One easy way to measure diffusion coefficients is the diaphragm cell shown in Fig. 2.2-4. These cells consist of two well-stirred volumes separated by a thin porous barrier or diaphragm. In the more accurate experiments, the diaphragm is often a sintered glass frit; in many successful experiments, it is just a piece of filter paper (see Section 5.5). To measure a diffusion coefficient with this cell, we fill the lower compartment with a solution of known concentration and the upper compartment with solvent. After a known time, we sample both upper and lower compartments and measure their concentrations. Find an equation that uses the known time and the measured concentrations to calculate the diffusion coefficient.