CHEMICAL BASIS OF THE ANIMAL BODY. 889 



ACIDS OF THE OLEIC (ACRYLIC) SERIES. H(C n H 27l - 3 )0 2 (monobasic). 



Many acids of this series occur as glycerin 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 prop- 

 erty is that of being converted by traces of N0 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 



HC 18 H 33 2 + 2KHO = KC 2 H 3 2 + KC 16 H 31 2 + H 2 . 

 Oleic Acid. C 18 H 33 0. OH. 



This is the only acid of the series which is phj^siologically important. It is found 

 united with glycerin in all the fats of the human body. 



When pure it is, at ordinary temperatures, a colorless, odorless, tasteless, oily 

 liquid, solidifying at 4 C. to a crystalline mass. Insoluble in water, it is soluble 

 in alcohol and ether. It cannot be distilled without decomposition. It readily 

 forms soaps with potassium and sodium, which are soluble in water; its com- 

 pounds with most other bases are insoluble. It may be distinguished from the 

 acids of the acetic series by its reaction with N0 2 and by the changes it under- 

 goes when exposed to the air. 



THE NEUTRAL FATS. 



These may be considered as ethers formed by replacing the exchangeable 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 ethers; 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. 



They possess certain general characteristics. Insoluble in water and cold alcohol, 

 they, are readily soluble in hot alcohol, ether, chloroform, etc. ; they also dissolve 

 one another. They are neutral bodies, colorless 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 pecu- 

 liar body, acrolein. (Glycerin contains the elements of one molecule of acrolein and 

 two molecules of water.) 



They possess no action on polarized light, 



They may readily be decomposed into glycerin and their respective fatty acids by 

 the action of caustic alkalies or of superheated steam. 



Palmitin (Tri-palmitin). J C A H ^ j 3 . 



V^ 16 n 36 Uj 3 j 



The following reaction for the formation of this fat is typical for all the others : 

 Glycerin. Palmitic acid. Palmitin. 



0, + 3'' =,< 2 + 3 0. 



Palmitin is slightly soluble in cold alcohol, readily so in hot alcohol, or in ether ; 

 when pure it crystallizes in fine needles ; if mixed with stearin, it generally forms 

 shapeless lumps, although the mixture may at times assume a crystalline form, and 

 was then regarded as a distinct body, namely, margarin. It possesses three differ- 

 ent melting-points, according to the previous temperatures to which it has been 

 subjected. It solidifies in all cases at 45 C. 



Preparation. From palm oil, by removing the free palmitic acid with alcohol 

 and crystallizing repeatedly from ether. 



Stearin (Tri-stearin). CCi^W)) a I ^ 



This is the hardest and least fusible of the ordinary fats of the body, is also the 

 least soluble, and hence is the first to crystallize out from solutions of the mixed 



