LIPIDES (fats and RELATED SUBSTANCES) 77 



Since natural fats are mixtures of various glycerides, a large number 

 of fatty acids is obtained on hydrolysis. The following table gives the 

 principal fatty acids of the saturated series: 



Table 4-3 



Saturated fatty acids 



A' awe Formula Typical Occurrence 



(C„H2„.iC00H) 



Formic HCOOH Not in fats 



Acetic CH3COOH Not in fats 



Propionic CILCH.COOH Not in fats 



Butyric CHsCCHJ.COOH Butter 



Caproic CH3(CH2)4C00H Butter, coconut and palm oils 



Capry^lic CH3(CH.)«C00H Coconut and palm oils, butter 



Capric CH3(CH.),sC00H Coconut and palm oils, butter 



Laurie CH3(CHo)]oCOOH Laurel, coconut and palm oils 



Myristic CH3(CH2)ioC00H Butter, wool fat, spermaceti 



Palmitic* CH3(CH=)i4C00H All animal and vegetable fats, notably 



lard 



Stearic * CH3(CH2)i6C00H Animal and vegetable fats, notably tal- 

 low 



Arachidic CH3(CH2)i8C00H Peanut oil 



* Most abundant fatty acids. See Table 4-5. 



An examination of the table shows that only fatty acids containing an 

 even number of carbon atoms are obtained from natural fats. Although 

 there are several important exceptions to this statement, it is nevertheless 

 true for the great majority of fats. This rule is rather suggestive of the 

 way in which the fats must be built up in nature. It is probable that 

 fatty acids are formed in nature by addition of units containing two 

 carbon atoms, giving rise only to acids with an even number of carbon 

 atoms. The saturated acid obtained in greatest amount from fats is 

 palmitic. Stearic acid is also obtained in large quantities but not to 

 the same extent as palmitic. The fatty acids, such as butyric, of lower 

 molecular weight are found to a considerable extent as glycerides in 

 butter and coconut oil, but except in these two fats they occur in com- 

 paratively small amounts. Some of the lower fatty acids such as formic, 

 acetic, and propionic acid belong to the series of saturated fatty acids, 

 but no glycerides of these acids are found in natural fats. Small amounts 

 of these acids, and other fatty acids of low molecular weight, are found 

 free in perspiration and urine. Salts and esters of fatty acids of "both 

 low and high molecular weight are contained in the feces. 



Butyric acid is a colorless, mobile liquid boiling at 162^C. and is com- 

 pletely miscible with water. Caproic and caprylic acids are also liquids 

 at room temperatures; capric acid is a semisolid, but lauric acid is defi- 

 nitely a solid. The change from liquid to solid is thus associated with 



