Nov. 24,1923 
Studies on Rancidity 
33 i 
compound as azelaic half aldehyde one might expect it to counteract the 
tendency of the aldehyde group to create odor. On theoretical grounds 
alone, therefore, one might hazard the prediction that azelaic half alde¬ 
hyde, in the matter of odor, would stand midway between nonylic aldehyde 
and the odorless azelaic acid and could contribute nothing additional 
toward the rancid odor. Similarly, on the basis of the color theory, it 
would appear that azelaic half aldehyde would be in no better position 
to yield a colored condensation product with phloroglucin than is no¬ 
nylic aldehyde, which reacted negatively to the Kreis test. It was con¬ 
cluded, therefore, that if azelaic half aldehyde be formed at any stage in 
the atmospheric oxidation of oleic acid, it is probably oxidized as rapidly 
as it is formed; and that in any event it could scarcely contribute ap¬ 
preciably toward the odor of rancid fats or account for their positive 
reaction in the Kreis test. 
Contrary to expectations, therefore, all the compounds thus far ex¬ 
amined may be excluded as being responsible for the behavior of rancid 
fats in the Kreis test. All but nonylic and heptylic aldehydes may be 
excluded as contributing anything essential toward the rancid odor. 
These latter substances are admittedly present in some rancid fats and 
probably in all, and admittedly explain in large measure their characteris¬ 
tic odor. To complete the rancid odor and to account for the Kreis test 
in rancid fats, however, the presence of at least one more substance 
would seem to be required. 
PREPARATION AND EXAMINATION OF OLEIC ACID OZONID 
In the first attempt at the preparation of azelaic half aldehyde, the 
oleic acid ozonid was observed to have a peculiar, penetrating odor, 
strongly suggestive of that quality in the odor of rancid fats which is 
not accounted for by the presence of heptylic and nonylic aldehydes. 
In the second attempt several other interesting observations were made 
which call for a somewhat detailed description of the experiment. 
Preparation of oleic acid ozonid. —The oleic acid ozonid was 
prepared in an improvised apparatus, essentially by the method of 
Harries and Thieme (38). The oleic acid employed was part of a speci¬ 
men which had been prepared in this laboratory from beef fat and ren¬ 
dered colorless and odorless by fractional distillation at a pressure of 
0.2 mm. Twenty grams of oleic acid were dissolved in 300 cc. of chloro¬ 
form, and a slow current of ozonized oxygen was passed through the 
solution for five successive days of seven hours each, after which ozoni- 
zation was judged to be complete. 
Examination of oleic acid ozonid. —A few drops of the chloroform 
solution of the oleic acid ozonid were tested directly with phloroglucin- 
hydrochloric acid. A pale yellow color that gradually deepened to an 
orange red was imparted to the hydrochloric acid layer. 
About 1 cc. of the chloroform solution was boiled with several cc. 
of water until the chloroform had disappeared, the ozonid undoubtedly 
experiencing a certain amount of hydrolysis. On submitting the residue 
to the Kreis test a pale yellow color was again obtained, but the color 
deepened more slowly than before and at the end of 30 minutes had 
acquired scarcely a tinge of pink. 
About 1 cc. of the chloroform solution was warmed gently in a watch 
glass until the chloroform had disappeared, no water being added. The 
