obtained, contains a large proportion of this resinous compound, which
can be isolated by treatment with a weak soda-lye; this substance, like
the crystallized acid, is soluble in alkalies, and can be precipitated
from an alkaline solution by an acid. Old hops furnish far less
crystallizable acid than new hops; from some samples I have been able to
obtain only a few crystals; the remainder had been transformed into the
resinous modification.

If pure hop-bitter acid be pulverized and exposed to the atmosphere, it
soon turns yellow and the surface assumes a resinous consistency. At
the same time, a more pronounced odor of fatty acids and aldehydes is
apparent. Still more rapidly will this oxidation occur if a thin layer
of an alcoholic solution of the acid is allowed to evaporate in the air.
On the other hand, we can allow hop-oil to stand for days without its
odor being perceptibly changed; it appears to me more than probable that
the peculiar smell of old hops is due far more to the oxidation of the
bitter substance than to the oxidation of oil.

Hop-bitter acid appears to possess the character of an aldehyde and of
a weak acid; for the present I am not in a position to state its
constitution more clearly. Most of the oxidizing processes have an
energetic effect on it, forming also considerable quantities of
valerianic acid.

The question as to whether the hop owes chiefly to this acid and its
resinous modifications the property of imparting a pronounced bitter
flavor to a solution, I must for the present leave unanswered. The acid
and its isomer are both insoluble in water; they are, on the other hand,
very readily dissolved in hop oil; they also furnish a tolerably bitter
solution, if boiled for a long time in water, probably on their account