FAT OF MILK. 4:3 



Besides the constituents enumerated above, there also exist 

 in the fat of milk traces of cholesterol (which doubtless replaces 

 a portion of the glycerol), lecithin, a colouring-matter, and 

 possibly also a hydrocarbon. 



Saponification. — On boilinfr with a solution of caustic alkali, 

 the fat undergoes hydrolysis, thus — 



\ '^ 

 * C'aHs { H, + 3NaOH = CaHj;(0H)3 + KaR + Kali, + A'aR, 



( R„ 



E, R^ and R^^ representing radicles of the fatty acids. 



If the hydrolysis be carried out in presence of alcohol a portion 

 of the caustic all^ali is converted into an alkali ethoxide (alcoholate) 

 thus — 



NaOH + C\,H-,OH = C.H,,ONa + H,(i. 



This acts in a sli<;litly different manner fioni the hydroxide, 

 though the ultimate products of hydrolysis are identical. 

 The actions are pro))ably as follows : — 



*(i.) SISTaOCHs + CsHs u", =C:3H5(ONa)3 +(:3l-IiiR + (-".H5il, + C'.,TI -,11,. 



(ii.) CsHslONaJa + SOH^ = C:3Hj(()H)3 + SNaOH. 



(iii.) 8NaOH + CbHbR -i C^Hsli, i- C,H,R„ 



= SCjHjOH -I NaR + NaR, + NaR„. 



In the first staf;e. sodium ethoxide and fat form sodium uiycir- 

 oxide and ethyl salts (esters). 



In the second, the ulycemxidc is decomposed by the water 

 present into glycerol and sodium hydroxide : while, in thr third, 

 the esters are liydrolysed by the hydroxide into alcohol and 

 sodium salts of the fatty acids (soaps). 



The action between the sodium hydroxide and the alcohol is 

 never complete, and it is probable that the formation of esters 

 is only partial : evidence of the formation of ethyl Inityrate can 

 be obtained by warming a little of the fat with alcoholic soda,, 

 when the characteristic pine-apple odour of ethyl butyrate is at 

 once developed. By carefully avoiding any excess of alkali and 

 distilling the ethyl butyrate as soon as possible. AVanklyn and 

 Fox have succeeded in obtaining about 3 per cent, of volatile 

 acid (probably chiefly butyric) in the form of ester. 



It is probable that the equation (ii.) may not represent the 

 way in which sodium glyceroxide acts on the substances present : 

 a portion may follow this equation — 



(iv.) C'.H,(()Xa)j -I- SCoH-.OH = C,H,(OH);, + 3CoH,0Xa. 



* These reactions probably take place in stages, one aoid radicle at a time 

 beiny attacked. 



