CH. XXV.] 



THE FATS. 



391 



in chemical composition and in certain physical characters, such 

 as melting-point and solubilities. Olein melts at -5 C., palmitin 

 at 45 C., and stearin at 53-66 C. It is thus olein which holds 

 the other two dissolved at the body temperature. Fats are all 

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



Chemical Constitution of the Fats. The fats are com- 

 pounds of fatty acids with glycerin, and may be termed gly- 

 cerules or glyceric ethers. The term hydrocarbon, applied to them 

 by some authors, is wholly incorrect. 



The fatty acids form a series of acids derived from the 

 monatomic alcohols by oxidation. Thus, to take ordinary ethyl 

 alcohol, C 2 H 6 0, the first stage in oxidation is the removal of two 

 atoms of hydrogen to form aldehyde, C 2 H 4 0; on further oxidation 

 an atom of oxygen is added to form acetic acid, C 2 H 4 2 . 



A similar acid can be obtained from all the other alcohols, 

 thus : 



From methyl alcohol 

 ethyl 

 propyl 

 butyl 

 amyl 

 hexyl 



CH S .HO, formic acid 

 C,H B .HO, acetic 

 C S H,.HO, propionic 

 C H 9 .HO, butyric 

 C 5 H U .HO, valeric 

 C a H ls .HO, caproic 



H.COOH is obtained. 

 CH S .COOH 

 C.H..COOH 

 C S H..COOH 

 C 4 H..COOH 

 C 5 H n .COOH 



and so on. 



Or in general terms : 



From the alcohol with formula C n H 2n +i.HO, the acid with 

 formula C n _iH 2n _i.COOH is obtained. The sixteenth term of 

 this series has the formula C 15 H 81 .COOH, and is called palmitic 

 acid ; the eighteenth has the formula C^H^.COOH, and is called 

 stearic acid. Each acid, as will be seen, consists of a radicle, 

 C n _iH 2n _iCO, united to hydroxyl (OH). Oleic acid, however, 

 is not a member of this series, but belongs to a somewhat similar 

 series known as the acrylic series, of which the general formula is 

 C n _ 1 H 2n _3.COOH. It is the eighteenth term of the series, and 

 its formula is C^Hss.COOH. 



Glycerin or Glycerol is a triatomic alcohol, C 3 H 5 (HO) 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 acetic acid called 

 acetyl (CH 3 .CO). The following formula) represent the deriva- 

 tives that can be obtained by replacing one, two, or all three 

 hydroxyl hydrogen atoms in this way : 



(OH 

 C.H.-j OH 



IOH 



roiycerinl 



OH 

 OH 

 O.CH S .CO 



[Monoacetin] 



(OH 



C S H J O.CH 8 .CO 

 I O.CH..CO 



[Dimcetin] 



