i8 CHEMICAL CONSTITUENTS OF BODY AND FOOD. 



Or, in general terms 



From the alcohol with formula C I1 H 2n+1 .HO the acid with formula 

 C n _ 1 H 2ll _ 1 .CO.OH is obtained. The sixteenth term of this series has the 

 formula C 15 H 31 .CO.OH, and is called palmitic acid; the eighteenth has the 

 formula C 1T H 35 .CO.OH, and is called stearic acid. Each acid, as will be seen, 

 consists of a radicle, C n _ 1 H 2ll jCO, united to hydroxyl (HO). 



Oleic acid, however, is not a member of this series, but belongs to a some- 

 what similar series of acids known as the acrylic series, 1 of which the general 

 formula is C n _ 1 H., n _ 3 COOH. It is the eighteenth term of the series, and 

 its formula is C 17 H 33 .CO.OH. 



Glycerin or glycerol is a triatornic alcohol, C 3 H 5 (OH) 3 i.e. three atoms of 

 hydroxyl united to a radicle glyceryl (C 3 H 5 ). 



The hydrogen in the hydroxyl atoms is replaceable by other organic radicles. 

 As an example, take the radicle of acetc acid, called aoetyl (CH 3 .CO). The 

 following formulae represent the derivatives that can be obtained by replacing 

 one, two, or all three hydroxyl hydrogen atoms in this way : 



(OH 

 C 3 H J OH 



[OH 



(glycerin) 



(OH (OH (O.CH 3 .CO 



iJOH C g HJo.CH 3 .CO C 3 HJO.CH 3 .CO 



[O.CH,.CO [O.CH 3 .CO [O.CH 8 .CO 



(monoacetin) (diacetin) (triacetin) 



The contents of the fat cells of adipose tissue in man are fluid during 

 life, the normal body temperature being higher than the melting point 

 of the mixture of fats found there ; but this is not the case in all 

 (even warm-blooded) animals, for beef fat melts at about 45 C., and 

 mutton fat at a still higher temperature. Human fat consists of 

 the three glycerides palmitin, stearin, and olein. They differ in 

 chemical composition, melting point, and solubilities. Olein melts at 

 -5 C., palmitin at 45 C., and stearin at 53 to 66 C. It is thus olein 

 which holds the other two dissolved at the body temperature. All are 

 soluble in hot alcohol, ether, and chloroform, but insoluble in water. 



The proportion in which these fats are mixed differs in different 

 animals ; in cold-blooded animals olein is much more abundant than in 

 warm-blooded animals. Human fat contains from 67 to 80 per cent, 

 of olein. Mixed with these neutral fats, there is generally a small 

 amount of free fatty acids. 



Fats are also found in the vegetable kingdom, especially in seeds and 

 fruits, but in many cases in the roots also. 



Stearin, palmitin, and olein ought more properly to be called tristearin, 

 tripalmitin, and triolein respectively. Each consists of glycerin, in which the 

 three atoms of hydrogen in the hydroxyls are replaced by radicles of the fatty 

 acid. This is represented in the following formulse : 



1 Acrylic acid itself (C 3 H 4 3 ) is obtained by the oxidation of acrolein (C 8 H 4 0), the 

 ddehyde of allyl alcohol. 



