APP."| CHEMICAL BASIS OF THE ANIMAL BODY. 737 



ACIDS OF THE OLEIC (ACRYLIC) SERIES. H (C M H 2n _ 3 ) O s (monobasic). 



Many acids of this series occur as glycerine compounds in various 

 fats. They are very unstable, and readily absorb oxygen when exposed 

 to the air. The higher members are decomposed on attempting to 

 distil them. Their most peculiar property is that of being converted 

 by traces of NO 2 into solid, stable metameric acids, capable of being 

 distilled. 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. Potassic acetate. Potassic palmitate. 



H0 1 .H M O t + 2KHO = KC i H a O f + KC l6 H 3l O, + H 9 . 



Oleic acid. C 18 H 33 O . OH. 



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 4C. to a crystalline mass. Insoluble 

 in water, it is soluble in alcohol and aether. It cannot be distilled 

 without decomposition. It readily forms with potassium and sodium 

 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 NO g and by the changes it undergoes when 

 exposed to the air. 



THE NEUTRAL FATS. 



These may be considered as aethers formed by replacing the exchange- 

 able atoms of hydrogen in the triatomic alcohol 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 aethers; only those, however, which belong to the 

 third class occur as natural constituents of the human body : those of 

 the fi rst and second are of theoretical importance only. 



They possess certain general characteristics. Insoluble in water and 

 cold alcohol, they are readily soluble in hot alcohol, aether, chloroform, 

 &c. ; they also dissolve one another. They are neutral bodies, colourless 

 and tasteless when pure; are not capable of being distilled without 

 undergoing decomposition, and yield as a result of this decomposition, 

 solid and liquid hydrocarbons, water, fatty acids, and a peculiar body, 

 acrolein. (Glycerin contains the elements of one molecule of acrolein, 

 and two molecules of water.) 



They possess no action on polarised light. 



They may readily be decomposed into glycerin and their respective 

 fatty acids by the action of caustic alkalis, or of superheated steam. 

 F. 47 



