The unsaturated fatty acids which occur chiefly in oils and fats are oleic acid, iodine value 90.07; erucic acid, iodine value 75.15; linolic acid, iodine value 181.42; linolenic acid, iodine value 274.1; and clupanodonic acid, iodine value 367.7.
Linolenic acid characterizes all vegetable drying oils; similarly clupanodonic acid characterizes all marine animal oils.
In the mixture of unsaturated fatty acids, by means of some more refined methods, clupanodonic acid, linolenic acid, linolic acid and oleic acid can be recognized.