The Carbonate Saturometer

A new instrument, the carbonate saturometer, makes it possible to measure the degree of departure of most aqueous solutions from saturation with respect to solid carbonates. The instrument utilizes the fact that the pH of a solution changes as carbonate is added to or removed from the solution. By use of a pH-sensitive electrode and a reference electrode, the instrument measures the change in potential obtained when the solution around the pH-sensitive electrode is equilibrated with a solid carbonate. A method has been developed to permit the absolute calibration of the instrument for any particular solution. The method utilizes a comparison between an acid-base and a sodium bicarbonate titration and does not require a chemical analysis of the solution. The calibration procedure is not invalidated by the presence of buffers in the solution. The sensitivity of the instrument for artificial sea water in the pH range from 7.5 to 8.3 is about 1 millivolt per part per million calcite.