1 8 CHEMICAL CONSTITUENTS OF BODY AND FOOD. 
Or, in general terms — 
From the alcohol with formula C n H> 11+1 .HO the acid with formula 
Cn_jH20_j.CO.OH is obtained. The sixteenth term of this series has the 
formula C 15 H :n .CO.OH, and is called 'palmitic acid; the eighteenth has the 
formula C ir H 35 .CO.OH, and is called stearic acid. Each acid, as will be seen, 
consists of a radicle, C„_ 1 H 2 „ a CO, 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.,„_ 3 CU(.)H. It is the eighteenth term of the series, and 
its formula is C ir H 33 .CO.OH. 
Glycerin or glycerol is a triatornic alcohol, C 3 H 5 (OH) 3 — i.e. three atoms of 
hydroxy! united to a radicle glyceryl (C .11 -). 
The hydrogen in the hydroxyl atoms is replaceable by other organic radicles. 
As an example, take the radicle of acetic acid, called acetyl (CrL.CO). The 
following formula? represent the derivatives that can be obtained by replacing 
one, two, or all three hydroxyl hydrogen atoms in this way: — 
(OH (OH (OH fO.CHg.CO 
C 3 hJ0H C3HJOH C 3 hJo.CH 3 .CO C3HJ0.CH3.CO 
(OH lO.CH ? .CO (O.CH s .CO (0.CH3.CO 
(glycerin) (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 formula? : — 
Acid. 
Radicle. 
Fat. 
Palmitic acid C 15 H 31 .C0OH 
Stearic acid . Ch.H35.COOH 
Oleic acid . C^H^.COOH 
Palmitvl C ls H 31 .C0 
Stear vl . C^^ 5. CO 
Oleyl . C 17 H 33 .CO 
Palmitin C 3 H 5 (0C 15 H 31 .C0) 3 
Stearin . C 3 H 5 (0C I -H 3 5.C0)3 
Olein . CH^OC^H^.CO), 
1 Acrylic acid itself (C 3 H 4 2 ) is obtained by the oxidation of acrolein (C 3 H 4 0), the 
aldehyde of allyl alcohol. 
