May 25, 1914 
Aroma of Hops 
123 
high specific gravity would usually be accompanied by a larger percent¬ 
age of high-boiling constituents, and vice versa. 
From Table II it is readily seen that the refraction of the California 
oils during each of the three years shows but little variation. During 
the successive seasons the refraction of the oils from the 1907 crop was 
somewhat higher than that of the two following years. This was ac¬ 
counted for by the fact that the index of refraction of the oils of the 
1907 crop was taken about two years later (1909), showing that a change 
had taken place in the oils. The refractive property of the Oregon, 
New York, and Washington oils, as compared with the California oils, 
was not greatly different. However, the oils from the imported hops 
showed a higher refractive index than any of the other oils. This, again, 
may be due to the presence of a somewhat higher percentage of highly 
refractive constituents in these oils. 
The solubility of a volatile oil in alcohol depends upon the composition 
of the oil. A high percentage of terpenes and sesquiterpenes decreases 
the solubility and a high content of oxygenated compounds increases it. 
Owing to the insolubility of hops oils in alcohol and the difficulty thereby 
encountered in obtaining comparative results, a deviation was made 
from the usual method employed for determining solubility. One vol¬ 
ume of the oil was thoroughly shaken with three volumes of 94 per cent 
alcohol in a graduated cylinder, after which the resinous insoluble matter 
was centrifuged, ^The amount of insoluble matter could then be easily 
read on the bottom of the cylinder and the percentage of dissolved mate¬ 
rial readily calculated. 
Apparently the most soluble oil among the number was the oil from 
the Oregon hops, one volume of oil from the 1909 crop dissolving com¬ 
pletely in three volumes of 94 per cent alcohol, the oil from the 1908 
crop being almost as soluble. Washington and New York oils from the 
crops of 1908 and 1909 were slightly less soluble than the Oregon 
oils. The California oils of these two seasons were a trifle less soluble 
than those from the Washington and New York hops, while the imported 
oils appeared to be the least soluble. 
The much lower solubility of the 1907 oils was due to the fact that the 
determinations were not made until two years af ter distillation. Although 
the oils had been kept in well-filled bottles and well protected from the 
light, decomposition had ensued, which resulted in the formation of less 
soluble constituents, thus decreasing the solubility of the oils. This 
plainly shows the effect of age on the solubility of the oils. 
From the information thus obtained it would appear that the oils 
with the highest solubility probably contained a larger percentage of 
oxygenated compounds and a lower percentage of terpenic compounds 
than the less soluble oils. 
