One method of studying diffusion in liquids used by Thomas Graham is that shown in Fig. $2\mathrm{.}1-2($b$).$ It consists of a small bottle of solution immersed in a large bath of solvent. Calculate the solute concentration in the bath as a function of time, and show how this variation can be used to determine the diffusion coefficient.$($a$)$

$($b$)$

Fig. $2\mathrm{.}1-2.$ Graham's diffusion apparatus for liquids. The equipment in $($a$)$ is the ancestor of free

diffusion experiments; that in $($b$)$ is a forerunner of the capillary method.