The results of precise measurements of volume and determination of the melting curve of sodium at pressures up to 22 kbar are reported. The experimental data are used to calculate the changes of the thermodynamic functions at melting. The parameter Γ = e 2/ r s kT, characterising the ratio of the Coulomb energy to the thermal one, is shown to tend along the melting curve of sodium to the value of 155 ± 10, obtained for the model of a classical one-component plasma.