One method of measuring diffusion coefficients of vapours is to measure the rate of evaporation of a liquid in narrow tubes. In one such experiment, a glass tube 1 cm in diameter was filled with water...

One method of measuring diffusion coefficients of vapours is to measure the rate of evaporation of a liquid in narrow tubes. In one such experiment, a glass tube 1 cm in diameter was filled with water at 20°C to within 4 cm of the top. Dry air at 20°C and 1.013 bar was blown across the top of the tube. At the end of 24 hours of steady-state operation, the level of the water dropped 0.1 cm. Calculate the diffusivity of the air-vapour system at 20°C.