Abstract: The pipe filled with 3% sugar solution and closed by the semipermeable membrane at its bottom is inserted into a large pool filled with pure water. For the semipermeable membrane-solution system，the solution level will be about 22 meters higher than the pure water level. A double semipermeable membrane-solution system is structured by the pipe added another semipermeable membrane in the middle (such as 10 m from the bottom). Is there the level of pure water in the pipe higher than the level of the water in the pool? Thermodynamic analysis shows that which is not possible for the case of the equilibrium solution and will be possible for the uniform solution. But the latter case does not violate the second law of thermodynamics.

Key words: semipermeable membrane, perpetual motion, chemical potential, equilibrium solution, uniform solution