COLORING-MATTERS OF FLOWERS.

BY FREMY AND CLOEZ.

Chemists