Apple slices 4 mm thick are exposed to sulfur fumes in a sulphuring house before drying. If the surface concentration of SO2 is 0.1 mol SO2/m3 , calculate how long it will take for the concentration on the non exposed surface of the apple slice to increase by 1% of the initial concentration difference at the 1.5 mm from the surface. Assume zero initial concentration of SO2 in the apple and a diffusion coefficient of SO2 in the apple of 1x10-9 m2 /s. The slice can be treated as a semi-infinite body.