ELEMENTAEY PHYSIOLOGICAL CHEMISTRY 



181 



hyde acrolein, CH 2 = CH - CHO, and this again can be further oxidised 

 to form acrylic acid, CH 2 = CH COOH. The eighteenth alcohol of 

 this series yields on oxidation oleic acid, which has therefore the 

 formula C 17 H 33 COOH. Now all bodies in which some of the C 

 atoms are bound together by two valencies are unstable and tend to 

 change into bodies in which the C. atoms are bound together by only 

 one band. To do this, they must have another element to satisfy the 

 extra valency so that they will act as reducing bodies. It is on this 

 account that oleic acid blackens osmic acid (tetroxide of osmium) by 

 appropriating some of its oxygen, and reducing it to a lower oxide 

 which is black. This reaction is given by all fats containing oleic acid. 



Not only are the lower fatty acids, such as acetic, capable of form- 

 ing salts with metals, but so are the higher members, such as palmitic, 

 stearic, and oleic. The compound in this case is called a Soap. 



Thus : 



C 15 H 31 COOH + NaOH = C 15 H 31 COONa + H 2 0. 



Palmitic acid. Sodium palmitate 



(a soap). 



If, instead of using an inorganic salt, we use an alcohol to combine 

 with the carboxyl group, a body called an ester is formed, and if, for 

 this purpose, we use the triatomic alcohol (i.e. containing three 

 hydroxyl groups) glycerine, we obtain a neutral fat. 



CH 2 -OH1 



CH -OH 



I 

 CH 2 -OH 



Glycerine. 



HOOOC 16 H 31 

 HOOCC 16 H 31 



HOOCC 15 H 3 



Palmitic acid. 



fCH 2 -OOCC 15 H 31 l 



fe. 



OOC C 15 H 31 



3H 2 



CH 2 OOC C 15 H 



Palmitin : a neutral fat. 



By boiling the neutral fat with caustic alkali it is split up into 

 its constituents, the glycerine being set free and the fatty acid uniting 

 with the alkali to form a soap. 



This process of saponification is usually carried out by using an 

 alcoholic solution of caustic potash. 



EXPERIMENT I. Saponification of neutral fat. Place about 50 c.c. 

 of alcoholic potash in a small flask, and heat on a water bath to near 

 boiling point. Melt some fat (about 10 grammes) in an evaporating dish 

 and drop the melted fat into the heated alcoholic potash, shaking the 

 latter every now and then. After all the fat has been added, continue 

 heating until the spirit begins to boil, and then test to see if saponifica- 

 tion be complete. This is done by dropping some of the solution in the 

 flask into a test tube containing about 10 c.c. of distilled water, when, 



