Which Substances Was The Dialysis Tubing Impermeable?

Which Substances Was The Dialysis Tubing Impermeable? Iodine was permeable because it crossed the dialysis tubing and reacted with the starch, turning it purple/black. The starch was impermeable because it would have reacted with the iodine in the water outside the dialysis tubing if it was permeable. 2. Which substances Cannot cross a dialysis tubing