May 2$, 1914 
Aroma of Hops 
117 
being dependent almost entirely upon the character of the chemical 
constituents of the oils. Refraction, although less important than either 
specific gravity or optical rotation, is of value, since some relationship is 
known to exist between the chemical compounds and their refractive 
power. Another physical property which is largely affected by the 
character of the constituents of the oil is its solubility in alcohol or in 
dilute alcohol. The presence of terpenes in oils retards solubility, while 
oxygenated compounds, such as esters and alcohols, increase it. 
The boiling points of the various constituents differ considerably. 
This property is often utilized in the examination of oils for the purpose 
of effecting a partial separation of the constituents by fractional dis¬ 
tillation. The thoroughness of this separation depends largely upon the 
form of the distilling flask and upon the rapidity of distillation. 
All these physical properties were determined for the various samples 
of hop oils in the hope of detecting any possible differences which might 
exist. 
For further comparison, acidity and saponification values were also 
determined, although they are of less importance. The determination of 
alcohols, while important in many oils, was not feasible in this investiga¬ 
tion because of the nature of hop oil. It was found that acetylization 
would not take place quantitatively, and, hence, a measurement of the 
alcohol content was impossible. 
An approximate comparison of the terpene and sesquiterpene con¬ 
tent was made possible from the fractionation experiments. 
Inasmuch as there is no direct method of assay available which is 
applicable to oil of hops, it was thought that a careful determination of 
certain physical and chemical properties of different hop oils would 
yield data from which a logical comparison could be made. All of the 
above-mentioned physical and chemical constants are likely to vary with 
the different conditions of climate, soil, cultivation, ripening, and curing 
of the hops. 
GKNFRAU PTAN OF COMPARISON OF VARIOUS HOPS AND HOP OILS 
In order to learn whether any constant differences exist in the various 
kinds of hops, it was planned to compare the oils distilled from hops 
grown in the hop-producing sections of the United States with the oil 
distilled from an authentic sample of imported hops, all the samples to 
be from hops grown during the same season. The sections chosen in 
the United States were California, Oregon, Washington, and New York. 
The imported hops were from Bohemia. 
A comparison of oils obtained from the hops during a single season 
would give results which would be valuable in determining differences 
for that particular season, but it was of the most importance to ascer¬ 
tain whether the same differences occurred from year to year. There¬ 
fore the experiments were carried on for four successive seasons, and 
