Determination of diffusivity for ether-air system the following data on the evaporation of ethyl ether (C₂H₅OC₂H₅) have been tabulated by Jost. ² The data are for a tube of 6.16 mm diameter, a total pressure of 747 mm Hg, and a temperature of 22°C. The molecular weight of ethyl ether is 74.12, and its vapor pressure at 22°C is 480 mm Hg. It may be assumed that the ether concentration at the open end of the tube is zero. Jost has given a value of D_AB for the ether-air system of 0.0786cm²/s at 0°C and 760 mm Hg. 

(a) Use the evaporation data to find D_AB at 747 mm Hg and 22°C, assuming that the arithmetic average gas-column lengths may be used for z₂ – z₁ in Fig. 18.2-1. Assume further that the ether-air mixture is ideal and that the diffusion can be regarded as binary. 

(b) Convert the result to D_AB at 760 mm Hg and 0°C using the results of S17.3.

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Time, in seconds, required for the indicated decrease of level Decrease of the ether level (measured from the open end of the tube), in mm Hg from 9 to 11 590 from 14 to 16 from 19 to 21 from 24 to 26 from 34 to 36 895 1185 1480 2055 from 44 to 46 2655