104 The Philippine Journal of Science isn 



not give any color with either reagent, and Nos. 4, 12, 20, 21, 23, 

 24, 25, 29, 30, 31, 35, 43, 44, and 48, which show color with 

 both reagents and possess a high acidity and rancid odor. In a 

 total of forty-eight oils with four tests for rancidity being used, 

 one or more of these tests do not agree with the others in 

 thirty cases. 



The organoleptic properties are the most dependable tests for 

 rancidity. In Table III the relationships of the other three tests 

 to the organoleptic properties are given. 



Table III. — Relationships of rancidity test to the organoleptic properties. 



Test. 



Disagree- 

 ments. 



Agree- 

 ments. 





Per cent. 

 21 

 29 

 33 



Per cent. 

 79 

 71 

 67 









From Table III it appears that high acidity is a more 

 reliable indication of the rancidity of an oil than the reactions 

 with diazobenzene sulphonic acid or decolorized fuchsin, but this 

 does not prove that rancidity is coterminous with acidity. They 

 occur simultaneously in many cases, but the one is not a neces- 

 sary corollary of the other. When oils of high acidity are steam- 

 distilled, the residue no longer possesses a rancid odor, but has 

 lost very little in total acidity. Samples 46 and 47 bring this 

 out very prominently. The acidity in these samples remains 

 high, but the rancidity, judged by the odor, has been lost. 

 Sample 45, which had been neutralized with sodium hydroxide 

 and carefully washed, was not freed of its odor though freed 

 of its acidity. Sample 48, which was washed with a solution of 

 sodium hydrogen sulphite to rid it of any aldehydes that might 

 be present, still retained its rancid odor. If rancid odor is due 

 to the presence of aldehydes, this sample should have lost its odor. 



Issoglio 15 describes a confirmatory test for rancidity in olive 

 oils, which he calls the "oxidisability value." He states that 

 when the oxidisability value exceeds 15 it will be usually found 

 that the oil is rancid or has undergone some other change. 



Table IV contains some oxidisability values and some acetyl 

 values, together with other data on Philippine coconut oils 

 before and after distillation with live steam. 



"Issoglio, G., Ann. chim. applic. (1916), 6, 1. 



