CHEMICAL BASIS OF THE ANIMAL BODY. 1229 



II. Acids of the Oleic (Acrylic) Series. C B H 2n _ 1 . COOH 



(monobasic). 



The acids of this series bear the same relationship to the 

 defines (C 2 H 4 ) that those of the acetic do to the paraffins 

 (CH 4 ). Some of the higher members of the series are found as 

 glycerin compounds in various fats. 



They bear an interesting relation to the acids of the acetic 

 series, breaking up when heated with caustic potash into acetic 

 acid and some other member of the same series : — thus, 



Oleic acid. Potassium acetate. Potassium palmitate. 



C 17 H 33 . COOH + 2KHO = KC 2 H 3 2 + KC 16 H 31 2 + H 2 . 

 Oleic acid. C 17 H 33 . COOH. 



This is the only acid of the series which is physiologically 

 important. It is found united with glycerin in all the fats of 

 the human body. 



When pure it is, at ordinary temperatures, a colourless, 

 odourless, tasteless, oily liquid, solidifying at 4° C. to a crys- 

 talline mass. Insoluble in water, it is soluble in alcohol and 

 in ether. It cannot be distilled without decomposition. It 

 readily forms, with potassium and sodium hydroxide, soaps 

 which are soluble in water : its compounds with most other 

 bases are insoluble. It may be distinguished from the acids of 

 the acetic series by its reaction with nitrous acid which con- 

 verts it into a solid (elaidic acid) and by the changes it under- 

 goes when exposed to the air. It may be converted into stearic 

 acid 



C 17 H 33 . COOH + H 2 = C 17 H 35 . COOH. 



m 



The Neutral Fats. 



These may be considered as ethereal salts formed by replac- 

 ing the exchangeable atoms of hydrogen in the triatomic alco- 

 hol glycerin (see below), by the acid radicles of the acetic and 

 oleic series. Since there are three such exchangeable atoms of 

 hydrogen in glycerin, it is possible to form three classes of these 

 ethereal salts ; only those, however, which belong to the third 

 class occur as natural constituents of the human body : those 

 of the first and second are of theoretical importance only. 



The following reaction, which represents the formation of 

 tri-palmitin from glycerin and palmitic acid, is typical for all 

 the others. 



Glycerin. Palmitic acid. Tri-palmitin. 



C 3 H 5 (OH) 3 + 3(C 15 H 31 . COOH) = C 3 H 5 (C 15 H 31 . CO . 0) 3 + 3H 2 0. 



They possess certain general characteristics. Insoluble in 

 water and but slightly in alcohol, they are readily soluble in 



