Nov. <4,1923 
Studies on Rancidity 
359 
According to the same principle some molecules of oleic acid might be 
oxidized to compounds containing more than three double bonds, which 
in turn might give rise to corresponding peroxids and their cleavage 
products. The hypothesis in this way might be made to account for 
the presence in rancid fats not only of the C 7 aldehydes and acids but of 
the whole series of saturated aldehydes and acids found by Scala, as 
well as for the presence of many other compounds not previously 
described. 
It can at least be said of this hypothesis that it does not appear to be 
contradicted by such experimental evidence as is available, and that in 
the absence of contradictory evidence it seems to explain much that is 
otherwise difficult to account for. Whether or not it can be substan¬ 
tiated by experimental evidence remains to be seen; but it is the author's 
intention, should his duties permit, to attempt the preparation of the 
substances, other than the epihydrin aldehyde compounds, that have 
been suggested to account for the positive Kreis test obtained with 
rancid fats, and to examine these substances as to their reaction with 
phloroglucin-hydrochloric acid. 
SUMMARY 
The results of the experiments recorded in this paper seem to justify 
a number of more or less definite statements regarding the odor and 
reactions of rancid fats and the cause of the rancid condition. 
1. The odor of heptylic aldehyde in itself and in presence of fresh fats 
is sufficiently suggestive of the rancid odor to establish the reasonable¬ 
ness of Scala’s contention that it is the component of rancid fats that is 
primarily responsible for their rancid odor. 
2. As a result of the direct examination of the following compounds, 
it appears that none of them contribute appreciably, if at all, toward 
the rancid odor of fats: 
Hydroxystearic acid. 
Dihydroxystearic acid. 
Diketostearic acid. 
Formic acid. 
Acetic acid. 
Butyric acid. 
Caproic acid. 
Heptylic acid. 
Caprylic acid. 
Nonylic acid. 
Azelaic acid. 
Formaldehyde. 
Acetaldehyde. 
Butyric aldehyde. 
Acrolein. 
Crotonic aldehyde. 
Methylglyoxal. 
Dihydroxy acetone. 
Acrylic acid. 
It also appears, on theoretical grounds, that neither ketoxystearic acid 
nor azelaic half aldehyde contributes to the odor of rancid fats. Direct 
examination of nonylic aldehyde, on the other hand, suggests that this 
compound may be partly responsible for the rancid odor. 
3. The typical rancid condition may be reproduced, in all essential 
respects at least, by the atmospheric oxidation of pure oleic acid, and 
by suitable treatment of oleic acid ozonid. The glycerin radical and the 
unsaponifiable matter of natural fats would appear, therefore, not to be 
necessarily involved in the development of rancidity. 
4. As the result of direct examination each of the following compounds 
has been eliminated as the cause of the Kreis test given by rancid fats: 
Hydroxystearic acid. 
Dihydroxystearic acid. 
Diketostearic acid. 
Formic acid. 
Acetic acid. 
Butyric acid. 
Caproic acid. 
Heptylic acid. 
Caprylic acid. 
Nonylic acid. 
Azelaic acid. 
Acrylic acid. 
Formaldehyde. 
Acetaldehyde. 
Butyric aldehyde. 
Heptylic aldehyde. 
Nonylic aldehyde. 
Acrolein. 
Crotonic aldehyde. 
Methylglyoxal. 
Dihy droxyacetone. 
Oleic acid ozonid. 
