470 
Philippine Journal of Science 
1919 
however, is much greater than that indicated by Walker’s 14 
results on oils of about the same acidity. The question deserves 
further investigation as the present study can offer but two oils 
for comparison, and Walker’s results are invalidated, as he 
says, by the variation in exposure to air. 
Air . — Table III substantiates the views quoted at the begin- 
ning of this article that oxygen is necessary for the development 
of rancidity but not of acidity. The greater increase of acidity 
in the open samples was probably due partly to an increased 
hydrolysis and partly to the breaking up of the oleic acid mole- 
cules. The general correspondence of the decrease in the iodine 
number with the development of rancidity confirms the view 
quoted from Brill and Parker that the unsaturation of oleic 
acid offers a point of attack for oxygen in the second stage of 
rancidity. That this attack is not the initial stage, but is de- 
pendent upon some other process, probably hydrolysis, is shown 
by the remarkable constancy of the iodine number of oil B, even 
when exposed to air and light. 
In this connection a comparison of the decrease in iodine 
number with the increase of acidity is interesting. A decrease 
of 1.0 per cent in the iodine number corresponds to the satura- 
tion 1.1 per cent of oleic acid. Now in series Od and 01 we 
have a decrease of iodine number during storage of approx- 
imately 0.3 to 2.0 per cent — certainly not less. This corre- 
sponds to 0.3 to 2.2 per cent of oleic acid. These calculated 
values of oleic acid come very close, in each case of series 
01, to the final values found for free acid, but are somewhat 
less than the final acidity in series Od. In the present state 
of uncertainty regarding the final products it is difficult to 
interpret this correspondence. Lewkowitsch 15 seems satisfied 
that the first stage of rancidity hydrolyzes stearin, palmitin, 
and olein without selection. If this is true the oxidation (shown 
by decrease in iodine number) must have attacked unhydrolyzed 
olein, because in the OI series it affected one-fourth of the total 
olein present. But Lewkowitsch’s prejudice against a possible 
selective hydrolysis of olein seems based on the experiments of 
Thum, 10 which are entirely unconvincing, as he merely compared 
the iodine number of the free fatty acids in each rancid oil to 
14 Philip. Journ. Sci. § A 3 (1908) 133. 
15 Lewkowitsch, J., Chemical Technology and Analysis of Oils, Fats, and 
Waxes. London, Macmillan & Co. 1 (1913) 55. 
16 Thum, A., Zeits. f. angew. Chem. (1890) 482 and 483 abs. in Journ. 
Soc. Chem. Ind. (1891) 70. 
