46o, Conditions Affecting Butter-Fat. 



acid would, no doubt, hasten the disintegration of the entire 

 glyceride, 



It is, however, to be noticed that the amount of free volatile 

 or soluble acids, in rancid butter-fat is much smaller than might 

 be expected if the explanations of rancidity here brought for- 

 ward are valid. Why is it that these acids do not appear to any 

 great extent in the free condition? This is probably explained 

 by the fact that the first products formed by the decomposition 

 of oleic acid are not acids but aldehydes : these aldehyde bodies 

 are further changed by oxidation into soluble acids, but this takes 

 place only in an advanced stage of rancidity, which explains a 

 fact frequently noticed, viz., that free soluble acids are not formed 

 to any great extent except in rancid fats of considerable age. 

 By the action of alcoholic potash aldehydes are decomposed into 

 acids and small quantities of dark resinous compounds. This 

 would account for the fact that the soluble acids of decom- 

 position do not appear until after saponification, and would also 

 explain the brown colouration that rancid fats undergo when 

 treated with alkalis. The peculiar odour, as well as the reducing 

 action on silver solutions, are both explained by the presence of 

 bodies of an aldehyde nature in rancid fat. 



Other changes which are usually noticed as a butter-fat 

 becomes rancid are the increase of the refractive index, and the 

 lowering of the Crismer number, this lowering being roughly 

 proportional to the acidity. . . 



If bodies of a nitrogenous character be mixed with the butter- 

 fat then rancidity occurs much more quickly, and the decom- 

 position of the glycerides is much accelerated by the aid of 

 micro-organisms, yeasts, and moulds. 



T. E. Thorpe., 



