ANIMAL LIFE AND ANIMAL PRODUCTS. FOODS 433 



Hydrolysis of Fats and Oils. The chief chemical property 

 of the fats and oils, and in fact of all esters, is that each can be 

 decomposed, or hydrolyzed, to give back the alcohol and acid from 

 which it is derived. Thus, when ethyl acetate is boiled with 

 water, it is slowly decomposed into ethyl alcohol and acetic acid : 



C 2 H 5 (C0 2 CH 3 ) + H 2 - C 2 H 5 OH + HC0 2 CH 3 . 



In the case of the fats and oils, if water alone is used, they must 

 be heated in a closed vessel, or autoclave, under pressure so as 

 to secure a high temperature (about 200) : 



3 + 3H 2 - C 3 H 5 (OH) 3 + 3HCO 2 Ci 6 H 3 i. 



palmitin glycerine palmitic acid 



When the mixture has cooled, the acid, which is insoluble in water, 

 forms a solid cake, while the glycerine is dissolved in the water. 



With water alone as a hydrolyzing agent, however, the reaction 

 is slow and incomplete and, at the high temperatures which it is 

 necessary to employ, some destruction of fatty matter is apt to 

 occur. In the presence of dilute sulphuric acid as a catalyst, the 

 hydrolysis can be carried out much more satisfactorily and rap- 

 idly, even at 100. Sulpho-derivatives of the fatty acids are still 

 more effective as catalysts, since they are freely soluble both in 

 fats and oils and in water, and hence promote the miscibility of 

 the two layers (Twitchell process). 



When tallow (beef fat) is treated in this way, the solid is a 

 mixture of palmitic, stearic, and oleic acids. The latter, being 

 liquid, is pressed out, and the solid material is used with paraffin in 

 making candles. The glycerine is separated from the water and 

 used in making nitroglycerine (p. 481) and in medicine. 



Hydrogenation of Oils. The market value of solid fats 

 is much higher than that of liquid oils. Many natural oils, in- 

 deed, possess disagreeable characteristics (taste, odor, etc.) which 

 render them totally unsuitable for edible purposes. They may 



r v be converted into more appetizing edible fats, however, by 



