30 



OLIVE OIL AND ITS SUBSTITUTES. 



Mallantyne" has shown tluit in many instances rancidity exists 

 before the formation of free acids, and that on the other hand free acids 

 may be liberated long before the oil becomes rancid. A. Schmidt/' 

 >tate> that an oil may have a high acidity without being rancid, and 

 that the oil becomes rancid upon partial or complete oxidation of the 

 free glycerin to aldehydes and ketones. Scale' found that olive oil 

 and lard contained no water soluble volatile acids in a fresh condition, 

 but these acids developed with age and consequent rancidity of the oil 

 and fat. Browne d has made a study of the changes incident to the 

 development of rancidity in butter fat and records some, interesting 

 results. Table XXI, taken from his work, shows the effect of the 

 development of rancidity upon the various values of the oil. As the 

 rancidity develops there is a decided increase in the acid, saponiiication, 

 ether, and Reichert values, a marked decrease in the iodin value and 

 the percentage of insoluble acids, and a slight decrease in the per- 

 centage of glycerin. 



TABLE XXI. Eff<ft of </trt'/<>/>u/t'iil of /nitcit/itif u/ion /////// r fat (Browne}. 



Kancidity may ailed the ])h\>ical and chemical values of oils and 

 in several ways. If large amounts of free acid are formed and 

 little oxidation takes place the specific gravity and index of refraction 

 may ! lowered and the iodin number very little affected. If oxida- 

 tion has taken place there will be an increase in the specific gravity, 

 index of refraction, and saponiiication number, and a decrease in the 

 iodin number. 



From the foregoing it is apparent that oils are extremely susceptible 



to change under the inlluence of light, air. and heat, and that dete- 

 rioration is in a large measure prevented by the exclusion of air and 



8 JCNir. Sor. ( 'In-ill. Ili.l., 1SI1, 10: LM. 



'/tsrhr. Anal, rii.-m.. |s.s. :{7 : 301, 



''Xtschr. Nahr.-rnt. lly-j. 11. \Va:m-nk.. is'.Hi. 10: L'::i. 



M..iif. AIIMT. ('linn. P '!: '::.. 



