58 PHYSIOLOGICAL CHEMISTRY. 



plates by crystallizing from hot alcohol. Stearic acid may be 

 obtained in the form of pearly crystalline plates or scales. It 

 melts at 71. 



PALMITIN or TRIPALMITIN, C 3 H 5 (C 1G H 31 O 2 ) 3 . The per- 

 fect separation of this fat from stearin, with which it is usually 

 associated is a matter of considerable difficulty. The fats are 

 much alike. The melting point is variously stated by different 

 observers, but appears to be about 51. A mixture of stearin 

 and palmitin was formerly supposed to be a distinct fat and 

 was called margarin, C 3 H 5 (C 17 H 33 O 2 )3. This fat has been 

 produced artificially but it does not appear to be a natural 

 product. Palmitic acid resembles stearic acid in appearance 

 and solubility; both acids are slowly soluble in strong hot 

 alcohol and yield crystalline plates on cooling. The melting 

 point of palmitic acid is about 62. 



OLEIN or TRIOLEIN, C 3 H 5 (C 18 H 33 O 2 ) 3 . This is a liquid 

 fat at the ordinary temperature and is a constituent of most 

 of the natural fats and oils. Some fatty oils are nearly pure 

 olein and become solid at a low temperature. The soft con- 

 sistence of lard, human fat and several other natural mixtures 

 is due to the olein present. Olein is a nonsaturated fat and 

 will therefore show an absorption coefficient as explained 

 below. By the action of reagents yielding nitrous acid it is 

 converted into an isomeric substance known as elaidin. 



Oleic acid in pure condition is not very stable, because of 

 its unsaturated structure. It is an oily liquid at the ordinary 

 temperature, but below 14 is converted into a crystalline 

 solid. By treatment with nitrous acid it yields the isomeric 

 elaidic acid. Oleic acid is characterized by forming a lead 

 salt which is soluble in ether while lead palmitate and stearate 

 are practically insoluble. 



LARD and TALLOW are essentially mixtures of the three 

 fats, palmitin, stearin and olein. By heating lard to its melt- 

 ing point, cooling slowly and subjecting the warm mass to 

 pressure in a filter press the softer portion, consisting mainly 

 of olein, may be separated. This is known as lard oil, while 



