The i.-r. spectroscopic determination of non-H-bonded OH-groups in water and alcohols are in agreement with the thermodynamic behaviour of these liquids. It is possible to calculate the specific heats, the heats of vaporization, the surface energies and the density with these spectroscopic results together with a simple model of the liquids. This method also gives the density maximum and the minimum of the specific heat of H2O. The conformity with the thermodynamic properties shows that these measurements can be employed to develop better theories of liquids and that the approximation methods used for the interpretation of the i.r. spectra are satisfactory.