330 
Journal of Agricultural Research 
Vol. XXVI, No. 8 
its presence in the rancid fats which he studied and held it to be respon¬ 
se for their rancid odor. 
A purchased sample proved to be somewhat impure and was fraction¬ 
ated, the fraction boiling between 152 0 and 156° C., as compared with 
155 0 C. for the pure product, being reserved for examination. In sub¬ 
stance heptylic aldehyde was found to possess a permeating odor, de¬ 
cidedly suggestive of the rancid odor, but accompanied by a fruity 
fragrance. When 0.25 per cent of heptylic aldehyde was added to a 
nonrancid lard an odor was obtained which was described by several 
judges as a typically rancid odor until the sample was compared with a 
rancid control. When this comparison was made, however, minor dif¬ 
ferences in odor were noted, the fat containing the heptylic aldehyde 
lacking a certain sharpness in odor which was present in the control, and 
possessing a faint fruity fragrance which the control lacked. Neither 
the aldehyde itself nor the lard to which it had been added responded 
to the Kreis test for rancidity. 
On the basis of these observations and the findings of Scala, it seems 
reasonable to suppose that all rancid fats contain heptylic aldehyde, and 
that this compound is largely, but not entirely, responsible for their char¬ 
acteristic rancid odor, but has no bearing on their conduct in the Kreis 
test. 
Butyric aldehyde. —Butyric aldehyde was also noted by Scala (57) 
in certain specimens of rancid fat. A purchased sample distilled for the 
most part between 73 0 and 77 0 C., the limits recorded for the pure prod¬ 
uct. Its odor was strong and permeating, and in quantities of 0.08 per 
cent it imparted a pronounced odor to a previously normal sample of 
lard. Both the substance itself and the lard to which it had been added, 
however, possessed an odor totally unlike that of a rancid control. If pres¬ 
ent in the rancid control, its amount must have been extremely small and 
its odor masked by that of other constituents. In the Kreis test small 
amounts of butyric aldehyde gave rise to a deep gold color which gradu¬ 
ally changed to a very pale pink, while larger quantities gave rise to an 
orange-colored precipitate. When a nonrancid lard containing butyric 
aldehyde was similarly tested, a pale pink color was sometimes obtained, 
though neither in intensity nor in quality did the color resemble that 
obtained with rancid fats. 
Acetaldehyde and formaldehyde. —These compounds are common 
laboratory reagents of familiar odor. The odor which they imparted to 
a nonrancid lard when added in small quantities was scarcely suggestive 
of the rancid odor; while neither the substances themselves, nor samples 
of fresh lard to which they had been added, responded to the Kreis test 
for rancidity. 
AzELAic half aldehyde. —The half aldehyde of azelaic acid has been 
mentioned by Harries and Thieme (38) as a cleavage product of oleic acid 
ozonid. It is described as being very easily oxidized and correspondingly 
difficult to isolate, and in two successive attempts to prepare it in this 
laboratory the product was apparently completely oxidized to azelaic acid. 
Harries and Turk (rd), however, succeeded in isolating azelaic half 
aldehyde, and have described it as a white solid that is ordinarily possessed 
of a weak odor, but that gives off a strong rose-like odor when warmed. 
Theoretical considerations would also seem to indicate that the compound 
could not contribute toward the odor of rancidity, for, according to 
Dtirrans (9), the carboxyl group tends to suppress odor, and in such a 
