Nov. 24, 1923 
Studies on Rancidity 
329 
characteristic odor possessed by many “sour" fats, but no suggestion 
of a rancid odor. Negative Kreis tests were obtained both with hep- 
tylic acid itself and with the lard to which it had been added. Even 
though present in rancid fats, therefore, it can scarcely be held to con¬ 
tribute toward their rancid odor or to be responsible for their conduct 
in the Kreis test. 
Caproic acid. —Caproic acid has also been isolated from rancid fats 
by Scala (57). A sample obtained by purchase boiled from 200° to 
205 0 C., as compared with 204.2 0 to 205 0 C. for the pure substance. 
It possessed a strong, disagreeable odor, which was in no way similar, 
however, to the rancid odor. In the amount of 1 per cent it imparted 
to a sweet lard a sour odor totally unlike that of a rancid control. Both 
the acid itself and the lard to which it had been added conducted them¬ 
selves negatively in the Kreis test. Even though present in rancid 
fats, it is in no way responsible for their rancid odor nor for their response 
to the Kreis test. 
Butyric acid. —Butyric acid has been isolated from a rancid fat by 
Scala (57). A purchased sample distilled mostly between 162.5° and 
164.1° C., as compared with 162.5° C. for the pure acid. An addition of 
0.06 per cent imparted to a nonrancid lard a pronounced odor which 
was distinctly different from that of a rancid control. Toward the 
Kreis reagent it conducted itself in the same manner as the acids pre¬ 
viously mentioned. 
Formic and acetic acids. —The odors of these acids were too familiar 
for a special examination to be required. As a matter of routine pro¬ 
cedure, however, these acids were subjected to the Kreis test, both 
by themselves and after addition to a nonrancid lard, with uniformly 
negative results. 
Nonylic aldehyde. —Nonylic aldehyde has been noted in rancid fats 
by Scala (,57). It has also been obtained by cleavage of oleic acid ozonid 
and is probably formed by cleavage of oleic acid peroxid. It therefore 
seemed reasonable to suppose that nonylic aldehyde would form an 
essential part of the picture of the rancid condition and would be found 
responsible for at least some of the properties distinctive of rancid fats. 
An attempt to prepare nonylic aldehyde by cleavage of oleic acid 
ozonid yielded a product too impure for direct examination, and too 
small in quantity for satisfactory purification. A small amount of a 
10 per cent alcoholic solution obtained in the meanwhile from another 
laboratory, with satisfactory assurances as to its purity, was therefore 
employed. Its odor was distinctly suggestive of the odor of rancidity, 
but of a rancid odor modified by a somewhat pleasing and fragrant 
quality. When added in small quantity to a sweet lard it imparted to 
the lard an odor very suggestive of the rancid odor, but lacking in some 
indefinable quality. Whether tested by itself or in the presence of 
nonrancid lard, it failed to give a positive reaction in the Kreis test. 
Where no fat was present, however, larger amounts of the aldehyde 
gave rise to the production of a yellow color in the aqueous phase or 
to the formation of a pale yellow precipitate in the Kreis test. 
While nonylic aldehyde, therefore, may be suspected of contributing 
toward the characteristic odor of rancid fats, it would seem that it is not 
responsible for their behavior in the Kreis test. 
HepTylic aldehyde. —Heptylic aldehyde, of all the compounds thus 
far noted in rancid fats, has been most prominently mentioned as the 
probable source of the rancid odor. Scala (57), in particular, proved 
