FATS AND OILS. WAXES. LECITHINS 177 



Composition. Hydrolysis. 



Fats are hydrolysed into their constituent fatty acids and glycerol 

 by boiling with water, treatment with steam; and by boiling with acids 

 and alkalies. This latter process of decomposing fats and esters is 

 known as saponification and is a special form of hydrolysis ; it was first 

 used in the manufacture of soap, hence the term. 



Fats undergo the process of hydrolysis during digestion. They are 

 decomposed by the enzyme lipase in the pancreatic juice and hydrolysed 

 into their constituents, fatty acids arid glycerol. Emulsification occurs 

 in the intestine, where the reaction is alkaline, during the process of 

 the hydrolysis. 



(a) Butter. 



A small quantity (2 gm.) of butter is heated with excess of alcoholic 

 sodium hydroxide until a clear yellow solution is obtanied. No oil 

 drops should be seen on pouring the solution into water. The aqueous 

 solution is heated to expel alcohol, acidified with dilute sulphuric acid 

 and again heated. The smell of butyric and other volatile fatty acids 

 is noticed. They are obtained by distilling the acid solution. The 

 higher fatty acids are also present, but do not distil and remain as an 

 oily layer on the surface of the hot liquid. 



() Olive Oil. 



If a little olive oil be dissolved in twice its quantity of ether and 

 5 times the volume of 2- per cent, alcoholic sodium hydroxide be 

 added, and the mixture be allowed to stand in a corked vessel, it 

 gradually solidifies and forms a jelly. Complete saponification has oc- 

 curred and soap has been formed. The jelly dissolves in water and 

 the soap solution will give (a) a precipitate of fatty acids 9n acidifying 

 with sulphuric acid and (fr) a precipitate of the calcium soap on adding 

 calcium chloride solution. 



(c) Lard. 



About 5 gm. of lard are boiled with 25 c.c. of 10 per cent, alcoholic 

 sodium hydroxide under a reflux condenser for 5-10 minutes to 

 saponify the fat. 25-50 c.c. of water are added ; if the saponification 

 is complete no oil drops should be seen ; if it be incomplete, the saponi- 

 fication is continued by adding alcoholic soda and again boiling. The 

 liquid is poured into an evaporating basin and the alcohol evaporated 

 on a water-bath. The solution is acidified with sulphuric acid ; the 

 fatty acids are precipitated and are filtered off through a wet paper and 

 washed free from acid with water. The filtrate contains the glycerol 

 which is detected as described below, 



