PREPARATION OF FATTY ACIDS 13 



1. By acting on the fat with superheated steam in the 

 presence of a Httle h'me or magnesia, which acts as a catalytic 

 agent. 



This method is the one most commonly adopted by 

 candle-makers for the preparation of fatty acids required in the 

 manufacture of candles. The fat is subjected to the action of 

 steam under pressure at 170° in large copper vessels in the 

 presence of a small quantity of lime. The resulting mixture 

 is then treated with sulphuric acid sufficient in amount to 

 combine with the lime, after which the free fatty acids rise to 

 the surface in a molten condition. 



2. By the action of concentrated sulphuric acid. 



The molten fats are stirred up in leaden vessels with 

 9 per cent of concentrated sulphuric acid, the mixture being 

 heated to about 120" C. The mixture is then warmed with 

 water to remove the acid, and the acids are further purified by 

 distillation with steam. 



SAPONIFICATION OF FATS. 

 Closely related to hydrolysis is the reaction known as 

 saponification ; this reaction, which literally means " soap- 

 making," is that which takes place when a fat is boiled with 

 caustic alkali. The alkali acts in much the same way as 

 water, breaking up the ester into glycerol and the fatty acid 

 which, however, in this case, combines with the alkali to form 

 a salt : — 



C17H35COOCH2 CH2OH 



C17H36COOCH + 3HOH = 3C17H35COOH + CHOH 



CiyHgsCOOCHa Potassium stearate, CH.pH 



Tristearin, a fat a soap Glycerol 



It so happens that the sodium and potassium salts of 

 palmitic, stearic, and oleic acids dissolve in water forming 

 opalescent alkaline solutions which readily give a lather, and 

 can, therefore, be used as soaps,* and hence the process by which 



* The sodium and potassium salts of oleic acid and of the higher fatty acids, 

 such as palmitic and stearic acids, when dissolved in water, are, to a large extent, 

 hydrolysed into free fatty acid and caustic soda according to the equation : — 



Ci^HgsCOONa + HoO = C17H35COOH + NaOH 

 Sodium stearate Stearic acid 



The stearic acid combines with some of the unhydrolysed soap to form an 



