xii, a. 2 Brill and Parker: Philippine Coconut Oil 97 



uring rancidity which have been recommended by the inves- 

 tigators of rancidity in oils. 



One of the methods, which has many advocates, as a test for 

 rancidity is the fuchsin-sulphurous acid color test. Walker "' 

 reports that in many commercial oils which gave organoleptic 

 tests for rancidity the color test failed to respond, while in many 

 instances oils which were sweet did give color tests. This test, 

 which is known as Schiff' s aldehyde test, is considered by some 

 to owe its activity to the presence of active oxygen for results. 

 Aldehydes have the property of activating the oxygen of the air. 

 One of the chemists to investigate the property of aldehydes to 

 give oxygen was Ludwig. 11 He found that the aldehydes inves- 

 tigated by him— acetaldehyde, paraldehyde, propylaldehyde, 

 isobutyraldehyde, and benzaldehyde— lost this power of giving 

 a reaction with potassium iodide if they were previously dis- 

 tilled in a stream of carbon dioxide. Urbain 12 claims that the 

 color, produced by aldehydes with decolorized fuchsin, is the 

 result of a condensation reaction. 



Kastle and Loevenhart ' 3 ascribed the oxidation activity of 

 benzaldehyde to the absorption of oxygen from the air to form 

 benzoyl hydrogen peroxide (C K H s CO-0-OH). This compound 

 readily gives up one oxygen and forms benzoic acid, which no 

 longer possesses the property of activating the oxygen of the 

 air. These authors believe the activity of oxidizing enzymes 

 arises from a similar reaction. 



The fact that certain oils which are unmistakably rancid do 

 not restore the color to decolorized fuchsin, while other oils which 

 are not rancid do produce a color with the reagent, shows that 

 the test is not reliable as an indication of the rancidity of the oil. 



Additional objections to the use of the fuchsin-reagent are that 

 it gives a color reaction with compounds other than aldehydes 

 (assuming that aldehydes are present when rancidity exists) 

 and that these colors are difficult and often impossible to distin- 

 guish in shade. 



An alkaline solution of diazobenzene sulphonic acid reacts with 

 aldehydes in the presence of sodium amalgam to give a violet-red 

 coloration. This reagent was used in the tests recorded in Ta- 

 ble I. 



Table I gives the color reactions of fuchsin-sulphurous acid 



" Op. cit. 



"Ludwig, E., Ber. d. deutsch. chem. Ges. (1896), 29, 1454. 



u Urbain, G., Bull. Soc. chim. (1896), 15, 455. 



u Kastle, J. H., and Loevenhart, A. S., Am. Chem. Joum. (1901), 26, 539. 



149622 4 



