  We propose a method for identifying holographic chemical potentials of
conserved charges. The guiding principle is the consistency of the
identification with the thermodynamic relations and the Legendre
transformation. We consider the baryon-charge chemical potential as an example,
and explain why the degree of freedom of the constant shift of the bulk U(1)
gauge field is absent when the Legendre transformation is well-defined. The
method proposed here suggests that the definition of the chemical potential may
be more complicated compared with the case of localized charge if we have a
nontrivial charge distribution along the radial direction of the bulk geometry.
