It is always water that's in question when talking about osmosis. But can't a similar concentration gradient, over a semipermeable membrane, drive the flow of another substance across that membrane? Let's say you have liquid nitrogen, a semipermeable membrane that doesn't allow sugars to pass, and sugar molecules on one side of the membrane. Wouldn't liquid nitrogen be driven across the membrane then, as well, by the same principle? Is it just that osmosis, by definition, only covers this physical principle on water?