Szilard ' s heat engine

In 1870, Maxwell [l] attempted to show the statistical character of the second law, through the device now called Maxwell's demon, which showed that manipulation of single molecules permits the creation of temperature gradients from an initially isothermal condition. Szilard [2] tried to understand how much energy the demon would consume in its operations, since Maxwell's description seemed to imply such consumption could be made arbitrarily small. Szilard's version consists of a movable partition in an isothermal cylinder with one single molecule as its operating gas (fig. I). An observer determines on which side of the partition the molecule is in, attaches some weights to the appropriate pulley, and allows the "gas" to expand isothermally, doing kTln2 work on the weights. He then removes the partition, reinserts it in the middle, and starts all over again.