These three glycerides have been usually considered the chief constituents of most oils and fats, but latterly there have been recognized as widely distributed trilinolin, the glyceride of linolic acid, and trilinolenin, the glyceride of linolenic acid.
These high saponification values are due to the presence of (glycerides of) volatile fatty acids, and are of extreme usefulness to the analyst, especially in testing butter-fat for added margarine and other fats.
The fixed oils and fats consist essentially of glycerides, i.e.
Nevertheless, it is convenient to apply the term "oil" to those glycerides which are fluid below about 20° C., and the term "fat" to those which are solid above this temperature.
The two last-named glycerides are characteristic of the semidrying and drying oils respectively.