The influence of neutral salts on the easily polarizable hydrogen bond of H5O2+ groupings in aqueous acid solutions is studied, using ir spectroscopy. The absorbance of the ir continuum, caused by the polarizable hydrogen bond in the H5O2+ groupings, usually decreases with increasing neutral salt concentration. This is explained by the polarization of the hydrogen bonds caused by local fields due to the neutral salt ions. The H+ becomes more or less trapped at one of the H2O of the H5O2+. The prominence of this effect increases with increasing cation field, i.e., from Cs+ to Li+, and is more pronounced with bivalent than with monovalent cations. The opposite effect is observed with tetraethylammonium chloride. The symmetry of H5O2+ groups is less strongly disturbed in the presence of neutral salts with ions with very large radii, i.e., small electrical fields, than in pure acid solutions. Considering the torsional vibration of the water molecules, it is finally shown that the hydrate structure network around the H5O2+ becomes disintegrated due to the presence of neutral salts.It is known from electrochemical investigations that the activity coefficient of the excess proton usually increases strongly due to the addition of neutral salts to acid solutions. The opposite is true with the addition of tetraethylammonium salt. Furthermore, the addition of neutral salt decreases the excess proton conductivity. All these observations are discussed on the basis of the ir spectroscopic results.