126 
Journal of Agricultural Research 
Vol. II, No. 3 
24. Three samples of Dauber, Auscher, and Oesterreich Gewachs hops 
of the 1910 crop possessed the ester numbers 15.7, 21.3, and 18, respec¬ 
tively. Figure 1 shows that the nine samples of foreign oils were uni¬ 
formly lower in esters than the American oils. 
The close relationship of the ester numbers of the California oils during 
the seasons of 1907, 1908, and 1909 is very evident. The general average 
ester number of the California oils was 45.5, as compared with 50.9 for 
New York, 52.8 for Washington, 58.8 for Oregon, and 23.5 for the im¬ 
ported. No important difference was noted in the various California 
oils. This is true also of the Washington oils, which, however, were dis¬ 
tilled during only two seasons. The ester content of the Oregon oils 
averaged considerably higher than the oils from any of the other hops 
and, with the exception of the oil from the 1906 crop, the history of 
which was doubtful, the oils bear close relationship from year to year. 
The New York oils were slightly more variable, but nevertheless occupy 
about the same relative position from year to year with respect to the 
other oils. 
In the case of the foreign oils, the ester numbers, which are a measure 
of the odorous constituents, would seem to point to a consistently lower 
content of these compounds. That this unusually low ester content is 
responsible for the generally acknowledged superior aroma of imported 
hops can not be positively stated, although it is highly probable, since it 
is known that other oils with a low ester content, notably lavender and 
peppermint oils, are more agreeable and fragrant than oils with a high 
ester content. 
The saponification numbers, which represent the total acids and esters 
in the oils, presented practically the same constant differences and simi¬ 
larities brought out by comparison of the ester numbers. 
While it is not known whether the ester numbers would continue lower 
indefinitely in case of the foreign oils, it may be assumed that such would 
probably be the case, since the authentic samples distilled during the 
five seasons showed abnormally low values as compared with the 
American oils. In like manner, it may also be assumed that the high 
ester numbers of the American oils would continue indefinitely, since 
they were fairly constant during the three seasons in which the experi¬ 
ments were carried on. 
FRACTIONATION OF THE) VARIOUS OILS 
Since volatile oils are composed of a number of constituents with 
boiling points which often vary considerably, fractional distillation has 
proved a useful and effective method for the partial separation of these 
constituents. Ordinarily a straight-neck distilling flask with side tube 
is used for this purpose, the bulb of the thermometer being placed im¬ 
mediately opposite the mouth of the tube and the fractions collected 
at different intervals. By this means a partial separation of the con- 
