  We propose a method to extract from experimental data the subdiffusion
parameter $\alpha$ and subdiffusion coefficient $D_\alpha$ which are defined by
means of the relation $<x^2> =2D_\alpha/\Gamma(1+\alpha) t^\alpha$ where
$<x^2>$ denotes a mean square displacement of a random walker starting from
$x=0$ at the initial time $t=0$. The method exploits a membrane system where a
substance of interest is transported in a solvent from one vessel to another
across a thin membrane which plays here only an auxiliary role. Using such a
system, we experimentally study a diffusion of glucose and sucrose in a gel
solvent. We find a fully analytic solution of the fractional subdiffusion
equation with the initial and boundary conditions representing the system under
study. Confronting the experimental data with the derived formulas, we show a
subdiffusive character of the sugar transport in gel solvent. We precisely
determine the parameter $\alpha$, which is smaller than 1, and the subdiffusion
coefficient $D_\alpha$.
