3 2 4 
Journal of Agricultural Research 
Vol. XXVI, No. 8 
initial attack by the atmospheric oxygen is the oleic acid radical (5, 36) 
we will have summarized briefly the present status of our knowledge 
concerning the chemistry of rancidity. 
While much of the incentive for more detailed study of the chemistry 
of rancidity was removed with the discovery that rancidity is caused by 
a process of oxidation and can be prevented by exclusion of light and air, 
such a study is still of interest from the point of view of food control, 
both in connection with the problem of detecting rancidity in fats and 
in its bearing upon the question of the wholesomeness of rancid fats 
when used as food. 
Logically, the term “rancid” is descriptive of odor and taste, and ran¬ 
cidity as such is properly detected and estimated by means of the sense 
perceptions; yet in practical laboratory work the need of a reliable 
chemical test for replacing the sense perceptions in making the finer 
discriminations is apparent. To be entirely satisfactory, such a test 
should be known to be specific either for the compound that supplies the 
rancid odor or for some accompanying substance that is known to be 
present in all rancid fats and in rancid fats only. Our present knowledge 
of the chemistry of rancidity, however, is not sufficient to afford such a 
test, while the empirical tests currently used are subject to empirical 
limitations. Thus, the value of the various peroxid tests rests upon 
the observation that rancid fats in general contain the peroxid radical, 
yet Kerr and Sorber (21) have found that peroxids may be formed before 
rancidity has developed. Again, all rancid fats contain aldehydes and 
respond to the Schiff test with decolorized fuchsin, yet Walker (40) has 
found that the results of this test do not always parallel those obtained 
with the peroxid test. The test which most nearly parallels the organo¬ 
leptic observations in its results is the Kreis test with phloroglucin- 
hydrochloric acid; yet even this test, as heretofore made, is given by 
certain nonrancid cottonseed oils, and, as will appear in the following, 
by none of the previously identified constituents of rancid fats. 
THEORETICAL 
It is a matter of common knowledge that samples of oleic acid acquire 
a rancid odor on exposure to air and light, and it has been found in this 
laboratory that the rancid acid responds to the chemical tests generally 
used for the detection of rancidity in fats. This fact, together with the 
fact that neither stearic acid nor glycerin behaves in a similar manner, 
would seem to indicate that the oleic acid radical is the point of attack 
in the development of rancidity, and that a study of the chemistry of 
rancidity should begin with a study of the oxidation of oleic acid. 
A considerable number of references to the oxidation of oleic acid are 
to be found in the literature. The mechanism of the process and the 
products obtained seem to depend somewhat upon the oxidizing agent 
used and the conditions of the experiment. Th‘e more important results 
are mentioned below. 
On oxidation of oleic acid with alkaline potassium permanganate 
Saytzeff (34) obtained dihydroxystearic acid as the initial product, 
together with small amounts of azelaic and volatile fatty acids, formed, 
presumably, by decomposition of the dihydroxystearic acid. Holde and 
Marcusson (i8)> following a somewhat more vigorous oxidation with a 
less alkaline permanganate solution, were able to isolate a small amount 
