Nov. 24,1923 
Studies on Rancidity 
343 
formed in solutions containing less than two molecules of hydrogen per- 
oxid per molecule of acrolein. The experiment in which this result was 
obtained was therefore repeated, a new preparation of acrolein being 
employed; but the original results could not be duplicated. The smallest 
addition of hydrogen peroxid to an acrolein solution resulted now in a 
positive Kreis test; and the peculiar results obtained in the original ex¬ 
periment were traced to the slight and accidental alkalinity of solutions 
1 and 2. The conclusions reached on the basis of the original experiment 
were therefore unjustified. 
Attention was again turned to the combining proportion of acrolein 
and hydrogen peroxid in the reaction: 
Acrolein + hydrogen peroxid—> substance K. 
Should this reaction proceed to completion, this proportion could 
probably be determined by preparing solutions containing like con¬ 
centrations of acrolein and various concentrations of hydrogen peroxid 
and noting the smallest concentration of hydrogen peroxid required for 
the maximum production of color m the Kreis test. If, however, the 
reaction stops short of completion, uncombined acrolein and hydrogen 
peroxid would always remain in solution, and so long as this condition 
obtained, the colorimetric method could yield no information as to their 
combining proportion. 
With the idea of determining whether or not the reaction proceeds to 
completion, a solution containing 0.41 molecules of hydrogen peroxid 
per molecule of acrolein was examined as follows for free hydrogen 
peroxid : 
(а) A 10 cc. aliquot of this solution, representing an original addition 
of hydrogen peroxid equivalent to 22 cc. of tenth-normal solution, was 
titrated with tenth-normal potassium permanganate in an attempt to 
determine, if possible, the unused hydrogen peroxid. A sharp end point 
could not be obtained. The solution was still uncolored, and reacted 
positively in the Kreis test after 22 cc. of permanganate had been added, 
but gave a negative Kreis test after 35 cc. had been added. Apparently 
the permanganate was reacting with the organic material as well as with 
free hydrogen peroxid. 
(б) When potassium iodid was added to 0.5 cc. of the same acrolein- 
hydrogen peroxid solution in neutral reaction, the presence of an organic 
peroxid was indicated by a liberation of iodin. After the solution had 
been decolorized with thiosulphate, the addition of acid called forth a 
fresh liberation of iodin, and the presence of free hydrogen peroxid was 
indicated. The total quantity of iodin liberated in the two stages was 
equivalent to 3.35 cc. of a nearly tenth-normal thiosulphate solution, or 
more than equivalent to the originally added hydrogen peroxid. The 
presence of uncombined hydrogen peroxid, which was confirmed by a 
chromic acid test, indicates that the reaction 
Acrolein+hydrogen peroxid—^substance K 
does not proceed to completion, m neutral or in weakly acid solution at 
least. 
(c) A 0.5 cc. aliquot of the same acrolein-hydrogen peroxid solution 
was added to 5 cc. of concentrated hydrochloric acid, after which the acid 
solution was treated with potassium iodid. The iodin liberated was 
equivalent to but 1.95 cc. of the same thiosulphate solution, as compared 
