124 
Journal of Agricultural Research 
Vol. II, No. a 
CHEMICAL PROPERTIES OF THE VARIOUS OILS 
In order to make a better comparison of the several oils with regard 
to their aromatic quality, determinations were made of the acid, ester, 
and saponification numbers. These constants are usually ascertained 
in order to get some idea of the odoriferous constituents. 
The determination of the acid number is readily accomplished by 
simple titration with standard alkali and is expressed by the number of 
milligrams of potassium hydroxid required to neutralize the free acidity 
contained in i gram of the oil. A number of factors may tend to in¬ 
fluence this value. Freshly distilled oils, in most instances, are low in 
free acidity, while old oils or oils distilled from old material usually pos¬ 
sess a larger quantity of free acids. Improper conditions of drying and 
storing have a tendency to cause changes to take place in the aromatic 
compounds, which result in the formation of free acids, and thereby 
increase the acid numbers. 
As previously stated, the esters, which consist of combinations of acids 
and alcohols, are considered the odor bearers. These values are easily 
determined by saponifying the oil with alcoholic alkali and calculating 
the number of milligrams of potassium hydroxid consumed in the reac¬ 
tion by i gram of oil. This represents an accurate measurement of the 
ester constituents. As in the case of free acidity, this value may also be 
affected by conditions under which the material is dried and stored. 
The stage of growth and development of the plant is^also a strong factor 
in modifying the ester content of volatile oils. 
The saponification number represents the total amount of alkali, 
expressed in milligrams, necessary to react completely with i gram of 
oil, being the sum of the acid and ester numbers. 
These constants which are so directly related to the odor were care¬ 
fully determined for each of the hop oils distilled from the various sam¬ 
ples of hops. A determination of the free alcohols in these oils was also 
made, but was barren of results in all cases. Acetylization with acetic- 
add anhydrid with subsequent saponification is necessary and is readily 
accomplished in many oils. However, the nature of some alcohols is 
such that a quantitative acetylization is impossible, owing to decompo¬ 
sition when boiled with the acetic-acid anhydrid. Modification of the 
usual method, altering the length of boiling and the quantity of acetic 
anhydrid, gave negative results in all cases. From this peculiar behavior 
of the oil it is inferred that either the oils have no free alcohol compounds 
or that the alcohol compounds, if present, are of such a nature as to be 
incapable of quantitative acetylization. 
The acid, ester, and saponification numbers of the oils from the Ameri¬ 
can and fordgn hops are recorded in Table III. 
