86 GENERAL BIOCHEMISTRY 



ture, twelve theoretical triglyceride isomers are possible. Likewise, 

 if five acids are involved, there are thirty possible mixed triglyc- 

 erides. Of course, in the foregoing discussion we have considered only 

 isomeric triglycerides. One must also remember that there will be 

 some isomeric mono- and diglycerides in the mixture. Stxch a situation 

 seriously complicates the problem of analysis, since no effective 

 methods are available for the isolation of one isomer from another. 

 Consequently fat analysis depends upon the collection of certain 

 available data which are more or less characteristic and constant for 

 each type of fat. These determinations are called fat constants. The 

 fat constants are physical and chemical measurements which seem to 

 remain relatively constant for fats prepared properly from the same 

 source. 



Among the physical constants most commonly determined are 

 refractive index, melting point, viscosity, and specific gravity. The 

 melting point, although not an extremely accurate determination, is a 

 guide in detecting adulteration of fats and also helps in approximating 

 the amount of unsaturated fatty acids present. Often, instead of de- 

 termining the melting point of a fat, the chemist will determine the 

 solidification point of the free fatty acids. This is accomplished by 

 saponifying the fat and treating the soaps with mineral acid, thus 

 liberating the mixture of the free fatty acids which can be isolated and 

 used to determine the solidification point. 



Chemical constants most frequently used in the analysis of a fat 

 include acid number, saponification number, iodine number, and 

 Reichert-Meissl number. The type of information desired concerning 

 the fat determines the number of these constants measured. 



The acid number, defined as the number of milligrams of KOH 

 required for the neutralization of 1 g. of fat, is useful as a measure 

 of the free fatty acids in a fat. Obviously, a fat which has been 

 exposed to moisttire for an extended period of time might have an 

 appreciable acid number, indicating that hydrolysis of glycerides has 

 occurred. A fat which has been both processed and stored properly 

 has a very low acid number. 



The saponification number is defined as the number of milligrams 

 of KOH required to saponify completely 1 g. of fat. This test is based 

 on the fact that all fatty acids, regardless of molecular weight, are 

 monocarboxylic, and therefore each acid molecule will imite with 

 only one potassium ion in the formation of soap. If the fat is composed 

 of acids of high molecular weight, such as palmitic, stearic, or oleic 

 acid, there will be fewer molecules of fatty acids per gram of fat. 

 Therefore, the number of milligrams of KOH required to saponify 



