According to Lermer, the formula of this substance is C_{32}H_{50}O_{7};
it possesses the properties of a weak acid and forms a characteristic
copper salt, which is soluble in ether. This hop bitter is, however,
produced from the hop by a very roundabout process, by treatment of the
extract with alkalies; it is not therefore regarded by many as present
in this form in the hop, and they hold that it is only produced by
the action of the alkalies. On the other hand, however, Etti, by a
complicated extracting process, but without using an alkali, succeeded
in producing a bitter substance from hops, which is, however, soluble in
water.

Several experiments convinced me that there really existed in hops a
crystallizable substance, insoluble in water, the alcoholic and alkaline
solution of which had a bitter flavor, in short, which possessed all
the properties of Lermer's hop bitter acid. Petroleum ether is the best
practical solvent in use for its isolation, as it does not dissolve
the majority of the remaining constituents of the hop, especially the
hop-resin, which they contain in considerable quantity. Still, the
extraction of hop-bitter acid from hops is a troublesome and thankless
job, the petroleum ether taking up certain substances which add greatly
to the difficulty of purifying the crystals. On the other hand, we can
readily and quickly attain our object, if we employ for our original
material fresh lupuline from unsulphured hops.

The following process has furnished me the best results:

The lupuline is first freed from gross impurities (hop-seed leaves,
etc.), and then covered with petroleum ether boiling at a low
temperature (40 deg. to 70 deg.) in stoppered flasks. The mixture is shaken up
from time to time. After twenty-four hours, by means of a Zullowsky