

102 LECTURE VI. 



The three fatty acids, oleic, Ci 8 H 34 02, stearic, CigH 36 2 , and palmitic, 

 CioH 32 02, play the principal role in the formation of fats. The last two 

 belong to the series of normal saturated fatty acids, CnH 2 nO 2 , whose lower 

 members are represented by formic, acetic, and propionic acids. Oleic acid, 

 however, is an unsaturated fatty acid: C 8 H 17 .HC : CH (CH 2 ) 7 .COOH. 

 These fatty acids combine with the triatomic alcohol, glycerol, (com- 

 monly called glycerin) splitting off water. We speak of tripcdmitin, tris- 

 tearin, and triolein according to the nature of the fatty acid concerned: 



CH 2 OH Ci 5 H 31 COOH CH 2 . O . CO . Ci 5 H 31 



CH . OH + Ci 5 H 31 COOH = CH . O . CO . d 5 H 31 + 3 H 2 



CH 2 OH Ci 5 H 3 iCOOH CH 2 . . CO . C I6 H 3 i 



Glycerol Palmitic acid Tripalmitin 



Tripalmitin and tristearin are solid at the ordinary temperature, while 

 triolein, on the other hand, is liquid. As fats are mainly mixtures of the 

 triglycerides, the solid or liquid condition of these depends entirely on the 

 quantity of triolein present. Besides these separate triglycerides there 

 are also mixtures, for instance, dipalmito-olein, a fat whose glycerol base 

 is united to two molecules of palmitic and one molecule of oleic acid; 

 again, we have distearopalmitin. Aside from the fatty acids mentioned, 

 there are the volatile members of the normal series; i.e., butyric, caproic 

 (hexoic), caprylic (octoic), and capric (decoic) acids. Thus in vegetable fats 

 almost all the different members of the normal fatty acid series have been 

 found. Even the higher fatty acids, such as lauric (Ci 2 H 24 O 2 ), myristic 

 (Ci4H 28 2 ), and arachidic (C 2 oH 40 O 2 ), as well as individual oxy-fatty 

 acids, have been observed. The latter have been isolated with certainty 

 only in the vegetable kingdom, while in the animal body the fatty acids 

 may combine with the higher alcohols instead of with glycerin. Rohmann 1 

 has shown that in the secretions from the oil-bags of birds a portion of 

 the fatty acids is combined with octadecyl alcohol, CH 3 . (CH 2 ) i6 . CH 2 OH. 

 The palmitic acid ester of cetyl alcohol, Ci 6 H 33 OH, from spermaceti, or 

 cetin, has long been known to occur in the cranium of the sperm whale. 

 The palmitic acid ester of myricyl alcohol (C 3 oH 61 OH) is found in bees- 

 wax. Analogous combinations are widely distributed in nature. In only 

 a few cases, however, has their identification been positive. 



While triolein and the glycerides of the lower fatty acids constitute the 

 major part of the vegetable fats, tripalmitin and tristearin predominate in 

 animal fat. An exception occurs only in the fat supply of cold-blooded 

 animals, which is very rich in triolein, as a consequence of which it remains 

 in a fluid state at temperatures which would cause solidification among 



1 Hofmeister's Beitrage, 5, 110 (1904). 



