336 
Journal oj Agricultural Research 
Vol. XXVI, No. 3 
(b) A few drops of dilute acrolein solution were treated with an equal 
quantity of a 3 per cent solution of pure hydrogen peroxid. The mixture 
was allowed to stand for about one minute, after which 5 cc. of concen¬ 
trated hydrochloric acid and 5 cc. of the Kreis reagent were added. An 
intense red color was immediately imparted to the hydrochloric acid 
layer. In similar tests with larger quantities of acrolein and hydrogen 
peroxid the condensation product separated as an intensely purple 
precipitate. 
It therefore appears that the hydrogen peroxid exerts its effect most 
rapidly and most completely when added directly to the acrolein, and 
that a derivative of acrolein is thereby produced which forms a red-colored 
condensation product with phloroglucin in presence of hydrochloric acid. 
Crotonic aldehyde. —Crotonic aldehyde was prepared by the method 
of Del£pine as given in Beilstein’s “Handbuch der Organischen Chemie” 
(2, v. i, p. 729). The product was not specially purified, but possessed 
the described odor and appearance of crotonic aldehyde. 
When a dilute aqueous solution of crotonic aldehyde was tested in the 
usual manner with phloroglucin-hydrochloric acid a deep red color was 
immediately imparted to the hydrochloric acid layer. When the solution 
was shaken, however, the color faded rapidly and disappeared within a few 
minutes. When hydrogen peroxid was added to the fully developed test 
the red color disappeared as rapidly as it had been formed; and when it 
was added to the crotonic aldehyde before addition of hydrochloric acid 
and pholoroglucin a negative test was obtained from the beginning. 
The red color obtained in the Kreis test on rancid fats does not fade so 
readily, and it is evident that crotonic aldehyde is not responsible for the 
conduct of rancid fats in this test. 
From the above experiments, it is evident that all unsaturated alde¬ 
hydes do not behave similarly in the Kreis test. It already is suggested 
that increased molecular weight of the aldehyde carries with it an in¬ 
creased tendency toward instability of such color as it may give rise to in 
the Kreis test, possibly through increased tendency toward rupture of the 
carbon chain at the double bond. At all events, it was decided to post¬ 
pone the examination of the higher members of this series until the reaction 
between the acrolein, hydrogen peroxid, and phloroglucin-hydrochloric 
acid could be more thoroughly investigated in its relation to the reactions 
of rancid fats. 
SPECTROSCOPIC COMPARISON OP COLORED CONDENSATION PRODUCTS OF 
PHLOROGLUCIN 
Because the product formed by the action of hydrogen peroxid on 
acrolein gives a more or less permanent red color in the Kreis test, it does 
not necessarily follow that it is identical with the similarly reacting sub¬ 
stance in rancid fats. Kobert has mentioned a whole series of compounds 
which give a similar reaction; and of the compounds available in this 
laboratory, vanillin, eugenol, cinnamic aldehyde, and aged turpentine 
were found to behave in the same manner. 
Analytical processes for comparing the substance formed by interac¬ 
tion of acrolein and hydrogen peroxid with the similarly reacting sub¬ 
stance in rancid fats, or for comparing the colored condensation products 
