CONSTANT PH VALUES OF AQUEOUS SALT-SOLUTIONS SEALED IN AMPOULES OF NEUTRAL GLASS

The pH decrease of unbuffered, neutral, aqueous salt (eg. NaCl) solutions observed during storage in sealed ampoules of so-called neutral glasses of the 1st hydrolytic class is not caused by a reaction of the solutions with the glass, eg. an exchange of ions, but by acidic gaseous impurities, which enter the ampoules during filling or during sealing by flame. It could thus be shown by a simple experiment that a pH decrease by DELTA pH greater-than-or-equal-to -2.5 had been caused by CO2 excluding safely the glass to be the cause of this effect.