470 Philippine Journal of Science i»« 



however, is much greater than that indicated by Walker's u 

 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 " 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 01 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/ 6 which are entirely unconvincing, as he merely compared 

 the iodine number of the free fatty acids in each rancid oil to 



"Philip. Journ. Sci. § A 3 (1908) 133. 



" Lewkowitsch, J., Chemical Technology and Analysis of Oils, Fats, and 

 Waxes. London, Macmillan & Co. 1 (1913) 55. 



"Thum, A., Zeits. f. angew. Chem. (1890) 482 and 483 abs. in Journ. 

 Soc. Chem. Ind. (1891) 70. 



