 Maxwell construction in density coordinates

The equal-area condition is naturally $\int (p-p_{\mathrm{coex}})dv=0$ in volume per particle $v$. In number density $n=1/v$, it becomes ${\int }_{n_g}^{n_l}[p(n)-p_{\mathrm{coex}}]dn/n^2=0$. Unweighted area in a pressure-versus-density plot is not the Maxwell construction.