  A method to extract the neutron-skin thickness of atomic nuclei from the
second and fourth moments of the charge density distribution is discussed. To
reduce the error in the estimation of the neutron root-mean-square radius due
to small effects like the magnetic form factors of nucleons, two neighbouring
even-even isotopes are used. It is found that uncertainty of the neutron radius
strongly depends on the accuracy of estimation of the fourth moment of the
proton density distribution. Consequently, extracting the neutron-skin
thickness from the charge second and fourth moments is hardly feasible.
