I have been able to find lots of information about experiments that have been done to determine how different compositions of matter respond in a gravitaional field. However, I have not been able to find any information about experiments done to determine any difference in strength of the gravitational field produced by different compositions of matter. Does anyone know of any experiments along those lines, most likely involving the torsion balance? Since I have been unable to find any evidence of such experiments, I am lead to beleive that there may be some reason for it. If so, does anyone know the reason? Please note that I am speaking of very small differences. Obviously if there were any large differences it would have been noticed a long time ago. I think that both classical and GR both postulate that all mass attracts equally. But where are the experiments?