Abstract: From the late nineteenth century to the early twentieth century, before the development and acceptance of the theory of general relativity, much attention was devoted to the experimental search of some hypothetical non-Newtonian gravitational effects. The influences that were investigated included eventual violations of the principle of equivalence between gravitational and inertial masses; the influence of radioactivity on gravitation; the hypothetical absorption of gravity by matter; the influence of temperature on gravitation; and the influence of chemical reactions upon weight. This paper presents an overview of those experimental investigations, which were mostly forgotten. Keywords: gravitation; mass; non-Newtonian effects; experiments on gravitation