Some other glycerides isolated from natural sources are analogous in composition to tristearin, but with this difference, that the three radicals which replace hydrogen in glycerin are not all identical; thus kephalin, myelin and lecithin are glycerides in which two hydrogens are replaced by fatty acid radicals, and the third by a complex phosphoric acid derivative.
The natural oils and fats are mixtures of at least two or three different triglycerides, the most important of which are tristearin, tripalmitin, C3H5(0'C16H310)3 and triolein, C 3 H 5 (0C1811330)3.
This is not only due to the fact that they are mixtures of several glycerides, but also that even pure glycerides, such as tristearin, exhibit two melting-points, a so-called "double melting-point," the triglycerides melting at a certain temperature, then solidifying at a higher temperature to melt again on further heating.