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.

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