Nov. 34, 1923 
Studies on Rancidity 
335 
In the Kreis test as employed for the detection of rancid fats, however, 
the aldehydes of the paraffin series have uniformly failed to give rise to 
distinctly colored products, even in the presence of hydrogen peroxid, 
and it would appear that under these conditions anhydridization does 
not occur with appreciable velocity. Thus it appears logical to suppose 
that the immediate and intense response of rancid fats in the Kreis test 
is called forth by the presence of a carbonyl compound which contains 
its own chromophore group and whose primary condensation product 
with phloroglucin is already colored, in exception to the general rule. 
Nitrogenous chromophores being excluded, it appeared, especially 
in view of Kobert’s work, that the double bond (>C : C<) would be the 
most likely chromophore group. And even though the formation of 
unsaturated compounds in the cleavage of oleic acid peroxid might be 
somewhat difficult to explain, for it would seem to involve the introduc¬ 
tion of new double bonds into the oleic acid carbon chain prior to any 
rupture at the peroxid group, the study of the unsaturated aldehydes 
and the unsaturated ketones in connection with the Kreis test seemed to 
be indicated. Of these substances the unsaturated aldehydes were 
examined first. 
EXAMINATION OF THE UN SATURATED ALDEHYDES 
Acrolein. —Of the unsaturated aldehydes, acrolein was studied first, 
as being the lowest member of the series and one of the easiest to prepare. 
It was prepared by the method of Bergh (j), by distillation from 
a metal retort of 95 parts of dry glycerin in presence of 5 parts of 85 
per cent phosphoric acid, followed by redistillation, drying, and frac¬ 
tionation of the raw product. Twenty gm. of material boiling between 
52.5° and 54 0 C., as compared with 52.4 0 C. for the pure product, were 
obtained in this way. It possessed the intensely sharp and penetrating 
odor and the tear-producing property which are characteristic of acrolein. 
When a few drops of a dilute aqueous solution of acrolein were tested 
in the usual way with phloroglucin-hydrochloric acid a flesh-colored 
precipitate was obtained. In other tests with smaller amounts of acrolein 
the hydrochloric acid layer remained colorless or showed at most an 
extremely faint pink tinge. None of these tests resembled those ob¬ 
tained with rancid fats. 
Before discarding the above-mentioned tests a few drops of hydrogen- 
peroxid solution were added to one of the test tubes. No immediate 
change occurred, but at the expiration of half an hour it was noticed 
that the hydrochloric acid layer in the tube receiving the hydrogen 
peroxid had acquired a very decided, though not an intense, pink color, 
similar to that obtained with slightly rancid fats in the Kreis test. 
The hydrogen peroxid was apparently effecting an oxidation of the 
condensation product; and in order that an indication might be obtained 
as to whether the oxidation was occurring in the acrolein or in the 
phloroglucin radical the following tests were performed: 
(a) Five cc. of the Kreis reagent were first treated with a few drops of 
a 3 per cent solution of pure hydrogen peroxid, the mixture being then 
added to another mixture containing a few drops of dilute acrolein solu¬ 
tion and 5 cc. of concentrated hydrochloric acid. The result was the 
same as when the hydrogen peroxid was added to the finished test, i. e., 
no immediate reaction, but a slow development of a pink color. 
