Gravitational phases induced on the neutron shall systematically be investigated in large neutron interferometers. In the perfect crystal interferometer, a single neutron is macroscopically separated by several centimetres and experiences phase shifts depending on the height of one path above the other. But the hitherto measured phase shifts are approximately 1% lower than expected. As the gravitational phase shift increases with the interferometer size the new generation of large neutron interferometers will be much more sensitive to gravitation. Our aim is the verification of the Newtonian gravitation law for a macroscopically separated very light sub-atomar quantum object. The same setup will be exploited for sensing hypothetic non-Newtonian short-range interactions by accurately measuring the coherent scattering length of silicon in a perfect crystal at different lattice reflections. A special feature of our setup is the sensitivity to the submicron interaction regime.