56 



INTilODUCTOEY — THE CONSTITUENTS OF MILK. 



It, towever, is present in many vegetable oils, and will thus 

 be a constituent of margarine. 



Linolic acid is an oily substance of slight yellow colour, havmg 

 a faint acid reaction ; it dissolves readily in alcohol and ether. 

 It remains fluid at low temperatures. 



The salts of linolic acid resemble those of oleic acid, but are 

 more soluble in alcohol and ether. Nitrous acid does not produce 

 a solid acid. Both the acid and its salts readily absorb oxygen 

 from the air, and form resinous substances. 



Linolic acid absorbs 4 atoms of bromine, forming tetra-brom- 

 stearic acid, which is a crystalline substance melting at 114° to 

 115° ; from this linolic acid can be prepared by reduction with 

 zinc in a solution of hydrochloric acid in alcohol. 



Acids of the Series, C,iH2„-6COOH — Linolenic Acid.— 

 This occurs in vegetable oils. It is a liquid, even at very low 

 temperatures, and has a fishy odour. It forms a hexa-brom- 

 compound melting at 177° C. 



Comparison of tlie Acids of the four Series. — The following table 

 (V.) will show the main differences between stearic, oleic, linolic, 

 and linolenic acids, the corresponding members of the four series : — 



TABLE V. — Comparison of the Four Typical Fatty Acids. 



