An experiment reported by Witteborn and Pallesen to search for compositional dependence of the gravitationally induced electric field near metals is criticized. It is argued that the null result of their experiment is expected and therefore cannot be interpreted as indicating compositional independence. The experiment does not test therefore the theory proposed by Dessler, Michel, Rorschach, and Trammell, under which a compositional dependence may be expected. © 1968 The American Physical Society.