Nov. 24, 1923 
Studies on Rancidity 
35i 
Distillation was then resumed and continued until the water bath in 
which the distilling flask was immersed had reached the boiling point. 
A small amount of material, insoluble in water and having the odor 
of heptylic aldehyde, was again recovered from the liquid-air trap. 
When dissolved in a little ether and tested with phloroglucin-hydro- 
chloric acid, a cream-colored precipitate and a slightly pink and cloudy 
hydrochloric acid layer was obtained. When the test was repeated after 
the previous addition of hydrogen peroxid, a slightly cloudy and yellow 
hydrochloric acid layer, but no precipitate, was obtained. Both tests 
were negative for all practical purposes. 
The main portion of the distillate had condensed in the main receiver. 
It gave a weakly positive Kreis test, the color showing the characteristic 
absorption spectrum. 
The undistilled beef fat still gave a strongly positive Kreis test. 
Vacuum distillation of rancid oleic acid (ii). —In this experiment 
a specially prepared sample of oleic acid was employed. The method 
followed in its preparation was essentially that described by Lew- 
kowitsch {2If, p. 52), except that the barium salt was recrystallized six 
times from benzene by the method of Famsteiner instead of from 
alcohol, and that the recovered oleic acid was further purified by vacuum 
distillation. In this manner a colorless and odorless product was 
obtained, which gave a negative test for peroxids and no suggestion of 
color in the Kreis test. Part of this sample was used for the preparation 
of oleic acid ozonid, as already described, while the remainder was exposed 
to the action of light and air. When it had become strongly rancid, as 
evidenced by its odor and by its response to the Kreis test, it was sub¬ 
jected to vacuum distillation, the distilling flask being connected directly 
with a receiver immersed in liquid air. 
The material in the distilling flask began to boil at room tempera¬ 
ture at a pressure of about 0.3 mm., but was heated gradually up to 
ioo° C. before distillation was interrupted. The receiver was found to 
be covered with a frostlike deposit, and contained in addition a small 
amount of white fatty solid. On thawing and washing out the receiver 
with water, the material appeared to be largely, but not entirely, soluble. 
In the Kreis test the aqueous suspension gave a dear, pale pink color 
that showed the characteristic absorption band on spectroscopic exami¬ 
nation. On repeating the test in presence of hydrogen peroxid the same 
result was obtained. A positive peroxid test was also obtained. The 
residue from this distillation seemed to give an undiminished response 
to the Kreis test and to the peroxid test. 
If acrolein were one of a group of compounds forming substance R, it 
would have distilled completely at a comparatively low temperature 
and upon addition of hydrogen peroxid the fraction containing the 
acrolein would have given a strong Kreis test while the undistilled residue 
would have given a negative test. Substance R appears, rather, to be a 
compound that is derived from oleic acid, that is practically nonvolatile 
at pressures of from 0.3 to 2.0 mm. and a temperature of ioo° C., and 
that is gradually decomposed at higher temperatures. 
Comparative; solubility of substance; r and epihydrin aldehyde 
diethylacetal. — (a) About 25 cc. of melted lard, giving a negative 
Kreis test, were shaken with two drops of epihydrin aldehyde diethyla¬ 
cetal, which dissolved in the fat almost immediately. The filtered lard 
reacted intensely in the Kreis test. The odor imparted to the fat was 
not the characteristic odor of rancidity. 
