Measurement of diffusivity by unsteady-state evaporation, use the following data to determine the diffusivity of ethyl propionate (species A) into a mixture of 20 mole% air and 80 mole% hydrogen (this mixture being treated as a pure gas B) 

These data were obtained by using a glass tube 200 cm long, with an inside diameter 1.043 cm; the temperature was 27.9°C and the pressure 761.2 mm Hg. The vapor pressure of ethyl propionate at this temperature is 41.5 mm Hg. Note that t is the actual time from the start of the evaporation, whereas the volume increase is measured from t ≈ 240 s.

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Vi (s2) Increase in vapor volume (cm³) 0.01 15.5 0.11 19.4 0.22 23.4 0.31 26.9 0.41 30.5 0.50 34.0 37.5 0.60 41.5 0.70