In an experiment, glucose and starch were put inside a dialysis membrane. this dialysis membrane was placed ..?

in a beaker which contained dH20(deionised water and I2KI (iodine2 potium iodine). after 30 mins the solution in the dialysis bag changed from a clear white colour to a black colour. how do i know which substance diffused? did the glucose/starch solution diffuse or did the H2O & I2KI diffuse?