124 SOAPS. 



sugar 1 . It is prepared in bulk by distilling in a current of superheated 

 steam the fluid residue left after the saponification of fats with lime. 



Soaps. 



When neutral fats are heated with lime or caustic alkalis under 

 pressure they are decomposed, the metal combining with the free fatty 

 or oleic acid to form a salt, leaving the glycerin in solution. These 

 salts are called soaps, being soluble in water if the metal is an alkali, 

 insoluble if it is calcium, lead, or other similar metal. The reaction 

 which takes place during the above saponification is as follows. 



Tri-stearin. Potassium stearate. Glycerin. 



C 5 H 5 (C 17 H 35 .CO.O) 3 + 3 KHO = 3 (C 17 H 35 .COOK) + C 3 H 5 (OH) 3 . 



A similar decomposition into glycerin and free fatty acid can be 

 effected by pancreatic juice (see p. 64), the acid uniting with the alkali 

 of the juice or of the bile to form a soap. This decomposition is however 

 quantitatively inconsiderable but qualitatively of great importance for 

 the absorption of fats, owing to the extraordinarily great emulsifying 

 power of a mixture of bile, free fatty acids and soluble soaps. The 

 same decomposition takes place when fats, more especially butter, turn 

 rancid. 



III. ACIDS OF THE GLYCOLIC AND OXALIC SERIES. 



When one atom of hydrogen in a paraffin is replaced by hydroxyl 

 a primary monatomic alcohol is obtained ; if a second atom is 

 replaced a parallel series of diatomic alcohols may be prepared which 

 are known as glycols. The replacement of a third atom of hydrogen 

 by hydroxyl yields the triatomic alcohols (e.g. glycerin). Further just as 

 the monatomic alcohols yield acids by oxidation, so also do the glycols ; 

 but from the latter two series of acids can be obtained, known respec- 

 tively as the glycolic and oxalic (succinic) series. Thus at first : 



Ethyl-glycol. Glycolic acid. 



C 2 H 4 (OH) 2 + 2 = CH 2 (OH) . COOH. + H 2 0. 



By further oxidation a member of the glycolic series can be con- 

 verted into a member of the oxalic series, thus : 



Glycolic acid. Oxalic acid. 



CH 2 (OH). COOH + 2 - (COOH) 2 + H 2 O. 



The acids of the glycolic series are monobasic, those of the oxalic 

 dibasic. 



The following table exhibits the above relationships in a convenient 

 form. 



1 Poof on v Ann J /7Jj/>t II Phfirm "Rd P.VT. flftSft^ S. 338. 



