Vitamin A is yellow flaky crystal or crystalline powder, insoluble in water and glycerin, soluble in most organic solvents such as alcohol, ether, hydrocarbon and halogenated hydrocarbon. Its chemical properties are relatively stable, but it is easily destroyed when exposed to heat, light or air, and should usually be kept away from light. Vitamin A is not a single compound, but a series of retinol derivatives including retinol, retinal, retinoic acid, retinyl acetate and retinyl palmitate. Vitamin A exists only in animals, and it is abundant in fish, especially cod liver oil. Plants do not contain vitamin A.