Molar Mass of Solute from Osmotic Pressure

Consider Eq. (2.19), $\pi = \dfrac{n_2 RT}{V}$. If the mass of the solute in $V$ litres of solution is $\mathrm{W_2}$ and its molar mass is $M_2$, then $n_2 = W_2/M_2$. With this value of $n_2$, Eq. (2.19) becomes

Every quantity on the right-hand side -- $\mathrm{W_2}$ (weighed out), $R$, $T$, $\pi$ (measured with the membrane apparatus) and $V$ -- is experimentally accessible, so the molar mass of the solute can be determined from the osmotic pressure.