Abstract BECAUSE of the complex nature of the coloring matters of egg yolk and despite the large number of researches of the properties of the substances involved, their exact identity and chemical delineation are somewhat controversial; especially since these substances reputed to be responsible for the yellow color of the yolk have also been studied for their vitamin properties. The pigments in the yolk of hen’s eggs are almost entirely xanthophylls,1 † which are unsaturated hydrocarbons of the same general formula C40 H56 O2. It would be instructive to examine at some length the chemistry of the carotinoids, which are defined as red, orange, and yellow pigments which can be extracted from all forms of living matter by fat solvents. Carotin, a typical carotinoid, because of its interesting nutritive properties and because it will be compared with xanthophyll later on, deserves special study along with xanthophyll. Carotin is an unsaturated hydrocarbon, of the . . .