Process for independently monitoring the presence of and controlling addition of silver and halide ions to a dispersing medium during silver halide precipitation

A process of precipitating a silver halide emulsion comprised of

• (a) introducing a dispersing medium and dissolved halide ions into a reaction vessel,
• (b) thereafter concurrently adding silver ions and halide ions to the dispersing medium to initiate growth of silver halide grains within the dispersing medium,
• (c) during step (b), monitoring the temperature of the dispersing medium to establish the equilibrium solubility product constant of silver an halide ions within the dispersing medium,
• (d) during step (b), using a reference electrode and a first indicator electrode each in contact with the dispersing medium within the reaction vessel, monitoring the halide ion activity within the dispersing medium and adjusting the level of dissolved halide ion in the reaction vessel by regulating the rate of addition to the reaction vessel of the halide ion to maintain a stoichiometric excess of halide ion, based on the equilibrium solubility product constant, and
• (e) during step (b), using a silver ion specific second indicator electrode in contact with the dispersing medium within the reaction vessel, monitoring the potential difference between the silver ion specific second indicator electrode and at least one of the first indicator electrode and the reference electrode to allow the level of dissolved silver ion in the dispersing medium to be determined independently of the equilibrium solubility product constant and adjusting the level of dissolved silver ion in the dispersing medium by regulating the rate of addition to the reaction vessel of the silver ion based on the potential difference thereby to maintain a selected activity profile of dissolved silver ion during silver halide grain growth.