928 Journal of Agricultural Research vol. vi.no. 24 



similar changes. Acids, aldehydes, alcohols, and esters, among other 

 things, may have been identified in spoiled fats, and even up to the 

 present time it has been customary to attribute their origin solely to the 

 fat itself. The reason for such deduction is evident. It is well known 

 that the fat of butter is in itself a most complex material. It is a com- 

 posite-, made up of mixtures of the glycerids of fatty acids. Among the 

 saturated glycerids butyrin is an essential ingredient, although palmitin 

 and myristin predominate. Olein has generally been considered to be 

 the only unsaturated glycerid in butter fat, yet quite recently Laxa and 

 Konecny (3) 1 claim to have found that the fatty acids of the "liquid fat" 

 of separator slime consist of 49.65 per cent of erucic acid and 21.24 P er 

 cent of oleic acids; but this assumption may not be entirely justified. 



The improbability of any chemical change occurring in the saturated 

 glycerids of storage butter is quite generally recognized; consequently 

 the glycerid olein, purely because it contains an unsaturated linkage in 

 the molecule and absorbs the halogens with avidity, has been considered 

 as the source from which are derived those decomposition products the 

 presence of which in fats influences their more or less decreased value. 

 As a matter of fact, any satisfactory and conclusive evidence that the 

 olein of butter fat is readily susceptible to oxidation under conditions 

 similar to those prevailing when butter is stored is entirely lacking. 

 On the other hand, it has been demonstrated that pure olive oil, the liquid 

 glycerids of which consist almost entirely of olein, shows very little 

 absorption of oxygen as measured by the iodin number, even after having 

 been kept for three years under ordinary conditions (5). Masters and 

 Smith (6), in preliminary experiments with butter fat, found but little 

 change in the iodin value during cooking experiments carried out with 

 this material. To obtain any pronounced change in the iodin value and 

 in the acidity, they found it necessary to heat their samples of butter fat 

 to as high a temperature as 200 C. while passing oxygen through the 

 material, the mere heating of the fat to such temperature under ordinary 

 conditions proving to be insufficient. From these two illustrations, as 

 well as from more recent work done by other investigators, the discussion 

 of which owing to limited space is omitted, it must be concluded that the 

 possibility of the olein of butter fat undergoing an appreciable oxidation 

 caused by the small quantity of atmospheric air inclosed in a package of 

 butter is very remote, especially when it is remembered that butter is 

 stored in the dark at a temperature considerably lower than the freezing 

 point of water. 



The inability of chemists to judge the quality of an edible fat because 

 of the absence of satisfactory chemical data has been frequently pointed 

 out, and this is attributable primarily to the lack of appropriate and com- 

 prehensive analytical procedure. For instance, rancidity has generally 

 been regarded as the natural concomitant of acidity, yet a pronounced 



1 Reference is made by number to " Literature cited," p. 951. 



