  We propose a method to measure the subdiffusion parameter $\alpha$ and
subdiffusion coefficient $D_{\alpha}$ which are defined by means of the
relation $<x^2> =\frac{2D_\alpha} {\Gamma(1+\alpha)} t^\alpha$ 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. We experimentally study
a diffusion of glucose and sucrose in a gel solvent, and we precisely determine
the parameters $\alpha$ and $D_{\alpha}$, using a fully analytic solution of
the fractional subdiffusion equation.
