A porous-glass membrane, with an average pore diameter of 40 a, is to be used to separate light gases at 25^oC under conditions where Knudsen flow may be dominant. The downstream pressure is 15 psia, while the upstream pressure is not greater than 120 psia. The membrane has been calibrated with pure helium gas, giving a constant permeability of 117,000 barrer over the operating pressure range. Experiments with pure CO2 over the pressure range give a permeability of 68,000 barrer. Assuming that helium is in Knudsen flow, predict the permeability of CO2. Is the value in agreement with the experimental value? If not, suggest an explanation.